Reapply "Add more functionality to LLFile and cleanup LLAPRFile""

# Conflicts:
#	indra/llcrashlogger/llcrashlock.cpp
#	indra/llrender/llshadermgr.cpp
#	indra/test/CMakeLists.txt

32 files changed, 1623 insertions, 891 deletions

diff --git a/indra/llappearanceutility/llappappearanceutility.cpp b/indra/llappearanceutility/llappappearanceutility.cpp
index d223c859ab..cdc9cfdf40 100644
--- a/indra/llappearanceutility/llappappearanceutility.cpp
+++ b/indra/llappearanceutility/llappappearanceutility.cpp
@@ -57,6 +57,8 @@
 #include "llprocesstexture.h"
 #include "llprocessskin.h"
 
+#include "apr_getopt.h"
+
 const std::string NOTHING_EXTRA("");
 
 ////////////////////////////////////////////
diff --git a/indra/llaudio/llaudiodecodemgr.cpp b/indra/llaudio/llaudiodecodemgr.cpp
index d8a6fffea6..232b429130 100755
--- a/indra/llaudio/llaudiodecodemgr.cpp
+++ b/indra/llaudio/llaudiodecodemgr.cpp
@@ -199,7 +199,7 @@ bool LLVorbisDecodeState::initDecode()
     LL_DEBUGS("AudioEngine") << "Initing decode from vfile: " << mUUID << LL_ENDL;
 
     mInFilep = new LLFileSystem(mUUID, LLAssetType::AT_SOUND);
-    if (!mInFilep || !mInFilep->getSize())
+    if (!mInFilep || mInFilep->getSize() <= 0)
     {
         LL_WARNS("AudioEngine") << "unable to open vorbis source vfile for reading" << LL_ENDL;
         delete mInFilep;
diff --git a/indra/llcommon/CMakeLists.txt b/indra/llcommon/CMakeLists.txt
index 597a222b32..cb3f0d7842 100644
--- a/indra/llcommon/CMakeLists.txt
+++ b/indra/llcommon/CMakeLists.txt
@@ -322,6 +322,7 @@ if (LL_TESTS)
   LL_ADD_INTEGRATION_TEST(lleventdispatcher "" "${test_libs}")
   LL_ADD_INTEGRATION_TEST(lleventfilter "" "${test_libs}")
   LL_ADD_INTEGRATION_TEST(llevents "" "${test_libs}")
+  LL_ADD_INTEGRATION_TEST(llfile "" "${test_libs}")
   LL_ADD_INTEGRATION_TEST(llframetimer "" "${test_libs}")
   LL_ADD_INTEGRATION_TEST(llhttpdate "" "${test_libs}")
   LL_ADD_INTEGRATION_TEST(llheteromap "" "${test_libs}")
diff --git a/indra/llcommon/llapp.cpp b/indra/llcommon/llapp.cpp
index 73b50d0a50..aa84895fb8 100644
--- a/indra/llcommon/llapp.cpp
+++ b/indra/llcommon/llapp.cpp
@@ -37,7 +37,7 @@
 #endif
 
 #include "llcommon.h"
-#include "llapr.h"
+
 #include "llerrorcontrol.h"
 #include "llframetimer.h"
 #include "lllivefile.h"
@@ -53,6 +53,8 @@
 //
 // Signal handling
 #ifndef LL_WINDOWS
+#include "apr_signal.h"
+
 # include <signal.h>
 # include <unistd.h> // for fork()
 void setup_signals();
diff --git a/indra/llcommon/llapr.cpp b/indra/llcommon/llapr.cpp
index 65ee383c6b..9ea7a34bac 100644
--- a/indra/llcommon/llapr.cpp
+++ b/indra/llcommon/llapr.cpp
@@ -526,226 +526,6 @@ S32 LLAPRFile::seek(apr_file_t* file_handle, apr_seek_where_t where, S32 offset)
     }
 }
 
-//static
-S32 LLAPRFile::readEx(const std::string& filename, void *buf, S32 offset, S32 nbytes, LLVolatileAPRPool* pool)
-{
-    LL_PROFILE_ZONE_SCOPED;
-    //*****************************************
-    LLAPRFilePoolScope scope(pool);
-    apr_file_t* file_handle = open(filename, scope.getVolatileAPRPool(), APR_READ|APR_BINARY);
-    //*****************************************
-    if (!file_handle)
-    {
-        return 0;
-    }
-
-    llassert(offset >= 0);
-
-    if (offset > 0)
-        offset = LLAPRFile::seek(file_handle, APR_SET, offset);
-
-    apr_size_t bytes_read;
-    if (offset < 0)
-    {
-        bytes_read = 0;
-    }
-    else
-    {
-        bytes_read = nbytes ;
-        apr_status_t s = apr_file_read(file_handle, buf, &bytes_read);
-        if (s != APR_SUCCESS)
-        {
-            LL_WARNS("APR") << " Attempting to read filename: " << filename << LL_ENDL;
-            ll_apr_warn_status(s);
-            bytes_read = 0;
-        }
-        else
-        {
-            llassert_always(bytes_read <= 0x7fffffff);
-        }
-    }
-
-    //*****************************************
-    close(file_handle) ;
-    //*****************************************
-    return (S32)bytes_read;
-}
-
-//static
-S32 LLAPRFile::writeEx(const std::string& filename, const void *buf, S32 offset, S32 nbytes, LLVolatileAPRPool* pool)
-{
-    LL_PROFILE_ZONE_SCOPED;
-    apr_int32_t flags = APR_CREATE|APR_WRITE|APR_BINARY;
-    if (offset < 0)
-    {
-        flags |= APR_APPEND;
-        offset = 0;
-    }
-
-    //*****************************************
-    LLAPRFilePoolScope scope(pool);
-    apr_file_t* file_handle = open(filename, scope.getVolatileAPRPool(), flags);
-    //*****************************************
-    if (!file_handle)
-    {
-        return 0;
-    }
-
-    if (offset > 0)
-    {
-        offset = LLAPRFile::seek(file_handle, APR_SET, offset);
-    }
-
-    apr_size_t bytes_written;
-    if (offset < 0)
-    {
-        bytes_written = 0;
-    }
-    else
-    {
-        bytes_written = nbytes ;
-        apr_status_t s = apr_file_write(file_handle, buf, &bytes_written);
-        if (s != APR_SUCCESS)
-        {
-            LL_WARNS("APR") << "Attempting to write filename: " << filename << LL_ENDL;
-            if (APR_STATUS_IS_ENOSPC(s))
-            {
-                LLApp::notifyOutOfDiskSpace();
-            }
-            ll_apr_warn_status(s);
-            bytes_written = 0;
-        }
-        else
-        {
-            llassert_always(bytes_written <= 0x7fffffff);
-        }
-    }
-
-    //*****************************************
-    LLAPRFile::close(file_handle);
-    //*****************************************
-
-    return (S32)bytes_written;
-}
-
-//static
-bool LLAPRFile::remove(const std::string& filename, LLVolatileAPRPool* pool)
-{
-    apr_status_t s;
-
-    LLAPRFilePoolScope scope(pool);
-    s = apr_file_remove(filename.c_str(), scope.getVolatileAPRPool());
-
-    if (s != APR_SUCCESS)
-    {
-        ll_apr_warn_status(s);
-        LL_WARNS("APR") << " Attempting to remove filename: " << filename << LL_ENDL;
-        return false;
-    }
-    return true;
-}
-
-//static
-bool LLAPRFile::rename(const std::string& filename, const std::string& newname, LLVolatileAPRPool* pool)
-{
-    apr_status_t s;
-
-    LLAPRFilePoolScope scope(pool);
-    s = apr_file_rename(filename.c_str(), newname.c_str(), scope.getVolatileAPRPool());
-
-    if (s != APR_SUCCESS)
-    {
-        ll_apr_warn_status(s);
-        LL_WARNS("APR") << " Attempting to rename filename: " << filename << LL_ENDL;
-        return false;
-    }
-    return true;
-}
-
-//static
-bool LLAPRFile::isExist(const std::string& filename, LLVolatileAPRPool* pool, apr_int32_t flags)
-{
-    apr_file_t* apr_file;
-    apr_status_t s;
-
-    LLAPRFilePoolScope scope(pool);
-    s = apr_file_open(&apr_file, filename.c_str(), flags, APR_OS_DEFAULT, scope.getVolatileAPRPool());
-
-    if (s != APR_SUCCESS || !apr_file)
-    {
-        return false;
-    }
-    else
-    {
-        apr_file_close(apr_file) ;
-        return true;
-    }
-}
-
-//static
-S32 LLAPRFile::size(const std::string& filename, LLVolatileAPRPool* pool)
-{
-    apr_file_t* apr_file;
-    apr_finfo_t info;
-    apr_status_t s;
-
-    LLAPRFilePoolScope scope(pool);
-    s = apr_file_open(&apr_file, filename.c_str(), APR_READ, APR_OS_DEFAULT, scope.getVolatileAPRPool());
-
-    if (s != APR_SUCCESS || !apr_file)
-    {
-        return 0;
-    }
-    else
-    {
-        apr_status_t s = apr_file_info_get(&info, APR_FINFO_SIZE, apr_file);
-
-        apr_file_close(apr_file) ;
-
-        if (s == APR_SUCCESS)
-        {
-            return (S32)info.size;
-        }
-        else
-        {
-            return 0;
-        }
-    }
-}
-
-//static
-bool LLAPRFile::makeDir(const std::string& dirname, LLVolatileAPRPool* pool)
-{
-    apr_status_t s;
-
-    LLAPRFilePoolScope scope(pool);
-    s = apr_dir_make(dirname.c_str(), APR_FPROT_OS_DEFAULT, scope.getVolatileAPRPool());
-
-    if (s != APR_SUCCESS)
-    {
-        ll_apr_warn_status(s);
-        LL_WARNS("APR") << " Attempting to make directory: " << dirname << LL_ENDL;
-        return false;
-    }
-    return true;
-}
-
-//static
-bool LLAPRFile::removeDir(const std::string& dirname, LLVolatileAPRPool* pool)
-{
-    apr_status_t s;
-
-    LLAPRFilePoolScope scope(pool);
-    s = apr_file_remove(dirname.c_str(), scope.getVolatileAPRPool());
-
-    if (s != APR_SUCCESS)
-    {
-        ll_apr_warn_status(s);
-        LL_WARNS("APR") << " Attempting to remove directory: " << dirname << LL_ENDL;
-        return false;
-    }
-    return true;
-}
 //
 //end of static components of LLAPRFile
 //*******************************************************************************************************************************
diff --git a/indra/llcommon/llapr.h b/indra/llcommon/llapr.h
index 0e1e4277e7..8795a0f2c4 100644
--- a/indra/llcommon/llapr.h
+++ b/indra/llcommon/llapr.h
@@ -35,10 +35,6 @@
 
 #include "llwin32headers.h"
 #include "apr_thread_proc.h"
-#include "apr_getopt.h"
-#include "apr_signal.h"
-
-#include "llstring.h"
 
 #include <mutex>
 
@@ -184,20 +180,7 @@ private:
     static apr_file_t* open(const std::string& filename, apr_pool_t* apr_pool, apr_int32_t flags);
     static apr_status_t close(apr_file_t* file) ;
     static S32 seek(apr_file_t* file, apr_seek_where_t where, S32 offset);
-public:
-    // returns false if failure:
-    static bool remove(const std::string& filename, LLVolatileAPRPool* pool = NULL);
-    static bool rename(const std::string& filename, const std::string& newname, LLVolatileAPRPool* pool = NULL);
-    static bool isExist(const std::string& filename, LLVolatileAPRPool* pool = NULL, apr_int32_t flags = APR_READ);
-    static S32 size(const std::string& filename, LLVolatileAPRPool* pool = NULL);
-    static bool makeDir(const std::string& dirname, LLVolatileAPRPool* pool = NULL);
-    static bool removeDir(const std::string& dirname, LLVolatileAPRPool* pool = NULL);
-
-    // Returns bytes read/written, 0 if read/write fails:
-    static S32 readEx(const std::string& filename, void *buf, S32 offset, S32 nbytes, LLVolatileAPRPool* pool = NULL);
-    static S32 writeEx(const std::string& filename, const void *buf, S32 offset, S32 nbytes, LLVolatileAPRPool* pool = NULL); // offset<0 means append
 //*******************************************************************************************************************************
 };
 
-
 #endif // LL_LLAPR_H
diff --git a/indra/llcommon/llerror.cpp b/indra/llcommon/llerror.cpp
index 8ae0fabcc6..5b42c83a14 100644..100755
--- a/indra/llcommon/llerror.cpp
+++ b/indra/llcommon/llerror.cpp
@@ -481,13 +481,9 @@ namespace
 
         std::string file = user_dir + "/logcontrol-dev.xml";
 
-        llstat stat_info;
-        if (LLFile::stat(file, &stat_info)) {
-            // NB: stat returns non-zero if it can't read the file, for example
-            // if it doesn't exist.  LLFile has no better abstraction for
-            // testing for file existence.
-
-            file = app_dir + "/logcontrol.xml";
+        if (!LLFile::isfile(file))
+        {
+             file = app_dir + "/logcontrol.xml";
         }
         return * new LogControlFile(file);
             // NB: This instance is never freed
diff --git a/indra/llcommon/llfile.cpp b/indra/llcommon/llfile.cpp
index a539e4fe28..ff87d8ce10 100644..100755
--- a/indra/llcommon/llfile.cpp
+++ b/indra/llcommon/llfile.cpp
@@ -29,22 +29,17 @@
 
 #include "linden_common.h"
 #include "llfile.h"
-#include "llstring.h"
 #include "llerror.h"
 #include "stringize.h"
 
 #if LL_WINDOWS
-#include "llwin32headers.h"
-#include <vector>
+#include <fcntl.h>
 #else
 #include <errno.h>
+#include <sys/file.h>
 #endif
 
-using namespace std;
-
-static std::string empty;
-
-// Many of the methods below use OS-level functions that mess with errno. Wrap
+// Some of the methods below use OS-level functions that mess with errno. Wrap
 // variants of strerror() to report errors.
 
 #if LL_WINDOWS
@@ -79,6 +74,7 @@ static errentry const errtable[]
     { ERROR_CURRENT_DIRECTORY,      EACCES    },  //   16
     { ERROR_NOT_SAME_DEVICE,        EXDEV     },  //   17
     { ERROR_NO_MORE_FILES,          ENOENT    },  //   18
+    { ERROR_SHARING_VIOLATION,      EACCES    },  //   32
     { ERROR_LOCK_VIOLATION,         EACCES    },  //   33
     { ERROR_BAD_NETPATH,            ENOENT    },  //   53
     { ERROR_NETWORK_ACCESS_DENIED,  EACCES    },  //   65
@@ -109,22 +105,25 @@ static errentry const errtable[]
     { ERROR_NOT_ENOUGH_QUOTA,       ENOMEM    }   // 1816
 };
 
-static int set_errno_from_oserror(unsigned long oserr)
+static int get_errno_from_oserror(int oserr)
 {
     if (!oserr)
         return 0;
 
     // Check the table for the Windows OS error code
-    for (const struct errentry &entry : errtable)
+    for (const struct errentry& entry : errtable)
     {
         if (oserr == entry.oserr)
         {
-            _set_errno(entry.errcode);
-            return -1;
+            return entry.errcode;
         }
     }
+    return EINVAL;
+}
 
-    _set_errno(EINVAL);
+static int set_errno_from_oserror(unsigned long oserr)
+{
+    _set_errno(get_errno_from_oserror(oserr));
     return -1;
 }
 
@@ -136,69 +135,8 @@ std::string strerr(int errn)
     return buffer;
 }
 
-inline bool is_slash(wchar_t const c)
-{
-    return c == L'\\' || c == L'/';
-}
-
-static std::wstring utf8path_to_wstring(const std::string& utf8path)
-{
-    if (utf8path.size() >= MAX_PATH)
-    {
-        // By prepending "\\?\" to a path, Windows widechar file APIs will not fail on long path names
-        std::wstring utf16path = L"\\\\?\\" + ll_convert<std::wstring>(utf8path);
-        // We need to make sure that the path does not contain forward slashes as above
-        // prefix does bypass the path normalization that replaces slashes with backslashes
-        // before passing the path to kernel mode APIs
-        std::replace(utf16path.begin(), utf16path.end(), L'/', L'\\');
-        return utf16path;
-    }
-    return ll_convert<std::wstring>(utf8path);
-}
-
-static unsigned short get_fileattr(const std::wstring& utf16path, bool dontFollowSymLink = false)
-{
-    unsigned long  flags = FILE_FLAG_BACKUP_SEMANTICS;
-    if (dontFollowSymLink)
-    {
-        flags |= FILE_FLAG_OPEN_REPARSE_POINT;
-    }
-    HANDLE file_handle = CreateFileW(utf16path.c_str(), FILE_READ_ATTRIBUTES,
-                                     FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
-                                     nullptr, OPEN_EXISTING, flags, nullptr);
-    if (file_handle != INVALID_HANDLE_VALUE)
-    {
-        FILE_ATTRIBUTE_TAG_INFO attribute_info;
-        if (GetFileInformationByHandleEx(file_handle, FileAttributeTagInfo, &attribute_info, sizeof(attribute_info)))
-        {
-            // A volume path alone (only drive letter) is not recognized as directory while it technically is
-            bool is_directory = (attribute_info.FileAttributes & FILE_ATTRIBUTE_DIRECTORY) ||
-                                (iswalpha(utf16path[0]) && utf16path[1] == ':' &&
-                                 (!utf16path[2] || (is_slash(utf16path[2]) && !utf16path[3])));
-            unsigned short st_mode = is_directory ? S_IFDIR :
-                                     (attribute_info.FileAttributes & FILE_ATTRIBUTE_REPARSE_POINT ? S_IFLNK : S_IFREG);
-            st_mode |= (attribute_info.FileAttributes & FILE_ATTRIBUTE_READONLY) ? S_IREAD : S_IREAD | S_IWRITE;
-            // we do not try to guess executable flag
-
-            // propagate user bits to group/other fields:
-            st_mode |= (st_mode & 0700) >> 3;
-            st_mode |= (st_mode & 0700) >> 6;
-
-            CloseHandle(file_handle);
-            return st_mode;
-        }
-    }
-    // Retrieve last error and set errno before calling CloseHandle()
-    set_errno_from_oserror(GetLastError());
-
-    if (file_handle != INVALID_HANDLE_VALUE)
-    {
-        CloseHandle(file_handle);
-    }
-    return 0;
-}
-
 #else
+
 // On Posix we want to call strerror_r(), but alarmingly, there are two
 // different variants. The one that returns int always populates the passed
 // buffer (except in case of error), whereas the other one always returns a
@@ -245,9 +183,50 @@ std::string strerr(int errn)
     return message_from(errn, buffer, sizeof(buffer),
                         strerror_r(errn, buffer, sizeof(buffer)));
 }
+
 #endif  // ! LL_WINDOWS
 
-static int warnif(const std::string& desc, const std::string& filename, int rc, int accept = 0)
+#if LL_WINDOWS && 0 // turn on to debug file-locking problems
+#define PROCESS_LOCKING_CHECK 1
+static void find_locking_process(const std::string& filename)
+{
+    // Only do any of this stuff (before LL_ENDL) if it will be logged.
+    LL_DEBUGS("LLFile") << "";
+    // wrong way
+    std::string TEMP = LLFile::tmpdir();
+    if (TEMP.empty())
+    {
+        LL_CONT << "No $TEMP, not running 'handle'";
+    }
+    else
+    {
+        std::string tf(TEMP);
+        tf += "\\handle.tmp";
+        // http://technet.microsoft.com/en-us/sysinternals/bb896655
+        std::string cmd(STRINGIZE("handle \"" << filename
+                        // "openfiles /query /v | fgrep -i \"" << filename
+                        << "\" > \"" << tf << '"'));
+        LL_CONT << cmd;
+        if (system(cmd.c_str()) != 0)
+        {
+            LL_CONT << "\nDownload 'handle.exe' from http://technet.microsoft.com/en-us/sysinternals/bb896655";
+        }
+        else
+        {
+            std::ifstream inf(tf);
+            std::string   line;
+            while (std::getline(inf, line))
+            {
+                LL_CONT << '\n' << line;
+            }
+        }
+        LLFile::remove(tf);
+    }
+    LL_CONT << LL_ENDL;
+}
+#endif // LL_WINDOWS hack to identify processes holding file open
+
+static int warnif(const std::string& desc, const std::string& filename, int rc, int suppress_warning = 0)
 {
     if (rc < 0)
     {
@@ -256,319 +235,951 @@ static int warnif(const std::string& desc, const std::string& filename, int rc,
 
         // For certain operations, a particular errno value might be
         // acceptable -- e.g. stat() could permit ENOENT, mkdir() could permit
-        // EEXIST. Don't warn if caller explicitly says this errno is okay.
-        if (errn != accept)
+        // EEXIST. Don't log a warning if caller explicitly says this errno is okay.
+        if (errn != suppress_warning)
         {
-            LL_WARNS("LLFile") << "Couldn't " << desc << " '" << filename
-                               << "' (errno " << errn << "): " << strerr(errn) << LL_ENDL;
+            LL_WARNS("LLFile") << "Couldn't " << desc << " '" << filename << "' (errno " << errn << "): " << strerr(errn) << LL_ENDL;
         }
-#if 0 && LL_WINDOWS                 // turn on to debug file-locking problems
+#if PROCESS_LOCKING_CHECK
         // If the problem is "Permission denied," maybe it's because another
         // process has the file open. Try to find out.
-        if (errn == EACCES)         // *not* EPERM
+        if (errn == EACCES) // *not* EPERM
         {
-            // Only do any of this stuff (before LL_ENDL) if it will be logged.
-            LL_DEBUGS("LLFile") << empty;
-            // would be nice to use LLDir for this, but dependency goes the
-            // wrong way
-            const char* TEMP = LLFile::tmpdir();
-            if (! (TEMP && *TEMP))
-            {
-                LL_CONT << "No $TEMP, not running 'handle'";
-            }
-            else
-            {
-                std::string tf(TEMP);
-                tf += "\\handle.tmp";
-                // http://technet.microsoft.com/en-us/sysinternals/bb896655
-                std::string cmd(STRINGIZE("handle \"" << filename
-                                          // "openfiles /query /v | fgrep -i \"" << filename
-                                          << "\" > \"" << tf << '"'));
-                LL_CONT << cmd;
-                if (system(cmd.c_str()) != 0)
-                {
-                    LL_CONT << "\nDownload 'handle.exe' from http://technet.microsoft.com/en-us/sysinternals/bb896655";
-                }
-                else
-                {
-                    std::ifstream inf(tf);
-                    std::string line;
-                    while (std::getline(inf, line))
-                    {
-                        LL_CONT << '\n' << line;
-                    }
-                }
-                LLFile::remove(tf);
-            }
-            LL_CONT << LL_ENDL;
+            find_locking_process(filename);
         }
-#endif  // LL_WINDOWS hack to identify processes holding file open
+#endif
     }
     return rc;
 }
 
-// static
-int LLFile::mkdir(const std::string& dirname, int perms)
+static int warnif(const std::string& desc, const std::string& filename, const std::error_code& ec, int suppress_warning = 0)
 {
-    // We often use mkdir() to ensure the existence of a directory that might
-    // already exist. There is no known case in which we want to call out as
-    // an error the requested directory already existing.
+    if (ec)
+    {
+        // get Posix errno from the std::error_code so we can compare it to the suppress_warning parameter
+        // to see when a caller wants us to not generate a warning for a particular error code
 #if LL_WINDOWS
-    // permissions are ignored on Windows
-    int rc = 0;
-    std::wstring utf16dirname = utf8path_to_wstring(dirname);
-    if (!CreateDirectoryW(utf16dirname.c_str(), nullptr))
+        int errn = get_errno_from_oserror(ec.value());
+#else
+        int errn = ec.value();
+#endif
+        // For certain operations, a particular errno value might be acceptable
+        // Don't warn if caller explicitly says this errno is okay.
+        if (errn != suppress_warning)
+        {
+            LL_WARNS("LLFile") << "Couldn't " << desc << " '" << filename << "' (errno " << errn << "): " << ec.message() << LL_ENDL;
+        }
+#if PROCESS_LOCKING_CHECK
+        // Try to detect locked files by other processes
+        if (ec.value() == ERROR_SHARING_VIOLATION || ec.value() == ERROR_LOCK_VIOLATION)
+        {
+            find_locking_process(filename);
+        }
+#endif
+        return -1;
+    }
+    return 0;
+}
+
+#if LL_WINDOWS
+
+inline int set_ec_from_system_error(std::error_code& ec, DWORD error)
+{
+    ec.assign(error, std::system_category());
+    return -1;
+}
+
+static int set_ec_from_system_error(std::error_code& ec)
+{
+    return set_ec_from_system_error(ec, GetLastError());
+}
+
+inline int set_ec_to_parameter_error(std::error_code& ec)
+{
+    return set_ec_from_system_error(ec, ERROR_INVALID_PARAMETER);
+}
+
+inline int set_ec_to_outofmemory_error(std::error_code& ec)
+{
+    return set_ec_from_system_error(ec, ERROR_NOT_ENOUGH_MEMORY);
+}
+
+inline DWORD decode_access_mode(std::ios_base::openmode omode)
+{
+    switch (omode & (LLFile::in | LLFile::out))
+    {
+        case LLFile::in:
+            return GENERIC_READ;
+        case LLFile::out:
+            return GENERIC_WRITE;
+        case static_cast<std::ios_base::openmode>(LLFile::in | LLFile::out):
+            return GENERIC_READ | GENERIC_WRITE;
+    }
+    if (omode & LLFile::app)
+    {
+        return GENERIC_WRITE;
+    }
+    return 0;
+}
+
+inline DWORD decode_open_create_flags(std::ios_base::openmode omode)
+{
+    if (omode & LLFile::noreplace)
     {
-        // Only treat other errors than an already existing file as a real error
-        unsigned long oserr = GetLastError();
-        if (oserr != ERROR_ALREADY_EXISTS)
+        return CREATE_NEW; // create if it does not exist, otherwise fail
+    }
+    if (omode & LLFile::trunc)
+    {
+        if (!(omode & LLFile::out))
         {
-            rc = set_errno_from_oserror(oserr);
+            return TRUNCATE_EXISTING; // open and truncate if it exists, otherwise fail
         }
+        return CREATE_ALWAYS; // open and truncate if it exists, otherwise create it
+    }
+    if (!(omode & LLFile::out))
+    {
+        return OPEN_EXISTING; // open if it exists, otherwise fail
     }
+    // LLFile::app or (LLFile::out and (!LLFile::trunc or !LLFile::noreplace))
+    return OPEN_ALWAYS; // open if it exists, otherwise create it
+}
+
+inline DWORD decode_share_mode(int omode)
+{
+    if (omode & LLFile::exclusive)
+    {
+        return 0; // allow no other access
+    }
+    if (omode & LLFile::shared)
+    {
+        return FILE_SHARE_READ; // allow read access
+    }
+    return FILE_SHARE_READ | FILE_SHARE_WRITE; // allow read and write access to others
+}
+
+inline DWORD decode_attributes(std::ios_base::openmode omode, int perm)
+{
+    return (perm & S_IWRITE) ? FILE_ATTRIBUTE_NORMAL : FILE_ATTRIBUTE_READONLY;
+}
+
+// Under Windows the values for the std::ios_base::seekdir constants match the according FILE_BEGIN
+// and other constants but we do a programmatic translation for now to be sure
+static DWORD seek_mode_from_dir(std::ios_base::seekdir seekdir)
+{
+    switch (seekdir)
+    {
+        case LLFile::beg:
+            return FILE_BEGIN;
+        case LLFile::cur:
+            return FILE_CURRENT;
+        case LLFile::end:
+            return FILE_END;
+    }
+    return FILE_BEGIN;
+}
+
 #else
-    int rc = ::mkdir(dirname.c_str(), (mode_t)perms);
-    if (rc < 0 && errno == EEXIST)
+
+inline int set_ec_from_system_error(std::error_code& ec, int error)
+{
+    ec.assign(error, std::system_category());
+    return -1;
+}
+
+static int set_ec_from_system_error(std::error_code& ec)
+{
+    return set_ec_from_system_error(ec, errno);
+}
+
+inline int set_ec_to_parameter_error(std::error_code& ec)
+{
+    return set_ec_from_system_error(ec, EINVAL);
+}
+
+inline int set_ec_to_outofmemory_error(std::error_code& ec)
+{
+    return set_ec_from_system_error(ec, ENOMEM);
+}
+
+inline int decode_access_mode(std::ios_base::openmode omode)
+{
+    if (omode & LLFile::out)
     {
-        // this is not the error you want, move along
-        return 0;
+        if (omode & LLFile::in)
+        {
+            return O_RDWR;
+        }
+        return O_WRONLY;
+    }
+    return O_RDONLY;
+
+    /*switch (omode & (LLFile::in | LLFile::out))
+    {
+        case LLFile::out:
+            return O_WRONLY;
+        case static_cast<std::ios_base::openmode>(LLFile::in | LLFile::out):
+            return O_RDWR;
+    }
+    return O_RDONLY;*/
+}
+
+inline int decode_open_mode(std::ios_base::openmode omode)
+{
+    int flags = O_CREAT | decode_access_mode(omode);
+    if (omode & LLFile::app)
+    {
+        flags |= O_APPEND;
     }
+    if (omode & LLFile::trunc)
+    {
+        flags |= O_TRUNC;
+    }
+    if (omode & LLFile::binary)
+    {
+        // Not a thing under *nix
+    }
+    if (omode & LLFile::noreplace)
+    {
+        flags |= O_EXCL;
+    }
+    return flags;
+}
+
+inline int decode_lock_mode(std::ios_base::openmode omode)
+{
+    int lmode = omode & LLFile::noblock ? LOCK_NB : 0;
+    if (omode & LLFile::lock_mask)
+    {
+        if (omode & LLFile::exclusive)
+        {
+            return lmode | LOCK_EX;
+        }
+        return lmode | LOCK_SH;
+    }
+    return lmode | LOCK_UN;
+}
+
+// Under Linux and Mac the values for the std::ios_base::seekdir constants match the according SEEK_SET
+// and other constants but we do a programmatic translation for now to be sure
+inline int seek_mode_from_dir(std::ios_base::seekdir seekdir)
+{
+    switch (seekdir)
+    {
+        case LLFile::beg:
+            return SEEK_SET;
+        case LLFile::cur:
+            return SEEK_CUR;
+        case LLFile::end:
+            return SEEK_END;
+    }
+    return SEEK_SET;
+}
+
 #endif
-    // anything else might be a problem
-    return warnif("mkdir", dirname, rc);
+
+inline int clear_error(std::error_code& ec)
+{
+    ec.clear();
+    return 0;
 }
 
-// static
-int LLFile::rmdir(const std::string& dirname, int suppress_error)
+inline bool are_open_mode_flags_invalid(std::ios_base::openmode omode)
+{
+    // at least one of input or output needs to be specified
+    if (!(omode & (LLFile::in | LLFile::out)))
+    {
+        return true;
+    }
+    // output must be possible for any of the extra options
+    if (!(omode & LLFile::out) && (omode & (LLFile::trunc | LLFile::app | LLFile::noreplace)))
+    {
+        return true;
+    }
+    // invalid combination, mutually exclusive
+    if ((omode & LLFile::app) && (omode & (LLFile::trunc | LLFile::noreplace)))
+    {
+        return true;
+    }
+    return false;
+}
+
+//----------------------------------------------------------------------------------------
+// class member functions
+//----------------------------------------------------------------------------------------
+int LLFile::open(const std::string& filename, std::ios_base::openmode omode, std::error_code& ec, int perm)
 {
+    close(ec);
+    if (are_open_mode_flags_invalid(omode))
+    {
+        return set_ec_to_parameter_error(ec);
+    }
 #if LL_WINDOWS
-    std::wstring utf16dirname = utf8path_to_wstring(dirname);
-    int rc = _wrmdir(utf16dirname.c_str());
+    DWORD access = decode_access_mode(omode),
+          share = decode_share_mode(omode),
+          create = decode_open_create_flags(omode),
+          attributes = decode_attributes(omode, perm);
+
+    std::wstring file_path = utf8StringToWstring(filename);
+    mHandle = CreateFileW(file_path.c_str(), access, share, nullptr, create, attributes, nullptr);
+    // The dwShareMode = share parameter takes care of locking the file for other processes if indicated,
+    // no need to do anything else for file locking here
 #else
-    int rc = ::rmdir(dirname.c_str());
+    int oflags = decode_open_mode(omode);
+    int lmode = omode & LLFile::lock_mask;
+    mHandle = ::open(filename.c_str(), oflags, perm);
+    if (mHandle != InvalidHandle && lmode && lock(lmode | LLFile::noblock, ec) != 0)
+    {
+        close();
+        return -1;
+    }
 #endif
-    return warnif("rmdir", dirname, rc, suppress_error);
+    if (mHandle == InvalidHandle)
+    {
+        return set_ec_from_system_error(ec);
+    }
+
+    if (omode & LLFile::ate && seek(0, LLFile::end, ec) != 0)
+    {
+        close();
+        return -1;
+    }
+    mOpen = omode;
+    return clear_error(ec);
 }
 
-// static
-LLFILE* LLFile::fopen(const std::string& filename, const char* mode)
+S64 LLFile::size(std::error_code& ec)
 {
 #if LL_WINDOWS
-    std::wstring utf16filename = utf8path_to_wstring(filename);
-    std::wstring utf16mode = ll_convert<std::wstring>(std::string(mode));
-    return _wfopen(utf16filename.c_str(), utf16mode.c_str());
+    LARGE_INTEGER value = { 0 };
+    if (GetFileSizeEx(mHandle, &value))
+    {
+        clear_error(ec);
+        return value.QuadPart;
+    }
 #else
-    return ::fopen(filename.c_str(),mode);
+    struct stat statval;
+    if (fstat(mHandle, &statval) == 0)
+    {
+        clear_error(ec);
+        return statval.st_size;
+    }
 #endif
+    return set_ec_from_system_error(ec);
 }
 
-// static
-int LLFile::close(LLFILE * file)
+S64 LLFile::tell(std::error_code& ec)
 {
-    int ret_value = 0;
-    if (file)
+#if LL_WINDOWS
+    LARGE_INTEGER value = { 0 };
+    if (SetFilePointerEx(mHandle, value, &value, FILE_CURRENT))
     {
-        ret_value = fclose(file);
+        clear_error(ec);
+        return value.QuadPart;
     }
-    return ret_value;
+#else
+    off_t offset = lseek(mHandle, 0, SEEK_CUR);
+    if (offset != -1)
+    {
+        clear_error(ec);
+        return offset;
+    }
+#endif
+    return set_ec_from_system_error(ec);
 }
 
-// static
-std::string LLFile::getContents(const std::string& filename)
+int LLFile::seek(S64 pos, std::error_code& ec)
 {
-    LLFILE* fp = LLFile::fopen(filename, "rb");
-    if (fp)
+    return seek(pos, LLFile::beg, ec);
+}
+
+int LLFile::seek(S64 offset, std::ios_base::seekdir dir, std::error_code& ec)
+{
+    S64 newOffset = 0;
+#if LL_WINDOWS
+    DWORD seekdir = seek_mode_from_dir(dir);
+    LARGE_INTEGER value;
+    value.QuadPart = offset;
+    if (SetFilePointerEx(mHandle, value, (PLARGE_INTEGER)&newOffset, seekdir))
+#else
+    newOffset = lseek(mHandle, offset, seek_mode_from_dir(dir));
+    if (newOffset != -1)
+#endif
     {
-        fseek(fp, 0, SEEK_END);
-        U32 length = ftell(fp);
-        fseek(fp, 0, SEEK_SET);
+        return clear_error(ec);
+    }
+    return set_ec_from_system_error(ec);
+}
 
-        std::vector<char> buffer(length);
-        size_t nread = fread(buffer.data(), 1, length, fp);
-        fclose(fp);
+#if LL_WINDOWS
+inline DWORD next_buffer_size(S64 nbytes)
+{
+    return nbytes > 0x80000000 ? 0x80000000 : (DWORD)nbytes;
+}
+#endif
 
-        return std::string(buffer.data(), nread);
+S64 LLFile::read(void* buffer, S64 nbytes, std::error_code& ec)
+{
+    if (nbytes == 0)
+    {
+        // Nothing to do
+        return clear_error(ec);
     }
+    else if (!buffer || nbytes < 0)
+    {
+        return set_ec_to_parameter_error(ec);
+    }
+#if LL_WINDOWS
+    S64 totalBytes = 0;
+    char *ptr = (char*)buffer;
+    DWORD bytesRead, bytesToRead = next_buffer_size(nbytes);
 
-    return LLStringUtil::null;
+    // Read in chunks to support >4GB which the S64 nbytes value makes possible
+    while (ReadFile(mHandle, ptr, bytesToRead, &bytesRead, nullptr))
+    {
+        totalBytes += bytesRead;
+        if (nbytes <= totalBytes || // requested amount read
+            bytesRead < bytesToRead) // ReadFile encountered eof
+        {
+            clear_error(ec);
+            return totalBytes;
+        }
+        ptr += bytesRead;
+        bytesToRead = next_buffer_size(nbytes - totalBytes);
+    }
+#else
+    ssize_t bytesRead = ::read(mHandle, buffer, nbytes);
+    if (bytesRead != -1)
+    {
+        clear_error(ec);
+        return bytesRead;
+    }
+#endif
+    return set_ec_from_system_error(ec);
 }
 
-// static
-int LLFile::remove(const std::string& filename, int suppress_error)
+S64 LLFile::write(const void* buffer, S64 nbytes, std::error_code& ec)
 {
+    if (nbytes == 0)
+    {
+        // Nothing to do here
+        return clear_error(ec);
+    }
+    else if (!buffer || nbytes < 0)
+    {
+        return set_ec_to_parameter_error(ec);
+    }
 #if LL_WINDOWS
-    // Posix remove() works on both files and directories although on Windows
-    // remove() and its wide char variant _wremove() only removes files just
-    // as its siblings unlink() and _wunlink().
-    // If we really only want to support files we should instead use
-    // unlink() in the non-Windows part below too
-    int rc = -1;
-    std::wstring utf16filename = utf8path_to_wstring(filename);
-    unsigned short st_mode = get_fileattr(utf16filename);
-    if (S_ISDIR(st_mode))
+    // If this was opened in append mode, we emulate it on Windows
+    if (mOpen & LLFile::app && seek(0, LLFile::end, ec) != 0)
+    {
+        return -1;
+    }
+
+    S64 totalBytes = 0;
+    char* ptr = (char*)buffer;
+    DWORD bytesWritten, bytesToWrite = next_buffer_size(nbytes);
+
+    // Write in chunks to support >4GB which the S64 nbytes value makes possible
+    while (WriteFile(mHandle, ptr, bytesToWrite, &bytesWritten, nullptr))
+    {
+        totalBytes += bytesWritten;
+        if (nbytes <= totalBytes)
+        {
+            clear_error(ec);
+            return totalBytes;
+        }
+        ptr += bytesWritten;
+        bytesToWrite = next_buffer_size(nbytes - totalBytes);
+    }
+#else
+    ssize_t bytesWritten = ::write(mHandle, buffer, nbytes);
+    if (bytesWritten != -1)
+    {
+        clear_error(ec);
+        return bytesWritten;
+    }
+#endif
+    return set_ec_from_system_error(ec);
+}
+
+S64 LLFile::printf(const char* fmt, ...)
+{
+    va_list args1;
+    va_start(args1, fmt);
+    va_list args2;
+    va_copy(args2, args1);
+    int length = vsnprintf(nullptr, 0, fmt, args1);
+    va_end(args1);
+    if (length < 0)
     {
-        rc = _wrmdir(utf16filename.c_str());
+        va_end(args2);
+        return -1;
     }
-    else if (S_ISREG(st_mode))
+    void* buffer = malloc(length + 1);
+    if (!buffer)
     {
-        rc = _wunlink(utf16filename.c_str());
+        va_end(args2);
+        return -1;
     }
-    else if (st_mode)
+    length = vsnprintf((char*)buffer, length + 1, fmt, args2);
+    va_end(args2);
+    std::error_code ec;
+    S64 written = write(buffer, length, ec);
+    free(buffer);
+    return written;
+}
+
+int LLFile::lock(int mode, std::error_code& ec)
+{
+#if LL_WINDOWS
+    if (!(mode & LLFile::lock_mask))
     {
-        // it is something else than a file or directory
-        // this should not really happen as long as we do not allow for symlink
-        // detection in the optional parameter to get_fileattr()
-        rc = set_errno_from_oserror(ERROR_INVALID_PARAMETER);
+        if (UnlockFile(mHandle, 0, 0, MAXDWORD, MAXDWORD))
+        {
+            return clear_error(ec);
+        }
     }
     else
     {
-        // get_fileattr() failed and already set errno, preserve it for correct error reporting
+        OVERLAPPED overlapped = { 0 };
+        DWORD flags = (mode & LLFile::noblock) ? LOCKFILE_FAIL_IMMEDIATELY : 0;
+        if (mode & LLFile::exclusive)
+        {
+            flags |= LOCKFILE_EXCLUSIVE_LOCK;
+        }
+        // We lock the maximum range, since flock only supports locking the entire file too
+        if (LockFileEx(mHandle, flags, 0, MAXDWORD, MAXDWORD, &overlapped))
+        {
+            return clear_error(ec);
+        }
     }
 #else
-    int rc = ::remove(filename.c_str());
+    if (flock(mHandle, decode_lock_mode(static_cast<std::ios_base::openmode>(mode))) == 0)
+    {
+        return clear_error(ec);
+    }
 #endif
-    return warnif("remove", filename, rc, suppress_error);
+    return set_ec_from_system_error(ec);
+}
+
+int LLFile::close(std::error_code& ec)
+{
+    if (mHandle != InvalidHandle)
+    {
+        llfile_handle_t handle = InvalidHandle;
+        std::swap(handle, mHandle);
+#if LL_WINDOWS
+        if (!CloseHandle(handle))
+#else
+        if (::close(handle))
+#endif
+        {
+            return set_ec_from_system_error(ec);
+        }
+    }
+    return clear_error(ec);
+}
+
+int LLFile::close()
+{
+    std::error_code ec;
+    return close(ec);
 }
 
+//----------------------------------------------------------------------------------------
+// static member functions
+//----------------------------------------------------------------------------------------
+
 // static
-int LLFile::rename(const std::string& filename, const std::string& newname, int suppress_error)
+LLFILE* LLFile::fopen(const std::string& filename, const char* mode, int lmode)
 {
+    LLFILE* file;
 #if LL_WINDOWS
-    // Posix rename() will gladly overwrite a file at newname if it exists, the Windows
-    // rename(), respectively _wrename(), will bark on that. Instead call directly the Windows
-    // API MoveFileEx() and use its flags to specify that overwrite is allowed.
-    std::wstring utf16filename = utf8path_to_wstring(filename);
-    std::wstring utf16newname = utf8path_to_wstring(newname);
-    int rc = 0;
-    if (!MoveFileExW(utf16filename.c_str(), utf16newname.c_str(), MOVEFILE_REPLACE_EXISTING | MOVEFILE_COPY_ALLOWED))
+    int shflag = _SH_DENYNO;
+    switch (lmode)
     {
-        rc = set_errno_from_oserror(GetLastError());
+        case LLFile::exclusive:
+            shflag = _SH_DENYRW;
+            break;
+        case LLFile::shared:
+            shflag = _SH_DENYWR;
+            break;
     }
+    std::wstring file_path = utf8StringToWstring(filename);
+    std::wstring utf16mode = ll_convert<std::wstring>(std::string(mode));
+    file = _wfsopen(file_path.c_str(), utf16mode.c_str(), shflag);
 #else
-    int rc = ::rename(filename.c_str(),newname.c_str());
+    file = ::fopen(filename.c_str(), mode);
+    if (file && (lmode & (LLFile::lock_mask)))
+    {
+        // Rather fail on a sharing conflict than block
+        if (flock(fileno(file), decode_lock_mode(static_cast<std::ios_base::openmode>(lmode | LLFile::noblock))))
+        {
+            ::fclose(file);
+            file = nullptr;
+        }
+    }
 #endif
-    return warnif(STRINGIZE("rename to '" << newname << "' from"), filename, rc, suppress_error);
+    return file;
+}
+
+// static
+int LLFile::close(LLFILE* file)
+{
+    int ret_value = 0;
+    if (file)
+    {
+        ret_value = ::fclose(file);
+    }
+    return ret_value;
+}
+
+// static
+std::string LLFile::getContents(const std::string& filename)
+{
+    std::error_code ec;
+    return getContents(filename, ec);
+}
+
+// static
+std::string LLFile::getContents(const std::string& filename, std::error_code& ec)
+{
+    std::string buffer;
+    LLFile file(filename, LLFile::in | LLFile::binary, ec);
+    if (file)
+    {
+        S64 length = file.size(ec);
+        if (!ec && length > 0)
+        {
+            buffer = std::string(length, 0);
+            file.read(&buffer[0], length, ec);
+            if (ec)
+            {
+                buffer.clear();
+            }
+        }
+    }
+    return buffer;
 }
 
-// Make this a define rather than using magic numbers multiple times in the code
-#define LLFILE_COPY_BUFFER_SIZE 16384
+// static
+int LLFile::mkdir(const std::string& dirname)
+{
+    std::error_code ec;
+    std::filesystem::path file_path = utf8StringToPath(dirname);
+    // We often use mkdir() to ensure the existence of a directory that might
+    // already exist. There is no known case in which we want to call out as
+    // an error the requested directory already existing.
+    std::filesystem::create_directory(file_path, ec);
+    // The return value is only true if the directory was actually created.
+    // But if it already existed, ec still indicates success.
+    return warnif("mkdir", dirname, ec);
+}
 
 // static
-bool LLFile::copy(const std::string& from, const std::string& to)
+int LLFile::remove(const std::string& filename, int suppress_warning)
 {
-    bool copied = false;
-    LLFILE* in = LLFile::fopen(from, "rb");
-    if (in)
+    std::error_code ec;
+    std::filesystem::path file_path = utf8StringToPath(filename);
+    std::filesystem::remove(file_path, ec);
+    return warnif("remove", filename, ec, suppress_warning);
+}
+
+// static
+int LLFile::rename(const std::string& filename, const std::string& newname, int suppress_warning)
+{
+    std::error_code ec;
+    std::filesystem::path file_path = utf8StringToPath(filename);
+    std::filesystem::path new_path = utf8StringToPath(newname);
+    std::filesystem::rename(file_path, new_path, ec);
+    return warnif(STRINGIZE("rename to '" << newname << "' from"), filename, ec, suppress_warning);
+}
+
+// static
+S64 LLFile::read(const std::string& filename, void* buf, S64 offset, S64 nbytes)
+{
+    std::error_code ec;
+    return read(filename, buf, offset, nbytes, ec);
+}
+
+// static
+S64 LLFile::read(const std::string& filename, void* buf, S64 offset, S64 nbytes, std::error_code& ec)
+{
+    // if number of bytes is 0 or less there is nothing to do here
+    if (nbytes <= 0)
+    {
+        clear_error(ec);
+        return 0;
+    }
+
+    if (!buf || offset < 0)
     {
-        LLFILE* out = LLFile::fopen(to, "wb");
-        if (out)
+        set_ec_to_parameter_error(ec);
+    }
+    else
+    {
+        std::ios_base::openmode omode = LLFile::in | LLFile::binary;
+
+        LLFile file(filename, omode, ec);
+        if (!ec && (bool)file)
         {
-            char buf[LLFILE_COPY_BUFFER_SIZE];
-            size_t readbytes;
-            bool write_ok = true;
-            while (write_ok && (readbytes = fread(buf, 1, LLFILE_COPY_BUFFER_SIZE, in)))
+            if (offset > 0)
+            {
+                file.seek(offset, ec);
+            }
+            // else (offset == 0) file was just opened and should already be at 0.
+            if (!ec)
             {
-                if (fwrite(buf, 1, readbytes, out) != readbytes)
+                S64 bytes_read = file.read(buf, nbytes, ec);
+                if (!ec)
                 {
-                    LL_WARNS("LLFile") << "Short write" << LL_ENDL;
-                    write_ok = false;
+                    return bytes_read;
                 }
             }
-            if ( write_ok )
+        }
+    }
+    return warnif("read from file failed", filename, ec);
+}
+
+// static
+S64 LLFile::write(const std::string& filename, const void* buf, S64 offset, S64 nbytes)
+{
+    std::error_code ec;
+    return write(filename, buf, offset, nbytes, ec);
+}
+
+// static
+S64 LLFile::write(const std::string& filename, const void* buf, S64 offset, S64 nbytes, std::error_code& ec)
+{
+    // if number of bytes is 0 or less there is nothing to do here
+    if (nbytes <= 0)
+    {
+        clear_error(ec);
+        return 0;
+    }
+
+    if (!buf)
+    {
+        set_ec_to_parameter_error(ec);
+    }
+    else
+    {
+        std::ios_base::openmode omode = LLFile::out | LLFile::binary;
+        if (offset < 0)
+        {
+            omode |= LLFile::app;
+        }
+
+        LLFile file(filename, omode, ec);
+        if (!ec && (bool)file)
+        {
+            if (offset > 0)
+            {
+                file.seek(offset, ec);
+            }
+            // else (offset == 0) we are not appending, file was just opened and should already be at 0.
+            if (!ec)
             {
-                copied = true;
+                S64 bytes_written = file.write(buf, nbytes, ec);
+                if (!ec)
+                {
+                    return bytes_written;
+                }
             }
-            fclose(out);
         }
-        fclose(in);
+    }
+    return warnif("write to file failed", filename, ec);
+}
+
+// static
+bool LLFile::copy(const std::string& source, const std::string& target)
+{
+    std::error_code ec;
+    return copy(source, target, std::filesystem::copy_options::overwrite_existing, ec);
+}
+
+// static
+bool LLFile::copy(const std::string& source, const std::string& target, std::filesystem::copy_options options, std::error_code& ec)
+{
+    std::filesystem::path source_path = utf8StringToPath(source);
+    std::filesystem::path target_path = utf8StringToPath(target);
+    bool copied = std::filesystem::copy_file(source_path, target_path, options, ec);
+    if (!copied)
+    {
+        warnif(STRINGIZE("copy failed, to '" << target << "' from"), source, ec);
     }
     return copied;
 }
 
 // static
-int LLFile::stat(const std::string& filename, llstat* filestatus, int suppress_error)
+int LLFile::stat(const std::string& filename, llstat* filestatus, const char *fname, int suppress_warning)
 {
 #if LL_WINDOWS
-    std::wstring utf16filename = utf8path_to_wstring(filename);
-    int rc = _wstat64(utf16filename.c_str(), filestatus);
+    std::wstring file_path = utf8StringToWstring(filename);
+    int rc = _wstat64(file_path.c_str(), filestatus);
 #else
     int rc = ::stat(filename.c_str(), filestatus);
 #endif
-    return warnif("stat", filename, rc, suppress_error);
+    return warnif(fname ? fname : "stat", filename, rc, suppress_warning);
 }
 
 // static
-unsigned short LLFile::getattr(const std::string& filename, bool dontFollowSymLink, int suppress_error)
+std::time_t LLFile::getCreationTime(const std::string& filename, int suppress_warning)
 {
-#if LL_WINDOWS
-    // _wstat64() is a bit heavyweight on Windows, use a more lightweight API
-    // to just get the attributes
-    int rc = -1;
-    std::wstring utf16filename = utf8path_to_wstring(filename);
-    unsigned short st_mode = get_fileattr(utf16filename, dontFollowSymLink);
-    if (st_mode)
+    // As of C++20 there is no functionality in std::filesystem to retrieve this information
+    llstat filestat;
+    int rc = stat(filename, &filestat, "getCreationTime", suppress_warning);
+    if (rc == 0)
     {
-        return st_mode;
-    }
+#if LL_DARWIN
+        return filestat.st_birthtime;
 #else
-    llstat filestatus;
-    int rc = dontFollowSymLink ? ::lstat(filename.c_str(), &filestatus) : ::stat(filename.c_str(), &filestatus);
+        // Linux stat() doesn't have a creation/birth time (st_ctime really is the last status
+        // change or inode attributes change) unless we would use statx() instead. But that is
+        // a major effort, which would require Linux specific changes to LLFile::stat() above
+        // and possibly adaptions for other platforms that we leave for a later exercise if it
+        // is ever desired.
+        return filestat.st_ctime;
+#endif
+    }
+    return 0;
+}
+
+// static
+std::time_t LLFile::getModificationTime(const std::string& filename, int suppress_warning)
+{
+    // tried to use std::filesystem::last_write_time() but the whole std::chrono infrastructure is as of
+    // C++20 still not fully implemented on all platforms. Specifically MacOS C++20 seems lacking here,
+    // and Windows requires a roundabout through std::chrono::utc_clock to then get a
+    // std::chrono::system_clock that can return a more useful time_t.
+    // So we take the easy way out in a similar way as with getCreationTime().
+    llstat filestat;
+    int rc = stat(filename, &filestat, "getModificationTime", suppress_warning);
     if (rc == 0)
     {
-        return filestatus.st_mode;
+        return filestat.st_mtime;
     }
-#endif
-    warnif("getattr", filename, rc, suppress_error);
     return 0;
 }
 
 // static
+S64 LLFile::size(const std::string& filename, int suppress_warning)
+{
+    std::error_code ec;
+    std::filesystem::path file_path = utf8StringToPath(filename);
+    std::intmax_t size = static_cast<std::intmax_t>(std::filesystem::file_size(file_path, ec));
+    if (ec)
+    {
+        return warnif("size", filename, ec, suppress_warning);
+    }
+    return size;
+}
+
+// static
+std::filesystem::file_status LLFile::getStatus(const std::string& filename, bool dontFollowSymLink, int suppress_warning)
+{
+    std::error_code ec;
+    std::filesystem::path file_path = utf8StringToPath(filename);
+    std::filesystem::file_status status;
+    if (dontFollowSymLink)
+    {
+        status = std::filesystem::symlink_status(file_path, ec);
+    }
+    else
+    {
+        status = std::filesystem::status(file_path, ec);
+    }
+    warnif("getStatus()", filename, ec, suppress_warning);
+    return status;
+}
+
+// static
+bool LLFile::exists(const std::string& filename)
+{
+    std::filesystem::file_status status = getStatus(filename);
+    return std::filesystem::exists(status);
+}
+
+// static
 bool LLFile::isdir(const std::string& filename)
 {
-    return S_ISDIR(getattr(filename));
+    std::filesystem::file_status status = getStatus(filename);
+    return std::filesystem::is_directory(status);
 }
 
 // static
 bool LLFile::isfile(const std::string& filename)
 {
-    return S_ISREG(getattr(filename));
+    std::filesystem::file_status status = getStatus(filename);
+    return std::filesystem::is_regular_file(status);
 }
 
 // static
 bool LLFile::islink(const std::string& filename)
 {
-    return S_ISLNK(getattr(filename, true));
+    std::filesystem::file_status status = getStatus(filename, true);
+    return std::filesystem::is_symlink(status);
 }
 
 // static
-const char *LLFile::tmpdir()
+const std::string& LLFile::tmpdir()
 {
-    static std::string utf8path;
-
-    if (utf8path.empty())
+    static std::string temppath;
+    if (temppath.empty())
     {
-        char sep;
-#if LL_WINDOWS
-        sep = '\\';
+        temppath = std::filesystem::temp_directory_path().string();
+    }
 
-        std::vector<wchar_t> utf16path(MAX_PATH + 1);
-        GetTempPathW(static_cast<DWORD>(utf16path.size()), &utf16path[0]);
-        utf8path = ll_convert_wide_to_string(&utf16path[0]);
+    char sep;
+#if LL_WINDOWS
+    sep = '\\';
 #else
-        sep = '/';
+    sep = '/';
+#endif
+    if (temppath[temppath.size() - 1] != sep)
+    {
+        temppath += sep;
+    }
+    return temppath;
+}
 
-        utf8path = LLStringUtil::getenv("TMPDIR", "/tmp/");
+// static
+std::filesystem::path LLFile::utf8StringToPath(const std::string& pathname)
+{
+#if LL_WINDOWS
+    return ll_convert<std::wstring>(pathname);
+#else
+    return pathname;
 #endif
-        if (utf8path[utf8path.size() - 1] != sep)
+}
+
+#if LL_WINDOWS
+
+// static
+std::wstring LLFile::utf8StringToWstring(const std::string& pathname)
+{
+    std::wstring utf16string(ll_convert<std::wstring>(pathname));
+    if (utf16string.size() >= MAX_PATH)
+    {
+        // By going through std::filesystem::path we get a lot of path sanitation done for us that
+        // is needed when passing a path with a kernel object space prefix to Windows API functions
+        // since this prefix disables the kernel32 path normalization
+        std::filesystem::path utf16path(utf16string);
+
+        // By prepending "\\?\" to a path, Windows widechar file APIs will not fail on long path names
+        utf16string.assign(L"\\\\?\\").append(utf16path);
+
+        /* remove trailing spaces and dots (yes, Windows really does that) */
+        size_t last_valid = utf16string.find_last_not_of(L" \t.");
+        if (last_valid == std::wstring::npos)
         {
-            utf8path += sep;
+            return std::wstring();
         }
+        return utf16string.substr(0, last_valid + 1);
     }
-    return utf8path.c_str();
+    return utf16string;
 }
 
-#if LL_WINDOWS
-
 /************** input file stream ********************************/
 
 llifstream::llifstream() {}
@@ -586,10 +1197,8 @@ void llifstream::open(const std::string& _Filename, ios_base::openmode _Mode)
                         _Mode | ios_base::in);
 }
 
-
 /************** output file stream ********************************/
 
-
 llofstream::llofstream() {}
 
 // explicit
@@ -605,30 +1214,4 @@ void llofstream::open(const std::string& _Filename, ios_base::openmode _Mode)
                         _Mode | ios_base::out);
 }
 
-/************** helper functions ********************************/
-
-std::streamsize llifstream_size(llifstream& ifstr)
-{
-    if(!ifstr.is_open()) return 0;
-    std::streampos pos_old = ifstr.tellg();
-    ifstr.seekg(0, ios_base::beg);
-    std::streampos pos_beg = ifstr.tellg();
-    ifstr.seekg(0, ios_base::end);
-    std::streampos pos_end = ifstr.tellg();
-    ifstr.seekg(pos_old, ios_base::beg);
-    return pos_end - pos_beg;
-}
-
-std::streamsize llofstream_size(llofstream& ofstr)
-{
-    if(!ofstr.is_open()) return 0;
-    std::streampos pos_old = ofstr.tellp();
-    ofstr.seekp(0, ios_base::beg);
-    std::streampos pos_beg = ofstr.tellp();
-    ofstr.seekp(0, ios_base::end);
-    std::streampos pos_end = ofstr.tellp();
-    ofstr.seekp(pos_old, ios_base::beg);
-    return pos_end - pos_beg;
-}
-
 #endif  // LL_WINDOWS
diff --git a/indra/llcommon/llfile.h b/indra/llcommon/llfile.h
index 04a2946ac4..0036e896c3 100644..100755
--- a/indra/llcommon/llfile.h
+++ b/indra/llcommon/llfile.h
@@ -35,118 +35,359 @@
  * Attempts to mostly mirror the POSIX style IO functions.
  */
 
-typedef FILE    LLFILE;
-
 #include <fstream>
+#include <filesystem>
 #include <sys/stat.h>
 
 #if LL_WINDOWS
+#include <windows.h>
 // The Windows version of stat function and stat data structure are called _stat64
 // We use _stat64 here to support 64-bit st_size and time_t values
-typedef struct _stat64  llstat;
+typedef struct _stat64 llstat;
 #else
-typedef struct stat     llstat;
 #include <sys/types.h>
+typedef struct stat llstat;
 #endif
 
-#ifndef S_ISREG
-# define S_ISREG(x) (((x) & S_IFMT) == S_IFREG)
-#endif
-
-#ifndef S_ISDIR
-# define S_ISDIR(x) (((x) & S_IFMT) == S_IFDIR)
-#endif
-
-// Windows C runtime library does not define this and does not support symlink detection in the
-// stat functions but we do in our getattr() function
-#ifndef S_IFLNK
-#define S_IFLNK 0xA000 /* symlink */
-#endif
-
-#ifndef S_ISLNK
-#define S_ISLNK(x) (((x) & S_IFMT) == S_IFLNK)
-#endif
+typedef FILE LLFILE;
 
 #include "llstring.h" // safe char* -> std::string conversion
 
-/// LLFile is a class of static functions operating on paths
+/// This class provides a selection of functions to operate on files through names and
+/// a class implementation to represent a file for reading and writing to it
 /// All the functions with a path string input take UTF8 path/filenames
+///
+/// @nosubgrouping
+///
 class LL_COMMON_API LLFile
 {
 public:
+    // ================================================================================
+    /// @name Constants
+    ///
+    ///@{
+    /** These can be passed to the omode parameter of LLFile::open() and its constructor
+
+    This is similar to the openmode flags for std:fstream but not exactly the same
+    std::fstream open() does not allow to open a file for writing without either
+    forcing the file to be truncated on open or all write operations being always
+    appended to the end of the file or failing to open when the file does not exist.
+    But to allow implementing the LLAPRFile::writeEx() functionality we need to be
+    able to write at a random position to the file without truncating it on open.
+
+    any other combinations than listed here are not allowed and will cause an error
+
+    bin    in     out    trunc  app    noreplace  File exists       File doesn't exist
+    ----------------------------------------------------------------------------------
+    -      +      -      -      -      -          Open at begin     Failure to open
+    +      +      -      -      -      -            "                 "
+    -      -      +      -      -      -            "               Create new
+    +      -      +      -      -      -            "                 "
+    -      +      +      -      -      -            "                 "
+    +      +      +      -      -      -            "                 "
+    ----------------------------------------------------------------------------------
+    -      -      +      +      -      -          Destroy contents  Create new
+    +      -      +      +      -      -            "                 "
+    -      +      +      +      -      -            "                 "
+    +      +      +      +      -      -            "                 "
+    ----------------------------------------------------------------------------------
+    -      -      +      x      -      +          Failure to open   Create new
+    +      -      +      x      -      +            "                 "
+    -      +      +      x      -      +            "                 "
+    +      +      +      x      -      +            "                 "
+    ----------------------------------------------------------------------------------
+    -      -      +      -      +      -          Write to end      Create new
+    +      -      +      -      +      -            "                 "
+    -      +      +      -      +      -            "                 "
+    +      +      +      -      +      -            "                 "
+    ----------------------------------------------------------------------------------
+    */
+    static const std::ios_base::openmode app       = static_cast<std::ios_base::openmode>(1 << 1);    // append to end
+    static const std::ios_base::openmode ate       = static_cast<std::ios_base::openmode>(1 << 2);    // initialize to end
+    static const std::ios_base::openmode binary    = static_cast<std::ios_base::openmode>(1 << 3);    // binary mode
+    static const std::ios_base::openmode in        = static_cast<std::ios_base::openmode>(1 << 4);    // for reading
+    static const std::ios_base::openmode out       = static_cast<std::ios_base::openmode>(1 << 5);    // for writing          // for writing and reading
+    static const std::ios_base::openmode trunc     = static_cast<std::ios_base::openmode>(1 << 6);    // truncate on open
+    static const std::ios_base::openmode noreplace = static_cast<std::ios_base::openmode>(1 << 7);    // no replace if it exists
+
+    /// Additional optional flags to omode in open() and lmode in fopen() or lock()
+    /// to indicate which sort of lock if any to attempt to get
+    ///
+    /// NOTE: there is a fundamental difference between platforms.
+    /// On Windows this lock is mandatory as it is part of the API to open a file handle and other
+    /// processes can not avoid it. If a file was opened denying other processes read and/or write
+    /// access, trying to open the same file in another process with that access will fail.
+    /// On Mac and Linux it is only an advisory lock implemented through the flock() system call.
+    /// This means that any other application needs to also attempt to at least acquire a shared
+    /// lock on the file in order to notice that the file is actually already locked. It can
+    /// therefore not be used to prevent random other applications from accessing the file, but it
+    /// works for other viewer processes when they use either the LLFile::open() or LLFile::fopen()
+    /// functions with the appropriate lock flags to open a file.
+    static const std::ios_base::openmode exclusive = static_cast<std::ios_base::openmode>(1 << 16);
+    static const std::ios_base::openmode shared    = static_cast<std::ios_base::openmode>(1 << 17);
+
+    /// Additional lmode flag to indicate to rather fail instead of blocking when trying
+    /// to acquire a lock with LLFile::lock()
+    static const std::ios_base::openmode noblock   = static_cast<std::ios_base::openmode>(1 << 18);
+
+    /// The mask value for the lock mask bits
+    static const std::ios_base::openmode lock_mask = static_cast<std::ios_base::openmode>(exclusive | shared);
+
+    /// One of these can be passed to the dir parameter of LLFile::seek()
+    static const std::ios_base::seekdir beg        = std::ios_base::beg;
+    static const std::ios_base::seekdir cur        = std::ios_base::cur;
+    static const std::ios_base::seekdir end        = std::ios_base::end;
+    ///@}
+
+    // ================================================================================
+    /// @name constructor/deconstructor
+    ///
+    ///@{
+    ///  default constructor
+    LLFile() : mHandle(InvalidHandle) {}
+
+    /// no copy constructor
+    LLFile(const LLFile&) = delete;
+
+    /// move constructor
+    LLFile(LLFile&& other) noexcept
+    {
+        mHandle = other.mHandle;
+        other.mHandle = InvalidHandle;
+    }
+
+    /// constructor opening the file
+    LLFile(const std::string& filename, std::ios_base::openmode omode, std::error_code& ec, int perm = 0666) :
+        mHandle(InvalidHandle)
+    {
+        open(filename, omode, ec, perm);
+    }
+
+    /// destructor always attempts to close the file
+    ~LLFile() { close(); }
+    ///@}
+
+    // ================================================================================
+    /// @name operators
+    ///
+    ///@{
+    /// copy assignment deleted
+    LLFile& operator=(const LLFile&) = delete;
+
+    /// move assignment
+    LLFile& operator=(LLFile&& other) noexcept
+    {
+        close();
+        std::swap(mHandle, other.mHandle);
+        return *this;
+    }
+
+    // detect whether the wrapped file descriptor/handle is open or not
+    explicit operator bool() const { return (mHandle != InvalidHandle); }
+    bool     operator!() { return (mHandle == InvalidHandle); }
+    ///@}
+
+    /// ================================================================================
+    /// @name  class member methods
+    ///
+    /// These methods provide read and write support as well as additional functionality to query the size of
+    /// the file, change the position of the current file pointer or query it.
+    ///
+    /// Most of these functions take as one of their parameters a std::error_code object which can be used to
+    /// determine in more detail what error occurred if required
+    ///@{
+
+    /// Open a file with the specific open mode flags
+    int open(const std::string& filename, std::ios_base::openmode omode, std::error_code& ec, int perm = 0666);
+    ///< @returns 0 on success, -1 on failure
+
+    /// Determine the size of the opened file
+    S64 size(std::error_code& ec);
+    ///< @returns the number of bytes in the file or -1 on failure
+
+    /// Query the position of the current file pointer in the file
+    S64 tell(std::error_code& ec);
+    ///< @returns the absolute offset of the file pointer in bytes relative to the start of the file or -1 on failure
+
+    /// Move the file pointer to the specified absolute position relative to the start of the file
+    int seek(S64 pos, std::error_code& ec);
+    ///< @returns 0 on success, -1 on failure
+
+    /// Move the file pointer to the specified position relative to dir
+    int seek(S64 offset, std::ios_base::seekdir dir, std::error_code& ec);
+    ///< @returns 0 on success, -1 on failure
+
+    /// Read the specified number of bytes into the buffer starting at the current file pointer
+    S64 read(void* buffer, S64 nbytes, std::error_code& ec);
+    ///< If the file ends before the requested amount of bytes could be read, the function succeeds and
+    ///  returns the bytes up to the end of the file. The return value indicates the number of actually
+    ///  read bytes and can be therefore smaller than the requested amount.
+    ///  @returns the number of bytes read from the file or -1 on failure
+
+    /// Write the specified number of bytes to the file starting at the current file pointer
+    S64 write(const void* buffer, S64 nbytes, std::error_code& ec);
+    ///< @returns the number of bytes written to the file or -1 on failure
+
+    /// Write into the file starting at the current file pointer using printf style format and
+    /// additional optional parameters as specified in the fmt string
+    S64 printf(const char* fmt, ...);
+    ///< @returns the number of bytes written to the file or -1 on failure
+
+    /// Attempt to acquire or release a lock on the file
+    int lock(int lmode, std::error_code& ec);
+    ///< lmode can be one of LLFile::exclusive or LLFile::shared to acquire the according lock
+    ///  or 0 to give up an earlier acquired lock. Adding LLFile::noblock together with one of
+    ///  the lock requests will cause the function to fail if the lock can not be acquired,
+    ///  otherwise the function will block until the lock can be acquired.
+    ///  @returns 0 on success, -1 on failure
+
+    /// close the file explicitly
+    int close(std::error_code& ec);
+    ///< @returns 0 on success, -1 on failure
+
+    /// Convenience function to close the file without additional parameters
+    int close();
+    ///< @returns 0 on success, -1 on failure
+    ///@}
+
+    /// ================================================================================
+    /// @name  static member functions
+    ///
+    /// These functions are static and operate with UTF8 filenames as one of their parameters.
+    ///
+    ///@{
     /// open a file with the specified access mode
-    static  LLFILE* fopen(const std::string& filename, const char* accessmode);  /* Flawfinder: ignore */
+    static LLFILE* fopen(const std::string& filename, const char* accessmode, int lmode = 0);
     ///< 'accessmode' follows the rules of the Posix fopen() mode parameter
-    /// "r" open the file for reading only and positions the stream at the beginning
-    /// "r+" open the file for reading and writing and positions the stream at the beginning
-    /// "w" open the file for reading and writing and truncate it to zero length
-    /// "w+" open or create the file for reading and writing and truncate to zero length if it existed
-    /// "a" open the file for reading and writing and position the stream at the end of the file
-    /// "a+" open or create the file for reading and writing and position the stream at the end of the file
+    ///  "r" open the file for reading only and positions the stream at the beginning
+    ///  "r+" open the file for reading and writing and positions the stream at the beginning
+    ///  "w" open the file for reading and writing and truncate it to zero length
+    ///  "w+" open or create the file for reading and writing and truncate to zero length if it existed
+    ///  "a" open the file for reading and writing and before every write position the stream at the end of the file
+    ///  "a+" open or create the file for reading and writing and before every write position the stream at the end of the file
+    ///
+    ///  in addition to these values, "b" can be appended to indicate binary stream access, but on Linux and Mac
+    ///  this is strictly for compatibility and has no effect. On Windows this makes the file functions not
+    ///  try to translate line endings. Windows also allows to append "t" to indicate text mode. If neither
+    ///  "b" or "t" is defined, Windows uses the value set by _fmode which by default is _O_TEXT.
+    ///  This means that it is always a good idea to append "b" specifically for binary file access to
+    ///  avoid corruption of the binary consistency of the data stream when reading or writing
+    ///  Other characters in 'accessmode', while possible on some platforms (Windows), will usually
+    ///  cause an error on other platforms as fopen will verify this parameter
     ///
-    /// in addition to these values, "b" can be appended to indicate binary stream access, but on Linux and Mac
-    /// this is strictly for compatibility and has no effect. On Windows this makes the file functions not
-    /// try to translate line endings. Windows also allows to append "t" to indicate text mode. If neither
-    /// "b" or "t" is defined, Windows uses the value set by _fmode which by default is _O_TEXT.
-    /// This means that it is always a good idea to append "b" specifically for binary file access to
-    /// avoid corruption of the binary consistency of the data stream when reading or writing
-    /// Other characters in 'accessmode' will usually cause an error as fopen will verify this parameter
-    /// @returns a valid LLFILE* pointer on success or NULL on failure
+    ///  lmode is optional and allows to lock the file for other processes either as a shared lock or an
+    ///  exclusive lock. If the requested lock conflicts with an already existing lock, the open fails.
+    ///  Pass either LLFIle::exclusive or LLFile::shared to this parameter if you want to prevent other
+    ///  processes from reading (exclusive lock) or writing (shared lock) to the file. It will always use
+    ///  LLFile::noblock, meaning the open will immediately fail if it conflicts with an existing lock on the
+    ///  file.
+    ///
+    ///  @returns a valid LLFILE* pointer on success that can be passed to the fread() and fwrite() functions
+    ///  and some other f<something> functions in the Standard C library that accept a FILE* as parameter
+    ///  or NULL on failure
 
+    /// Close a file handle opened with fopen() above
     static  int     close(LLFILE * file);
-
-    /// retrieve the content of a file into a string
-    static std::string getContents(const std::string& filename);
-    ///< @returns the content of the file or an empty string on failure
+    ///< @returns 0 on success and -1 on failure.
 
     /// create a directory
-    static  int     mkdir(const std::string& filename, int perms = 0700);
-    ///< perms is a permissions mask like 0777 or 0700.  In most cases it will be
-    ///  overridden by the user's umask. It is ignored on Windows.
-    ///  mkdir() considers "directory already exists" to be not an error.
-    ///  @returns 0 on success and -1 on failure.
-
-    //// remove a directory
-    static  int     rmdir(const std::string& filename, int suppress_error = 0);
-    ///< pass ENOENT in the optional 'suppress_error' parameter
-    ///  if you don't want a warning in the log when the directory does not exist
+    static  int     mkdir(const std::string& filename);
+    ///< mkdir() considers "directory already exists" to be not an error.
     ///  @returns 0 on success and -1 on failure.
 
     /// remove a file or directory
-    static  int     remove(const std::string& filename, int suppress_error = 0);
-    ///< pass ENOENT in the optional 'suppress_error' parameter
-    ///  if you don't want a warning in the log when the directory does not exist
+    static  int     remove(const std::string& filename, int suppress_warning = 0);
+    ///< pass an errno value (e.g., ENOENT) in the optional 'suppress_warning' parameter if you want to
+    ///  suppress a warning in the log when the failure matches that errno (e.g., suppress warning if
+    ///  the file or directory does not exist)
     ///  @returns 0 on success and -1 on failure.
 
     /// rename a file
-    static  int     rename(const std::string& filename, const std::string& newname, int suppress_error = 0);
+    static  int     rename(const std::string& filename, const std::string& newname, int suppress_warning = 0);
     ///< it will silently overwrite newname if it exists without returning an error
     ///  Posix guarantees that if newname already exists, then there will be no moment
     ///  in which for other processes newname does not exist. There is no such guarantee
-    ///  under Windows at this time. It may do it in the same way but the used Windows API
-    ///  does not make such guarantees.
+    ///  under Windows at this time. It may do it in the same way but the used Windows
+    ///  APIs do not make such guarantees.
     ///  @returns 0 on success and -1 on failure.
 
+    /// copy the contents of the file from 'source' to 'target'
+    static  bool    copy(const std::string& source, const std::string& target);
+    ///< Copies the contents of the file 'source' to the file 'target', overwriting 'target' if it already
+    ///  existed.
+    ///  This is a convenience function that implements the previous behavior of silently overwriting an
+    ///  already existing target file. Consider using the function below if you desire a different
+    ///  behavior when the target file already exists
+    ///  @returns true on success and false on failure.
 
-    /// copy the contents of file from 'from' to 'to' filename
-    static  bool    copy(const std::string& from, const std::string& to);
-    ///< @returns true on success and false on failure.
+    /// copy the contents of the file from 'from' to 'to'
+    static  bool    copy(const std::string& source, const std::string& target, std::filesystem::copy_options options, std::error_code& ec);
+    ///< Copies the contents of the file 'source' to the file 'target'. The options parameter allows to
+    ///  specify what should happen if the "target" file already exists:
+    ///   std::filesystem::copy_options::none - return an error in ec and fail
+    ///   std::filesystem::copy_options::skip_existing - skip the operation and do not overwrite file
+    ///   std::filesystem::copy_options::overwrite_existing - overwrite the file
+    ///   std::filesystem::copy_options::update_existing - overwrite the file only if it is older than the file being copied
+    ///  @returns true on success and false on failure.
+
+    /// retrieve the content of a file into a string
+    static std::string getContents(const std::string& filename);
+    static std::string getContents(const std::string& filename, std::error_code& ec);
+    ///< @returns the entire content of the file as std::string or an empty string on failure
+
+    /// read nBytes from the file into the buffer, starting at offset in the file
+    static  S64     read(const std::string& filename, void* buf, S64 offset, S64 nbytes);
+    static  S64     read(const std::string& filename, void* buf, S64 offset, S64 nbytes, std::error_code& ec);
+    ///< @returns bytes read on success, or -1 on failure
+
+    /// write nBytes from the buffer into the file, starting at offset in the file
+    static  S64     write(const std::string& filename, const void* buf, S64 offset, S64 nbytes);
+    static  S64     write(const std::string& filename, const void* buf, S64 offset, S64 nbytes, std::error_code& ec);
+    ///< If a negative offset is provided, the file is opened in append mode and the
+    ///  write will be appended to the end of the file.
+    ///  @returns bytes written on success, or -1 on failure
 
     /// return the file stat structure for filename
-    static  int     stat(const std::string& filename, llstat* file_status, int suppress_error = ENOENT);
+    static  int     stat(const std::string& filename, llstat* file_status, const char *operation = nullptr, int suppress_warning = ENOENT);
     ///< for compatibility with existing uses of LL_File::stat() we use ENOENT as default in the
-    ///  optional 'suppress_error' parameter to avoid spamming the log with warnings when the API
+    ///  optional 'suppress_warning' parameter to avoid spamming the log with warnings when the API
     ///  is used to detect if a file exists
     ///  @returns 0 on success and -1 on failure.
 
-    /// get the file or directory attributes for filename
-    static  unsigned short getattr(const std::string& filename, bool dontFollowSymLink = false, int suppress_error = ENOENT);
-    ///< a more lightweight function on Windows to stat, that just returns the file attribute flags
-    ///  dontFollowSymLinks set to true returns the attributes of the symlink if it is one, rather than resolving it
-    ///  we pass by default ENOENT in the optional 'suppress_error' parameter to not spam the log with
-    ///  warnings when the file or directory does not exist
-    ///  @returns 0 on failure and a st_mode value with either S_IFDIR or S_IFREG set otherwise
-    ///  together with the three access bits which under Windows only the write bit is relevant.
+    /// get the creation data and time of a file
+    static std::time_t getCreationTime(const std::string& filename, int suppress_warning = 0);
+    ///< Different systems have different support for this. Under Windows this is supposedly
+    ///  the actual time the file was created, on the Mac this is the actual birth date of
+    ///  the file which is in fact the creation time. The according ctime entry in the stat
+    ///  structure under Linux (and any other *nix really) is however contrary to what one
+    ///  might expect based on the c in ctime not the creation time but the time the last
+    ///  change to the inode entry was made. Changing access rights to a file will update
+    ///  this value too. In order to have a true creation time under Linux, we would have
+    ///  to use the statx() call which is available since kernel 4.19, but that will require
+    ///  considerable changes to the implementation of above stat() function.
+    ///  @returns the creation time (last status change under Linux) of the file or 0 on error
+
+    /// get the last modification data and time of a file
+    static std::time_t getModificationTime(const std::string& filename, int suppress_warning = 0);
+    ///< @returns the modification time of the file or 0 on error
+
+    /// get the std::filesystem::file_status for filename
+    static std::filesystem::file_status getStatus(const std::string& filename, bool dontFollowSymLink = false, int suppress_warning  = ENOENT);
+    ///< dontFollowSymLinks set to true returns the std::filesystem::file_status of the symlink if it
+    ///  is one, rather than resolving it. We pass by default ENOENT in the optional 'suppress_warning'
+    ///  parameter to not spam the log with warnings when the file or directory does not exist
+    ///  @returns a std::filesystem::file_status value that can be passed to the appropriate std::filesystem::exists()
+    ///  and other APIs accepting a file_status.
+
+    /// get the size of a file in bytes
+    static  S64     size(const std::string& filename, int suppress_warning = ENOENT);
+    ///< we pass by default ENOENT in the optional 'suppress_warning' parameter to not spam
+    ///  the log with warnings when the file does not exist
+    ///  @returns the file size on success or -1 on failure.
+
+    /// check if filename is an existing file or directory
+    static  bool    exists(const std::string& filename);
+    ///< @returns true if the path is for an existing file or directory
 
     /// check if filename is an existing directory
     static  bool    isdir(const std::string& filename);
@@ -161,70 +402,44 @@ public:
     ///< @returns true if the path is pointing at a symlink
 
     /// return a path to the temporary directory on the system
-    static  const char * tmpdir();
-};
-
-/// RAII class
-class LLUniqueFile
-{
-public:
-    // empty
-    LLUniqueFile(): mFileHandle(nullptr) {}
-    // wrap (e.g.) result of LLFile::fopen()
-    LLUniqueFile(LLFILE* f): mFileHandle(f) {}
-    // no copy
-    LLUniqueFile(const LLUniqueFile&) = delete;
-    // move construction
-    LLUniqueFile(LLUniqueFile&& other) noexcept
-    {
-        mFileHandle = other.mFileHandle;
-        other.mFileHandle = nullptr;
-    }
-    // The point of LLUniqueFile is to close on destruction.
-    ~LLUniqueFile()
-    {
-        close();
-    }
-
-    // simple assignment
-    LLUniqueFile& operator=(LLFILE* f)
-    {
-        close();
-        mFileHandle = f;
-        return *this;
-    }
-    // copy assignment deleted
-    LLUniqueFile& operator=(const LLUniqueFile&) = delete;
-    // move assignment
-    LLUniqueFile& operator=(LLUniqueFile&& other) noexcept
-    {
-        close();
-        std::swap(mFileHandle, other.mFileHandle);
-        return *this;
-    }
+    static const std::string& tmpdir();
 
-    // explicit close operation
-    void close()
-    {
-        if (mFileHandle)
-        {
-            // in case close() throws, set mFileHandle null FIRST
-            LLFILE* h{nullptr};
-            std::swap(h, mFileHandle);
-            LLFile::close(h);
-        }
-    }
-
-    // detect whether the wrapped LLFILE is open or not
-    explicit operator bool() const { return bool(mFileHandle); }
-    bool operator!() { return ! mFileHandle; }
-
-    // LLUniqueFile should be usable for any operation that accepts LLFILE*
-    // (or FILE* for that matter)
-    operator LLFILE*() const { return mFileHandle; }
+    /// converts a string containing a path in utf8 encoding into an explicit filesystem path
+    static std::filesystem::path utf8StringToPath(const std::string& pathname);
+    ///< @returns the path as a std::filesystem::path
+    ///@}
 
 private:
-    LLFILE* mFileHandle;
+#if LL_WINDOWS
+    typedef HANDLE        llfile_handle_t;
+    const llfile_handle_t InvalidHandle = INVALID_HANDLE_VALUE;
+#else
+    typedef int           llfile_handle_t;
+    const llfile_handle_t InvalidHandle = -1;
+#endif
+
+    /// ================================================================================
+    /// @name private static member functions
+    ///
+#if LL_WINDOWS
+    /// convert a string containing a path in utf8 encoding into a Windows format std::wstring
+    static std::wstring utf8StringToWstring(const std::string& pathname);
+    ///< this will prepend the path with the Windows kernel object space prefix when the path is
+    ///  equal or longer than MAX_PATH characters and do some sanitation on the path.
+    ///  This allows the underlaying Windows APIs to process long path names. Do not pass such a path
+    ///  to std::filesystem functions. These functions are not guaranteed to handle such paths properly.
+    ///  It's only useful to pass the resulting string buffer to Microsoft Windows widechar APIs or
+    ///  the Microsoft C runtime widechar file functions.
+    ///
+    ///  Example:
+    ///
+    ///  std::wstring file_path = utf8StringToWstring(filename);
+    ///  HANDLE CreateFileW(file_path.c_str(), ......);
+    ///
+    ///  @returns the path as a std::wstring path
+#endif
+    llfile_handle_t mHandle;       // The file handle/descriptor
+    std::ios_base::openmode mOpen; // Used to emulate std::ios_base::app under Windows
 };
 
 #if LL_WINDOWS
@@ -315,17 +530,6 @@ class LL_COMMON_API llofstream : public std::ofstream
               ios_base::openmode _Mode = ios_base::out|ios_base::trunc);
 };
 
-
-/**
- * @brief filesize helpers.
- *
- * The file size helpers are not considered particularly efficient,
- * and should only be used for config files and the like -- not in a
- * loop.
- */
-std::streamsize LL_COMMON_API llifstream_size(llifstream& fstr);
-std::streamsize LL_COMMON_API llofstream_size(llofstream& fstr);
-
 #else // ! LL_WINDOWS
 
 // on non-windows, llifstream and llofstream are just mapped directly to the std:: equivalents
diff --git a/indra/llcommon/tests/llfile_test.cpp b/indra/llcommon/tests/llfile_test.cpp
new file mode 100644
index 0000000000..9f2a9b2988
--- /dev/null
+++ b/indra/llcommon/tests/llfile_test.cpp
@@ -0,0 +1,253 @@
+/**
+ * @file llfile_tut.cpp
+ * @author Frederick Martian
+ * @date 2025-11
+ * @brief LLFile test cases.
+ *
+ * $LicenseInfo:firstyear=2025&license=viewerlgpl$
+ * Second Life Viewer Source Code
+ * Copyright (C) 2025, Linden Research, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation;
+ * version 2.1 of the License only.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * Linden Research, Inc., 945 Battery Street, San Francisco, CA  94111  USA
+ * $/LicenseInfo$
+ */
+
+#include <tut/tut.hpp>
+#include "lltut.h"
+#include "linden_common.h"
+#include "llfile.h"
+
+namespace tut
+{
+    static void clear_entire_dir(std::filesystem::path &dir)
+    {
+        std::error_code ec;
+        std::filesystem::remove_all(dir, ec);
+    }
+
+    static std::filesystem::path append_filename(const std::filesystem::path& dir, const std::string& element)
+    {
+        std::filesystem::path path = dir;
+        return path.append(element);
+    }
+
+    static std::filesystem::path get_testdir(const std::filesystem::path& tempdir)
+    {
+        return append_filename(tempdir, std::string("test_dir"));
+    }
+
+    struct llfile_test
+    {
+        std::filesystem::path tempdir = LLFile::tmpdir();
+        std::filesystem::path testdir = get_testdir(tempdir);
+    };
+    typedef test_group<llfile_test> llfile_test_t;
+    typedef llfile_test_t::object   llfile_test_object_t;
+    tut::llfile_test_t              tut_llfile_test("llfile_test");
+
+    template<> template<>
+    void llfile_test_object_t::test<1>()
+    {
+        // Test creating directories and files and deleting them and checking if the
+        // relevant status functions work as expected
+        ensure("LLFile::tmpdir() empty", !tempdir.empty());
+        ensure("LLFile::tmpdir() doesn't exist", LLFile::exists(tempdir.string()));
+        ensure("LLFile::tmpdir() is not a directory", LLFile::isdir(tempdir.string()));
+        ensure("LLFile::tmpdir() should not be a file", !LLFile::isfile(tempdir.string()));
+
+        // Make sure there is nothing left from a previous test run
+        clear_entire_dir(testdir);
+        ensure("llfile_test should not exist anymore", !LLFile::exists(testdir.string()));
+
+        int rc = LLFile::mkdir(testdir.string());
+        ensure("LLFile::mkdir() failed", rc == 0);
+        ensure("llfile_test should be a directory", LLFile::isdir(testdir.string()));
+        rc = LLFile::mkdir(testdir.string());
+        ensure("LLFile::mkdir() should not fail when the directory already exists", rc == 0);
+
+        std::filesystem::path testfile1 = testdir;
+        testfile1.append("llfile_test.dat");
+        ensure("llfile_test1.dat should not yet exist", !LLFile::exists(testfile1.string()));
+
+        const char* testdata = "testdata";
+        S64 bytes = LLFile::write(testfile1.string(), testdata, 0, sizeof(testdata));
+        ensure("LLFile::write() did not write correctly", bytes == sizeof(testdata));
+
+        rc = LLFile::remove(testfile1.string());
+        ensure("LLFile::remove() for file test_file.dat", rc == 0);
+        ensure("llfile_test.dat should not exist anymore", !LLFile::exists(testfile1.string()));
+        ensure("llfile_test.dat should not be a file", !LLFile::isfile(testfile1.string()));
+        ensure("llfile_test.dat should not be a directory", !LLFile::isdir(testfile1.string()));
+        ensure("llfile_test.dat should not be a symlink", !LLFile::islink(testfile1.string()));
+
+        rc = LLFile::remove(testdir.string());
+        ensure("LLFile::remove() for directory llfile_test failed", rc == 0);
+        ensure("llfile_test should not exist anymore", !LLFile::exists(testdir.string()));
+    }
+
+    template<> template<>
+    void llfile_test_object_t::test<2>()
+    {
+        // High level static file IO functions to read and write data files
+        LLFile::mkdir(testdir.string());
+        ensure("llfile_test should exist", LLFile::isdir(testdir.string()));
+
+        std::filesystem::path testfile1 = testdir;
+        testfile1.append("llfile_test.dat");
+
+        std::string testdata1("testdata");
+        std::string testdata2("datateststuff");
+        std::time_t current = time(nullptr);
+        S64 bytes = LLFile::write(testfile1.string(), testdata1.c_str(), 0, testdata1.length());
+        ensure("LLFile::write() did not write correctly", bytes == testdata1.length());
+        ensure("llfile_test.dat should exist", LLFile::exists(testfile1.string()));
+        ensure("llfile_test.dat should be a file", LLFile::isfile(testfile1.string()));
+        ensure("llfile_test.dat should not be a directory", !LLFile::isdir(testfile1.string()));
+
+        bytes = LLFile::size(testfile1.string());
+        ensure("LLFile::size() did not return the correct size", bytes == testdata1.length());
+
+        std::string data = LLFile::getContents(testfile1.string());
+        ensure("LLFile::getContents() did not return the correct size data", data.length() == testdata1.length());
+        ensure_memory_matches("LLFile::getContents() did not read correct data", testdata1.c_str(), (U32)testdata1.length(), data.c_str(), (U32)data.length());
+
+        std::time_t ctime = LLFile::getCreationTime(testfile1.string());
+        ensure_approximately_equals_range("LLFile::getCreationTime() did not return correct time", (F32)(ctime - current), 0.f, 1);
+
+        std::time_t mtime = LLFile::getModificationTime(testfile1.string());
+        ensure_approximately_equals_range("LLFile::getModificationTime() did not return correct time", (F32)(mtime - current), 0.f, 1);
+
+        char buffer[1024];
+        bytes = LLFile::read(testfile1.string(), buffer, 0, testdata1.length());
+        ensure("LLFile:read() did not return the correct size", bytes == testdata1.length());
+        ensure_memory_matches("LLFile::read() did not read correct data", testdata1.c_str(), (U32)bytes, buffer, (U32)bytes);
+
+        // What if we try to read more data than there is in the file?
+        bytes = LLFile::read(testfile1.string(), buffer, 0, bytes + 10);
+        ensure("LLFile:read() did not correctly stop on eof", bytes == testdata1.length());
+        ensure_memory_matches("LLFile::read() did not read correct data", testdata1.c_str(), (U32)bytes, buffer, (U32)bytes);
+
+        // Let's append more data
+        bytes = LLFile::write(testfile1.string(), testdata2.c_str(), -1, testdata2.length());
+        ensure("LLFile::write() did not write correctly", bytes == testdata2.length());
+
+        bytes = LLFile::size(testfile1.string());
+        ensure("LLFile::size() did not return the correct size", bytes == testdata1.length() + testdata2.length());
+        bytes = LLFile::read(testfile1.string(), buffer, 0, bytes);
+        ensure("LLFile:read() did not read correct number of bytes", bytes == testdata1.length() + testdata2.length());
+        ensure_memory_matches("LLFile:read() did not read correct testdata1", testdata1.c_str(), (U32)testdata1.length(), buffer, (U32)testdata1.length());
+        ensure_memory_matches("LLFile:read() did not read correct testdata2", testdata2.c_str(), (U32)testdata2.length(), buffer + testdata1.length(), (U32)testdata2.length());
+    }
+
+    template<> template<>
+    void llfile_test_object_t::test<3>()
+    {
+        const size_t numints = 1024;
+
+        // Testing the LLFile class implementation
+        std::filesystem::path testfile = testdir;
+        testfile.append("llfile_test.bin");
+
+        int data[numints];
+        for (int &t : data)
+        {
+            t = rand();
+        }
+
+        std::error_code ec;
+        LLFile fileout(testfile.string(), LLFile::out, ec);
+        ensure("LLFile constructor did not open correctly", (bool)fileout);
+        ensure("error_code from LLFile constructor should not indicate an error", !ec);
+        if (fileout)
+        {
+            S64 length = fileout.size(ec);
+            ensure("freshly created file should be empty", length == 0);
+            ensure("error_code from LLFile::size() should not indicate an error", !ec);
+            S64 bytes = fileout.write(data, sizeof(data), ec);
+            ensure("LLFile::write() did not write correctly", bytes == sizeof(data));
+            ensure("error_code from LLFile::write() should not indicate an error", !ec);
+            bytes = fileout.write(data, sizeof(data), ec);
+            ensure("LLFile::write() did not write correctly", bytes == sizeof(data));
+            ensure("error_code from LLFile::write() should not indicate an error", !ec);
+            bytes = fileout.size(ec);
+            ensure("LLFile::size() returned wrong size", bytes == 2 * sizeof(data));
+            ensure("error_code from LLFile::size() should not indicate an error", !ec);
+            fileout.close();
+        }
+
+        LLFile filein(testfile.string(), LLFile::in, ec);
+        ensure("LLFile constructor did not open correctly", (bool)filein);
+        ensure("error_code from LLFile constructor should not indicate an error", !ec);
+        if (filein)
+        {
+            S64 length = filein.size(ec);
+            ensure("LLFile::size() returned wrong size", length == 2 * sizeof(data));
+            ensure("error_code from LLFile::size() should not indicate an error", !ec);
+            char* buffer = (char*)malloc(length);
+            S64 bytes  = filein.read(buffer, length, ec);
+            ensure("LLFile::read() did not read correctly", bytes == length);
+            ensure("error_code from LLFile::read() should not indicate an error", !ec);
+            ensure_memory_matches("LLFile:read() did not read correct data1", data, (U32)sizeof(data), buffer, (U32)sizeof(data));
+            ensure_memory_matches("LLFile:read() did not read correct data2", data, (U32)sizeof(data), buffer + sizeof(data), (U32)sizeof(data));
+            S64 offset = filein.tell(ec);
+            ensure("LLFile::tell() returned a bad offset", offset == length);
+            ensure("error_code from LLFile::read() should not indicate an error", !ec);
+            offset = sizeof(data) / 2;
+            int rc = filein.seek(offset, ec);
+            ensure("LLFile::seek() indicated an error", rc == 0);
+            ensure("error_code from LLFile::seek() should not indicate an error", !ec);
+            bytes = filein.read(buffer, 2 * sizeof(data), ec);
+            ensure("LLFile::read() did not read correctly", bytes == sizeof(data) + offset);
+            ensure("error_code from LLFile::read() should not indicate an error", !ec);
+            ensure_memory_matches("LLFile:read() did not read correct data3", (char*)data + offset, (U32)offset, buffer, (U32)offset);
+            ensure_memory_matches("LLFile:read() did not read correct data4", (char*)data, (U32)sizeof(data), buffer + offset, (U32)sizeof(data));
+            filein.close();
+
+            free(buffer);
+        }
+    }
+
+    template<> template<>
+    void llfile_test_object_t::test<4>()
+    {
+        // Testing the LLFile class implementation with wrong paths and parameters
+        std::filesystem::path testfile = testdir;
+        testfile.append("llfile_test.bin");
+
+        std::error_code ec;
+        LLFile file(testfile.string(), LLFile::out | LLFile::noreplace, ec);
+        ensure("LLFile constructor should not have opened the already existing file", !file);
+        ensure("error_code from LLFile constructor should indicate an error", (bool)ec);
+
+        LLFile::remove(testfile.string());
+        file = LLFile(testfile.string(), LLFile::out | LLFile::app | LLFile::trunc, ec);
+        ensure("LLFile constructor should not have opened the file with conflicting flags", !file);
+        ensure("error_code from LLFile constructor should indicate an error", (bool)ec);
+
+        file = LLFile(testfile.string(), LLFile::out | LLFile::app | LLFile::noreplace, ec);
+        ensure("LLFile constructor should not have opened the file with conflicting flags", !file);
+        ensure("error_code from LLFile constructor should indicate an error", (bool)ec);
+
+        testfile = testdir;
+        testfile.append("llfile_test");
+        testfile.append("llfile_test.bin");
+
+        file = LLFile(testfile.string(), LLFile::in, ec);
+        ensure("LLFile constructor should not have been able to open the file in the non-existing directory", !file);
+        ensure("error_code from LLFile constructor should indicate an error", (bool)ec);
+    }
+} // namespace tut
diff --git a/indra/llfilesystem/lldir.cpp b/indra/llfilesystem/lldir.cpp
index 190539cea5..eb3c2d9909 100644..100755
--- a/indra/llfilesystem/lldir.cpp
+++ b/indra/llfilesystem/lldir.cpp
@@ -30,8 +30,6 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <errno.h>
-#else
-#include <direct.h>
 #endif
 
 #include "lldir.h"
@@ -43,7 +41,6 @@
 #include "lldiriterator.h"
 #include "stringize.h"
 #include "llstring.h"
-#include <boost/filesystem.hpp>
 #include <boost/bind.hpp>
 #include <algorithm>
 
@@ -93,30 +90,20 @@ LLDir::~LLDir()
 
 std::vector<std::string> LLDir::getFilesInDir(const std::string &dirname)
 {
-    //Returns a vector of fullpath filenames.
-
-#ifdef LL_WINDOWS // or BOOST_WINDOWS_API
-    boost::filesystem::path p(ll_convert<std::wstring>(dirname));
-#else
-    boost::filesystem::path p(dirname);
-#endif
-
+    // Returns a vector of filenames in the directory.
+    std::filesystem::path p = LLFile::utf8StringToPath(dirname);
     std::vector<std::string> v;
-
-    boost::system::error_code ec;
-    if (exists(p, ec) && !ec.failed())
+    std::error_code ec;
+    if (std::filesystem::is_directory(p, ec))
     {
-        if (is_directory(p, ec) && !ec.failed())
+        std::filesystem::directory_iterator end_iter;
+        for (std::filesystem::directory_iterator dir_itr(p);
+             dir_itr != end_iter;
+             ++dir_itr)
         {
-            boost::filesystem::directory_iterator end_iter;
-            for (boost::filesystem::directory_iterator dir_itr(p);
-                 dir_itr != end_iter;
-                 ++dir_itr)
+            if (std::filesystem::is_regular_file(dir_itr->status()))
             {
-                if (boost::filesystem::is_regular_file(dir_itr->status()))
-                {
-                    v.push_back(dir_itr->path().filename().string());
-                }
+                v.push_back(dir_itr->path().filename().string());
             }
         }
     }
@@ -186,28 +173,23 @@ U32 LLDir::deleteDirAndContents(const std::string& dir_name)
     //Removes the directory and its contents.  Returns number of files deleted.
 
     U32 num_deleted = 0;
+    std::filesystem::path dir_path    = LLFile::utf8StringToPath(dir_name);
 
     try
     {
-#ifdef LL_WINDOWS // or BOOST_WINDOWS_API
-        boost::filesystem::path dir_path(ll_convert<std::wstring>(dir_name));
-#else
-        boost::filesystem::path dir_path(dir_name);
-#endif
-
-       if (boost::filesystem::exists(dir_path))
+       if (std::filesystem::is_directory(dir_path))
        {
-          if (!boost::filesystem::is_empty(dir_path))
+          if (!std::filesystem::is_empty(dir_path))
           {   // Directory has content
-             num_deleted = (U32)boost::filesystem::remove_all(dir_path);
+             num_deleted = (U32)std::filesystem::remove_all(dir_path);
           }
           else
           {   // Directory is empty
-             boost::filesystem::remove(dir_path);
+             std::filesystem::remove(dir_path);
           }
        }
     }
-    catch (boost::filesystem::filesystem_error &er)
+    catch (std::filesystem::filesystem_error &er)
     {
         LL_WARNS() << "Failed to delete " << dir_name << " with error " << er.code().message() << LL_ENDL;
     }
@@ -1105,15 +1087,15 @@ void dir_exists_or_crash(const std::string &dir_name)
 #if LL_WINDOWS
     // *FIX: lame - it doesn't do the same thing on windows. not so
     // important since we don't deploy simulator to windows boxes.
-    LLFile::mkdir(dir_name, 0700);
+    LLFile::mkdir(dir_name);
 #else
-    struct stat dir_stat;
+    llstat dir_stat;
     if(0 != LLFile::stat(dir_name, &dir_stat))
     {
         S32 stat_rv = errno;
         if(ENOENT == stat_rv)
         {
-           if(0 != LLFile::mkdir(dir_name, 0700))       // octal
+           if(0 != LLFile::mkdir(dir_name))
            {
                LL_ERRS() << "Unable to create directory: " << dir_name << LL_ENDL;
            }
diff --git a/indra/llfilesystem/lldir_win32.cpp b/indra/llfilesystem/lldir_win32.cpp
index 9624b1197f..1cfa157634 100644..100755
--- a/indra/llfilesystem/lldir_win32.cpp
+++ b/indra/llfilesystem/lldir_win32.cpp
@@ -376,18 +376,7 @@ std::string LLDir_Win32::getCurPath()
 
 bool LLDir_Win32::fileExists(const std::string &filename) const
 {
-    llstat stat_data;
-    // Check the age of the file
-    // Now, we see if the files we've gathered are recent...
-    int res = LLFile::stat(filename, &stat_data);
-    if (!res)
-    {
-        return true;
-    }
-    else
-    {
-        return false;
-    }
+    return LLFile::exists(filename);
 }
 
 
diff --git a/indra/llfilesystem/llfilesystem.cpp b/indra/llfilesystem/llfilesystem.cpp
index 541266af4f..0c220fe7cf 100644..100755
--- a/indra/llfilesystem/llfilesystem.cpp
+++ b/indra/llfilesystem/llfilesystem.cpp
@@ -77,21 +77,17 @@ bool LLFileSystem::getExists(const LLUUID& file_id, const LLAssetType::EType fil
     LL_PROFILE_ZONE_SCOPED;
     const std::string filename = LLDiskCache::metaDataToFilepath(file_id, file_type);
 
-    llifstream file(filename, std::ios::binary);
-    if (file.is_open())
-    {
-        file.seekg(0, std::ios::end);
-        return file.tellg() > 0;
-    }
-    return false;
+    // not only test for existence but for the file to be not empty
+    S64 size =  LLFile::size(filename);
+    return size > 0;
 }
 
 // static
-bool LLFileSystem::removeFile(const LLUUID& file_id, const LLAssetType::EType file_type, int suppress_error /*= 0*/)
+bool LLFileSystem::removeFile(const LLUUID& file_id, const LLAssetType::EType file_type, int suppress_warning /*= 0*/)
 {
     const std::string filename = LLDiskCache::metaDataToFilepath(file_id, file_type);
 
-    LLFile::remove(filename.c_str(), suppress_error);
+    LLFile::remove(filename.c_str(), suppress_warning);
 
     return true;
 }
@@ -116,19 +112,10 @@ bool LLFileSystem::renameFile(const LLUUID& old_file_id, const LLAssetType::ETyp
 }
 
 // static
-S32 LLFileSystem::getFileSize(const LLUUID& file_id, const LLAssetType::EType file_type)
+S64 LLFileSystem::getFileSize(const LLUUID& file_id, const LLAssetType::EType file_type)
 {
     const std::string filename = LLDiskCache::metaDataToFilepath(file_id, file_type);
-
-    S32 file_size = 0;
-    llifstream file(filename, std::ios::binary);
-    if (file.is_open())
-    {
-        file.seekg(0, std::ios::end);
-        file_size = (S32)file.tellg();
-    }
-
-    return file_size;
+    return LLFile::size(filename);
 }
 
 bool LLFileSystem::read(U8* buffer, S32 bytes)
@@ -269,7 +256,7 @@ S32 LLFileSystem::tell() const
 
 S32 LLFileSystem::getSize() const
 {
-    return LLFileSystem::getFileSize(mFileID, mFileType);
+    return (S32)LLFileSystem::getFileSize(mFileID, mFileType);
 }
 
 S32 LLFileSystem::getMaxSize() const
diff --git a/indra/llfilesystem/llfilesystem.h b/indra/llfilesystem/llfilesystem.h
index 10649b6920..7188683e7f 100644
--- a/indra/llfilesystem/llfilesystem.h
+++ b/indra/llfilesystem/llfilesystem.h
@@ -61,10 +61,10 @@ class LLFileSystem
         void updateFileAccessTime(const std::string& file_path);
 
         static bool getExists(const LLUUID& file_id, const LLAssetType::EType file_type);
-        static bool removeFile(const LLUUID& file_id, const LLAssetType::EType file_type, int suppress_error = 0);
+        static bool removeFile(const LLUUID& file_id, const LLAssetType::EType file_type, int suppress_warning = 0);
         static bool renameFile(const LLUUID& old_file_id, const LLAssetType::EType old_file_type,
                                const LLUUID& new_file_id, const LLAssetType::EType new_file_type);
-        static S32 getFileSize(const LLUUID& file_id, const LLAssetType::EType file_type);
+        static S64 getFileSize(const LLUUID& file_id, const LLAssetType::EType file_type);
 
     public:
         static const S32 READ;
diff --git a/indra/llfilesystem/tests/lldir_test.cpp b/indra/llfilesystem/tests/lldir_test.cpp
index a2104d1ef9..8b86da40b3 100644..100755
--- a/indra/llfilesystem/tests/lldir_test.cpp
+++ b/indra/llfilesystem/tests/lldir_test.cpp
@@ -557,8 +557,8 @@ namespace tut
          LLFile::remove(dir1files[i]);
          LLFile::remove(dir2files[i]);
       }
-      LLFile::rmdir(dir1);
-      LLFile::rmdir(dir2);
+      LLFile::remove(dir1);
+      LLFile::remove(dir2);
    }
 
     template<> template<>
diff --git a/indra/llmessage/llassetstorage.cpp b/indra/llmessage/llassetstorage.cpp
index 10fd56a68e..34eeacb273 100644
--- a/indra/llmessage/llassetstorage.cpp
+++ b/indra/llmessage/llassetstorage.cpp
@@ -467,7 +467,7 @@ bool LLAssetStorage::findInCacheAndInvokeCallback(const LLUUID& uuid, LLAssetTyp
         else
         {
             LL_WARNS("AssetStorage") << "Asset vfile " << uuid << ":" << type
-                                     << " found in static cache with bad size " << file.getSize() << ", ignoring" << LL_ENDL;
+                                     << " found in static cache with bad size " << size << ", ignoring" << LL_ENDL;
         }
     }
     return false;
diff --git a/indra/llmessage/tests/llmessageconfig_test.cpp b/indra/llmessage/tests/llmessageconfig_test.cpp
index 93443467a2..b8942e99b3 100644..100755
--- a/indra/llmessage/tests/llmessageconfig_test.cpp
+++ b/indra/llmessage/tests/llmessageconfig_test.cpp
@@ -62,7 +62,7 @@ namespace tut
             int rmfile = LLFile::remove((mTestConfigDir + "/message.xml"));
             ensure_equals("rmfile value", rmfile, 0);
             // rm temp dir
-            int rmdir = LLFile::rmdir(mTestConfigDir);
+            int rmdir = LLFile::remove(mTestConfigDir);
             ensure_equals("rmdir value", rmdir, 0);
         }
 
diff --git a/indra/llmessage/tests/message_test.cpp b/indra/llmessage/tests/message_test.cpp
index 11cd710ef6..6fb2b92803 100644..100755
--- a/indra/llmessage/tests/message_test.cpp
+++ b/indra/llmessage/tests/message_test.cpp
@@ -113,7 +113,7 @@ namespace tut
             ensure_equals("rmfile value", rmfile, 0);
 
             // rm temp dir
-            int rmdir = LLFile::rmdir(mTestConfigDir);
+            int rmdir = LLFile::remove(mTestConfigDir);
             ensure_equals("rmdir value", rmdir, 0);
         }
 
diff --git a/indra/llrender/llshadermgr.cpp b/indra/llrender/llshadermgr.cpp
index 1da71e6bf4..7e8d31232b 100644
--- a/indra/llrender/llshadermgr.cpp
+++ b/indra/llrender/llshadermgr.cpp
@@ -1014,7 +1014,6 @@ void LLShaderMgr::initShaderCache(bool enabled, const LLUUID& old_cache_version,
 
     mShaderCacheDir = gDirUtilp->getExpandedFilename(LL_PATH_CACHE, "shader_cache");
     LLFile::mkdir(mShaderCacheDir);
-
     {
         std::string meta_out_path = gDirUtilp->add(mShaderCacheDir, "shaderdata.llsd");
         if (gDirUtilp->fileExists(meta_out_path))
@@ -1077,7 +1076,7 @@ void LLShaderMgr::persistShaderCacheMetadata()
     // Settings and shader cache get saved at different time, thus making
     // RenderShaderCacheVersion unreliable when running multiple viewer
     // instances, or for cases where viewer crashes before saving settings.
-    // Dupplicate version to the cache itself.
+    // Duplicate version to the cache itself.
     out["version"] = mShaderCacheVersion;
     out["shaders"] = LLSD::emptyMap();
     LLSD &shaders = out["shaders"];
@@ -1130,11 +1129,11 @@ bool LLShaderMgr::loadCachedProgramBinary(LLGLSLShader* shader)
         {
             std::vector<U8> in_data;
             in_data.resize(shader_info.mBinaryLength);
-
-            LLUniqueFile filep = LLFile::fopen(in_path, "rb");
-            if (filep)
+            std::error_code ec;
+            LLFile filep = LLFile(in_path, LLFile::in | LLFile::binary, ec);
+            if (!ec && (bool)filep)
             {
-                size_t result = fread(in_data.data(), sizeof(U8), in_data.size(), filep);
+                size_t result = filep.read(in_data.data(), in_data.size(), ec);
                 filep.close();
 
                 if (result == in_data.size())
@@ -1179,11 +1178,12 @@ bool LLShaderMgr::saveCachedProgramBinary(LLGLSLShader* shader)
         if (error == GL_NO_ERROR)
         {
             std::string out_path = gDirUtilp->add(mShaderCacheDir, shader->mShaderHash.asString() + ".shaderbin");
-            LLUniqueFile outfile = LLFile::fopen(out_path, "wb");
-            if (outfile)
+            std::error_code ec;
+            LLFile filep = LLFile(out_path, LLFile::out | LLFile::binary, ec);
+            if (filep)
             {
-                fwrite(program_binary.data(), sizeof(U8), program_binary.size(), outfile);
-                outfile.close();
+                filep.write(program_binary.data(), program_binary.size(), ec);
+                filep.close();
 
                 binary_info.mLastUsedTime = (F32)LLTimer::getTotalSeconds();
 
diff --git a/indra/llxml/tests/llcontrol_test.cpp b/indra/llxml/tests/llcontrol_test.cpp
index 4192e029c5..e15117fc29 100644..100755
--- a/indra/llxml/tests/llcontrol_test.cpp
+++ b/indra/llxml/tests/llcontrol_test.cpp
@@ -69,7 +69,7 @@ namespace tut
                 LLFile::remove(filename);
             }
             LLFile::remove(mTestConfigFile);
-            LLFile::rmdir(mTestConfigDir);
+            LLFile::remove(mTestConfigDir);
         }
         void writeSettingsFile(const LLSD& config)
         {
diff --git a/indra/newview/llappviewer.cpp b/indra/newview/llappviewer.cpp
index ea380896ca..6058973176 100644..100755
--- a/indra/newview/llappviewer.cpp
+++ b/indra/newview/llappviewer.cpp
@@ -2267,7 +2267,7 @@ void errorCallback(LLError::ELevel level, const std::string &error_string)
         LLAppViewer::instance()->writeDebugInfo();
 
         std::string error_marker_file = gDirUtilp->getExpandedFilename(LL_PATH_LOGS, ERROR_MARKER_FILE_NAME);
-        if (!LLAPRFile::isExist(error_marker_file, NULL, LL_APR_RB))
+        if (!LLFile::isfile(error_marker_file))
         {
             // If marker doesn't exist, create a marker with llerror code for next launch
             // otherwise don't override existing file
@@ -3030,13 +3030,11 @@ void LLAppViewer::initStrings()
         }
         else
         {
-            llstat st;
-            int rc = LLFile::stat(strings_path_full, &st);
-            if (rc != 0)
+            if (!LLFile::exists(strings_path_full))
             {
-                crash_reason = "The file '" + strings_path_full + "' failed to get status. Error code: " + std::to_string(rc);
+                crash_reason = "The file '" + strings_path_full + "' doesn't seem to exist";
             }
-            else if (S_ISDIR(st.st_mode))
+            else if (LLFile::isdir(strings_path_full))
             {
                 crash_reason = "The filename '" + strings_path_full + "' is a directory name";
             }
@@ -3891,7 +3889,7 @@ void LLAppViewer::processMarkerFiles()
     bool marker_is_same_version = true;
     // first, look for the marker created at startup and deleted on a clean exit
     mMarkerFileName = gDirUtilp->getExpandedFilename(LL_PATH_LOGS,MARKER_FILE_NAME);
-    if (LLAPRFile::isExist(mMarkerFileName, NULL, LL_APR_RB))
+    if (LLFile::isfile(mMarkerFileName))
     {
         // File exists...
         // first, read it to see if it was created by the same version (we need this later)
@@ -3983,7 +3981,7 @@ void LLAppViewer::processMarkerFiles()
     // check for any last exec event report based on whether or not it happened during logout
     // (the logout marker is created when logout begins)
     std::string logout_marker_file =  gDirUtilp->getExpandedFilename(LL_PATH_LOGS, LOGOUT_MARKER_FILE_NAME);
-    if(LLAPRFile::isExist(logout_marker_file, NULL, LL_APR_RB))
+    if(LLFile::isfile(logout_marker_file))
     {
         if (markerIsSameVersion(logout_marker_file))
         {
@@ -3995,11 +3993,11 @@ void LLAppViewer::processMarkerFiles()
         {
             LL_INFOS("MarkerFile") << "Logout crash marker '"<< logout_marker_file << "' found, but versions did not match" << LL_ENDL;
         }
-        LLAPRFile::remove(logout_marker_file);
+        LLFile::remove(logout_marker_file);
     }
     // and last refine based on whether or not a marker created during a non-llerr crash is found
     std::string error_marker_file = gDirUtilp->getExpandedFilename(LL_PATH_LOGS, ERROR_MARKER_FILE_NAME);
-    if(LLAPRFile::isExist(error_marker_file, NULL, LL_APR_RB))
+    if(LLFile::isfile(error_marker_file))
     {
         S32 marker_code = getMarkerErrorCode(error_marker_file);
         if (marker_code >= 0)
@@ -4024,7 +4022,7 @@ void LLAppViewer::processMarkerFiles()
         {
             LL_INFOS("MarkerFile") << "Error marker '"<< error_marker_file << "' marker found, but versions did not match" << LL_ENDL;
         }
-        LLAPRFile::remove(error_marker_file);
+        LLFile::remove(error_marker_file);
     }
 
 #if LL_DARWIN
@@ -4051,7 +4049,7 @@ void LLAppViewer::removeMarkerFiles()
         if (mMarkerFile.getFileHandle())
         {
             mMarkerFile.close() ;
-            LLAPRFile::remove( mMarkerFileName );
+            LLFile::remove( mMarkerFileName );
             LL_DEBUGS("MarkerFile") << "removed exec marker '"<<mMarkerFileName<<"'"<< LL_ENDL;
         }
         else
@@ -4062,7 +4060,7 @@ void LLAppViewer::removeMarkerFiles()
         if (mLogoutMarkerFile.getFileHandle())
         {
             mLogoutMarkerFile.close();
-            LLAPRFile::remove( mLogoutMarkerFileName );
+            LLFile::remove( mLogoutMarkerFileName );
             LL_DEBUGS("MarkerFile") << "removed logout marker '"<<mLogoutMarkerFileName<<"'"<< LL_ENDL;
         }
         else
@@ -4284,7 +4282,7 @@ void LLAppViewer::migrateCacheDirectory()
                 LLFile::remove(ds_store);
             }
 #endif
-            if (LLFile::rmdir(old_cache_dir) != 0)
+            if (LLFile::remove(old_cache_dir) != 0)
             {
                 LL_WARNS() << "could not delete old cache directory " << old_cache_dir << LL_ENDL;
             }
@@ -5430,7 +5428,7 @@ void LLAppViewer::createErrorMarker(eLastExecEvent error_code) const
 bool LLAppViewer::errorMarkerExists() const
 {
     std::string error_marker_file = gDirUtilp->getExpandedFilename(LL_PATH_LOGS, ERROR_MARKER_FILE_NAME);
-    return LLAPRFile::isExist(error_marker_file, NULL, LL_APR_RB);
+    return LLFile::isfile(error_marker_file);
 }
 
 void LLAppViewer::outOfMemorySoftQuit()
diff --git a/indra/newview/llfloaterpreference.cpp b/indra/newview/llfloaterpreference.cpp
index 425e9e2269..4fa14a199d 100644..100755
--- a/indra/newview/llfloaterpreference.cpp
+++ b/indra/newview/llfloaterpreference.cpp
@@ -1500,7 +1500,7 @@ bool LLFloaterPreference::moveTranscriptsAndLog()
         //Couldn't move the log and created a new directory so remove the new directory
         if(madeDirectory)
         {
-            LLFile::rmdir(chatLogPath);
+            LLFile::remove(chatLogPath);
         }
         return false;
     }
@@ -1526,7 +1526,7 @@ bool LLFloaterPreference::moveTranscriptsAndLog()
 
         if(madeDirectory)
         {
-            LLFile::rmdir(chatLogPath);
+            LLFile::remove(chatLogPath);
         }
 
         return false;
@@ -2031,17 +2031,15 @@ void LLFloaterPreference::changed()
 {
     if (LLConversationLog::instance().getIsLoggingEnabled())
     {
-    getChild<LLButton>("clear_log")->setEnabled(LLConversationLog::instance().getConversations().size() > 0);
+        getChild<LLButton>("clear_log")->setEnabled(LLConversationLog::instance().getConversations().size() > 0);
     }
     else
     {
         // onClearLog clears list, then notifies changed() and only then clears file,
         // so check presence of conversations before checking file, file will cleared later.
-        llstat st;
         bool has_logs = LLConversationLog::instance().getConversations().size() > 0
-                        && LLFile::stat(LLConversationLog::instance().getFileName(), &st) == 0
-                        && S_ISREG(st.st_mode)
-                        && st.st_size > 0;
+                        && LLFile::isfile(LLConversationLog::instance().getFileName())
+                        && LLFile::size(LLConversationLog::instance().getFileName()) > 0;
         getChild<LLButton>("clear_log")->setEnabled(has_logs);
     }
 
diff --git a/indra/newview/llfloateruipreview.cpp b/indra/newview/llfloateruipreview.cpp
index c3bc24c6b9..0bf0946c42 100644..100755
--- a/indra/newview/llfloateruipreview.cpp
+++ b/indra/newview/llfloateruipreview.cpp
@@ -484,47 +484,47 @@ bool LLFloaterUIPreview::postBuild()
     bool found_en_us = false;
     std::string language_directory;
     std::string xui_dir = get_xui_dir();    // directory containing localizations -- don't forget trailing delim
-    mLanguageSelection->removeall();                                                                                // clear out anything temporarily in list from XML
+    mLanguageSelection->removeall();                                           // clear out anything temporarily in list from XML
 
     LLDirIterator iter(xui_dir, "*");
-    while(found)                                                                                                    // for every directory
+    while (found)                                                              // for every directory
     {
-        if((found = iter.next(language_directory)))                         // get next directory
+        if ((found = iter.next(language_directory)))                           // get next directory
         {
             std::string full_path = gDirUtilp->add(xui_dir, language_directory);
-            if(LLFile::isfile(full_path.c_str()))                                                                   // if it's not a directory, skip it
+            if (!LLFile::isdir(full_path.c_str()))                             // if it's not a directory, skip it
             {
                 continue;
             }
 
-            if(strncmp("template",language_directory.c_str(),8) && -1 == language_directory.find("."))              // if it's not the template directory or a hidden directory
+            if (strncmp("template",language_directory.c_str(), 8) && -1 == language_directory.find(".")) // if it's not the template directory or a hidden directory
             {
-                if(!strncmp("en",language_directory.c_str(),5))                                                 // remember if we've seen en, so we can make it default
+                if (!strncmp("en",language_directory.c_str(), 5))              // remember if we've seen en, so we can make it default
                 {
                     found_en_us = true;
                 }
                 else
                 {
-                    mLanguageSelection->add(std::string(language_directory));                                           // add it to the language selection dropdown menu
+                    mLanguageSelection->add(std::string(language_directory));  // add it to the language selection dropdown menu
                     mLanguageSelection_2->add(std::string(language_directory));
                 }
             }
         }
     }
-    if(found_en_us)
+    if (found_en_us)
     {
-        mLanguageSelection->add(std::string("en"),ADD_TOP);                                                         // make en first item if we found it
-        mLanguageSelection_2->add(std::string("en"),ADD_TOP);
+        mLanguageSelection->add(std::string("en"), ADD_TOP);                   // make en first item if we found it
+        mLanguageSelection_2->add(std::string("en"), ADD_TOP);
     }
     else
     {
         std::string warning = std::string("No EN localization found; check your XUI directories!");
         popupAndPrintWarning(warning);
     }
-    mLanguageSelection->selectFirstItem();                                                                          // select the first item
+    mLanguageSelection->selectFirstItem();                                     // select the first item
     mLanguageSelection_2->selectFirstItem();
 
-    refreshList();                                                                                                  // refresh the list of available floaters
+    refreshList();                                                             // refresh the list of available floaters
 
     return true;
 }
@@ -892,8 +892,7 @@ void LLFloaterUIPreview::displayFloater(bool click, S32 ID)
     // Add localization to title so user knows whether it's localized or defaulted to en
     std::string full_path = getLocalizedDirectory() + path;
     std::string floater_lang = "EN";
-    llstat dummy;
-    if(!LLFile::stat(full_path.c_str(), &dummy))    // if the file does not exist
+    if (LLFile::isfile(full_path.c_str()))    // use localized language if the file exists
     {
         floater_lang = getLocStr(ID);
     }
@@ -966,9 +965,8 @@ void LLFloaterUIPreview::onClickEditFloater()
         }
         file_path = getLocalizedDirectory() + file_name;
 
-        // stat file to see if it exists (some localized versions may not have it there are no diffs, and then we try to open an nonexistent file)
-        llstat dummy;
-        if(LLFile::stat(file_path.c_str(), &dummy))                             // if the file does not exist
+        // Does it exist? (Some localized versions may not have it when there are no diffs, and then we try to open a nonexistent file)
+        if (!LLFile::isfile(file_path.c_str()))                             // if the file does not exist
         {
             popupAndPrintWarning("No file for this floater exists in the selected localization.  Opening the EN version instead.");
             file_path = get_xui_dir() + mDelim + "en" + mDelim + file_name; // open the en version instead, by default
@@ -1117,15 +1115,14 @@ void LLFloaterUIPreview::onClickToggleDiffHighlighting()
         std::string path_in_textfield = mDiffPathTextBox->getText();    // get file path
         bool error = false;
 
-        if(std::string("") == path_in_textfield)                                    // check for blank file
+        if(std::string("") == path_in_textfield)                        // check for blank file
         {
             std::string warning = "Unable to highlight differences because no file was provided; fill in the relevant text field";
             popupAndPrintWarning(warning);
             error = true;
         }
 
-        llstat dummy;
-        if(LLFile::stat(path_in_textfield.c_str(), &dummy) && !error)           // check if the file exists (empty check is reduntant but useful for the informative error message)
+        if (!LLFile::isfile(path_in_textfield.c_str()) && !error)       // check if the file exists (empty check is redundant but useful for the informative error message)
         {
             std::string warning = std::string("Unable to highlight differences because an invalid path to a difference file was provided:\"") + path_in_textfield + "\"";
             popupAndPrintWarning(warning);
diff --git a/indra/newview/llpreviewnotecard.cpp b/indra/newview/llpreviewnotecard.cpp
index 9a991727b2..4fe661b055 100644..100755
--- a/indra/newview/llpreviewnotecard.cpp
+++ b/indra/newview/llpreviewnotecard.cpp
@@ -575,8 +575,7 @@ void LLPreviewNotecard::syncExternal()
 {
     // Sync with external editor.
     std::string tmp_file = getTmpFileName();
-    llstat s;
-    if (LLFile::stat(tmp_file, &s) == 0) // file exists
+    if (LLFile::isfile(tmp_file)) // file exists
     {
         if (mLiveFile) mLiveFile->ignoreNextUpdate();
         writeToFile(tmp_file);
diff --git a/indra/newview/llpreviewscript.cpp b/indra/newview/llpreviewscript.cpp
index c2aa4925bd..2c436198e3 100644..100755
--- a/indra/newview/llpreviewscript.cpp
+++ b/indra/newview/llpreviewscript.cpp
@@ -694,8 +694,7 @@ void LLScriptEdCore::sync()
     if (mLiveFile)
     {
         std::string tmp_file = mLiveFile->filename();
-        llstat s;
-        if (LLFile::stat(tmp_file, &s) == 0) // file exists
+        if (LLFile::isfile(tmp_file)) // file exists
         {
             mLiveFile->ignoreNextUpdate();
             writeToFile(tmp_file);
diff --git a/indra/newview/lltexturecache.cpp b/indra/newview/lltexturecache.cpp
index 612af0d147..be6c71ab86 100644..100755
--- a/indra/newview/lltexturecache.cpp
+++ b/indra/newview/lltexturecache.cpp
@@ -180,8 +180,7 @@ private:
 bool LLTextureCacheLocalFileWorker::doRead()
 {
     LL_PROFILE_ZONE_SCOPED_CATEGORY_TEXTURE;
-    S32 local_size = LLAPRFile::size(mFileName, mCache->getLocalAPRFilePool());
-
+    S32 local_size = (S32)LLFile::size(mFileName);
     if (local_size > 0 && mFileName.size() > 4)
     {
         mDataSize = local_size; // Only a complete file is valid
@@ -210,8 +209,7 @@ bool LLTextureCacheLocalFileWorker::doRead()
     }
     mReadData = (U8*)ll_aligned_malloc_16(mDataSize);
 
-    S32 bytes_read = LLAPRFile::readEx(mFileName, mReadData, mOffset, mDataSize, mCache->getLocalAPRFilePool());
-
+    S32 bytes_read = (S32)LLFile::read(mFileName, mReadData, mOffset, mDataSize);
     if (bytes_read != mDataSize)
     {
 //      LL_WARNS() << "Error reading file from local cache: " << mFileName
@@ -296,7 +294,7 @@ bool LLTextureCacheRemoteWorker::doRead()
         // Is it a JPEG2000 file?
         {
             local_filename = filename + ".j2c";
-            local_size = LLAPRFile::size(local_filename, mCache->getLocalAPRFilePool());
+            local_size = (S32)LLFile::size(local_filename);
             if (local_size > 0)
             {
                 mImageFormat = IMG_CODEC_J2C;
@@ -306,7 +304,7 @@ bool LLTextureCacheRemoteWorker::doRead()
         if (local_size == 0)
         {
             local_filename = filename + ".jpg";
-            local_size = LLAPRFile::size(local_filename, mCache->getLocalAPRFilePool());
+            local_size = (S32)LLFile::size(local_filename);
             if (local_size > 0)
             {
                 mImageFormat = IMG_CODEC_JPEG;
@@ -317,7 +315,7 @@ bool LLTextureCacheRemoteWorker::doRead()
         if (local_size == 0)
         {
             local_filename = filename + ".tga";
-            local_size = LLAPRFile::size(local_filename, mCache->getLocalAPRFilePool());
+            local_size = (S32)LLFile::size(local_filename);
             if (local_size > 0)
             {
                 mImageFormat = IMG_CODEC_TGA;
@@ -346,12 +344,10 @@ bool LLTextureCacheRemoteWorker::doRead()
 
         if (mReadData)
         {
-            S32 bytes_read = LLAPRFile::readEx( local_filename,
-                                                mReadData,
-                                                mOffset,
-                                                mDataSize,
-                                                mCache->getLocalAPRFilePool());
-
+            S32 bytes_read = (S32)LLFile::read(local_filename,
+                                               mReadData,
+                                               mOffset,
+                                               mDataSize);
             if (bytes_read != mDataSize)
             {
                 LL_WARNS() << "Error reading file from local cache: " << local_filename
@@ -410,8 +406,7 @@ bool LLTextureCacheRemoteWorker::doRead()
         mReadData = (U8*)ll_aligned_malloc_16(size);
         if (mReadData)
         {
-            S32 bytes_read = LLAPRFile::readEx(mCache->mHeaderDataFileName,
-                                                 mReadData, offset, size, mCache->getLocalAPRFilePool());
+            S32 bytes_read = (S32)LLFile::read(mCache->mHeaderDataFileName, mReadData, offset, size);
             if (bytes_read != size)
             {
                 LL_WARNS() << "LLTextureCacheWorker: "  << mID
@@ -446,9 +441,9 @@ bool LLTextureCacheRemoteWorker::doRead()
     if (!done && (mState == BODY))
     {
         std::string filename = mCache->getTextureFileName(mID);
-        S32 filesize = LLAPRFile::size(filename, mCache->getLocalAPRFilePool());
+        S32 filesize = (S32)LLFile::size(filename);
 
-        if (filesize && (filesize + TEXTURE_CACHE_ENTRY_SIZE) > mOffset)
+        if (filesize > 0 && (filesize + TEXTURE_CACHE_ENTRY_SIZE) > mOffset)
         {
             S32 max_datasize = TEXTURE_CACHE_ENTRY_SIZE + filesize - mOffset;
             mDataSize = llmin(max_datasize, mDataSize);
@@ -487,10 +482,9 @@ bool LLTextureCacheRemoteWorker::doRead()
                 mReadData = data;
 
                 // Read the data at last
-                S32 bytes_read = LLAPRFile::readEx(filename,
-                                                 mReadData + data_offset,
-                                                 file_offset, file_size,
-                                                 mCache->getLocalAPRFilePool());
+                S32 bytes_read = (S32)LLFile::read(filename,
+                                                   mReadData + data_offset,
+                                                   file_offset, file_size);
                 if (bytes_read != file_size)
                 {
                     LL_WARNS() << "LLTextureCacheWorker: "  << mID
@@ -636,13 +630,13 @@ bool LLTextureCacheRemoteWorker::doWrite()
                 U8* padBuffer = (U8*)ll_aligned_malloc_16(TEXTURE_CACHE_ENTRY_SIZE);
                 memset(padBuffer, 0, TEXTURE_CACHE_ENTRY_SIZE);     // Init with zeros
                 memcpy(padBuffer, mWriteData, mDataSize);           // Copy the write buffer
-                bytes_written = LLAPRFile::writeEx(mCache->mHeaderDataFileName, padBuffer, offset, size, mCache->getLocalAPRFilePool());
+                bytes_written = (S32)LLFile::write(mCache->mHeaderDataFileName, padBuffer, offset, size);
                 ll_aligned_free_16(padBuffer);
             }
             else
             {
                 // Write the header record (== first TEXTURE_CACHE_ENTRY_SIZE bytes of the raw file) in the header file
-                bytes_written = LLAPRFile::writeEx(mCache->mHeaderDataFileName, mWriteData, offset, size, mCache->getLocalAPRFilePool());
+                bytes_written = (S32)LLFile::write(mCache->mHeaderDataFileName, mWriteData, offset, size);
             }
 
             if (bytes_written <= 0)
@@ -678,15 +672,11 @@ bool LLTextureCacheRemoteWorker::doWrite()
         else
         {
             S32 file_size = mDataSize - TEXTURE_CACHE_ENTRY_SIZE;
-
             {
                 // build the cache file name from the UUID
                 std::string filename = mCache->getTextureFileName(mID);
                 //          LL_INFOS() << "Writing Body: " << filename << " Bytes: " << file_offset+file_size << LL_ENDL;
-                S32 bytes_written = LLAPRFile::writeEx(filename,
-                                                       mWriteData + TEXTURE_CACHE_ENTRY_SIZE,
-                                                       0, file_size,
-                                                       mCache->getLocalAPRFilePool());
+                S32 bytes_written = (S32)LLFile::write(filename, mWriteData + TEXTURE_CACHE_ENTRY_SIZE, 0, file_size);
                 if (bytes_written <= 0)
                 {
                     LL_WARNS() << "LLTextureCacheWorker: " << mID
@@ -891,7 +881,7 @@ bool LLTextureCache::isInLocal(const LLUUID& id)
     // Is it a JPEG2000 file?
     {
         local_filename = filename + ".j2c";
-        local_size = LLAPRFile::size(local_filename, getLocalAPRFilePool());
+        local_size = (S32)LLFile::size(local_filename);
         if (local_size > 0)
         {
             return true ;
@@ -901,7 +891,7 @@ bool LLTextureCache::isInLocal(const LLUUID& id)
     // If not, is it a jpeg file?
     {
         local_filename = filename + ".jpg";
-        local_size = LLAPRFile::size(local_filename, getLocalAPRFilePool());
+        local_size = (S32)LLFile::size(local_filename);
         if (local_size > 0)
         {
             return true ;
@@ -911,7 +901,7 @@ bool LLTextureCache::isInLocal(const LLUUID& id)
     // Hmm... What about a targa file? (used for UI texture mostly)
     {
         local_filename = filename + ".tga";
-        local_size = LLAPRFile::size(local_filename, getLocalAPRFilePool());
+        local_size = (S32)LLFile::size(local_filename);
         if (local_size > 0)
         {
             return true ;
@@ -964,11 +954,10 @@ void LLTextureCache::purgeCache(ELLPath location, bool remove_dir)
         if(LLFile::isdir(mTexturesDirName))
         {
             std::string file_name = gDirUtilp->getExpandedFilename(location, entries_filename);
-            // mHeaderAPRFilePoolp because we are under header mutex, and can be in main thread
-            LLAPRFile::remove(file_name, mHeaderAPRFilePoolp);
+            LLFile::remove(file_name);
 
             file_name = gDirUtilp->getExpandedFilename(location, cache_filename);
-            LLAPRFile::remove(file_name, mHeaderAPRFilePoolp);
+            LLFile::remove(file_name);
 
             purgeAllTextures(true);
         }
@@ -1069,10 +1058,9 @@ void LLTextureCache::readEntriesHeader()
 {
     // mHeaderEntriesInfo initializes to default values so safe not to read it
     llassert_always(mHeaderAPRFile == NULL);
-    if (LLAPRFile::isExist(mHeaderEntriesFileName, mHeaderAPRFilePoolp))
+    if (LLFile::isfile(mHeaderEntriesFileName))
     {
-        LLAPRFile::readEx(mHeaderEntriesFileName, (U8*)&mHeaderEntriesInfo, 0, sizeof(EntriesInfo),
-                          mHeaderAPRFilePoolp);
+        LLFile::read(mHeaderEntriesFileName, (U8*)&mHeaderEntriesInfo, 0, sizeof(EntriesInfo));
     }
     else //create an empty entries header.
     {
@@ -1088,7 +1076,7 @@ void LLTextureCache::setEntriesHeader()
         // For simplicity we use predefined size of header, so if version string
         // doesn't fit, either getEngineInfo() returned malformed string or
         // sHeaderEncoderStringSize need to be increased.
-        // Also take into accout that c_str() returns additional null character
+        // Also take into account that c_str() returns additional null character
         LL_ERRS() << "Version string doesn't fit in header" << LL_ENDL;
     }
 
@@ -1103,8 +1091,7 @@ void LLTextureCache::writeEntriesHeader()
     llassert_always(mHeaderAPRFile == NULL);
     if (!mReadOnly)
     {
-        LLAPRFile::writeEx(mHeaderEntriesFileName, (U8*)&mHeaderEntriesInfo, 0, sizeof(EntriesInfo),
-                           mHeaderAPRFilePoolp);
+        LLFile::write(mHeaderEntriesFileName, (U8*)&mHeaderEntriesInfo, 0, sizeof(EntriesInfo));
     }
 }
 
@@ -1208,8 +1195,7 @@ void LLTextureCache::writeEntryToHeaderImmediately(S32& idx, Entry& entry, bool
             idx = -1 ;//mark the idx invalid.
             return ;
         }
-
-        mHeaderAPRFile->seek(APR_SET, offset);
+        aprfile->seek(APR_SET, offset);
     }
     else
     {
@@ -1618,7 +1604,7 @@ void LLTextureCache::purgeAllTextures(bool purge_directories)
         gDirUtilp->deleteFilesInDir(mTexturesDirName, mask); // headers, fast cache
         if (purge_directories)
         {
-            LLFile::rmdir(mTexturesDirName);
+            LLFile::remove(mTexturesDirName);
         }
     }
     mHeaderIDMap.clear();
@@ -1798,8 +1784,7 @@ void LLTextureCache::purgeTextures(bool validate)
             {
                 std::string filename = getTextureFileName(entries[idx].mID);
                 LL_DEBUGS("TextureCache") << "Validating: " << filename << "Size: " << entries[idx].mBodySize << LL_ENDL;
-                // mHeaderAPRFilePoolp because this is under header mutex in main thread
-                S32 bodysize = LLAPRFile::size(filename, mHeaderAPRFilePoolp);
+                S32 bodysize = (S32)LLFile::size(filename);
                 if (bodysize != entries[idx].mBodySize)
                 {
                     LL_WARNS("TextureCache") << "TEXTURE CACHE BODY HAS BAD SIZE: " << bodysize << " != " << entries[idx].mBodySize << filename << LL_ENDL;
@@ -2150,7 +2135,7 @@ void LLTextureCache::openFastCache(bool first_time)
                 mFastCachePadBuffer = (U8*)ll_aligned_malloc_16(TEXTURE_FAST_CACHE_ENTRY_SIZE);
             }
             mFastCachePoolp = new LLVolatileAPRPool(); // is_local= true by default, so not thread safe by default
-            if (LLAPRFile::isExist(mFastCacheFileName, mFastCachePoolp))
+            if (LLFile::isfile(mFastCacheFileName))
             {
                 mFastCachep = new LLAPRFile(mFastCacheFileName, APR_READ|APR_WRITE|APR_BINARY, mFastCachePoolp) ;
             }
@@ -2233,9 +2218,7 @@ void LLTextureCache::removeCachedTexture(const LLUUID& id)
         mTexturesSizeMap.erase(id);
     }
     mHeaderIDMap.erase(id);
-    // We are inside header's mutex so mHeaderAPRFilePoolp is safe to use,
-    // but getLocalAPRFilePool() is not safe, it might be in use by worker
-    LLAPRFile::remove(getTextureFileName(id), mHeaderAPRFilePoolp);
+    LLFile::remove(getTextureFileName(id));
 }
 
 //called after mHeaderMutex is locked.
@@ -2248,9 +2231,7 @@ void LLTextureCache::removeEntry(S32 idx, Entry& entry, std::string& filename)
         if (entry.mBodySize == 0)   // Always attempt to remove when mBodySize > 0.
         {
           // Sanity check. Shouldn't exist when body size is 0.
-          // We are inside header's mutex so mHeaderAPRFilePoolp is safe to use,
-          // but getLocalAPRFilePool() is not safe, it might be in use by worker
-          if (LLAPRFile::isExist(filename, mHeaderAPRFilePoolp))
+          if (LLFile::isfile(filename))
           {
               LL_WARNS("TextureCache") << "Entry has body size of zero but file " << filename << " exists. Deleting this file, too." << LL_ENDL;
           }
@@ -2270,7 +2251,7 @@ void LLTextureCache::removeEntry(S32 idx, Entry& entry, std::string& filename)
 
     if (file_maybe_exists)
     {
-        LLAPRFile::remove(filename, mHeaderAPRFilePoolp);
+        LLFile::remove(filename);
     }
 }
 
diff --git a/indra/newview/llviewerassetstorage.cpp b/indra/newview/llviewerassetstorage.cpp
index 141f370ecb..e76d340eda 100644
--- a/indra/newview/llviewerassetstorage.cpp
+++ b/indra/newview/llviewerassetstorage.cpp
@@ -182,7 +182,7 @@ void LLViewerAssetStorage::storeAssetData(
             else
             {
                 // LLAssetStorage metric: Successful Request
-                S32 size = LLFileSystem::getFileSize(asset_id, asset_type);
+                S32 size = (S32)LLFileSystem::getFileSize(asset_id, asset_type);
                 const char *message = "Added to upload queue";
                 reportMetric( asset_id, asset_type, LLStringUtil::null, LLUUID::null, size, MR_OKAY, __FILE__, __LINE__, message );
 
diff --git a/indra/newview/llviewerassetupload.cpp b/indra/newview/llviewerassetupload.cpp
index 65a69acc88..5ac7d6b1fe 100644
--- a/indra/newview/llviewerassetupload.cpp
+++ b/indra/newview/llviewerassetupload.cpp
@@ -45,11 +45,7 @@
 #include "llappviewer.h"
 #include "llviewerstats.h"
 #include "llfilesystem.h"
-#include "llgesturemgr.h"
-#include "llpreviewnotecard.h"
-#include "llpreviewgesture.h"
 #include "llcoproceduremanager.h"
-#include "llthread.h"
 #include "llkeyframemotion.h"
 #include "lldatapacker.h"
 #include "llvoavatarself.h"
@@ -405,6 +401,7 @@ LLSD LLNewFileResourceUploadInfo::exportTempFile()
 
     std::string errorMessage;
     std::string errorLabel;
+    std::error_code ec;
 
     bool error = false;
 
@@ -475,30 +472,38 @@ LLSD LLNewFileResourceUploadInfo::exportTempFile()
         error = true;
 
         // read from getFileName()
-        LLAPRFile infile;
-        infile.open(getFileName(),LL_APR_RB);
-        if (!infile.getFileHandle())
+        LLFile infile(getFileName(), LLFile::in | LLFile::binary, ec);
+        if (ec || !infile)
         {
             LL_WARNS() << "Couldn't open file for reading: " << getFileName() << LL_ENDL;
             errorMessage = llformat("Failed to open animation file %s\n", getFileName().c_str());
         }
         else
         {
-            S32 size = LLAPRFile::size(getFileName());
+            S64 size = infile.size(ec);
+            if (ec || size <= 0)
+            {
+                LLError::LLUserWarningMsg::showMissingFiles();
+                LL_ERRS() << "Invalid file" << LL_ENDL;
+            }
+            else if (size > INT_MAX)
+            {
+                LL_ERRS() << "File is too big, size: " << size << LL_ENDL;
+            }
             U8* buffer = new(std::nothrow) U8[size];
             if (!buffer)
             {
                 LLError::LLUserWarningMsg::showOutOfMemory();
                 LL_ERRS() << "Bad memory allocation for buffer, size: " << size << LL_ENDL;
             }
-            S32 size_read = infile.read(buffer,size);
-            if (size_read != size)
+            S64 size_read = infile.read(buffer, size, ec);
+            if (ec || size_read != size)
             {
                 errorMessage = llformat("Failed to read animation file %s: wanted %d bytes, got %d\n", getFileName().c_str(), size, size_read);
             }
             else
             {
-                LLDataPackerBinaryBuffer dp(buffer, size);
+                LLDataPackerBinaryBuffer dp(buffer, (S32)size);
                 LLKeyframeMotion *motionp = new LLKeyframeMotion(getAssetId());
                 motionp->setCharacter(gAgentAvatarp);
                 if (motionp->deserialize(dp, getAssetId(), false))
@@ -544,18 +549,17 @@ LLSD LLNewFileResourceUploadInfo::exportTempFile()
     setAssetType(assetType);
 
     // copy this file into the cache for upload
-    S32 file_size;
-    LLAPRFile infile;
-    infile.open(filename, LL_APR_RB, NULL, &file_size);
-    if (infile.getFileHandle())
+    LLFile infile(filename, LLFile::in | LLFile::binary, ec);
+    if (!ec && infile.size(ec) > 0)
     {
         LLFileSystem file(getAssetId(), assetType, LLFileSystem::APPEND);
 
+        S64 read_bytes;
         const S32 buf_size = 65536;
         U8 copy_buf[buf_size];
-        while ((file_size = infile.read(copy_buf, buf_size)))
+        while (((read_bytes = infile.read(copy_buf, buf_size, ec))) > 0)
         {
-            file.write(copy_buf, file_size);
+            file.write(copy_buf, (S32)read_bytes);
         }
     }
     else
@@ -569,7 +573,6 @@ LLSD LLNewFileResourceUploadInfo::exportTempFile()
     }
 
     return LLSD();
-
 }
 
 //=========================================================================
diff --git a/indra/newview/llviewerdisplay.cpp b/indra/newview/llviewerdisplay.cpp
index ce59e844ec..5ad3344a6e 100644..100755
--- a/indra/newview/llviewerdisplay.cpp
+++ b/indra/newview/llviewerdisplay.cpp
@@ -1139,15 +1139,12 @@ std::string getProfileStatsFilename()
     // same second), may produce (e.g.) sec==61, but avoids collisions and
     // preserves chronological filename sort order.
     std::string name;
-    std::error_code ec;
     do
     {
         // base + missing 2-digit seconds, append ".json"
         // post-increment sec in case we have to try again
         name = stringize(base, std::setw(2), std::setfill('0'), sec++, ".json");
-    } while (std::filesystem::exists(fsyspath(name), ec));
-    // Ignoring ec means we might potentially return a name that does already
-    // exist -- but if we can't check its existence, what more can we do?
+    } while (LLFile::exists(fsyspath(name)));
     return name;
 }
 
diff --git a/indra/newview/llviewermedia.cpp b/indra/newview/llviewermedia.cpp
index 071a66209b..a8eaadc426 100644..100755
--- a/indra/newview/llviewermedia.cpp
+++ b/indra/newview/llviewermedia.cpp
@@ -1833,12 +1833,11 @@ LLPluginClassMedia* LLViewerMediaImpl::newSourceFromMediaType(std::string media_
         user_data_path_cache += gDirUtilp->getDirDelimiter();
 
         // See if the plugin executable exists
-        llstat s;
-        if(LLFile::stat(launcher_name, &s))
+        if (!LLFile::isfile(launcher_name))
         {
             LL_WARNS_ONCE("Media") << "Couldn't find launcher at " << launcher_name << LL_ENDL;
         }
-        else if(LLFile::stat(plugin_name, &s))
+        else if (!LLFile::isfile(plugin_name))
         {
             LL_WARNS_ONCE("Media") << "Couldn't find plugin at " << plugin_name << LL_ENDL;
         }
diff --git a/indra/newview/llvocache.cpp b/indra/newview/llvocache.cpp
index 5d456b1a19..cdc41baa88 100644..100755
--- a/indra/newview/llvocache.cpp
+++ b/indra/newview/llvocache.cpp
@@ -1250,7 +1250,7 @@ void LLVOCache::removeCache(ELLPath location, bool started)
     std::string cache_dir = gDirUtilp->getExpandedFilename(location, object_cache_dirname);
     LL_INFOS() << "Removing cache at " << cache_dir << LL_ENDL;
     gDirUtilp->deleteFilesInDir(cache_dir, mask); //delete all files
-    LLFile::rmdir(cache_dir);
+    LLFile::remove(cache_dir);
 
     clearCacheInMemory();
     mInitialized = false;
@@ -1370,7 +1370,7 @@ void LLVOCache::removeFromCache(HeaderEntryInfo* entry)
     std::string filename;
     getObjectCacheFilename(entry->mHandle, filename);
     LL_WARNS("GLTF", "VOCache") << "Removing object cache for handle " << entry->mHandle << "Filename: " << filename << LL_ENDL;
-    LLAPRFile::remove(filename, mLocalAPRFilePoolp);
+    LLFile::remove(filename);
 
     // Note: `removeFromCache` should take responsibility for cleaning up all cache artefacts specfic to the handle/entry.
     // as such this now includes the generic extras
@@ -1394,7 +1394,7 @@ void LLVOCache::readCacheHeader()
     clearCacheInMemory();
 
     bool success = true ;
-    if (LLAPRFile::isExist(mHeaderFileName, mLocalAPRFilePoolp))
+    if (LLFile::isfile(mHeaderFileName))
     {
         LLAPRFile apr_file(mHeaderFileName, APR_READ|APR_BINARY, mLocalAPRFilePoolp);
 
diff --git a/indra/newview/llvoicevivox.cpp b/indra/newview/llvoicevivox.cpp
index d132cbfa36..e58a6577f1 100644..100755
--- a/indra/newview/llvoicevivox.cpp
+++ b/indra/newview/llvoicevivox.cpp
@@ -943,8 +943,7 @@ bool LLVivoxVoiceClient::startAndLaunchDaemon()
         gDirUtilp->append(exe_path, "SLVoice");
 #endif
         // See if the vivox executable exists
-        llstat s;
-        if (!LLFile::stat(exe_path, &s))
+        if (LLFile::isfile(exe_path))
         {
             // vivox executable exists.  Build the command line and launch the daemon.
             LLProcess::Params params;