SL-18837: Make llsdserialize_test debug output conditional.

Move hexdump() and hexmix() stream formatters to new hexdump.h for potential
use by other tests.

In toPythonUsing() helper function, add a temp file to receive Python script
debug output, and direct debug output to that file. On test failure, dump the
contents of that file to the log.

Give NamedTempFile::peep() an optional target std::ostream; refactor
implementation as peep_via() that accepts a callable to process each text
line. Add operator<<() to stream the contents of a NamedTempFile object to
ostream -- but don't use that with LL_DEBUGS(), as it flattens the file
contents into a single log line. Instead add peep_log(), which streams each
individual text line to LL_DEBUGS().

2 files changed, 118 insertions, 4 deletions

diff --git a/indra/test/hexdump.h b/indra/test/hexdump.h
new file mode 100644
index 0000000000..dd7cbaaa3c
--- /dev/null
+++ b/indra/test/hexdump.h
@@ -0,0 +1,97 @@
+/**
+ * @file   hexdump.h
+ * @author Nat Goodspeed
+ * @date   2023-09-08
+ * @brief  Provide hexdump() and hexmix() ostream formatters
+ * 
+ * $LicenseInfo:firstyear=2023&license=viewerlgpl$
+ * Copyright (c) 2023, Linden Research, Inc.
+ * $/LicenseInfo$
+ */
+
+#if ! defined(LL_HEXDUMP_H)
+#define LL_HEXDUMP_H
+
+#include <cctype>
+#include <iomanip>
+#include <iostream>
+#include <string_view>
+
+// Format a given byte string as 2-digit hex values, no separators
+// Usage: std::cout << hexdump(somestring) << ...
+class hexdump
+{
+public:
+    hexdump(const std::string_view& data):
+        hexdump(data.data(), data.length())
+    {}
+
+    hexdump(const char* data, size_t len):
+        hexdump(reinterpret_cast<const unsigned char*>(data), len)
+    {}
+
+    hexdump(const unsigned char* data, size_t len):
+        mData(data, data + len)
+    {}
+
+    friend std::ostream& operator<<(std::ostream& out, const hexdump& self)
+    {
+        auto oldfmt{ out.flags() };
+        auto oldfill{ out.fill() };
+        out.setf(std::ios_base::hex, std::ios_base::basefield);
+        out.fill('0');
+        for (auto c : self.mData)
+        {
+            out << std::setw(2) << unsigned(c);
+        }
+        out.setf(oldfmt, std::ios_base::basefield);
+        out.fill(oldfill);
+        return out;
+    }
+
+private:
+    std::vector<unsigned char> mData;
+};
+
+// Format a given byte string as a mix of printable characters and, for each
+// non-printable character, "\xnn"
+// Usage: std::cout << hexmix(somestring) << ...
+class hexmix
+{
+public:
+    hexmix(const std::string_view& data):
+        mData(data)
+    {}
+
+    hexmix(const char* data, size_t len):
+        mData(data, len)
+    {}
+
+    friend std::ostream& operator<<(std::ostream& out, const hexmix& self)
+    {
+        auto oldfmt{ out.flags() };
+        auto oldfill{ out.fill() };
+        out.setf(std::ios_base::hex, std::ios_base::basefield);
+        out.fill('0');
+        for (auto c : self.mData)
+        {
+            // std::isprint() must be passed an unsigned char!
+            if (std::isprint(static_cast<unsigned char>(c)))
+            {
+                out << c;
+            }
+            else
+            {
+                out << "\\x" << std::setw(2) << unsigned(c);
+            }
+        }
+        out.setf(oldfmt, std::ios_base::basefield);
+        out.fill(oldfill);
+        return out;
+    }
+
+private:
+    std::string mData;
+};
+
+#endif /* ! defined(LL_HEXDUMP_H) */
diff --git a/indra/test/namedtempfile.h b/indra/test/namedtempfile.h
index 3a994ae798..ad14cebbd1 100644
--- a/indra/test/namedtempfile.h
+++ b/indra/test/namedtempfile.h
@@ -67,14 +67,31 @@ public:
 
     std::string getName() const { return mPath.string(); }
 
-    void peep()
+    template <typename CALLABLE>
+    void peep_via(CALLABLE&& callable) const
     {
-        std::cout << "File '" << mPath << "' contains:\n";
+        std::forward<CALLABLE>(callable)(stringize("File '", mPath, "' contains:"));
         boost::filesystem::ifstream reader(mPath, std::ios::binary);
         std::string line;
         while (std::getline(reader, line))
-            std::cout << line << '\n';
-        std::cout << "---\n";
+            std::forward<CALLABLE>(callable)(line);
+        std::forward<CALLABLE>(callable)("---");
+    }
+
+    void peep_log() const
+    {
+        peep_via([](const std::string& line){ LL_DEBUGS() << line << LL_ENDL; });
+    }
+
+    void peep(std::ostream& out=std::cout) const
+    {
+        peep_via([&out](const std::string& line){ out << line << '\n'; });
+    }
+
+    friend std::ostream& operator<<(std::ostream& out, const NamedTempFile& self)
+    {
+        self.peep(out);
+        return out;
     }
 
     static boost::filesystem::path temp_path(const std::string_view& pfx="",