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/**
* @file lltempredirect.h
* @author Nat Goodspeed
* @date 2019-10-31
* @brief RAII low-level file-descriptor redirection
*
* $LicenseInfo:firstyear=2019&license=viewerlgpl$
* Copyright (c) 2019, Linden Research, Inc.
* $/LicenseInfo$
*/
#if ! defined(LL_LLTEMPREDIRECT_H)
#define LL_LLTEMPREDIRECT_H
// Functions in this namespace are intended to insulate the caller from the
// aggravating distinction between ::close() and Microsoft _close().
namespace llfd
{
int close(int fd);
int dup(int target);
int dup2(int target, int reference);
FILE* open(int fd, const char* mode);
int fileno(FILE* stream);
} // namespace llfd
/**
* LLTempRedirect is an RAII class that performs file redirection on low-level
* file descriptors, expressed as ints. (Use llfd::fileno() to obtain the file
* descriptor from a classic-C FILE*. There is no portable way to obtain the
* file descriptor from a std::fstream.)
*
* Instantiate LLTempRedirect with a target file descriptor (e.g. for some
* open file) and a reference file descriptor (e.g. for stderr). From that
* point until the LLTempRedirect instance is destroyed, all OS-level writes
* to the reference file descriptor will be redirected to the target file.
*
* Because dup2() is used for redirection, the original passed target file
* descriptor remains open. If you want LLTempRedirect's destructor to close
* the target file, close() the target file descriptor after passing it to
* LLTempRedirect's constructor.
*
* LLTempRedirect's constructor saves the original target of the reference
* file descriptor. Its destructor restores the reference file descriptor to
* point once again to its original target.
*/
class LLTempRedirect
{
public:
LLTempRedirect();
/**
* For the lifespan of this LLTempRedirect instance, all writes to
* 'reference' will be redirected to 'target'. When this LLTempRedirect is
* destroyed, the original target for 'reference' will be restored.
*
* Pass 'target' as NULL if you simply want to save and restore
* 'reference' against possible redirection in the meantime.
*/
LLTempRedirect(FILE* target, FILE* reference);
/**
* For the lifespan of this LLTempRedirect instance, all writes to
* 'reference' will be redirected to 'target'. When this LLTempRedirect is
* destroyed, the original target for 'reference' will be restored.
*
* Pass 'target' as -1 if you simply want to save and restore
* 'reference' against possible redirection in the meantime.
*/
LLTempRedirect(int target, int reference);
LLTempRedirect(const LLTempRedirect&) = delete;
LLTempRedirect(LLTempRedirect&& other);
~LLTempRedirect();
LLTempRedirect& operator=(const LLTempRedirect&) = delete;
LLTempRedirect& operator=(LLTempRedirect&& other);
/// returns (duplicate file descriptor for) the original target of the
/// 'reference' file descriptor passed to our constructor
int getOriginalTarget() const { return mOrigTarget; }
/// returns the original 'reference' file descriptor passed to our
/// constructor
int getReference() const { return mReference; }
private:
void reset();
int mOrigTarget, mReference;
};
#endif /* ! defined(LL_LLTEMPREDIRECT_H) */
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