2005.10.15 16:24 "[Tiff] Re: Small bug report, and error handler parameter issue", by Joris Van Damme

This change would break many existing applications that use libtiff (as I understand the change), and thus I don't think it could be contemplated except as part of a major generational step, presumably to libtiff 4.0.

So, my position is that it should not be done till we are needing to do alot of other disruption. These sort of API changes in a stable and established library like libtiff cause alot of waves.

Yes, I understand your reasons to keep API stable, and I totally agree.

But, I think there is a nice way to have our cake and eat it too, I think is the expression. The following is from tif_warning.c and tifio.h, but the error stuff works the same way:

typedef void (*TIFFErrorHandler)(const char*, const char*, va_list);

TIFFErrorHandler
TIFFSetWarningHandler(TIFFErrorHandler handler)
{
 TIFFErrorHandler prev = _TIFFwarningHandler;
 _TIFFwarningHandler = handler;
 return (prev);
}

void
TIFFWarning(const char* module, const char* fmt, ...)
{
 if (_TIFFwarningHandler) {
  va_list ap;
  va_start(ap, fmt);
  (*_TIFFwarningHandler)(module, fmt, ap);
  va_end(ap);
 }
}

We're lucky in that the calling of the application-level warning and error handlers is packed, and is not used directly anywhere. From within LibTiff, TIFFWarning is called, which in turn is the only place where _TIFFwarningHandler is called directly. So we could change it to the following:

typedef void (*TIFFErrorHandler)(const char*, const char*, va_list); typedef void (*TIFFErrorHandlerExt)(TIFF*, const char*, const char*, va_list);

TIFFErrorHandler
TIFFSetWarningHandler(TIFFErrorHandler handler)
{
 TIFFErrorHandler prev = _TIFFwarningHandler;
 _TIFFwarningHandler = handler;
 return (prev);
}

TIFFErrorHandlerExt
TIFFSetWarningHandlerExt(TIFFErrorHandlerExt handler)
{
 TIFFErrorHandlerExt prev = _TIFFwarningHandlerExt;
 _TIFFwarningHandlerExt = handler;
 return (prev);
}

void
TIFFWarning(TIFF* tif, const char* module, const char* fmt, ...)
{
 if (_TIFFwarningHandler) {
  va_list ap;
  va_start(ap, fmt);
  (*_TIFFwarningHandler)(module, fmt, ap);
  (*_TIFFwarningHandlerExt)(tif,module, fmt, ap);
  va_end(ap);
 }
}

So as to call the 'old' warning and error handlers the old way, so as to not break old code, while additionally calling the 'new' warning and error handlers the new way, so as to enable old cold to track down the context of the reported warning or error.

Does this sound acceptable? Is it even correct? (I am not a C coder, sorry if I made a stupid mistake somewhere.)

Joris Van Damme
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http://www.awaresystems.be/
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