Author :
DRC
Date :
2024-09-05 11:10:44
Hash :c519d7b6 Message :Don't ignore JPEG buf size with TJPARAM_NOREALLOC
Since the introduction of TJFLAG_NOREALLOC in libjpeg-turbo 1.2.x, the
TurboJPEG C API documentation has (confusingly) stated that:
- if the JPEG buffer pointer points to a pre-allocated buffer, then the
JPEG buffer size must be specified, and
- the JPEG buffer size should be specified if the JPEG buffer is
pre-allocated to an arbitrary size.
The documentation never explicitly stated that the JPEG buffer size
should be specified if the JPEG buffer is pre-allocated to a worst-case
size, but since focus does not imply exclusion, it also never explicitly
stated the reverse. Furthermore, the documentation never stated that
this was contingent upon TJPARAM_NOREALLOC/TJFLAG_NOREALLOC. However,
effectively the compression and lossless transformation functions
ignored the JPEG buffer size(s) passed to them, and assumed that the
JPEG buffer(s) had been allocated to a worst-case size, if
TJPARAM_NOREALLOC/TJFLAG_NOREALLOC was set. This behavior was an
accidental and undocumented throwback to libjpeg-turbo 1.1.x, in which
the tjCompress() function provided no way to specify the JPEG buffer
size. It was always a bad idea for applications to rely upon that
behavior (although our own TJBench application unfortunately did.)
However, if such applications exist in the wild, the new behavior would
constitute a breaking change, so it has been introduced only into
libjpeg-turbo 3.1.x and only into TurboJPEG 3 API functions. The
previous behavior has been retained when calling functions from the
TurboJPEG 2.1.x API and prior versions.
Did I mention that APIs are hard?
DRC