Release Notes

Open Source Used In AsyncOS 8.8 for Cisco Web Security Appliances
78
data is wanted. In typical applications, it should read fresh data
into the buffer (ignoring the current state of next_input_byte and
bytes_in_buffer), reset the pointer & count to the start of the
buffer, and return TRUE indicating that the buffer has been reloaded.
It is not necessary to fill the buffer entirely, only to obtain at
least one more byte. bytes_in_buffer MUST be set to a positive value
if TRUE is returned. A FALSE return should only be used when I/O
suspension is desired (this mode is discussed in the next section).
skip_input_data (j_decompress_ptr cinfo, long num_bytes)
Skip num_bytes worth of data. The buffer pointer and count should
be advanced over num_bytes input bytes, refilling the buffer as
needed. This is used to skip over a potentially large amount of
uninteresting data (such as an APPn marker). In some applications
it may be possible to optimize away the reading of the skipped data,
but it's not clear that being smart is worth much trouble; large
skips are uncommon. bytes_in_buffer may be zero on return.
A zero or negative skip count should be treated as a no-op.
resync_to_restart (j_decompress_ptr cinfo, int desired)
This routine is called only when the decompressor has failed to find
a restart (RSTn) marker where one is expected. Its mission is to
find a suitable point for resuming decompression. For most
applications, we recommend that you just use the default resync
procedure, jpeg_resync_to_restart(). However, if you are able to back
up in the input data stream, or if you have a-priori knowledge about
the likely location of restart markers, you may be able to do better.
Read the read_restart_marker() and jpeg_resync_to_restart() routines
in jdmarker.c if you think you'd like to implement your own resync
procedure.
term_source (j_decompress_ptr cinfo)
Terminate source --- called by jpeg_finish_decompress() after all
data has been read. Often a no-op.
For both fill_input_buffer() and skip_input_data(), there is no such thing
as an EOF return. If the end of the file has been reached, the routine has
a choice of exiting via ERREXIT() or inserting fake data into the buffer.
In most cases, generating a warning message and inserting a fake EOI marker
is the best course of action --- this will allow the decompressor to output
however much of the image is there. In pathological cases, the decompressor
may swallow the EOI and again demand data ... just keep feeding it fake EOIs.
jdatasrc.c illustrates the recommended error recovery behavior.
term_source() is NOT called by jpeg_abort() or jpeg_destroy(). If you want
the source manager to be cleaned up during an abort, you must do it yourself.
You will also need code to create a jpeg_source_mgr struct, fill in its method