Release Notes

Open Source Used In AsyncOS 8.8 for Cisco Web Security Appliances
57
to read from a stdio stream. You can use your own source module if you want
to do something else, as discussed later.
If you use the standard source module, you must open the source stdio stream
beforehand. Typical code for this step looks like:
FILE * infile;
...
if ((infile = fopen(filename, "rb")) == NULL) {
 fprintf(stderr, "can't open %s\n", filename);
 exit(1);
}
jpeg_stdio_src(&cinfo, infile);
where the last line invokes the standard source module.
WARNING: it is critical that the binary compressed data be read unchanged.
On non-Unix systems the stdio library may perform newline translation or
otherwise corrupt binary data. To suppress this behavior, you may need to use
a "b" option to fopen (as shown above), or use setmode() or another routine to
put the stdio stream in binary mode. See cjpeg.c and djpeg.c for code that
has been found to work on many systems.
You may not change the data source between calling jpeg_read_header() and
jpeg_finish_decompress(). If you wish to read a series of JPEG images from
a single source file, you should repeat the jpeg_read_header() to
jpeg_finish_decompress() sequence without reinitializing either the JPEG
object or the data source module; this prevents buffered input data from
being discarded.
3. Call jpeg_read_header() to obtain image info.
Typical code for this step is just
jpeg_read_header(&cinfo, TRUE);
This will read the source datastream header markers, up to the beginning
of the compressed data proper. On return, the image dimensions and other
info have been stored in the JPEG object. The application may wish to
consult this information before selecting decompression parameters.
More complex code is necessary if
* A suspending data source is used --- in that case jpeg_read_header()
may return before it has read all the header data. See "I/O suspension",
below. The normal stdio source manager will NOT cause this to happen.
* Abbreviated JPEG files are to be processed --- see the section on
abbreviated datastreams. Standard applications that deal only in