Re: EXIF support in PNG

On Mon, Jan 2, 2017 at 9:51 PM, Cosmin Truta <[email protected]> wrote:

> It's deflateInit(), then deflate(), then deflateEnd().


I know those are the names of the three functions you are talking about; I
want to know what the *calls* are, what the *parameters* are that you are
proposing making three function calls with.  So far as I can see what you
are suggesting simply does not work unless you know a trick that I am
unaware of.

I was really talking about *READING* the stuff; I guess writing it is an
issue too when we are talking about transcoding.  Anyway the issue is the
same for both deflate and inflate:

z_struct zs.

memset(&zs, 0, sizeof zs);
<init the malloc fields>
zs.next_in = chunk_data_pointer;
zs.avail_in = chunk_length-1; /* Known */
zs.next_out = malloc(NUMBER/*UNKNOWN!*/);
zs.avail_out = NUMBER;

inflateInit(&zs);
if (inflate(&zs, Z_FINISH) != Z_STREAM_END)
    /* WHAT DO I DO NOW? */
inflateEnd(&zs);

This doesn't work; I have an unknown NUMBER and a far from obvious return
code check (IRC you have to read zlib.h very carefully to find the above.)

Unless you know a trick this is way beyond what an app programmer will do.

John Bowler

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