Re: Why is it that png files are not dependable over the long haul

On Thu, 2 Aug 2018 at 02:37, J Decker wrote:
> Experimenting with the chromium modified zlib, I found a flag  INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR

That's in the original zlib, also. But you don't need it.

What you need is the following libpng function call:

    png_set_option(png_ptr,
        PNG_MAXIMUM_INFLATE_WINDOW,
        PNG_OPTION_ON);

See the libpng manual for details.

To conclude the story from my previous email:

If PNG_MAXIMUM_INFLATE_WINDOW is set to PNG_OPTION_OFF (i.e. the
default), libpng can diagnose the error, but not recover from it.
Conversely, if PNG_MAXIMUM_INFLATE_WINDOW is set to PNG_OPTION_ON,
libpng can decode the image, but not know that the image had an error.
It's an either/or proposition, unfortunately.

Sincerely,
Cosmin

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