load png with custom zlib, why not provide uncompressed size? about lodepng HOT 3 CLOSED

An example of using a custom codec is here:
https://github.com/google/zopfli/blob/master/src/zopflipng/zopflipng_lib.cc#L171
It's an encoder there, but it's simimar to set a decoder.

An example of using zlib (deflate) with unknown size is here:
https://github.com/madler/zlib/blob/master/test/example.c#L258

What you suggest could be interesting: Normally you do not know the decompressed size of a zlib stream beforehand, but in the case of PNG you can of course compute it given width, height, color model etc... It's of course not a trivial computation (with various subtleties about how to end sub-byte pixels at scanlines etc...) but possible. Of course a bad PNG file could contain a zlib stream in it that has a larger size anyway for some reason, so it would never be guaranteed. This may be a possible optimization in the future. For now, it's with unknown size though.

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I said so because there are already 'predict' bytes memory allocated to scanlines, its size is 'predict and expecting decoded size is 'predict' too.

  // here predict bytes memory are allocated (reserved) to scanlines
  if(!state->error && !ucvector_reserve(&scanlines, predict)) state->error = 83; /*alloc fail*/
  if(!state->error)
  {
    state->error = zlib_decompress(&scanlines.data, &scanlines.size, idat.data,
                                   idat.size, &state->decoder.zlibsettings);
    if(!state->error && scanlines.size != predict) state->error = 91; /*decompressed size doesn't match prediction*/
  }

but it does not matter since it is possible to decode with unknown size, thank you for the link.

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do you have some examples of using standard zlib with lodepng ?

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