Think the custom_zlib api is incomplete. about lodepng HOT 3 OPEN

/*expected_size is expected output size, to avoid intermediate allocations. Set to 0 if not known. */
static unsigned zlib_decompress(unsigned char** out, size_t* outsize, size_t expected_size,
                                const unsigned char* in, size_t insize, const LodePNGDecompressSettings* settings) {
  unsigned error;
  if(settings->custom_zlib) {
    ucvector v = ucvector_init(*out, *outsize);
    if(expected_size) {
        /*reserve the memory to avoid intermediate reallocations*/
        ucvector_resize(&v, expected_size);
        v.size = expected_size;
    }
      
    // this only happens on iccp block
    if (*outsize == 0 && expected_size == 0) {
        expected_size = 16*1024;
        ucvector_resize(&v, expected_size);
    }
      
    error = settings->custom_zlib(&v.data, &v.size, in, insize, settings);
    if(error) {
      /*the custom zlib is allowed to have its own error codes, however, we translate it to code 110*/
      error = 110;
      /*if there's a max output size, and the custom zlib returned error, then indicate that error instead*/
      if(settings->max_output_size && *outsize > settings->max_output_size) error = 109;
    }
      
    *out = v.data;
    *outsize = v.size;
  } 

// wrap miniz decompress, since it ignores crc checksum and is faster than default png
unsigned LodepngDecompressUsingMiniz(
    unsigned char** dstData, size_t* dstDataSize,
    const unsigned char* srcData, size_t srcDataSize,
    const LodePNGDecompressSettings* settings)
{
    // mz_ulong doesn't line up with size_t on Windows, but does on macOS
    KASSERT(*dstDataSize != 0);
    
#if USE_LIBCOMPRESSION
    // this returns 121 dstSize instead of 16448 on 126 srcSize.  
    // Open src dir to see this.  Have to advance by 2 to fix this.
    if (srcDataSize <= 2) {
        return MZ_DATA_ERROR;
    }
    
    char scratchBuffer[compression_decode_scratch_buffer_size(COMPRESSION_ZLIB)];
    size_t bytesDecoded = compression_decode_buffer(
         (uint8_t*)*dstData, *dstDataSize,
         (const uint8_t*)srcData + 2, srcDataSize - 2,
        scratchBuffer, // scratch-buffer that could speed up to pass
         COMPRESSION_ZLIB);
    
    int result = MZ_OK;
    if (bytesDecoded != *dstDataSize) {
        result = MZ_DATA_ERROR;
        *dstDataSize = 0;
    }
#else
    // This works.
    mz_ulong bytesDecoded = *dstDataSize;
    int result = mz_uncompress(*dstData, &bytesDecoded,
                               srcData, srcDataSize);
    
    if (result != MZ_OK || bytesDecoded != *dstDataSize) {
        *dstDataSize = 0;
    }
    else {
        *dstDataSize = bytesDecoded;
    }
#endif

    return result;
}