chromium/third_party/libpng/pngrio.c

/* pngrio.c - functions for data input
 *
 * Copyright (c) 2018 Cosmin Truta
 * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
 * Copyright (c) 1996-1997 Andreas Dilger
 * Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 *
 * This file provides a location for all input.  Users who need
 * special handling are expected to write a function that has the same
 * arguments as this and performs a similar function, but that possibly
 * has a different input method.  Note that you shouldn't change this
 * function, but rather write a replacement function and then make
 * libpng use it at run time with png_set_read_fn(...).
 */

#include "pngpriv.h"

#ifdef PNG_READ_SUPPORTED

/* Read the data from whatever input you are using.  The default routine
 * reads from a file pointer.  Note that this routine sometimes gets called
 * with very small lengths, so you should implement some kind of simple
 * buffering if you are using unbuffered reads.  This should never be asked
 * to read more than 64K on a 16-bit machine.
 */
void /* PRIVATE */
png_read_data(png_structrp png_ptr, png_bytep data, size_t length)
{ … }

#ifdef PNG_STDIO_SUPPORTED
/* This is the function that does the actual reading of data.  If you are
 * not reading from a standard C stream, you should create a replacement
 * read_data function and use it at run time with png_set_read_fn(), rather
 * than changing the library.
 */
void PNGCBAPI
png_default_read_data(png_structp png_ptr, png_bytep data, size_t length)
{ … }
#endif

/* This function allows the application to supply a new input function
 * for libpng if standard C streams aren't being used.
 *
 * This function takes as its arguments:
 *
 * png_ptr      - pointer to a png input data structure
 *
 * io_ptr       - pointer to user supplied structure containing info about
 *                the input functions.  May be NULL.
 *
 * read_data_fn - pointer to a new input function that takes as its
 *                arguments a pointer to a png_struct, a pointer to
 *                a location where input data can be stored, and a 32-bit
 *                unsigned int that is the number of bytes to be read.
 *                To exit and output any fatal error messages the new write
 *                function should call png_error(png_ptr, "Error msg").
 *                May be NULL, in which case libpng's default function will
 *                be used.
 */
void PNGAPI
png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
    png_rw_ptr read_data_fn)
{ … }
#endif /* READ */