1
  2/* pngrio.c - functions for data input
  3 *
  4 * Last changed in libpng 1.6.17 [March 26, 2015]
  5 * Copyright (c) 1998-2015 Glenn Randers-Pehrson
  6 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  7 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  8 *
  9 * This code is released under the libpng license.
 10 * For conditions of distribution and use, see the disclaimer
 11 * and license in png.h
 12 *
 13 * This file provides a location for all input.  Users who need
 14 * special handling are expected to write a function that has the same
 15 * arguments as this and performs a similar function, but that possibly
 16 * has a different input method.  Note that you shouldn't change this
 17 * function, but rather write a replacement function and then make
 18 * libpng use it at run time with png_set_read_fn(...).
 19 */
 20
 21#include "pngpriv.h"
 22
 23#ifdef PNG_READ_SUPPORTED
 24
 25/* Read the data from whatever input you are using.  The default routine
 26 * reads from a file pointer.  Note that this routine sometimes gets called
 27 * with very small lengths, so you should implement some kind of simple
 28 * buffering if you are using unbuffered reads.  This should never be asked
 29 * to read more than 64K on a 16 bit machine.
 30 */
 31void /* PRIVATE */
 32png_read_data(png_structrp png_ptr, png_bytep data, png_size_t length)
 33{
 34   png_debug1(4, "reading %d bytes", (int)length);
 35
 36   if (png_ptr->read_data_fn != NULL)
 37      (*(png_ptr->read_data_fn))(png_ptr, data, length);
 38
 39   else
 40      png_error(png_ptr, "Call to NULL read function");
 41}
 42
 43#ifdef PNG_STDIO_SUPPORTED
 44/* This is the function that does the actual reading of data.  If you are
 45 * not reading from a standard C stream, you should create a replacement
 46 * read_data function and use it at run time with png_set_read_fn(), rather
 47 * than changing the library.
 48 */
 49void PNGCBAPI
 50png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
 51{
 52   png_size_t check;
 53
 54   if (png_ptr == NULL)
 55      return;
 56
 57   /* fread() returns 0 on error, so it is OK to store this in a png_size_t
 58    * instead of an int, which is what fread() actually returns.
 59    */
 60   check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
 61
 62   if (check != length)
 63      png_error(png_ptr, "Read Error");
 64}
 65#endif
 66
 67/* This function allows the application to supply a new input function
 68 * for libpng if standard C streams aren't being used.
 69 *
 70 * This function takes as its arguments:
 71 *
 72 * png_ptr      - pointer to a png input data structure
 73 *
 74 * io_ptr       - pointer to user supplied structure containing info about
 75 *                the input functions.  May be NULL.
 76 *
 77 * read_data_fn - pointer to a new input function that takes as its
 78 *                arguments a pointer to a png_struct, a pointer to
 79 *                a location where input data can be stored, and a 32-bit
 80 *                unsigned int that is the number of bytes to be read.
 81 *                To exit and output any fatal error messages the new write
 82 *                function should call png_error(png_ptr, "Error msg").
 83 *                May be NULL, in which case libpng's default function will
 84 *                be used.
 85 */
 86void PNGAPI
 87png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
 88   png_rw_ptr read_data_fn)
 89{
 90   if (png_ptr == NULL)
 91      return;
 92
 93   png_ptr->io_ptr = io_ptr;
 94
 95#ifdef PNG_STDIO_SUPPORTED
 96   if (read_data_fn != NULL)
 97      png_ptr->read_data_fn = read_data_fn;
 98
 99   else
100      png_ptr->read_data_fn = png_default_read_data;
101#else
102   png_ptr->read_data_fn = read_data_fn;
103#endif
104
105#ifdef PNG_WRITE_SUPPORTED
106   /* It is an error to write to a read device */
107   if (png_ptr->write_data_fn != NULL)
108   {
109      png_ptr->write_data_fn = NULL;
110      png_warning(png_ptr,
111          "Can't set both read_data_fn and write_data_fn in the"
112          " same structure");
113   }
114#endif
115
116#ifdef PNG_WRITE_FLUSH_SUPPORTED
117   png_ptr->output_flush_fn = NULL;
118#endif
119}
120#endif /* READ */