/src/FreeImage/Source/LibPNG/pngrio.c

  1
  2/* pngrio.c - functions for data input
  3 *
  4 * Last changed in libpng 1.5.0 [January 6, 2011]
  5 * Copyright (c) 1998-2011 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 then 64K on a 16 bit machine.
 30 */
 31void /* PRIVATE */
 32png_read_data(png_structp 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 */
 49#  ifndef USE_FAR_KEYWORD
 50void PNGCBAPI
 51png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
 52{
 53   png_size_t check;
 54
 55   if (png_ptr == NULL)
 56      return;
 57
 58   /* fread() returns 0 on error, so it is OK to store this in a png_size_t
 59    * instead of an int, which is what fread() actually returns.
 60    */
 61   check = fread(data, 1, length, (png_FILE_p)png_ptr->io_ptr);
 62
 63   if (check != length)
 64      png_error(png_ptr, "Read Error");
 65}
 66#  else
 67/* This is the model-independent version. Since the standard I/O library
 68   can't handle far buffers in the medium and small models, we have to copy
 69   the data.
 70*/
 71
 72#define NEAR_BUF_SIZE 1024
 73#define MIN(a,b) (a <= b ? a : b)
 74
 75static void PNGCBAPI
 76png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
 77{
 78   png_size_t check;
 79   png_byte *n_data;
 80   png_FILE_p io_ptr;
 81
 82   if (png_ptr == NULL)
 83      return;
 84
 85   /* Check if data really is near. If so, use usual code. */
 86   n_data = (png_byte *)CVT_PTR_NOCHECK(data);
 87   io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
 88
 89   if ((png_bytep)n_data == data)
 90   {
 91      check = fread(n_data, 1, length, io_ptr);
 92   }
 93
 94   else
 95   {
 96      png_byte buf[NEAR_BUF_SIZE];
 97      png_size_t read, remaining, err;
 98      check = 0;
 99      remaining = length;
100
101      do
102      {
103         read = MIN(NEAR_BUF_SIZE, remaining);
104         err = fread(buf, 1, read, io_ptr);
105         png_memcpy(data, buf, read); /* copy far buffer to near buffer */
106
107         if (err != read)
108            break;
109
110         else
111            check += err;
112
113         data += read;
114         remaining -= read;
115      }
116      while (remaining != 0);
117   }
118
119   if ((png_uint_32)check != (png_uint_32)length)
120      png_error(png_ptr, "read Error");
121}
122#  endif
123#endif
124
125/* This function allows the application to supply a new input function
126 * for libpng if standard C streams aren't being used.
127 *
128 * This function takes as its arguments:
129 *
130 * png_ptr      - pointer to a png input data structure
131 *
132 * io_ptr       - pointer to user supplied structure containing info about
133 *                the input functions.  May be NULL.
134 *
135 * read_data_fn - pointer to a new input function that takes as its
136 *                arguments a pointer to a png_struct, a pointer to
137 *                a location where input data can be stored, and a 32-bit
138 *                unsigned int that is the number of bytes to be read.
139 *                To exit and output any fatal error messages the new write
140 *                function should call png_error(png_ptr, "Error msg").
141 *                May be NULL, in which case libpng's default function will
142 *                be used.
143 */
144void PNGAPI
145png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
146   png_rw_ptr read_data_fn)
147{
148   if (png_ptr == NULL)
149      return;
150
151   png_ptr->io_ptr = io_ptr;
152
153#ifdef PNG_STDIO_SUPPORTED
154   if (read_data_fn != NULL)
155      png_ptr->read_data_fn = read_data_fn;
156
157   else
158      png_ptr->read_data_fn = png_default_read_data;
159#else
160   png_ptr->read_data_fn = read_data_fn;
161#endif
162
163   /* It is an error to write to a read device */
164   if (png_ptr->write_data_fn != NULL)
165   {
166      png_ptr->write_data_fn = NULL;
167      png_warning(png_ptr,
168          "Can't set both read_data_fn and write_data_fn in the"
169          " same structure");
170   }
171
172#ifdef PNG_WRITE_FLUSH_SUPPORTED
173   png_ptr->output_flush_fn = NULL;
174#endif
175}
176#endif /* PNG_READ_SUPPORTED */