pngrio.c 5.11 KB
Newer Older
wester committed
1 2 3

/* pngrio.c - functions for data input
 *
wester committed
4 5
 * Last changed in libpng 1.5.0 [January 6, 2011]
 * Copyright (c) 1998-2002,2004,2006-2011 Glenn Randers-Pehrson
wester committed
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 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
wester committed
29
 * to read more than 64K on a 16 bit machine.
wester committed
30 31
 */
void /* PRIVATE */
wester committed
32
png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
wester committed
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
{
   png_debug1(4, "reading %d bytes", (int)length);

   if (png_ptr->read_data_fn != NULL)
      (*(png_ptr->read_data_fn))(png_ptr, data, length);

   else
      png_error(png_ptr, "Call to NULL read function");
}

#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.
 */
wester committed
49
#  ifndef USE_FAR_KEYWORD
wester committed
50 51 52 53 54 55 56 57 58 59 60
void PNGCBAPI
png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
   png_size_t check;

   if (png_ptr == NULL)
      return;

   /* fread() returns 0 on error, so it is OK to store this in a png_size_t
    * instead of an int, which is what fread() actually returns.
    */
wester committed
61
   check = fread(data, 1, length, (png_FILE_p)png_ptr->io_ptr);
wester committed
62 63 64 65

   if (check != length)
      png_error(png_ptr, "Read Error");
}
wester committed
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122
#  else
/* This is the model-independent version. Since the standard I/O library
   can't handle far buffers in the medium and small models, we have to copy
   the data.
*/

#define NEAR_BUF_SIZE 1024
#define MIN(a,b) (a <= b ? a : b)

static void PNGCBAPI
png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
   png_size_t check;
   png_byte *n_data;
   png_FILE_p io_ptr;

   if (png_ptr == NULL)
      return;

   /* Check if data really is near. If so, use usual code. */
   n_data = (png_byte *)CVT_PTR_NOCHECK(data);
   io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);

   if ((png_bytep)n_data == data)
   {
      check = fread(n_data, 1, length, io_ptr);
   }

   else
   {
      png_byte buf[NEAR_BUF_SIZE];
      png_size_t read, remaining, err;
      check = 0;
      remaining = length;

      do
      {
         read = MIN(NEAR_BUF_SIZE, remaining);
         err = fread(buf, 1, read, io_ptr);
         png_memcpy(data, buf, read); /* copy far buffer to near buffer */

         if (err != read)
            break;

         else
            check += err;

         data += read;
         remaining -= read;
      }
      while (remaining != 0);
   }

   if ((png_uint_32)check != (png_uint_32)length)
      png_error(png_ptr, "read Error");
}
#  endif
wester committed
123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144
#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
wester committed
145
png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
a  
Kai Westerkamp committed
146
   png_rw_ptr read_data_fn)
wester committed
147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175
{
   if (png_ptr == NULL)
      return;

   png_ptr->io_ptr = io_ptr;

#ifdef PNG_STDIO_SUPPORTED
   if (read_data_fn != NULL)
      png_ptr->read_data_fn = read_data_fn;

   else
      png_ptr->read_data_fn = png_default_read_data;
#else
   png_ptr->read_data_fn = read_data_fn;
#endif

   /* It is an error to write to a read device */
   if (png_ptr->write_data_fn != NULL)
   {
      png_ptr->write_data_fn = NULL;
      png_warning(png_ptr,
          "Can't set both read_data_fn and write_data_fn in the"
          " same structure");
   }

#ifdef PNG_WRITE_FLUSH_SUPPORTED
   png_ptr->output_flush_fn = NULL;
#endif
}
wester committed
176
#endif /* PNG_READ_SUPPORTED */