src/png/pngrio.c

   1
   2 /* pngrio.c - functions for data input
   3  *
   4  * Last changed in libpng 1.4.1 [February 25, 2010]
   5  * Copyright (c) 1998-2010 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 #define PNG_NO_PEDANTIC_WARNINGS
  22 #include "png.h"
  23 #ifdef PNG_READ_SUPPORTED
  24 #include "pngpriv.h"
  25
  26 /* Read the data from whatever input you are using.  The default routine
  27  * reads from a file pointer.  Note that this routine sometimes gets called
  28  * with very small lengths, so you should implement some kind of simple
  29  * buffering if you are using unbuffered reads.  This should never be asked
  30  * to read more then 64K on a 16 bit machine.
  31  */
  32 void /* PRIVATE */
  33 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  34 {
  35    png_debug1(4, "reading %d bytes", (int)length);
  36
  37    if (png_ptr->read_data_fn != NULL)
  38       (*(png_ptr->read_data_fn))(png_ptr, data, length);
  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
  50 void PNGAPI
  51 png_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    /* 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_FILE_p)png_ptr->io_ptr);
  61
  62    if (check != length)
  63       png_error(png_ptr, "Read Error");
  64 }
  65 #else
  66 /* This is the model-independent version. Since the standard I/O library
  67    can't handle far buffers in the medium and small models, we have to copy
  68    the data.
  69 */
  70
  71 #define NEAR_BUF_SIZE 1024
  72 #define MIN(a,b) (a <= b ? a : b)
  73
  74 static void PNGAPI
  75 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  76 {
  77    png_size_t check;
  78    png_byte *n_data;
  79    png_FILE_p io_ptr;
  80
  81    if (png_ptr == NULL)
  82       return;
  83    /* Check if data really is near. If so, use usual code. */
  84    n_data = (png_byte *)CVT_PTR_NOCHECK(data);
  85    io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
  86    if ((png_bytep)n_data == data)
  87    {
  88       check = fread(n_data, 1, length, io_ptr);
  89    }
  90    else
  91    {
  92       png_byte buf[NEAR_BUF_SIZE];
  93       png_size_t read, remaining, err;
  94       check = 0;
  95       remaining = length;
  96       do
  97       {
  98          read = MIN(NEAR_BUF_SIZE, remaining);
  99          err = fread(buf, 1, read, io_ptr);
 100          png_memcpy(data, buf, read); /* copy far buffer to near buffer */
 101          if (err != read)
 102             break;
 103          else
 104             check += err;
 105          data += read;
 106          remaining -= read;
 107       }
 108       while (remaining != 0);
 109    }
 110    if ((png_uint_32)check != (png_uint_32)length)
 111       png_error(png_ptr, "read Error");
 112 }
 113 #endif
 114 #endif
 115
 116 /* This function allows the application to supply a new input function
 117  * for libpng if standard C streams aren't being used.
 118  *
 119  * This function takes as its arguments:
 120  * png_ptr      - pointer to a png input data structure
 121  * io_ptr       - pointer to user supplied structure containing info about
 122  *                the input functions.  May be NULL.
 123  * read_data_fn - pointer to a new input function that takes as its
 124  *                arguments a pointer to a png_struct, a pointer to
 125  *                a location where input data can be stored, and a 32-bit
 126  *                unsigned int that is the number of bytes to be read.
 127  *                To exit and output any fatal error messages the new write
 128  *                function should call png_error(png_ptr, "Error msg").
 129  *                May be NULL, in which case libpng's default function will
 130  *                be used.
 131  */
 132 void PNGAPI
 133 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
 134    png_rw_ptr read_data_fn)
 135 {
 136    if (png_ptr == NULL)
 137       return;
 138    png_ptr->io_ptr = io_ptr;
 139
 140 #ifdef PNG_STDIO_SUPPORTED
 141    if (read_data_fn != NULL)
 142       png_ptr->read_data_fn = read_data_fn;
 143    else
 144       png_ptr->read_data_fn = png_default_read_data;
 145 #else
 146    png_ptr->read_data_fn = read_data_fn;
 147 #endif
 148
 149    /* It is an error to write to a read device */
 150    if (png_ptr->write_data_fn != NULL)
 151    {
 152       png_ptr->write_data_fn = NULL;
 153       png_warning(png_ptr,
 154          "It's an error to set both read_data_fn and write_data_fn in the ");
 155       png_warning(png_ptr,
 156          "same structure.  Resetting write_data_fn to NULL");
 157    }
 158
 159 #ifdef PNG_WRITE_FLUSH_SUPPORTED
 160    png_ptr->output_flush_fn = NULL;
 161 #endif
 162 }
 163 #endif /* PNG_READ_SUPPORTED */