src/png/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  */
  31 void /* PRIVATE */
  32 png_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
  50 void PNGCBAPI
  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
  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
  75 static void PNGCBAPI
  76 png_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  */
 144 void PNGAPI
 145 png_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 */