src/libpng/pngrio.c

   1
   2 /* pngrio.c - functions for data input
   3  *
   4  * Last changed in libpng 1.2.37 [June 4, 2009]
   5  * For conditions of distribution and use, see copyright notice in png.h
   6  * Copyright (c) 1998-2009 Glenn Randers-Pehrson
   7  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
   8  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
   9  *
  10  * This file provides a location for all input.  Users who need
  11  * special handling are expected to write a function that has the same
  12  * arguments as this and performs a similar function, but that possibly
  13  * has a different input method.  Note that you shouldn't change this
  14  * function, but rather write a replacement function and then make
  15  * libpng use it at run time with png_set_read_fn(...).
  16  */
  17
  18 #define PNG_INTERNAL
  19 #include "png.h"
  20 #if defined(PNG_READ_SUPPORTED)
  21
  22 /* Read the data from whatever input you are using.  The default routine
  23  * reads from a file pointer.  Note that this routine sometimes gets called
  24  * with very small lengths, so you should implement some kind of simple
  25  * buffering if you are using unbuffered reads.  This should never be asked
  26  * to read more then 64K on a 16 bit machine.
  27  */
  28 void /* PRIVATE */
  29 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  30 {
  31    png_debug1(4, "reading %d bytes", (int)length);
  32    if (png_ptr->read_data_fn != NULL)
  33       (*(png_ptr->read_data_fn))(png_ptr, data, length);
  34    else
  35       png_error(png_ptr, "Call to NULL read function");
  36 }
  37
  38 #if !defined(PNG_NO_STDIO)
  39 /* This is the function that does the actual reading of data.  If you are
  40  * not reading from a standard C stream, you should create a replacement
  41  * read_data function and use it at run time with png_set_read_fn(), rather
  42  * than changing the library.
  43  */
  44 #ifndef USE_FAR_KEYWORD
  45 void PNGAPI
  46 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  47 {
  48    png_size_t check;
  49
  50    if (png_ptr == NULL)
  51       return;
  52    /* fread() returns 0 on error, so it is OK to store this in a png_size_t
  53     * instead of an int, which is what fread() actually returns.
  54     */
  55 #if defined(_WIN32_WCE)
  56    if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
  57       check = 0;
  58 #else
  59    check = (png_size_t)fread(data, (png_size_t)1, length,
  60       (png_FILE_p)png_ptr->io_ptr);
  61 #endif
  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 PNGAPI
  76 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  77 {
  78    int check;
  79    png_byte *n_data;
  80    png_FILE_p io_ptr;
  81
  82    if (png_ptr == NULL)
  83       return;
  84    /* Check if data really is near. If so, use usual code. */
  85    n_data = (png_byte *)CVT_PTR_NOCHECK(data);
  86    io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
  87    if ((png_bytep)n_data == data)
  88    {
  89 #if defined(_WIN32_WCE)
  90       if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
  91          check = 0;
  92 #else
  93       check = fread(n_data, 1, length, io_ptr);
  94 #endif
  95    }
  96    else
  97    {
  98       png_byte buf[NEAR_BUF_SIZE];
  99       png_size_t read, remaining, err;
 100       check = 0;
 101       remaining = length;
 102       do
 103       {
 104          read = MIN(NEAR_BUF_SIZE, remaining);
 105 #if defined(_WIN32_WCE)
 106          if ( !ReadFile((HANDLE)(io_ptr), buf, read, &err, NULL) )
 107             err = 0;
 108 #else
 109          err = fread(buf, (png_size_t)1, read, io_ptr);
 110 #endif
 111          png_memcpy(data, buf, read); /* copy far buffer to near buffer */
 112          if (err != read)
 113             break;
 114          else
 115             check += err;
 116          data += read;
 117          remaining -= read;
 118       }
 119       while (remaining != 0);
 120    }
 121    if ((png_uint_32)check != (png_uint_32)length)
 122       png_error(png_ptr, "read Error");
 123 }
 124 #endif
 125 #endif
 126
 127 /* This function allows the application to supply a new input function
 128  * for libpng if standard C streams aren't being used.
 129  *
 130  * This function takes as its arguments:
 131  * png_ptr      - pointer to a png input data structure
 132  * io_ptr       - pointer to user supplied structure containing info about
 133  *                the input functions.  May be NULL.
 134  * read_data_fn - pointer to a new input function that takes as its
 135  *                arguments a pointer to a png_struct, a pointer to
 136  *                a location where input data can be stored, and a 32-bit
 137  *                unsigned int that is the number of bytes to be read.
 138  *                To exit and output any fatal error messages the new write
 139  *                function should call png_error(png_ptr, "Error msg").
 140  *                May be NULL, in which case libpng's default function will
 141  *                be used.
 142  */
 143 void PNGAPI
 144 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
 145    png_rw_ptr read_data_fn)
 146 {
 147    if (png_ptr == NULL)
 148       return;
 149    png_ptr->io_ptr = io_ptr;
 150
 151 #if !defined(PNG_NO_STDIO)
 152    if (read_data_fn != NULL)
 153       png_ptr->read_data_fn = read_data_fn;
 154    else
 155       png_ptr->read_data_fn = png_default_read_data;
 156 #else
 157    png_ptr->read_data_fn = read_data_fn;
 158 #endif
 159
 160    /* It is an error to write to a read device */
 161    if (png_ptr->write_data_fn != NULL)
 162    {
 163       png_ptr->write_data_fn = NULL;
 164       png_warning(png_ptr,
 165          "It's an error to set both read_data_fn and write_data_fn in the ");
 166       png_warning(png_ptr,
 167          "same structure.  Resetting write_data_fn to NULL.");
 168    }
 169
 170 #if defined(PNG_WRITE_FLUSH_SUPPORTED)
 171    png_ptr->output_flush_fn = NULL;
 172 #endif
 173 }
 174 #endif /* PNG_READ_SUPPORTED */