src/png/pngrio.c

   1
   2 /* pngrio.c - functions for data input
   3  *
   4  * Last changed in libpng 1.2.13 November 13, 2006
   5  * For conditions of distribution and use, see copyright notice in png.h
   6  * Copyright (c) 1998-2006 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
  21 #if defined(PNG_READ_SUPPORTED)
  22
  23 /* Read the data from whatever input you are using.  The default routine
  24    reads from a file pointer.  Note that this routine sometimes gets called
  25    with very small lengths, so you should implement some kind of simple
  26    buffering if you are using unbuffered reads.  This should never be asked
  27    to read more then 64K on a 16 bit machine. */
  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\n", (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 #ifndef USE_FAR_KEYWORD
  44 void PNGAPI
  45 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  46 {
  47    png_size_t check;
  48
  49    if(png_ptr == NULL) return;
  50    /* fread() returns 0 on error, so it is OK to store this in a png_size_t
  51     * instead of an int, which is what fread() actually returns.
  52     */
  53 #if defined(_WIN32_WCE)
  54    if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
  55       check = 0;
  56 #else
  57    check = (png_size_t)fread(data, (png_size_t)1, length,
  58       (png_FILE_p)png_ptr->io_ptr);
  59 #endif
  60
  61    if (check != length)
  62       png_error(png_ptr, "Read Error");
  63 }
  64 #else
  65 /* this is the model-independent version. Since the standard I/O library
  66    can't handle far buffers in the medium and small models, we have to copy
  67    the data.
  68 */
  69
  70 #define NEAR_BUF_SIZE 1024
  71 #define MIN(a,b) (a <= b ? a : b)
  72
  73 static void PNGAPI
  74 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  75 {
  76    int check;
  77    png_byte *n_data;
  78    png_FILE_p io_ptr;
  79
  80    if(png_ptr == NULL) return;
  81    /* Check if data really is near. If so, use usual code. */
  82    n_data = (png_byte *)CVT_PTR_NOCHECK(data);
  83    io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
  84    if ((png_bytep)n_data == data)
  85    {
  86 #if defined(_WIN32_WCE)
  87       if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
  88          check = 0;
  89 #else
  90       check = fread(n_data, 1, length, io_ptr);
  91 #endif
  92    }
  93    else
  94    {
  95       png_byte buf[NEAR_BUF_SIZE];
  96       png_size_t read, remaining, err;
  97       check = 0;
  98       remaining = length;
  99       do
 100       {
 101          read = MIN(NEAR_BUF_SIZE, remaining);
 102 #if defined(_WIN32_WCE)
 103          if ( !ReadFile((HANDLE)(io_ptr), buf, read, &err, NULL) )
 104             err = 0;
 105 #else
 106          err = fread(buf, (png_size_t)1, read, io_ptr);
 107 #endif
 108          png_memcpy(data, buf, read); /* copy far buffer to near buffer */
 109          if(err != read)
 110             break;
 111          else
 112             check += err;
 113          data += read;
 114          remaining -= read;
 115       }
 116       while (remaining != 0);
 117    }
 118    if ((png_uint_32)check != (png_uint_32)length)
 119       png_error(png_ptr, "read Error");
 120 }
 121 #endif
 122 #endif
 123
 124 /* This function allows the application to supply a new input function
 125    for libpng if standard C streams aren't being used.
 126
 127    This function takes as its arguments:
 128    png_ptr      - pointer to a png input data structure
 129    io_ptr       - pointer to user supplied structure containing info about
 130                   the input functions.  May be NULL.
 131    read_data_fn - pointer to a new input function that takes as its
 132                   arguments a pointer to a png_struct, a pointer to
 133                   a location where input data can be stored, and a 32-bit
 134                   unsigned int that is the number of bytes to be read.
 135                   To exit and output any fatal error messages the new write
 136                   function should call png_error(png_ptr, "Error msg"). */
 137 void PNGAPI
 138 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
 139    png_rw_ptr read_data_fn)
 140 {
 141    if(png_ptr == NULL) return;
 142    png_ptr->io_ptr = io_ptr;
 143
 144 #if !defined(PNG_NO_STDIO)
 145    if (read_data_fn != NULL)
 146       png_ptr->read_data_fn = read_data_fn;
 147    else
 148       png_ptr->read_data_fn = png_default_read_data;
 149 #else
 150    png_ptr->read_data_fn = read_data_fn;
 151 #endif
 152
 153    /* It is an error to write to a read device */
 154    if (png_ptr->write_data_fn != NULL)
 155    {
 156       png_ptr->write_data_fn = NULL;
 157       png_warning(png_ptr,
 158          "It's an error to set both read_data_fn and write_data_fn in the ");
 159       png_warning(png_ptr,
 160          "same structure.  Resetting write_data_fn to NULL.");
 161    }
 162
 163 #if defined(PNG_WRITE_FLUSH_SUPPORTED)
 164    png_ptr->output_flush_fn = NULL;
 165 #endif
 166 }
 167 #endif /* PNG_READ_SUPPORTED */