src/png/pngrio.c

   1
   2 /* pngrio.c - functions for data input
   3  *
   4  * Last changed in libpng 1.2.30 [August 15, 2008]
   5  * For conditions of distribution and use, see copyright notice in png.h
   6  * Copyright (c) 1998-2008 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 void /* PRIVATE */
  28 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  29 {
  30    png_debug1(4, "reading %d bytes", (int)length);
  31    if (png_ptr->read_data_fn != NULL)
  32       (*(png_ptr->read_data_fn))(png_ptr, data, length);
  33    else
  34       png_error(png_ptr, "Call to NULL read function");
  35 }
  36
  37 #if !defined(PNG_NO_STDIO)
  38 /* This is the function that does the actual reading of data.  If you are
  39    not reading from a standard C stream, you should create a replacement
  40    read_data function and use it at run time with png_set_read_fn(), rather
  41    than changing the library. */
  42 #ifndef USE_FAR_KEYWORD
  43 void PNGAPI
  44 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  45 {
  46    png_size_t check;
  47
  48    if (png_ptr == NULL) return;
  49    /* fread() returns 0 on error, so it is OK to store this in a png_size_t
  50     * instead of an int, which is what fread() actually returns.
  51     */
  52 #if defined(_WIN32_WCE)
  53    if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
  54       check = 0;
  55 #else
  56    check = (png_size_t)fread(data, (png_size_t)1, length,
  57       (png_FILE_p)png_ptr->io_ptr);
  58 #endif
  59
  60    if (check != length)
  61       png_error(png_ptr, "Read Error");
  62 }
  63 #else
  64 /* this is the model-independent version. Since the standard I/O library
  65    can't handle far buffers in the medium and small models, we have to copy
  66    the data.
  67 */
  68
  69 #define NEAR_BUF_SIZE 1024
  70 #define MIN(a,b) (a <= b ? a : b)
  71
  72 static void PNGAPI
  73 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  74 {
  75    int check;
  76    png_byte *n_data;
  77    png_FILE_p io_ptr;
  78
  79    if (png_ptr == NULL) return;
  80    /* Check if data really is near. If so, use usual code. */
  81    n_data = (png_byte *)CVT_PTR_NOCHECK(data);
  82    io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
  83    if ((png_bytep)n_data == data)
  84    {
  85 #if defined(_WIN32_WCE)
  86       if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
  87          check = 0;
  88 #else
  89       check = fread(n_data, 1, length, io_ptr);
  90 #endif
  91    }
  92    else
  93    {
  94       png_byte buf[NEAR_BUF_SIZE];
  95       png_size_t read, remaining, err;
  96       check = 0;
  97       remaining = length;
  98       do
  99       {
 100          read = MIN(NEAR_BUF_SIZE, remaining);
 101 #if defined(_WIN32_WCE)
 102          if ( !ReadFile((HANDLE)(io_ptr), buf, read, &err, NULL) )
 103             err = 0;
 104 #else
 105          err = fread(buf, (png_size_t)1, read, io_ptr);
 106 #endif
 107          png_memcpy(data, buf, read); /* copy far buffer to near buffer */
 108          if (err != read)
 109             break;
 110          else
 111             check += err;
 112          data += read;
 113          remaining -= read;
 114       }
 115       while (remaining != 0);
 116    }
 117    if ((png_uint_32)check != (png_uint_32)length)
 118       png_error(png_ptr, "read Error");
 119 }
 120 #endif
 121 #endif
 122
 123 /* This function allows the application to supply a new input function
 124    for libpng if standard C streams aren't being used.
 125
 126    This function takes as its arguments:
 127    png_ptr      - pointer to a png input data structure
 128    io_ptr       - pointer to user supplied structure containing info about
 129                   the input functions.  May be NULL.
 130    read_data_fn - pointer to a new input function that takes as its
 131                   arguments a pointer to a png_struct, a pointer to
 132                   a location where input data can be stored, and a 32-bit
 133                   unsigned int that is the number of bytes to be read.
 134                   To exit and output any fatal error messages the new write
 135                   function should call png_error(png_ptr, "Error msg"). */
 136 void PNGAPI
 137 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
 138    png_rw_ptr read_data_fn)
 139 {
 140    if (png_ptr == NULL) return;
 141    png_ptr->io_ptr = io_ptr;
 142
 143 #if !defined(PNG_NO_STDIO)
 144    if (read_data_fn != NULL)
 145       png_ptr->read_data_fn = read_data_fn;
 146    else
 147       png_ptr->read_data_fn = png_default_read_data;
 148 #else
 149    png_ptr->read_data_fn = read_data_fn;
 150 #endif
 151
 152    /* It is an error to write to a read device */
 153    if (png_ptr->write_data_fn != NULL)
 154    {
 155       png_ptr->write_data_fn = NULL;
 156       png_warning(png_ptr,
 157          "It's an error to set both read_data_fn and write_data_fn in the ");
 158       png_warning(png_ptr,
 159          "same structure.  Resetting write_data_fn to NULL.");
 160    }
 161
 162 #if defined(PNG_WRITE_FLUSH_SUPPORTED)
 163    png_ptr->output_flush_fn = NULL;
 164 #endif
 165 }
 166 #endif /* PNG_READ_SUPPORTED */