src/png/pngrio.c

   1
   2 /* pngrio.c - functions for data input
   3  *
   4  * libpng 1.0.3 - January 14, 1999
   5  * For conditions of distribution and use, see copyright notice in png.h
   6  * Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
   7  * Copyright (c) 1996, 1997 Andreas Dilger
   8  * Copyright (c) 1998, 1999 Glenn Randers-Pehrson
   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 /* Read the data from whatever input you are using.  The default routine
  22    reads from a file pointer.  Note that this routine sometimes gets called
  23    with very small lengths, so you should implement some kind of simple
  24    buffering if you are using unbuffered reads.  This should never be asked
  25    to read more then 64K on a 16 bit machine. */
  26 void
  27 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  28 {
  29    png_debug1(4,"reading %d bytes\n", length);
  30    if (png_ptr->read_data_fn != NULL)
  31       (*(png_ptr->read_data_fn))(png_ptr, data, length);
  32    else
  33       png_error(png_ptr, "Call to NULL read function");
  34 }
  35
  36 #if !defined(PNG_NO_STDIO)
  37 /* This is the function that does the actual reading of data.  If you are
  38    not reading from a standard C stream, you should create a replacement
  39    read_data function and use it at run time with png_set_read_fn(), rather
  40    than changing the library. */
  41 #ifndef USE_FAR_KEYWORD
  42 #ifdef __VISAGECPP__
  43 static void _Optlink
  44 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  45 #else
  46 static void
  47 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  48 #endif
  49 {
  50    png_size_t check;
  51
  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    check = (png_size_t)fread(data, (png_size_t)1, length,
  56       (FILE *)png_ptr->io_ptr);
  57
  58    if (check != length)
  59    {
  60       png_error(png_ptr, "Read Error");
  61    }
  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
  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    FILE *io_ptr;
  78
  79    /* Check if data really is near. If so, use usual code. */
  80    n_data = (png_byte *)CVT_PTR_NOCHECK(data);
  81    io_ptr = (FILE *)CVT_PTR(png_ptr->io_ptr);
  82    if ((png_bytep)n_data == data)
  83    {
  84       check = fread(n_data, 1, length, io_ptr);
  85    }
  86    else
  87    {
  88       png_byte buf[NEAR_BUF_SIZE];
  89       png_size_t read, remaining, err;
  90       check = 0;
  91       remaining = length;
  92       do
  93       {
  94          read = MIN(NEAR_BUF_SIZE, remaining);
  95          err = fread(buf, (png_size_t)1, read, io_ptr);
  96          png_memcpy(data, buf, read); /* copy far buffer to near buffer */
  97          if(err != read)
  98             break;
  99          else
 100             check += err;
 101          data += read;
 102          remaining -= read;
 103       }
 104       while (remaining != 0);
 105    }
 106    if ((png_uint_32)check != (png_uint_32)length)
 107    {
 108       png_error(png_ptr, "read Error");
 109    }
 110 }
 111 #endif
 112 #endif
 113
 114 /* This function allows the application to supply a new input function
 115    for libpng if standard C streams aren't being used.
 116
 117    This function takes as its arguments:
 118    png_ptr      - pointer to a png input data structure
 119    io_ptr       - pointer to user supplied structure containing info about
 120                   the input functions.  May be NULL.
 121    read_data_fn - pointer to a new input function that takes as its
 122                   arguments a pointer to a png_struct, a pointer to
 123                   a location where input data can be stored, and a 32-bit
 124                   unsigned int that is the number of bytes to be read.
 125                   To exit and output any fatal error messages the new write
 126                   function should call png_error(png_ptr, "Error msg"). */
 127 void
 128 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
 129    png_rw_ptr read_data_fn)
 130 {
 131    png_ptr->io_ptr = io_ptr;
 132
 133 #if !defined(PNG_NO_STDIO)
 134    if (read_data_fn != NULL)
 135       png_ptr->read_data_fn = read_data_fn;
 136    else
 137       png_ptr->read_data_fn = png_default_read_data;
 138 #else
 139    png_ptr->read_data_fn = read_data_fn;
 140 #endif
 141
 142    /* It is an error to write to a read device */
 143    if (png_ptr->write_data_fn != NULL)
 144    {
 145       png_ptr->write_data_fn = NULL;
 146       png_warning(png_ptr,
 147          "It's an error to set both read_data_fn and write_data_fn in the ");
 148       png_warning(png_ptr,
 149          "same structure.  Resetting write_data_fn to NULL.");
 150    }
 151
 152 #if defined(PNG_WRITE_FLUSH_SUPPORTED)
 153    png_ptr->output_flush_fn = NULL;
 154 #endif /* PNG_WRITE_FLUSH_SUPPORTED */
 155 }
 156