src/png/pngrio.c

   1
   2 /* pngrio.c - functions for data input
   3  *
   4  * libpng 1.2.5rc3 - September 18, 2002
   5  * For conditions of distribution and use, see copyright notice in png.h
   6  * Copyright (c) 1998-2002 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 /* 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 /* PRIVATE */
  27 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  28 {
  29    png_debug1(4,"reading %d bytes\n", (int)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 void PNGAPI
  43 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  44 {
  45    png_size_t check;
  46
  47    /* fread() returns 0 on error, so it is OK to store this in a png_size_t
  48     * instead of an int, which is what fread() actually returns.
  49     */
  50 #if defined(_WIN32_WCE)
  51    if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
  52       check = 0;
  53 #else
  54    check = (png_size_t)fread(data, (png_size_t)1, length,
  55       (png_FILE_p)png_ptr->io_ptr);
  56 #endif
  57
  58    if (check != length)
  59       png_error(png_ptr, "Read Error");
  60 }
  61 #else
  62 /* this is the model-independent version. Since the standard I/O library
  63    can't handle far buffers in the medium and small models, we have to copy
  64    the data.
  65 */
  66
  67 #define NEAR_BUF_SIZE 1024
  68 #define MIN(a,b) (a <= b ? a : b)
  69
  70 static void /* PRIVATE */
  71 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
  72 {
  73    int check;
  74    png_byte *n_data;
  75    png_FILE_p io_ptr;
  76
  77    /* Check if data really is near. If so, use usual code. */
  78    n_data = (png_byte *)CVT_PTR_NOCHECK(data);
  79    io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
  80    if ((png_bytep)n_data == data)
  81    {
  82 #if defined(_WIN32_WCE)
  83       if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
  84          check = 0;
  85 #else
  86       check = fread(n_data, 1, length, io_ptr);
  87 #endif
  88    }
  89    else
  90    {
  91       png_byte buf[NEAR_BUF_SIZE];
  92       png_size_t read, remaining, err;
  93       check = 0;
  94       remaining = length;
  95       do
  96       {
  97          read = MIN(NEAR_BUF_SIZE, remaining);
  98 #if defined(_WIN32_WCE)
  99          if ( !ReadFile((HANDLE)(io_ptr), buf, read, &err, NULL) )
 100             err = 0;
 101 #else
 102          err = fread(buf, (png_size_t)1, read, io_ptr);
 103 #endif
 104          png_memcpy(data, buf, read); /* copy far buffer to near buffer */
 105          if(err != read)
 106             break;
 107          else
 108             check += err;
 109          data += read;
 110          remaining -= read;
 111       }
 112       while (remaining != 0);
 113    }
 114    if ((png_uint_32)check != (png_uint_32)length)
 115       png_error(png_ptr, "read Error");
 116 }
 117 #endif
 118 #endif
 119
 120 /* This function allows the application to supply a new input function
 121    for libpng if standard C streams aren't being used.
 122
 123    This function takes as its arguments:
 124    png_ptr      - pointer to a png input data structure
 125    io_ptr       - pointer to user supplied structure containing info about
 126                   the input functions.  May be NULL.
 127    read_data_fn - pointer to a new input function that takes as its
 128                   arguments a pointer to a png_struct, a pointer to
 129                   a location where input data can be stored, and a 32-bit
 130                   unsigned int that is the number of bytes to be read.
 131                   To exit and output any fatal error messages the new write
 132                   function should call png_error(png_ptr, "Error msg"). */
 133 void PNGAPI
 134 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
 135    png_rw_ptr read_data_fn)
 136 {
 137    png_ptr->io_ptr = io_ptr;
 138
 139 #if !defined(PNG_NO_STDIO)
 140    if (read_data_fn != NULL)
 141       png_ptr->read_data_fn = read_data_fn;
 142    else
 143       png_ptr->read_data_fn = png_default_read_data;
 144 #else
 145    png_ptr->read_data_fn = read_data_fn;
 146 #endif
 147
 148    /* It is an error to write to a read device */
 149    if (png_ptr->write_data_fn != NULL)
 150    {
 151       png_ptr->write_data_fn = NULL;
 152       png_warning(png_ptr,
 153          "It's an error to set both read_data_fn and write_data_fn in the ");
 154       png_warning(png_ptr,
 155          "same structure.  Resetting write_data_fn to NULL.");
 156    }
 157
 158 #if defined(PNG_WRITE_FLUSH_SUPPORTED)
 159    png_ptr->output_flush_fn = NULL;
 160 #endif
 161 }