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