1
2/* pngrio.c - functions for data input
3 *
4 * Last changed in libpng 1.4.1 [February 25, 2010]
5 * Copyright (c) 1998-2010 Glenn Randers-Pehrson
6 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
7 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
8 *
9 * This code is released under the libpng license.
10 * For conditions of distribution and use, see the disclaimer
11 * and license in png.h
12 *
13 * This file provides a location for all input.  Users who need
14 * special handling are expected to write a function that has the same
15 * arguments as this and performs a similar function, but that possibly
16 * has a different input method.  Note that you shouldn't change this
17 * function, but rather write a replacement function and then make
18 * libpng use it at run time with png_set_read_fn(...).
19 */
20
21#define PNG_NO_PEDANTIC_WARNINGS
22#include "png.h"
23#ifdef PNG_READ_SUPPORTED
24#include "pngpriv.h"
25
26/* Read the data from whatever input you are using.  The default routine
27 * reads from a file pointer.  Note that this routine sometimes gets called
28 * with very small lengths, so you should implement some kind of simple
29 * buffering if you are using unbuffered reads.  This should never be asked
30 * to read more then 64K on a 16 bit machine.
31 */
32void /* PRIVATE */
33png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
34{
35   png_debug1(4, "reading %d bytes", (int)length);
36
37   if (png_ptr->read_data_fn != NULL)
38      (*(png_ptr->read_data_fn))(png_ptr, data, length);
39   else
40      png_error(png_ptr, "Call to NULL read function");
41}
42
43#ifdef PNG_STDIO_SUPPORTED
44/* This is the function that does the actual reading of data.  If you are
45 * not reading from a standard C stream, you should create a replacement
46 * read_data function and use it at run time with png_set_read_fn(), rather
47 * than changing the library.
48 */
49#ifndef USE_FAR_KEYWORD
50void PNGAPI
51png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
52{
53   png_size_t check;
54
55   if (png_ptr == NULL)
56      return;
57   /* fread() returns 0 on error, so it is OK to store this in a png_size_t
58    * instead of an int, which is what fread() actually returns.
59    */
60   check = fread(data, 1, length, (png_FILE_p)png_ptr->io_ptr);
61
62   if (check != length)
63      png_error(png_ptr, "Read Error");
64}
65#else
66/* This is the model-independent version. Since the standard I/O library
67   can't handle far buffers in the medium and small models, we have to copy
68   the data.
69*/
70
71#define NEAR_BUF_SIZE 1024
72#define MIN(a,b) (a <= b ? a : b)
73
74static void PNGAPI
75png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
76{
77   png_size_t check;
78   png_byte *n_data;
79   png_FILE_p io_ptr;
80
81   if (png_ptr == NULL)
82      return;
83   /* Check if data really is near. If so, use usual code. */
84   n_data = (png_byte *)CVT_PTR_NOCHECK(data);
85   io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
86   if ((png_bytep)n_data == data)
87   {
88      check = fread(n_data, 1, length, io_ptr);
89   }
90   else
91   {
92      png_byte buf[NEAR_BUF_SIZE];
93      png_size_t read, remaining, err;
94      check = 0;
95      remaining = length;
96      do
97      {
98         read = MIN(NEAR_BUF_SIZE, remaining);
99         err = fread(buf, 1, read, io_ptr);
100         png_memcpy(data, buf, read); /* copy far buffer to near buffer */
101         if (err != read)
102            break;
103         else
104            check += err;
105         data += read;
106         remaining -= read;
107      }
108      while (remaining != 0);
109   }
110   if ((png_uint_32)check != (png_uint_32)length)
111      png_error(png_ptr, "read Error");
112}
113#endif
114#endif
115
116/* This function allows the application to supply a new input function
117 * for libpng if standard C streams aren't being used.
118 *
119 * This function takes as its arguments:
120 * png_ptr      - pointer to a png input data structure
121 * io_ptr       - pointer to user supplied structure containing info about
122 *                the input functions.  May be NULL.
123 * read_data_fn - pointer to a new input function that takes as its
124 *                arguments a pointer to a png_struct, a pointer to
125 *                a location where input data can be stored, and a 32-bit
126 *                unsigned int that is the number of bytes to be read.
127 *                To exit and output any fatal error messages the new write
128 *                function should call png_error(png_ptr, "Error msg").
129 *                May be NULL, in which case libpng's default function will
130 *                be used.
131 */
132void PNGAPI
133png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
134   png_rw_ptr read_data_fn)
135{
136   if (png_ptr == NULL)
137      return;
138   png_ptr->io_ptr = io_ptr;
139
140#ifdef PNG_STDIO_SUPPORTED
141   if (read_data_fn != NULL)
142      png_ptr->read_data_fn = read_data_fn;
143   else
144      png_ptr->read_data_fn = png_default_read_data;
145#else
146   png_ptr->read_data_fn = read_data_fn;
147#endif
148
149   /* It is an error to write to a read device */
150   if (png_ptr->write_data_fn != NULL)
151   {
152      png_ptr->write_data_fn = NULL;
153      png_warning(png_ptr,
154         "It's an error to set both read_data_fn and write_data_fn in the ");
155      png_warning(png_ptr,
156         "same structure.  Resetting write_data_fn to NULL");
157   }
158
159#ifdef PNG_WRITE_FLUSH_SUPPORTED
160   png_ptr->output_flush_fn = NULL;
161#endif
162}
163#endif /* PNG_READ_SUPPORTED */
164