1
2/* pngrio.c - functions for data input
3 *
4 * Last changed in libpng 1.2.43 [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_INTERNAL
22#define PNG_NO_PEDANTIC_WARNINGS
23#include "png.h"
24#ifdef PNG_READ_SUPPORTED
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#ifdef _WIN32_WCE
61   if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
62      check = 0;
63#else
64   check = (png_size_t)fread(data, (png_size_t)1, length,
65      (png_FILE_p)png_ptr->io_ptr);
66#endif
67
68   if (check != length)
69      png_error(png_ptr, "Read Error");
70}
71#else
72/* This is the model-independent version. Since the standard I/O library
73   can't handle far buffers in the medium and small models, we have to copy
74   the data.
75*/
76
77#define NEAR_BUF_SIZE 1024
78#define MIN(a,b) (a <= b ? a : b)
79
80static void PNGAPI
81png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
82{
83   int check;
84   png_byte *n_data;
85   png_FILE_p io_ptr;
86
87   if (png_ptr == NULL)
88      return;
89   /* Check if data really is near. If so, use usual code. */
90   n_data = (png_byte *)CVT_PTR_NOCHECK(data);
91   io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
92   if ((png_bytep)n_data == data)
93   {
94#ifdef _WIN32_WCE
95      if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check,
96          NULL) )
97         check = 0;
98#else
99      check = fread(n_data, 1, length, io_ptr);
100#endif
101   }
102   else
103   {
104      png_byte buf[NEAR_BUF_SIZE];
105      png_size_t read, remaining, err;
106      check = 0;
107      remaining = length;
108      do
109      {
110         read = MIN(NEAR_BUF_SIZE, remaining);
111#ifdef _WIN32_WCE
112         if ( !ReadFile((HANDLE)(io_ptr), buf, read, &err, NULL) )
113            err = 0;
114#else
115         err = fread(buf, (png_size_t)1, read, io_ptr);
116#endif
117         png_memcpy(data, buf, read); /* copy far buffer to near buffer */
118         if (err != read)
119            break;
120         else
121            check += err;
122         data += read;
123         remaining -= read;
124      }
125      while (remaining != 0);
126   }
127   if ((png_uint_32)check != (png_uint_32)length)
128      png_error(png_ptr, "read Error");
129}
130#endif
131#endif
132
133/* This function allows the application to supply a new input function
134 * for libpng if standard C streams aren't being used.
135 *
136 * This function takes as its arguments:
137 * png_ptr      - pointer to a png input data structure
138 * io_ptr       - pointer to user supplied structure containing info about
139 *                the input functions.  May be NULL.
140 * read_data_fn - pointer to a new input function that takes as its
141 *                arguments a pointer to a png_struct, a pointer to
142 *                a location where input data can be stored, and a 32-bit
143 *                unsigned int that is the number of bytes to be read.
144 *                To exit and output any fatal error messages the new write
145 *                function should call png_error(png_ptr, "Error msg").
146 *                May be NULL, in which case libpng's default function will
147 *                be used.
148 */
149void PNGAPI
150png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
151   png_rw_ptr read_data_fn)
152{
153   if (png_ptr == NULL)
154      return;
155   png_ptr->io_ptr = io_ptr;
156
157#ifdef PNG_STDIO_SUPPORTED
158   if (read_data_fn != NULL)
159      png_ptr->read_data_fn = read_data_fn;
160   else
161      png_ptr->read_data_fn = png_default_read_data;
162#else
163   png_ptr->read_data_fn = read_data_fn;
164#endif
165
166   /* It is an error to write to a read device */
167   if (png_ptr->write_data_fn != NULL)
168   {
169      png_ptr->write_data_fn = NULL;
170      png_warning(png_ptr,
171         "It's an error to set both read_data_fn and write_data_fn in the ");
172      png_warning(png_ptr,
173         "same structure.  Resetting write_data_fn to NULL.");
174   }
175
176#ifdef PNG_WRITE_FLUSH_SUPPORTED
177   png_ptr->output_flush_fn = NULL;
178#endif
179}
180#endif /* PNG_READ_SUPPORTED */
181