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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 */
32 void /* PRIVATE */
33 png_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
50 void PNGAPI
51 png_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
74 static void PNGAPI
75 png_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 */
132 void PNGAPI
133 png_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 */