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pngrio.c
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1
2 /* pngrio.c - functions for data input
3 *
4 * Last changed in libpng 1.5.0 [January 6, 2011]
5 * Copyright (c) 1998-2011 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 #include "pngpriv.h"
22
23 #ifdef PNG_READ_SUPPORTED
24
25 /* Read the data from whatever input you are using. The default routine
26 * reads from a file pointer. Note that this routine sometimes gets called
27 * with very small lengths, so you should implement some kind of simple
28 * buffering if you are using unbuffered reads. This should never be asked
29 * to read more then 64K on a 16 bit machine.
30 */
31 void /* PRIVATE */
32 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
33 {
34 png_debug1(4, "reading %d bytes", (int)length);
35
36 if (png_ptr->read_data_fn != NULL)
37 (*(png_ptr->read_data_fn))(png_ptr, data, length);
38
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 PNGCBAPI
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
58 /* fread() returns 0 on error, so it is OK to store this in a png_size_t
59 * instead of an int, which is what fread() actually returns.
60 */
61 check = fread(data, 1, length, (png_FILE_p)png_ptr->io_ptr);
62
63 if (check != length)
64 png_error(png_ptr, "Read Error");
65 }
66 # else
67 /* This is the model-independent version. Since the standard I/O library
68 can't handle far buffers in the medium and small models, we have to copy
69 the data.
70 */
71
72 #define NEAR_BUF_SIZE 1024
73 #define MIN(a,b) (a <= b ? a : b)
74
75 static void PNGCBAPI
76 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
77 {
78 png_size_t check;
79 png_byte *n_data;
80 png_FILE_p io_ptr;
81
82 if (png_ptr == NULL)
83 return;
84
85 /* Check if data really is near. If so, use usual code. */
86 n_data = (png_byte *)CVT_PTR_NOCHECK(data);
87 io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
88
89 if ((png_bytep)n_data == data)
90 {
91 check = fread(n_data, 1, length, io_ptr);
92 }
93
94 else
95 {
96 png_byte buf[NEAR_BUF_SIZE];
97 png_size_t read, remaining, err;
98 check = 0;
99 remaining = length;
100
101 do
102 {
103 read = MIN(NEAR_BUF_SIZE, remaining);
104 err = fread(buf, 1, read, io_ptr);
105 png_memcpy(data, buf, read); /* copy far buffer to near buffer */
106
107 if (err != read)
108 break;
109
110 else
111 check += err;
112
113 data += read;
114 remaining -= read;
115 }
116 while (remaining != 0);
117 }
118
119 if ((png_uint_32)check != (png_uint_32)length)
120 png_error(png_ptr, "read Error");
121 }
122 # endif
123 #endif
124
125 /* This function allows the application to supply a new input function
126 * for libpng if standard C streams aren't being used.
127 *
128 * This function takes as its arguments:
129 *
130 * png_ptr - pointer to a png input data structure
131 *
132 * io_ptr - pointer to user supplied structure containing info about
133 * the input functions. May be NULL.
134 *
135 * read_data_fn - pointer to a new input function that takes as its
136 * arguments a pointer to a png_struct, a pointer to
137 * a location where input data can be stored, and a 32-bit
138 * unsigned int that is the number of bytes to be read.
139 * To exit and output any fatal error messages the new write
140 * function should call png_error(png_ptr, "Error msg").
141 * May be NULL, in which case libpng's default function will
142 * be used.
143 */
144 void PNGAPI
145 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
146 png_rw_ptr read_data_fn)
147 {
148 if (png_ptr == NULL)
149 return;
150
151 png_ptr->io_ptr = io_ptr;
152
153 #ifdef PNG_STDIO_SUPPORTED
154 if (read_data_fn != NULL)
155 png_ptr->read_data_fn = read_data_fn;
156
157 else
158 png_ptr->read_data_fn = png_default_read_data;
159 #else
160 png_ptr->read_data_fn = read_data_fn;
161 #endif
162
163 /* It is an error to write to a read device */
164 if (png_ptr->write_data_fn != NULL)
165 {
166 png_ptr->write_data_fn = NULL;
167 png_warning(png_ptr,
168 "Can't set both read_data_fn and write_data_fn in the"
169 " same structure");
170 }
171
172 #ifdef PNG_WRITE_FLUSH_SUPPORTED
173 png_ptr->output_flush_fn = NULL;
174 #endif
175 }
176 #endif /* PNG_READ_SUPPORTED */
png_memcpy
#define png_memcpy
Definition: pngpriv.h:226
CVT_PTR_NOCHECK
#define CVT_PTR_NOCHECK(ptr)
Definition: pngpriv.h:221
read
int read(int fd, char *buf, int nbytes)
Definition: tif_acorn.c:331
PNGCBAPI
#define PNGCBAPI
Definition: pngconf.h:253
MIN
#define MIN(a, b)
Definition: jpegint.h:269
png_uint_32
unsigned long png_uint_32
Definition: pngconf.h:480
PNGAPI
#define PNGAPI
Definition: pngconf.h:256
png_structp
png_struct FAR * png_structp
Definition: png.h:797
png_default_read_data
void PNGCBAPI png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
Definition: pngrio.c:51
png_byte
unsigned char png_byte
Definition: pngconf.h:485
png_warning
void PNGAPI png_warning(png_structp png_ptr, png_const_charp warning_message)
Definition: pngerror.c:108
png_debug1
#define png_debug1(l, m, p1)
Definition: pngdebug.h:152
png_set_read_fn
void PNGAPI png_set_read_fn(png_structp png_ptr, png_voidp io_ptr, png_rw_ptr read_data_fn)
Definition: pngrio.c:145
png_bytep
png_byte FAR * png_bytep
Definition: pngconf.h:562
png_read_data
void png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
Definition: pngrio.c:32
pngpriv.h
CVT_PTR
#define CVT_PTR(ptr)
Definition: pngpriv.h:220
png_voidp
void FAR * png_voidp
Definition: pngconf.h:560
png_size_t
size_t png_size_t
Definition: pngconf.h:490
data
JSAMPIMAGE data
Definition: jpeglib.h:945