1
2 /* pngrio.c - functions for data input
3 *
4 * Last changed in libpng 1.6.9 [February 6, 2014]
5 * Copyright (c) 1998-2014 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 */
png_read_data(png_structrp png_ptr,png_bytep data,png_size_t length)32 png_read_data(png_structrp 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 #ifdef PNG_INDEX_SUPPORTED
42 png_ptr->total_data_read += length;
43 #endif
44 }
45
46 #ifdef PNG_INDEX_SUPPORTED
47 void /* PRIVATE */
png_seek_data(png_structp png_ptr,png_uint_32 offset)48 png_seek_data(png_structp png_ptr, png_uint_32 offset)
49 {
50 if (png_ptr->seek_data_fn != NULL)
51 (*(png_ptr->seek_data_fn))(png_ptr, offset);
52 else
53 png_error(png_ptr, "Call to NULL seek function");
54 }
55 #endif
56
57 #ifdef PNG_STDIO_SUPPORTED
58 /* This is the function that does the actual reading of data. If you are
59 * not reading from a standard C stream, you should create a replacement
60 * read_data function and use it at run time with png_set_read_fn(), rather
61 * than changing the library.
62 */
63 void PNGCBAPI
png_default_read_data(png_structp png_ptr,png_bytep data,png_size_t length)64 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
65 {
66 png_size_t check;
67
68 if (png_ptr == NULL)
69 return;
70
71 /* fread() returns 0 on error, so it is OK to store this in a png_size_t
72 * instead of an int, which is what fread() actually returns.
73 */
74 check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
75
76 if (check != length)
77 png_error(png_ptr, "Read Error");
78 }
79 #endif
80
81 /* This function allows the application to supply a new input function
82 * for libpng if standard C streams aren't being used.
83 *
84 * This function takes as its arguments:
85 *
86 * png_ptr - pointer to a png input data structure
87 *
88 * io_ptr - pointer to user supplied structure containing info about
89 * the input functions. May be NULL.
90 *
91 * read_data_fn - pointer to a new input function that takes as its
92 * arguments a pointer to a png_struct, a pointer to
93 * a location where input data can be stored, and a 32-bit
94 * unsigned int that is the number of bytes to be read.
95 * To exit and output any fatal error messages the new write
96 * function should call png_error(png_ptr, "Error msg").
97 * May be NULL, in which case libpng's default function will
98 * be used.
99 */
100 void PNGAPI
png_set_read_fn(png_structrp png_ptr,png_voidp io_ptr,png_rw_ptr read_data_fn)101 png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
102 png_rw_ptr read_data_fn)
103 {
104 if (png_ptr == NULL)
105 return;
106
107 png_ptr->io_ptr = io_ptr;
108
109 #ifdef PNG_STDIO_SUPPORTED
110 if (read_data_fn != NULL)
111 png_ptr->read_data_fn = read_data_fn;
112
113 else
114 png_ptr->read_data_fn = png_default_read_data;
115 #else
116 png_ptr->read_data_fn = read_data_fn;
117 #endif
118
119 #ifdef PNG_WRITE_SUPPORTED
120 /* It is an error to write to a read device */
121 if (png_ptr->write_data_fn != NULL)
122 {
123 png_ptr->write_data_fn = NULL;
124 png_warning(png_ptr,
125 "Can't set both read_data_fn and write_data_fn in the"
126 " same structure");
127 }
128 #endif
129
130 #ifdef PNG_WRITE_FLUSH_SUPPORTED
131 png_ptr->output_flush_fn = NULL;
132 #endif
133 }
134
135 #ifdef PNG_INDEX_SUPPORTED
136 void PNGAPI
png_set_seek_fn(png_structp png_ptr,png_seek_ptr seek_data_fn)137 png_set_seek_fn(png_structp png_ptr, png_seek_ptr seek_data_fn)
138 {
139 if (png_ptr == NULL)
140 return;
141 png_ptr->seek_data_fn = seek_data_fn;
142 }
143 #endif
144
145 #endif /* PNG_READ_SUPPORTED */
146