1
2 /* pngrio.c - functions for data input
3 *
4 * Copyright (c) 2018 Cosmin Truta
5 * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
6 * Copyright (c) 1996-1997 Andreas Dilger
7 * 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 than 64K on a 16-bit machine.
30 */
31 void /* PRIVATE */
32 png_read_data(png_structrp png_ptr, png_bytep data, 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 void PNGCBAPI
50 png_default_read_data(png_structp png_ptr, png_bytep data, size_t length)
51 {
52 size_t check;
53
54 if (png_ptr == NULL)
55 return;
56
57 /* fread() returns 0 on error, so it is OK to store this in a size_t
58 * instead of an int, which is what fread() actually returns.
59 */
60 check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
61
62 if (check != length)
63 png_error(png_ptr, "Read Error");
64 }
65 #endif
66
67 /* This function allows the application to supply a new input function
68 * for libpng if standard C streams aren't being used.
69 *
70 * This function takes as its arguments:
71 *
72 * png_ptr - pointer to a png input data structure
73 *
74 * io_ptr - pointer to user supplied structure containing info about
75 * the input functions. May be NULL.
76 *
77 * read_data_fn - pointer to a new input function that takes as its
78 * arguments a pointer to a png_struct, a pointer to
79 * a location where input data can be stored, and a 32-bit
80 * unsigned int that is the number of bytes to be read.
81 * To exit and output any fatal error messages the new write
82 * function should call png_error(png_ptr, "Error msg").
83 * May be NULL, in which case libpng's default function will
84 * be used.
85 */
86 void PNGAPI
87 png_set_read_fn(png_structrp png_ptr, png_voidp io_ptr,
88 png_rw_ptr read_data_fn)
89 {
90 if (png_ptr == NULL)
91 return;
92
93 png_ptr->io_ptr = io_ptr;
94
95 #ifdef PNG_STDIO_SUPPORTED
96 if (read_data_fn != NULL)
97 png_ptr->read_data_fn = read_data_fn;
98
99 else
100 png_ptr->read_data_fn = png_default_read_data;
101 #else
102 png_ptr->read_data_fn = read_data_fn;
103 #endif
104
105 #ifdef PNG_WRITE_SUPPORTED
106 /* It is an error to write to a read device */
107 if (png_ptr->write_data_fn != NULL)
108 {
109 png_ptr->write_data_fn = NULL;
110 png_warning(png_ptr,
111 "Can't set both read_data_fn and write_data_fn in the"
112 " same structure");
113 }
114 #endif
115
116 #ifdef PNG_WRITE_FLUSH_SUPPORTED
117 png_ptr->output_flush_fn = NULL;
118 #endif
119 }
120 #endif /* READ */