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1
2/* pngwio.c - functions for data output
3 *
4 * Copyright (c) 2018 Cosmin Truta
5 * Copyright (c) 1998-2002,2004,2006-2014,2016,2018 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 output. Users who need
14 * special handling are expected to write functions that have the same
15 * arguments as these and perform similar functions, but that possibly
16 * use different output methods. Note that you shouldn't change these
17 * functions, but rather write replacement functions and then change
18 * them at run time with png_set_write_fn(...).
19 */
20
21#include "pngpriv.h"
22
23#ifdef PNG_WRITE_SUPPORTED
24
25/* Write the data to whatever output you are using. The default routine
26 * writes to 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 writes. This should never be asked
29 * to write more than 64K on a 16-bit machine.
30 */
31
32void /* PRIVATE */
33png_write_data(png_structrp png_ptr, png_const_bytep data, size_t length)
34{
35 /* NOTE: write_data_fn must not change the buffer! */
36 if (png_ptr->write_data_fn != NULL )
37 (*(png_ptr->write_data_fn))(png_ptr, png_constcast(png_bytep,data),
38 length);
39
40 else
41 png_error(png_ptr, "Call to NULL write function");
42}
43
44#ifdef PNG_STDIO_SUPPORTED
45/* This is the function that does the actual writing of data. If you are
46 * not writing to a standard C stream, you should create a replacement
47 * write_data function and use it at run time with png_set_write_fn(), rather
48 * than changing the library.
49 */
50void PNGCBAPI
51png_default_write_data(png_structp png_ptr, png_bytep data, size_t length)
52{
53 size_t check;
54
55 if (png_ptr == NULL)
56 return;
57
58 check = fwrite(data, 1, length, (png_FILE_p)(png_ptr->io_ptr));
59
60 if (check != length)
61 png_error(png_ptr, "Write Error");
62}
63#endif
64
65/* This function is called to output any data pending writing (normally
66 * to disk). After png_flush is called, there should be no data pending
67 * writing in any buffers.
68 */
69#ifdef PNG_WRITE_FLUSH_SUPPORTED
70void /* PRIVATE */
71png_flush(png_structrp png_ptr)
72{
73 if (png_ptr->output_flush_fn != NULL)
74 (*(png_ptr->output_flush_fn))(png_ptr);
75}
76
77# ifdef PNG_STDIO_SUPPORTED
78void PNGCBAPI
79png_default_flush(png_structp png_ptr)
80{
81 png_FILE_p io_ptr;
82
83 if (png_ptr == NULL)
84 return;
85
86 io_ptr = png_voidcast(png_FILE_p, (png_ptr->io_ptr));
87 fflush(io_ptr);
88}
89# endif
90#endif
91
92/* This function allows the application to supply new output functions for
93 * libpng if standard C streams aren't being used.
94 *
95 * This function takes as its arguments:
96 * png_ptr - pointer to a png output data structure
97 * io_ptr - pointer to user supplied structure containing info about
98 * the output functions. May be NULL.
99 * write_data_fn - pointer to a new output function that takes as its
100 * arguments a pointer to a png_struct, a pointer to
101 * data to be written, and a 32-bit unsigned int that is
102 * the number of bytes to be written. The new write
103 * function should call png_error(png_ptr, "Error msg")
104 * to exit and output any fatal error messages. May be
105 * NULL, in which case libpng's default function will
106 * be used.
107 * flush_data_fn - pointer to a new flush function that takes as its
108 * arguments a pointer to a png_struct. After a call to
109 * the flush function, there should be no data in any buffers
110 * or pending transmission. If the output method doesn't do
111 * any buffering of output, a function prototype must still be
112 * supplied although it doesn't have to do anything. If
113 * PNG_WRITE_FLUSH_SUPPORTED is not defined at libpng compile
114 * time, output_flush_fn will be ignored, although it must be
115 * supplied for compatibility. May be NULL, in which case
116 * libpng's default function will be used, if
117 * PNG_WRITE_FLUSH_SUPPORTED is defined. This is not
118 * a good idea if io_ptr does not point to a standard
119 * *FILE structure.
120 */
121void PNGAPI
122png_set_write_fn(png_structrp png_ptr, png_voidp io_ptr,
123 png_rw_ptr write_data_fn, png_flush_ptr output_flush_fn)
124{
125 if (png_ptr == NULL)
126 return;
127
128 png_ptr->io_ptr = io_ptr;
129
130#ifdef PNG_STDIO_SUPPORTED
131 if (write_data_fn != NULL)
132 png_ptr->write_data_fn = write_data_fn;
133
134 else
135 png_ptr->write_data_fn = png_default_write_data;
136#else
137 png_ptr->write_data_fn = write_data_fn;
138#endif
139
140#ifdef PNG_WRITE_FLUSH_SUPPORTED
141# ifdef PNG_STDIO_SUPPORTED
142
143 if (output_flush_fn != NULL)
144 png_ptr->output_flush_fn = output_flush_fn;
145
146 else
147 png_ptr->output_flush_fn = png_default_flush;
148
149# else
150 png_ptr->output_flush_fn = output_flush_fn;
151# endif
152#else
153 PNG_UNUSED(output_flush_fn)
154#endif /* WRITE_FLUSH */
155
156#ifdef PNG_READ_SUPPORTED
157 /* It is an error to read while writing a png file */
158 if (png_ptr->read_data_fn != NULL)
159 {
160 png_ptr->read_data_fn = NULL;
161
162 png_warning(png_ptr,
163 "Can't set both read_data_fn and write_data_fn in the"
164 " same structure");
165 }
166#endif
167}
168#endif /* WRITE */
169

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