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1
2 /* pngrio.c - functions for data input
3 *
4 * libpng 1.0.1
5 * For conditions of distribution and use, see copyright notice in png.h
6 * Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
7 * Copyright (c) 1996, 1997 Andreas Dilger
8 * Copyright (c) 1998, Glenn Randers-Pehrson
9 * March 15, 1998
10 *
11 * This file provides a location for all input. Users which need
12 * special handling are expected to write a function which has the same
13 * arguments as this, and perform a similar function, but possibly has
14 * a different input method. Note that you shouldn't change this
15 * function, but rather write a replacement function and then make
16 * libpng use it at run time with png_set_read_fn(...).
17 */
18
19 #define PNG_INTERNAL
20 #include "../png/png.h"
21
22 /* Read the data from whatever input you are using. The default routine
23 reads from a file pointer. Note that this routine sometimes gets called
24 with very small lengths, so you should implement some kind of simple
25 buffering if you are using unbuffered reads. This should never be asked
26 to read more then 64K on a 16 bit machine. */
27 void
28 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
29 {
30 png_debug1(4,"reading %d bytes\n", length);
31 if (png_ptr->read_data_fn != NULL)
32 (*(png_ptr->read_data_fn))(png_ptr, data, length);
33 else
34 png_error(png_ptr, "Call to NULL read function");
35 }
36
37 #if !defined(PNG_NO_STDIO)
38 /* This is the function which does the actual reading of data. If you are
39 not reading from a standard C stream, you should create a replacement
40 read_data function and use it at run time with png_set_read_fn(), rather
41 than changing the library. */
42 #ifndef USE_FAR_KEYWORD
43 static void
44 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
45 {
46 png_size_t check;
47
48 /* fread() returns 0 on error, so it is OK to store this in a png_size_t
49 * instead of an int, which is what fread() actually returns.
50 */
51 check = (png_size_t)fread(data, (png_size_t)1, length,
52 (FILE *)png_ptr->io_ptr);
53
54 if (check != length)
55 {
56 png_error(png_ptr, "Read Error");
57 }
58 }
59 #else
60 /* this is the model-independent version. Since the standard I/O library
61 can't handle far buffers in the medium and small models, we have to copy
62 the data.
63 */
64
65 #define NEAR_BUF_SIZE 1024
66 #define MIN(a,b) (a <= b ? a : b)
67
68 static void
69 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
70 {
71 int check;
72 png_byte *n_data;
73 FILE *io_ptr;
74
75 /* Check if data really is near. If so, use usual code. */
76 n_data = (png_byte *)CVT_PTR_NOCHECK(data);
77 io_ptr = (FILE *)CVT_PTR(png_ptr->io_ptr);
78 if ((png_bytep)n_data == data)
79 {
80 check = fread(n_data, 1, length, io_ptr);
81 }
82 else
83 {
84 png_byte buf[NEAR_BUF_SIZE];
85 png_size_t read, remaining, err;
86 check = 0;
87 remaining = length;
88 do
89 {
90 read = MIN(NEAR_BUF_SIZE, remaining);
91 err = fread(buf, (png_size_t)1, read, io_ptr);
92 png_memcpy(data, buf, read); /* copy far buffer to near buffer */
93 if(err != read)
94 break;
95 else
96 check += err;
97 data += read;
98 remaining -= read;
99 }
100 while (remaining != 0);
101 }
102 if ((png_uint_32)check != (png_uint_32)length)
103 {
104 png_error(png_ptr, "read Error");
105 }
106 }
107 #endif
108 #endif
109
110 /* This function allows the application to supply a new input function
111 for libpng if standard C streams aren't being used.
112
113 This function takes as its arguments:
114 png_ptr - pointer to a png input data structure
115 io_ptr - pointer to user supplied structure containing info about
116 the input functions. May be NULL.
117 read_data_fn - pointer to a new input function which takes as it's
118 arguments a pointer to a png_struct, a pointer to
119 a location where input data can be stored, and a 32-bit
120 unsigned int which is the number of bytes to be read.
121 To exit and output any fatal error messages the new write
122 function should call png_error(png_ptr, "Error msg"). */
123 void
124 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
125 png_rw_ptr read_data_fn)
126 {
127 png_ptr->io_ptr = io_ptr;
128
129 #if !defined(PNG_NO_STDIO)
130 if (read_data_fn != NULL)
131 png_ptr->read_data_fn = read_data_fn;
132 else
133 png_ptr->read_data_fn = png_default_read_data;
134 #else
135 png_ptr->read_data_fn = read_data_fn;
136 #endif
137
138 /* It is an error to write to a read device */
139 png_ptr->write_data_fn = NULL;
140
141 #if defined(PNG_WRITE_FLUSH_SUPPORTED)
142 png_ptr->output_flush_fn = NULL;
143 #endif /* PNG_WRITE_FLUSH_SUPPORTED */
144 }
145