1
2 /* pngrio.c - functions for data input
3 *
4 * Last changed in libpng 1.2.13 November 13, 2006
5 * For conditions of distribution and use, see copyright notice in png.h
6 * Copyright (c) 1998-2006 Glenn Randers-Pehrson
7 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
8 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
9 *
10 * This file provides a location for all input. Users who need
11 * special handling are expected to write a function that has the same
12 * arguments as this and performs a similar function, but that possibly
13 * has a different input method. Note that you shouldn't change this
14 * function, but rather write a replacement function and then make
15 * libpng use it at run time with png_set_read_fn(...).
16 */
17
18 #define PNG_INTERNAL
19 #include "png.h"
20
21 #if defined(PNG_READ_SUPPORTED)
22
23 /* Read the data from whatever input you are using. The default routine
24 reads from a file pointer. Note that this routine sometimes gets called
25 with very small lengths, so you should implement some kind of simple
26 buffering if you are using unbuffered reads. This should never be asked
27 to read more then 64K on a 16 bit machine. */
28 void /* PRIVATE */
png_read_data(png_structp png_ptr,png_bytep data,png_size_t length)29 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
30 {
31 png_debug1(4,"reading %d bytes\n", (int)length);
32 if (png_ptr->read_data_fn != NULL)
33 (*(png_ptr->read_data_fn))(png_ptr, data, length);
34 else
35 png_error(png_ptr, "Call to NULL read function");
36 }
37
38 #if !defined(PNG_NO_STDIO)
39 /* This is the function that does the actual reading of data. If you are
40 not reading from a standard C stream, you should create a replacement
41 read_data function and use it at run time with png_set_read_fn(), rather
42 than changing the library. */
43 #ifndef USE_FAR_KEYWORD
44 void PNGAPI
png_default_read_data(png_structp png_ptr,png_bytep data,png_size_t length)45 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
46 {
47 png_size_t check;
48
49 if(png_ptr == NULL) return;
50 /* fread() returns 0 on error, so it is OK to store this in a png_size_t
51 * instead of an int, which is what fread() actually returns.
52 */
53 #if defined(_WIN32_WCE)
54 if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
55 check = 0;
56 #else
57 check = (png_size_t)fread(data, (png_size_t)1, length,
58 (png_FILE_p)png_ptr->io_ptr);
59 #endif
60
61 if (check != length)
62 png_error(png_ptr, "Read Error");
63 }
64 #else
65 /* this is the model-independent version. Since the standard I/O library
66 can't handle far buffers in the medium and small models, we have to copy
67 the data.
68 */
69
70 #define NEAR_BUF_SIZE 1024
71 #define MIN(a,b) (a <= b ? a : b)
72
73 static void PNGAPI
png_default_read_data(png_structp png_ptr,png_bytep data,png_size_t length)74 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
75 {
76 int check;
77 png_byte *n_data;
78 png_FILE_p io_ptr;
79
80 if(png_ptr == NULL) return;
81 /* Check if data really is near. If so, use usual code. */
82 n_data = (png_byte *)CVT_PTR_NOCHECK(data);
83 io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
84 if ((png_bytep)n_data == data)
85 {
86 #if defined(_WIN32_WCE)
87 if ( !ReadFile((HANDLE)(png_ptr->io_ptr), data, length, &check, NULL) )
88 check = 0;
89 #else
90 check = fread(n_data, 1, length, io_ptr);
91 #endif
92 }
93 else
94 {
95 png_byte buf[NEAR_BUF_SIZE];
96 png_size_t read, remaining, err;
97 check = 0;
98 remaining = length;
99 do
100 {
101 read = MIN(NEAR_BUF_SIZE, remaining);
102 #if defined(_WIN32_WCE)
103 if ( !ReadFile((HANDLE)(io_ptr), buf, read, &err, NULL) )
104 err = 0;
105 #else
106 err = fread(buf, (png_size_t)1, read, io_ptr);
107 #endif
108 png_memcpy(data, buf, read); /* copy far buffer to near buffer */
109 if(err != read)
110 break;
111 else
112 check += err;
113 data += read;
114 remaining -= read;
115 }
116 while (remaining != 0);
117 }
118 if ((png_uint_32)check != (png_uint_32)length)
119 png_error(png_ptr, "read Error");
120 }
121 #endif
122 #endif
123
124 /* This function allows the application to supply a new input function
125 for libpng if standard C streams aren't being used.
126
127 This function takes as its arguments:
128 png_ptr - pointer to a png input data structure
129 io_ptr - pointer to user supplied structure containing info about
130 the input functions. May be NULL.
131 read_data_fn - pointer to a new input function that takes as its
132 arguments a pointer to a png_struct, a pointer to
133 a location where input data can be stored, and a 32-bit
134 unsigned int that is the number of bytes to be read.
135 To exit and output any fatal error messages the new write
136 function should call png_error(png_ptr, "Error msg"). */
137 void PNGAPI
png_set_read_fn(png_structp png_ptr,png_voidp io_ptr,png_rw_ptr read_data_fn)138 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
139 png_rw_ptr read_data_fn)
140 {
141 if(png_ptr == NULL) return;
142 png_ptr->io_ptr = io_ptr;
143
144 #if !defined(PNG_NO_STDIO)
145 if (read_data_fn != NULL)
146 png_ptr->read_data_fn = read_data_fn;
147 else
148 png_ptr->read_data_fn = png_default_read_data;
149 #else
150 png_ptr->read_data_fn = read_data_fn;
151 #endif
152
153 /* It is an error to write to a read device */
154 if (png_ptr->write_data_fn != NULL)
155 {
156 png_ptr->write_data_fn = NULL;
157 png_warning(png_ptr,
158 "It's an error to set both read_data_fn and write_data_fn in the ");
159 png_warning(png_ptr,
160 "same structure. Resetting write_data_fn to NULL.");
161 }
162
163 #if defined(PNG_WRITE_FLUSH_SUPPORTED)
164 png_ptr->output_flush_fn = NULL;
165 #endif
166 }
167 #endif /* PNG_READ_SUPPORTED */
168