2 /* pngrio.c - functions for data input
4 * Last changed in libpng 1.5.0 [January 6, 2011]
5 * Copyright (c) 1998-2011 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.)
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
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(...).
23 #ifdef PNG_READ_SUPPORTED
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.
32 png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
34 png_debug1(4, "reading %d bytes", (int)length);
36 if (png_ptr->read_data_fn != NULL)
37 (*(png_ptr->read_data_fn))(png_ptr, data, length);
40 png_error(png_ptr, "Call to NULL read function");
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.
49 # ifndef USE_FAR_KEYWORD
51 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
58 /* fread() returns 0 on error, so it is OK to store this in a png_size_t
59 * instead of an int, which is what fread() actually returns.
61 check = fread(data, 1, length, (png_FILE_p)png_ptr->io_ptr);
64 png_error(png_ptr, "Read Error");
67 /* This is the model-independent version. Since the standard I/O library
68 can't handle far buffers in the medium and small models, we have to copy
72 #define NEAR_BUF_SIZE 1024
73 #define MIN(a,b) (a <= b ? a : b)
76 png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
85 /* Check if data really is near. If so, use usual code. */
86 n_data = (png_byte *)CVT_PTR_NOCHECK(data);
87 io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
89 if ((png_bytep)n_data == data)
91 check = fread(n_data, 1, length, io_ptr);
96 png_byte buf[NEAR_BUF_SIZE];
97 png_size_t read, remaining, err;
103 read = MIN(NEAR_BUF_SIZE, remaining);
104 err = fread(buf, 1, read, io_ptr);
105 png_memcpy(data, buf, read); /* copy far buffer to near buffer */
116 while (remaining != 0);
119 if ((png_uint_32)check != (png_uint_32)length)
120 png_error(png_ptr, "read Error");
125 /* This function allows the application to supply a new input function
126 * for libpng if standard C streams aren't being used.
128 * This function takes as its arguments:
130 * png_ptr - pointer to a png input data structure
132 * io_ptr - pointer to user supplied structure containing info about
133 * the input functions. May be NULL.
135 * read_data_fn - pointer to a new input function that takes as its
136 * arguments a pointer to a png_struct, a pointer to
137 * a location where input data can be stored, and a 32-bit
138 * unsigned int that is the number of bytes to be read.
139 * To exit and output any fatal error messages the new write
140 * function should call png_error(png_ptr, "Error msg").
141 * May be NULL, in which case libpng's default function will
145 png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
146 png_rw_ptr read_data_fn)
151 png_ptr->io_ptr = io_ptr;
153 #ifdef PNG_STDIO_SUPPORTED
154 if (read_data_fn != NULL)
155 png_ptr->read_data_fn = read_data_fn;
158 png_ptr->read_data_fn = png_default_read_data;
160 png_ptr->read_data_fn = read_data_fn;
163 /* It is an error to write to a read device */
164 if (png_ptr->write_data_fn != NULL)
166 png_ptr->write_data_fn = NULL;
168 "Can't set both read_data_fn and write_data_fn in the"
172 #ifdef PNG_WRITE_FLUSH_SUPPORTED
173 png_ptr->output_flush_fn = NULL;
176 #endif /* PNG_READ_SUPPORTED */