/* pngrio.c - functions for data input
*
* Last changed in libpng 1.5.0 [January 6, 2011]
* Copyright (c) 1998-2011 Glenn Randers-Pehrson
* (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
* (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
*
* This code is released under the libpng license.
* For conditions of distribution and use, see the disclaimer
* and license in png.h
*
* This file provides a location for all input. Users who need
* special handling are expected to write a function that has the same
* arguments as this and performs a similar function, but that possibly
* has a different input method. Note that you shouldn't change this
* function, but rather write a replacement function and then make
* libpng use it at run time with png_set_read_fn(...).
*/
#include "pngpriv.h"
#ifdef PNG_READ_SUPPORTED
/* Read the data from whatever input you are using. The default routine
* reads from a file pointer. Note that this routine sometimes gets called
* with very small lengths, so you should implement some kind of simple
* buffering if you are using unbuffered reads. This should never be asked
* to read more then 64K on a 16 bit machine.
*/
void /* PRIVATE */
png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
png_debug1(4, "reading %d bytes", (int)length);
if (png_ptr->read_data_fn != NULL)
(*(png_ptr->read_data_fn))(png_ptr, data, length);
else
png_error(png_ptr, "Call to NULL read function");
}
#ifdef PNG_STDIO_SUPPORTED
/* This is the function that does the actual reading of data. If you are
* not reading from a standard C stream, you should create a replacement
* read_data function and use it at run time with png_set_read_fn(), rather
* than changing the library.
*/
# ifndef USE_FAR_KEYWORD
void PNGCBAPI
png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
png_size_t check;
if (png_ptr == NULL)
return;
/* fread() returns 0 on error, so it is OK to store this in a png_size_t
* instead of an int, which is what fread() actually returns.
*/
check = fread(data, 1, length, (png_FILE_p)png_ptr->io_ptr);
if (check != length)
png_error(png_ptr, "Read Error");
}
# else
/* This is the model-independent version. Since the standard I/O library
can't handle far buffers in the medium and small models, we have to copy
the data.
*/
#define NEAR_BUF_SIZE 1024
#define MIN(a,b) (a <= b ? a : b)
static void PNGCBAPI
png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
png_size_t check;
png_byte *n_data;
png_FILE_p io_ptr;
if (png_ptr == NULL)
return;
/* Check if data really is near. If so, use usual code. */
n_data = (png_byte *)CVT_PTR_NOCHECK(data);
io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
if ((png_bytep)n_data == data)
{
check = fread(n_data, 1, length, io_ptr);
}
else
{
png_byte buf[NEAR_BUF_SIZE];
png_size_t read, remaining, err;
check = 0;
remaining = length;
do
{
read = MIN(NEAR_BUF_SIZE, remaining);
err = fread(buf, 1, read, io_ptr);
png_memcpy(data, buf, read); /* copy far buffer to near buffer */
if (err != read)
break;
else
check += err;
data += read;
remaining -= read;
}
while (remaining != 0);
}
if ((png_uint_32)check != (png_uint_32)length)
png_error(png_ptr, "read Error");
}
# endif
#endif
/* This function allows the application to supply a new input function
* for libpng if standard C streams aren't being used.
*
* This function takes as its arguments:
*
* png_ptr - pointer to a png input data structure
*
* io_ptr - pointer to user supplied structure containing info about
* the input functions. May be NULL.
*
* read_data_fn - pointer to a new input function that takes as its
* arguments a pointer to a png_struct, a pointer to
* a location where input data can be stored, and a 32-bit
* unsigned int that is the number of bytes to be read.
* To exit and output any fatal error messages the new write
* function should call png_error(png_ptr, "Error msg").
* May be NULL, in which case libpng's default function will
* be used.
*/
void PNGAPI
png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
png_rw_ptr read_data_fn)
{
if (png_ptr == NULL)
return;
png_ptr->io_ptr = io_ptr;
#ifdef PNG_STDIO_SUPPORTED
if (read_data_fn != NULL)
png_ptr->read_data_fn = read_data_fn;
else
png_ptr->read_data_fn = png_default_read_data;
#else
png_ptr->read_data_fn = read_data_fn;
#endif
/* It is an error to write to a read device */
if (png_ptr->write_data_fn != NULL)
{
png_ptr->write_data_fn = NULL;
png_warning(png_ptr,
"Can't set both read_data_fn and write_data_fn in the"
" same structure");
}
#ifdef PNG_WRITE_FLUSH_SUPPORTED
png_ptr->output_flush_fn = NULL;
#endif
}
#endif /* PNG_READ_SUPPORTED */