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/* pngrio.c - functions for data input
*
* Copyright (c) 2018 Cosmin Truta
* Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
* Copyright (c) 1996-1997 Andreas Dilger
* 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 than 64K on a 16-bit machine.
*/
void /* PRIVATE */
png_read_data(png_structrp png_ptr, png_bytep data, 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.
*/
void PNGCBAPI
png_default_read_data(png_structp png_ptr, png_bytep data, size_t length)
{
size_t check;
if (png_ptr == NULL)
return;
/* fread() returns 0 on error, so it is OK to store this in a size_t
* instead of an int, which is what fread() actually returns.
*/
check = fread(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
if (check != length)
png_error(png_ptr, "Read Error");
}
#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_structrp 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
#ifdef PNG_WRITE_SUPPORTED
/* 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");
}
#endif
#ifdef PNG_WRITE_FLUSH_SUPPORTED
png_ptr->output_flush_fn = NULL;
#endif
}
#endif /* READ */
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