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pngwio.c
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pngwio.c
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/* pngwio.c - functions for data output
*
* Copyright (c) 2018 Cosmin Truta
* Copyright (c) 1998-2002,2004,2006-2014,2016,2018 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 output. Users who need
* special handling are expected to write functions that have the same
* arguments as these and perform similar functions, but that possibly
* use different output methods. Note that you shouldn't change these
* functions, but rather write replacement functions and then change
* them at run time with png_set_write_fn(...).
*/
#include "pngpriv.h"
#ifdef PNG_WRITE_SUPPORTED
/* Write the data to whatever output you are using. The default routine
* writes to 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 writes. This should never be asked
* to write more than 64K on a 16-bit machine.
*/
void /* PRIVATE */
png_write_data(png_structrp png_ptr, png_const_bytep data, size_t length)
{
/* NOTE: write_data_fn must not change the buffer! */
if (png_ptr->write_data_fn != NULL )
(*(png_ptr->write_data_fn))(png_ptr, png_constcast(png_bytep,data),
length);
else
png_error(png_ptr, "Call to NULL write function");
}
#ifdef PNG_STDIO_SUPPORTED
/* This is the function that does the actual writing of data. If you are
* not writing to a standard C stream, you should create a replacement
* write_data function and use it at run time with png_set_write_fn(), rather
* than changing the library.
*/
void PNGCBAPI
png_default_write_data(png_structp png_ptr, png_bytep data, size_t length)
{
size_t check;
if (png_ptr == NULL)
return;
check = fwrite(data, 1, length, (png_FILE_p)(png_ptr->io_ptr));
if (check != length)
png_error(png_ptr, "Write Error");
}
#endif
/* This function is called to output any data pending writing (normally
* to disk). After png_flush is called, there should be no data pending
* writing in any buffers.
*/
#ifdef PNG_WRITE_FLUSH_SUPPORTED
void /* PRIVATE */
png_flush(png_structrp png_ptr)
{
if (png_ptr->output_flush_fn != NULL)
(*(png_ptr->output_flush_fn))(png_ptr);
}
# ifdef PNG_STDIO_SUPPORTED
void PNGCBAPI
png_default_flush(png_structp png_ptr)
{
png_FILE_p io_ptr;
if (png_ptr == NULL)
return;
io_ptr = png_voidcast(png_FILE_p, (png_ptr->io_ptr));
fflush(io_ptr);
}
# endif
#endif
/* This function allows the application to supply new output functions for
* libpng if standard C streams aren't being used.
*
* This function takes as its arguments:
* png_ptr - pointer to a png output data structure
* io_ptr - pointer to user supplied structure containing info about
* the output functions. May be NULL.
* write_data_fn - pointer to a new output function that takes as its
* arguments a pointer to a png_struct, a pointer to
* data to be written, and a 32-bit unsigned int that is
* the number of bytes to be written. The new write
* function should call png_error(png_ptr, "Error msg")
* to exit and output any fatal error messages. May be
* NULL, in which case libpng's default function will
* be used.
* flush_data_fn - pointer to a new flush function that takes as its
* arguments a pointer to a png_struct. After a call to
* the flush function, there should be no data in any buffers
* or pending transmission. If the output method doesn't do
* any buffering of output, a function prototype must still be
* supplied although it doesn't have to do anything. If
* PNG_WRITE_FLUSH_SUPPORTED is not defined at libpng compile
* time, output_flush_fn will be ignored, although it must be
* supplied for compatibility. May be NULL, in which case
* libpng's default function will be used, if
* PNG_WRITE_FLUSH_SUPPORTED is defined. This is not
* a good idea if io_ptr does not point to a standard
* *FILE structure.
*/
void PNGAPI
png_set_write_fn(png_structrp png_ptr, png_voidp io_ptr,
png_rw_ptr write_data_fn, png_flush_ptr output_flush_fn)
{
if (png_ptr == NULL)
return;
png_ptr->io_ptr = io_ptr;
#ifdef PNG_STDIO_SUPPORTED
if (write_data_fn != NULL)
png_ptr->write_data_fn = write_data_fn;
else
png_ptr->write_data_fn = png_default_write_data;
#else
png_ptr->write_data_fn = write_data_fn;
#endif
#ifdef PNG_WRITE_FLUSH_SUPPORTED
# ifdef PNG_STDIO_SUPPORTED
if (output_flush_fn != NULL)
png_ptr->output_flush_fn = output_flush_fn;
else
png_ptr->output_flush_fn = png_default_flush;
# else
png_ptr->output_flush_fn = output_flush_fn;
# endif
#else
PNG_UNUSED(output_flush_fn)
#endif /* WRITE_FLUSH */
#ifdef PNG_READ_SUPPORTED
/* It is an error to read while writing a png file */
if (png_ptr->read_data_fn != NULL)
{
png_ptr->read_data_fn = NULL;
png_warning(png_ptr,
"Can't set both read_data_fn and write_data_fn in the"
" same structure");
}
#endif
}
#endif /* WRITE */