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/* pngwio.c - functions for data output
* Last changed in libpng 1.7.0 [(PENDING RELEASE)]
* Copyright (c) 1998-2002,2004,2006-2016 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 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"
#define PNG_SRC_FILE PNG_SRC_FILE_pngwio
/* 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_voidp data, png_size_t length)
/* This was guaranteed by prior versions of libpng, so app callbacks may
* assume it even though it isn't documented to be the case.
debug(length > 0U);
/* NOTE: write_data_fn must not change the buffer!
* This cast is required because of the API; changing the type of the
* callback would require every app to change the callback and that change
* would have to be conditional on the libpng version.
if (png_ptr->rw_data_fn != NULL )
png_constcast(png_bytep,png_voidcast(png_const_bytep,data)), length);
png_app_error(png_ptr, "No write function");
/* 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.
png_default_write_data(png_structp png_ptr, png_bytep data, png_size_t length)
png_size_t check;
if (png_ptr == NULL)
check = fwrite(data, 1, length, png_voidcast(png_FILE_p, png_ptr->io_ptr));
if (check != length)
png_error(png_ptr, "Write Error");
png_default_flush(png_structp png_ptr)
if (png_ptr == NULL)
fflush(png_voidcast(png_FILE_p, (png_ptr->io_ptr)));
# 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.
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)
if (png_ptr->read_struct)
png_app_error(png_ptr, "cannot set a write function on a read struct");
if (write_data_fn == NULL)
"API change: png_set_write_fn requires a function");
png_ptr->io_ptr = io_ptr;
png_ptr->rw_data_fn = write_data_fn;
if (output_flush_fn != NULL)
png_ptr->output_flush_fn = output_flush_fn;
# else
# endif /* WRITE_FLUSH */
#endif /* WRITE */