php man page for stream_filter_append

STREAM_FILTER_APPEND(3) 						 1						   STREAM_FILTER_APPEND(3)

stream_filter_append - Attach a filter to a stream

SYNOPSIS
       resource stream_filter_append (resource	$stream, string  $filtername, [int  $read_write], [mixed  $params])

DESCRIPTION
	Adds $filtername to the list of filters attached to $stream.

PARAMETERS
	      o $stream
		- The target stream.

	      o $filtername
		- The filter name.

	      o $read_write
		-  By  default,  stream_filter_append(3)  will attach the filter to the read filter chain if the file was opened for reading (i.e.
		File Mode: r, and/or +). The filter will also be attached to the write filter chain if the file was opened for writing (i.e.  File
		Mode:  w,  a,  and/or +).  STREAM_FILTER_READ, STREAM_FILTER_WRITE, and/or STREAM_FILTER_ALL can also be passed to the $read_write
		parameter to override this behavior.

	      o $params
		- This filter will be added with the specified $params to the end of the list and will therefore  be  called  last  during  stream
		operations. To add a filter to the beginning of the list, use stream_filter_prepend(3).

RETURN VALUES
	Returns a resource which can be used to refer to this filter instance during a call to stream_filter_remove(3).

CHANGELOG
       +--------+---------------------------------------------------+
       |Version |						    |
       |	|						    |
       |	|		     Description		    |
       |	|						    |
       +--------+---------------------------------------------------+
       | 5.1.0	|						    |
       |	|						    |
       |	|  Prior  to  PHP 5.1.0, this function returns TRUE |
       |	| on success or FALSE on failure.		    |
       |	|						    |
       +--------+---------------------------------------------------+
EXAMPLES
       Example #1

	      Controlling where filters are applied

	      <?php
	      /* Open a test file for reading and writing */
	      $fp = fopen('test.txt', 'w+');

	      /* Apply the ROT13 filter to the
	       * write filter chain, but not the
	       * read filter chain */
	      stream_filter_append($fp, "string.rot13", STREAM_FILTER_WRITE);

	      /* Write a simple string to the file
	       * it will be ROT13 transformed on the
	       * way out */
	      fwrite($fp, "This is a test
");

	      /* Back up to the beginning of the file */
	      rewind($fp);

	      /* Read the contents of the file back out.
	       * Had the filter been applied to the
	       * read filter chain as well, we would see
	       * the text ROT13ed back to its original state */
	      fpassthru($fp);

	      fclose($fp);

	      /* Expected Output
		 ---------------

	      Guvf vf n grfg

	       */
	      ?>

NOTES
       Note

	      When using custom (user) filters

	      stream_filter_register(3) must be called first in order to register the desired user filter to $filtername.

       Note

	       Stream data is read from resources (both local and remote) in chunks, with any unconsumed data kept in internal buffers. When a new
	      filter is appended to a stream, data in the internal buffers is processed through the new filter at that time. This differs from the
	      behavior of stream_filter_prepend(3).

       Note

	       When a filter is added for read and write, two instances of the filter are created. stream_filter_append(3) must  be  called  twice
	      with STREAM_FILTER_READ and STREAM_FILTER_WRITE to get both filter resources.

SEE ALSO 
stream_filter_register(3), stream_filter_prepend(3), stream_get_filters(3).
PHP Documentation Group 												   STREAM_FILTER_APPEND(3)