PHP Manual: Attach a filter to a stream

Description

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

Adds filtername to the list of filters attached to stream.

Parameters

stream: The target stream.
filtername: The filter name.
read_write: By default, stream_filter_append 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.
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.

Return Values

Returns a resource on success or FALSE on failure. The resource can be used to refer to this filter instance during a call to stream_filter_remove.

FALSE is returned if stream is not a resource or if filtername cannot be located.

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\n");

/* 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 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.

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

stream_filter_append