# stream_filter_append

(PHP 4 >= 4.3.0, PHP 5, PHP 7)

stream_filter_append — Attach a filter to a stream

### Description

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

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.

### See Also

- stream_filter_register() - Register a user defined stream filter
- stream_filter_prepend() - Attach a filter to a stream
- stream_get_filters() - Retrieve list of registered filters