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# stream_filter_append

(PHP 4 >= 4.3.0, PHP 5)

stream_filter_append -- 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. 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().

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.

As of PHP 5.1.0, this function returns a resource which can be used to refer to this filter instance during a call to stream_filter_remove(). Prior to PHP 5.1.0, this function returns `TRUE` on success or `FALSE` on failure.

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 */ ?>`

> 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().

See also stream_filter_register(), stream_filter_prepend(), and stream_get_filters().

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