Register a user defined stream filter

# stream_filter_register

(PHP 5, PHP 7, PHP 8)

stream_filter_register — Register a user defined stream filter

### Description

stream_filter_register(string `$filter_name`, string `$class`): bool

stream_filter_register() allows you to implement your own filter on any registered stream used with all the other filesystem functions (such as fopen(), fread() etc.).

### Parameters

`filter_name`

  The filter name to be registered.

`class`

  To implement a filter, you need to define a class as an extension of php_user_filter with a number of member functions. When performing read/write operations on the stream to which your filter is attached, PHP will pass the data through your filter (and any other filters attached to that stream) so that the data may be modified as desired. You must implement the methods exactly as described in php_user_filter - doing otherwise will lead to undefined behaviour.

### Return Values

Returns `true` on success or `false` on failure.

stream_filter_register() will return `false` if the `filter_name` is already defined.

### Examples

Example #1 Filter for capitalizing characters on foo-bar.txt stream

The example below implements a filter named `strtoupper` on the foo-bar.txt stream which will capitalize all letter characters written to/read from that stream.

`<?php
/* Define our filter class */
class strtoupper_filter extends php_user_filter {
function filter($in, $out, &$consumed, $closing)
{
while ($bucket = stream_bucket_make_writeable($in)) {
$bucket->data = strtoupper($bucket->data);
$consumed += $bucket->datalen;
stream_bucket_append($out, $bucket);
}
return PSFS_PASS_ON;
}
}
/* Register our filter with PHP */
stream_filter_register("strtoupper", "strtoupper_filter")
or die("Failed to register filter");
$fp = fopen("foo-bar.txt", "w");
/* Attach the registered filter to the stream just opened */
stream_filter_append($fp, "strtoupper");
fwrite($fp, "Line1\n");
fwrite($fp, "Word - 2\n");
fwrite($fp, "Easy As 123\n");
fclose($fp);
/* Read the contents back out
*/
readfile("foo-bar.txt");
?>`

The above example will output:

    LINE1
    WORD - 2
    EASY AS 123

Example #2 Registering a generic filter class to match multiple filter names.

`<?php
/* Define our filter class */
class string_filter extends php_user_filter {
var $mode;
function filter($in, $out, &$consumed, $closing)
{
while ($bucket = stream_bucket_make_writeable($in)) {
if ($this->mode == 1) {
$bucket->data = strtoupper($bucket->data);
} elseif ($this->mode == 0) {
$bucket->data = strtolower($bucket->data);
}
$consumed += $bucket->datalen;
stream_bucket_append($out, $bucket);
}
return PSFS_PASS_ON;
}
function onCreate()
{
if ($this->filtername == 'str.toupper') {
$this->mode = 1;
} elseif ($this->filtername == 'str.tolower') {
$this->mode = 0;
} else {
/* Some other str.* filter was asked for,
report failure so that PHP will keep looking */
return false;
}
return true;
}
}
/* Register our filter with PHP */
stream_filter_register("str.*", "string_filter")
or die("Failed to register filter");
$fp = fopen("foo-bar.txt", "w");
/* Attach the registered filter to the stream just opened
We could alternately bind to str.tolower here */
stream_filter_append($fp, "str.toupper");
fwrite($fp, "Line1\n");
fwrite($fp, "Word - 2\n");
fwrite($fp, "Easy As 123\n");
fclose($fp);
/* Read the contents back out
*/
readfile("foo-bar.txt");
?>`

The above example will output:

    LINE1
    WORD - 2
    EASY AS 123

### See Also

- stream_wrapper_register() - Register a URL wrapper implemented as a PHP class
- stream_filter_append() - Attach a filter to a stream
- stream_filter_prepend() - Attach a filter to a stream

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