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# stream_filter_register

(PHP 5)

stream_filter_register -- Register a stream filter implemented as a PHP class derived from php_user_filter

## Description

bool stream_filter_register ( string filtername, string classname )

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.).

To implement a filter, you need to define a class as an extension of php_user_filter with a number of member functions as defined below. 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 below - doing otherwise will lead to undefined behaviour.

stream_filter_register() will return `FALSE` if the filtername is already defined.

int filter ( resource in, resource out, int &consumed, bool closing )

This method is called whenever data is read from or written to the attached stream (such as with fread() or fwrite()). in is a resource pointing to a bucket brigade which contains one or more bucket objects containing data to be filtered. out is a resource pointing to a second bucket brigade into which your modified buckets should be placed. consumed, which must always be declared by reference, should be incremented by the length of the data which your filter reads in and alters. In most cases this means you will increment consumed by $bucket->datalen for each $bucket. If the stream is in the process of closing (and therefore this is the last pass through the filterchain), the closing parameter will be set to `TRUE` The `filter` method must return one of three values upon completion.

Return Value | Meaning
--- | ---
`PSFS_PASS_ON` | Filter processed successfully with data available in the out bucket brigade.
`PSFS_FEED_ME` | Filter processed successfully, however no data was available to return. More data is required from the stream or prior filter.
`PSFS_ERR_FATAL` (default) | The filter experienced an unrecoverable error and cannot continue.

bool onCreate ( void )

This method is called during instantiation of the filter class object. If your filter allocates or initializes any other resources (such as a buffer), this is the place to do it. Your implementation of this method should return `FALSE` on failure, or `TRUE` on success.

When your filter is first instantiated, and yourfilter->onCreate() is called, a number of properties will be available as shown in the table below.

Property | Contents
--- | ---
FilterClass->filtername | A string containing the name the filter was instantiated with. Filters may be registered under multiple names or under wildcards. Use this property to determine which name was used.
FilterClass->params | The contents of the params parameter passed to stream_filter_append() or stream_filter_prepend().

void onClose ( void )

This method is called upon filter shutdown (typically, this is also during stream shutdown), and is executed after the flush method is called. If any resources were allocated or initialzed during onCreate this would be the time to destroy or dispose of them.

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.

Example 1. Filter for capitalizing characters on foo-bar.txt 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(), stream_filter_prepend(), and stream_filter_append().

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