stream_filter_register

Description

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.

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.

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.

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.

<?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");

?>

LINE1
WORD - 2
EASY AS 123

<?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");
?>

LINE1
WORD - 2
EASY AS 123

See also stream_wrapper_register(), stream_filter_prepend(), and stream_filter_append().