stream_filter_append()

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

Attach a filter to a stream

说明

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

Adds$filternameto the list of filters attached to$stream.

参数

$stream

The target stream.

$filtername

The filter name.

$read_write

By default,stream_filter_append()will attach the filter to theread filter chainif the file was opened for reading (i.e. File Mode:r, and/or+). The filter will also be attached to thewrite filter chainif the file was opened for writing (i.e. File Mode:w,a, and/or+).STREAM_FILTER_READ,STREAM_FILTER_WRITE, and/orSTREAM_FILTER_ALLcan also be passed to the$read_writeparameter to override this behavior.

$params

This filter will be added with the specified$paramsto theendof the list and will therefore be called last during stream operations. To add a filter to the beginning of the list,usestream_filter_prepend().

返回值

Returns a resource on success orFALSEon failure. The resource can be used to refer to this filter instance during a call tostream_filter_remove().

FALSEis returned if$streamis not a resource or if$filternamecannot be located.

更新日志

范例

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
 */
?>

注释

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 ofstream_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 withSTREAM_FILTER_READandSTREAM_FILTER_WRITEto get both filter resources.

参见

• stream_filter_register()Register a user defined stream filter
• stream_filter_prepend()Attach a filter to a stream
• stream_get_filters() 获取已注册的数据流过滤器列表

Note that stream filters applied to STDOUT are not called when outputting via echo or print.
This is easily demonstrated with the standard ROT13 filter:
<?php
stream_filter_append( STDOUT, "string.rot13" );
print "Hello PHP\n";
// Prints "Hello PHP"
fprintf( STDOUT, "Hello PHP\n" );
// Prints "Uryyb CUC"
?>
If you want to filter STDOUT, you may have better luck with an output buffering callback added via ob_start:
http://php.net/manual/en/function.ob-start.php
At the time of this writing, there is an open PHP feature request to support echo and print for stream filters:
https://bugs.php.net/bug.php?id=30583

While using compression filters on a large set of files during one script invocation i've got
    Fatal error: Allowed memory size of xxx bytes exhausted
even when my max memory limit settings was insane high (128MB)
Workaround is to remember to remove filter after work done with stream_filter_remove:
<?php
foreach($lot_of_files as $filename)
{
  $fp = fopen($filename, 'rb');
  $filter_params = array('level' => 2, 'window' => 15, $memory => 6);
  $s_filter = stream_filter_append($fp, 'zlib.deflate', STREAM_FILTER_READ, $filter_params);
  // here stream-operating code        
  stream_filter_remove($s_filter);
  fclose($fp);
}
?>

Hello firends
The difference betweem adding a stream filter first or last in the filte list in only the order they will be applied to streams.
For example, if you're reading data from a file, and a given filter is placed in first place with stream_filter_prepend()the data will be processed by that filter first.
This example reads out file data and the filter is applied at the beginning of the reading operation:
<?php
/* Open a test file for reading */
$fp = fopen("test.txt", "r");
/* Apply the ROT13 filter to the
 * read filter chain, but not the
 * write filter chain */
stream_filter_prepend($fp, "string.rot13",
STREAM_FILTER_READ);
// read file data
$contents=fread($fp,1024);
// file data is first filtered and stored in $contents
echo $contents;
fclose($fp);
?>
On the other hand, if stream_filter_append() is used, then the filter will be applied at the end of the data operation. The thing about this is only the order filters are applied to streams. Back to the example, it's not the same thing removing new lines from file data and then counting the number of characters, than performing the inverse process. In this case, the order that filters are applied to stream is important.
This example writes a test string to a file. The filter is applied at the end of the writing operation:
<?php
/* Open a test file for 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 at the end of the
stream operation
 * way out */
fwrite($fp, "This is a test\n"); // string data is
first written, then ROT13 tranformed and lastly
written to file
/* Back up to the beginning of the file */
rewind($fp);
$contents=fread($fp,512);
fclose($fp);
echo $contents;
?>
In the first case, data is transformed at the end of the writing operation, while in the second one, data is first filtered and then stored in $contents.
             With Regards 
               Hossein