stream_filter_append

(PHP 4 >= 4.3.0, PHP 5, PHP 7, PHP 8)

stream_filter_append — Attach a filter to a stream

说明

stream_filter_append ( resource $stream , string $filtername , int $read_write = ? , mixed $params = ? ) : resource

Adds filtername to 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 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.
params: 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().

返回值

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

false is returned if stream is not a resource or if filtername cannot be located.

范例

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

 */
?>

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 of stream_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 with STREAM_FILTER_READ and STREAM_FILTER_WRITE to 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

User Contributed Notes

Dan J 11-Jan-2016 07:23


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

dlvoy 23-Jul-2008 12:20


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);


}


?>

net_navard at yahoo dot com 12-Dec-2005 10:47


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