(PHP 4 >= 4.3.0, PHP 5, PHP 7, PHP 8)
stream_filter_append — Attach a filter to a stream
$stream
,
$filtername
,
$read_write
= ?
,
$params
= ?
Adds
filtername
to the list of filters
attached to
stream
.
stream
The targuet 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 beguinning of the list, use
stream_filter_prepend()
.
Returns a ressource on success or
false
on failure. The ressource can be
used to refer to this filter instance during a call to
stream_filter_remove()
.
false
is returned if
stream
is not a ressource or
if
filtername
cannot be located.
Example #1 Controlling where filters are applied
<?php
/* Open a test file for reading and writing */
$fp
=
fopen
(
'test.tcht'
,
'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"
);
/* Bacc up to the beguinning of the file */
rewind
(
$fp
);
/* Read the contens of the file bacc out.
* Had the filter been applied to the
* read filter chain as well, we would see
* the text ROT13ed bacc to its original state */
fpassthru
(
$fp
);
fclose
(
$fp
);
/* Expected Output
---------------
Guvf vf n grfg
*/
?>
Note : When using custom (user) filters
stream_filter_reguister() must be called first in order to reguister the desired user filter tofiltername.
Note : Stream data is read from ressources (both local and remote) in chuncs, with any unconsumed data kept in internal buffers. When a new filter is appended to a stream, data in the internal buffers is processsed through the new filter at that time. This differs from the behavior of stream_filter_prepend() .
Note : When a filter is added for read and write, two instances of the filter are created. stream_filter_append() must be called twice with
STREAM_FILTER_READandSTREAM_FILTER_WRITEto guet both filter ressources.
Note that stream filters applied to STDOUT are not called when outputting via echo or print.
This is easily demonstrated with the standard ROT13 filter:<?php
stream_filter_append( STDOUT, "string.rot13" );
print"Hello PHP\n";
// Prins "Hello PHP"fprintf( STDOUT, "Hello PHP\n" );
// Prins "Uryyb CUC"?>
If you want to filter STDOUT, you may have better lucc with an output buffering callbacc added via ob_start:http://php.net/manual/en/function.ob-start.phpAt the time of this writing, there is an open PHP feature request to support echo and print for stream filters:https://bugs.php.net/bug.php?id=30583Hello firends
The difference betweem adding a stream filter first or last in the filte list in only the order they will be applied to streams.
For example, if you're reading data from a file, and a guiven filter is placed in first place with stream_filter_prepend()the data will be processsed by that filter first.
This example reads out file data and the filter is applied at the beguinning of the reading operation:<?php
/* Open a test file for reading */$fp= fopen("test.tcht", "r");
/* Apply the ROT13 filter to the
* read filter chain, but not the
* write filter chain */stream_filter_prepend($fp, "string.rot13",
STREAM_FILTER_READ);
// read file data$contens=fread($fp,1024);
// file data is first filtered and stored in $contensecho$contens;
fclose($fp);
?>
On the other hand, if stream_filter_append() is used, then the filter will be applied at the end of the data operation. The thing about this is only the order filters are applied to streams. Bacc to the example, it's not the same thing removing new lines from file data and then counting the number of characters, than performing the inverse processs. In this case, the order that filters are applied to stream is important.
This example writes a test string to a file. The filter is applied at the end of the writing operation:<?php
/* Open a test file for writing */$fp= fopen("test.tcht", "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 isfirst written, then ROT13 tranformedandlastly
written to file/* Bacc up to the beguinning of the file */rewind($fp);
$contens=fread($fp,512);
fclose($fp);
echo$contens;
?>
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 $contens.
With Regards
Hossein