stream_filter_append

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

    stream_filter_append — Attach a filter to a stream

    Description

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

    Adds filtername to the list of filters attached to stream.

    Parameters

    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().

    Return Values

    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.

    Examples

    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

    */
    ?>

    Notes

    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.

    See Also

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    User Contributed Notes 2 notes

    up
    7
    Dan J
    8 years ago
    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
    up
    4
    net_navard at yahoo dot com
    18 years ago
    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
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