Example class registered as stream wrapper

    The example below implements a var:// protocol handler that allows read/write access to a named global variable using standard filesystem stream functions such as fread(). The var:// protocol implemented below, given the URL "var://foo" will read/write data to/from $GLOBALS["foo"].

    Example #1 A Stream for reading/writing global variables

    <?php

    class VariableStream {
    var     $position;
    var     $varname;

    function     stream_open($path, $mode, $options, &$opened_path)
    {
    $url = parse_url($path);
    $this->varname = $url["host"];
    $this->position = 0;

    return     true;
    }

    function     stream_read($count)
    {
    $ret = substr($GLOBALS[$this->varname], $this->position, $count);
    $this->position += strlen($ret);
    return     $ret;
    }

    function     stream_write($data)
    {
    $left = substr($GLOBALS[$this->varname], 0, $this->position);
    $right = substr($GLOBALS[$this->varname], $this->position + strlen($data));
    $GLOBALS[$this->varname] = $left . $data . $right;
    $this->position += strlen($data);
    return     strlen($data);
    }

    function     stream_tell()
    {
    return     $this->position;
    }

    function     stream_eof()
    {
    return     $this->position >= strlen($GLOBALS[$this->varname]);
    }

    function     stream_seek($offset, $whence)
    {
    switch (    $whence) {
    case     SEEK_SET:
    if (    $offset < strlen($GLOBALS[$this->varname]) && $offset >= 0) {
    $this->position = $offset;
    return     true;
    } else {
    return     false;
    }
    break;

    case     SEEK_CUR:
    if (    $offset >= 0) {
    $this->position += $offset;
    return     true;
    } else {
    return     false;
    }
    break;

    case     SEEK_END:
    if (    strlen($GLOBALS[$this->varname]) + $offset >= 0) {
    $this->position = strlen($GLOBALS[$this->varname]) + $offset;
    return     true;
    } else {
    return     false;
    }
    break;

    default:
    return     false;
    }
    }

    function     stream_metadata($path, $option, $var)
    {
    if(    $option == STREAM_META_TOUCH) {
    $url = parse_url($path);
    $varname = $url["host"];
    if(!isset(    $GLOBALS[$varname])) {
    $GLOBALS[$varname] = '';
    }
    return     true;
    }
    return     false;
    }
    }

    stream_wrapper_register("var", "VariableStream")
    or die(    "Failed to register protocol");

    $myvar = "";

    $fp = fopen("var://myvar", "r+");

    fwrite($fp, "line1\n");
    fwrite($fp, "line2\n");
    fwrite($fp, "line3\n");

    rewind($fp);
    while (!    feof($fp)) {
    echo     fgets($fp);
    }
    fclose($fp);
    var_dump($myvar);

    ?>

    The above example will output:

    line1
line2
line3
string(18) "line1
line2
line3
"

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    User Contributed Notes 1 note

    up
    17
    pfe dot skh at gmail dot com
    14 years ago
    Example of stream used with databases :

    Requirement :
    A MySQL database with a table named data structured as follow :
    CREATE TABLE IF NOT EXISTS `data` (
    `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
    `data` varchar(255) NOT NULL,
    `when_inserted` datetime NOT NULL,
    PRIMARY KEY (`id`)
    ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;

    Now with the stream implementation :

    <?php

    class DBStream {
    private     $_pdo;
    private     $_ps;
    private     $_rowId = 0;

    function     stream_open($path, $mode, $options, &$opath)
    {
    $url = parse_url($path);
    $url['path'] = substr($url['path'], 1);
    try{
    $this->_pdo = new PDO("mysql:host={$url['host']};dbname={$url['path']}", $url['user'], isset($url['pass'])? $url['pass'] : '', array());
    } catch(    PDOException $e){ return false; }
    switch (    $mode){
    case     'w' :
    $this->_ps = $this->_pdo->prepare('INSERT INTO data VALUES(null, ?, NOW())');
    break;
    case     'r' :
    $this->_ps = $this->_pdo->prepare('SELECT id, data FROM data WHERE id > ? LIMIT 1');
    break;
    default : return     false;
    }
    return     true;
    }

    function     stream_read()
    {
    $this->_ps->execute(array($this->_rowId));
    if(    $this->_ps->rowCount() == 0) return false;
    $this->_ps->bindcolumn(1, $this->_rowId);
    $this->_ps->bindcolumn(2, $ret);
    $this->_ps->fetch();
    return     $ret;
    }

    function     stream_write($data)
    {
    $this->_ps->execute(array($data));
    return     strlen($data);
    }

    function     stream_tell()
    {
    return     $this->_rowId;
    }

    function     stream_eof()
    {
    $this->_ps->execute(array($this->_rowId));
    return (bool)     $this->_ps->rowCount();
    }

    function     stream_seek($offset, $step)
    {
    //No need to be implemented
    }
    }

    stream_register_wrapper('db', 'DBStream');

    $fr = fopen('db://testuser@localhost/testdb', 'r');
    $fw = fopen('db://testuser:testpassword@localhost/testdb', 'w');
    //The two forms above are accepted : for the former, the default password "" will be used

    $alg = hash_algos();
    $al = $alg[array_rand($alg)];
    $data = hash($al, rand(rand(0, 9), rand(10, 999))); // Some random data to be written
    fwrite($fw, $data); // Writing the data to the wrapper
    while($a = fread($fr, 256)){ //A loop for reading from the wrapper
    echo $a . '<br />';
    }
    ?>

    Hope it helps, cheers ;)
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