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
18
pfe dot skh at gmail dot com
12 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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