Cesar D. Rodas

PHP since version 4 comes with a great feature that is with the possibility to register new Stream Wrapper. (see this articles are good, this, an this too).

Usually IO functions (fopen, unlink, mkdir and others) are handle by the Operating System or an Deamon(service) that works with the hardware for do the operation. PHP because is an JIT (just in time compiling, a kind of interpreted language) gives a tool to developers that is create a Class that manage a type of IO operations, for example take a look behind:

<?php
//open a file
$fp = fopen(“type://file/path“,“r“);
fclose($fp);
//create a dir
mkdir(“type://file/path“);

//delete a dir
rmdir(“type://file/path“);

//delete a file
unlink(“type://file/path“);
?>

The “type://” do not exist and if you try this code will give you an error, this is because PHP is asking to the host OS, and the host OS do not have idea about “type://”. So here came the “PHP magic”. Now lets create a class for handle “type://”

<?phpclass VariableStream {
    //private vars 

     /* fopen */
    function stream_open($path, $mode, $options, &$opened_path)
    {
        return true; //or false
    }
    /* fread */
    function stream_read($count)
    {
        return “string of data“;
    }
    /* fwrite */
    function stream_write($data)
    {
        return 1; //number of bytes writed
    }
    /*ftell */
    function stream_tell()
    {
        return 0;//actual position 
    }
    /* feof */
    function stream_eof()
    {
        return true;//or false
    }

    /* fseek */
    function stream_seek($offset, $whence)
    {        //$whence: SEEK_SET, SEEK_CUR, SEEK_END

        return true; //or false;

    }

    /* fstats */

    function url_stat (  $path,  $flags )
    {

}    /* opendir */
    function dir_opendir ( $path, $options ) {
    }

/* readdir */

    function dir_readdir() {

}

/* rewinddir */

    function dir_rewinddir() {

    }

    /* close dir*/

    function dir_closedir (  ) {

    }

}

//register type be handler for the class “VariableStream”

stream_wrapper_register(“type“, “VariableStream“)

    or die(“Failed to register protocol“);

?>

So every time that we call IO functions with “type://” as scheme PHP internaly will instance the class “VariableStream” and that class will handle the functions. For further details visit this page.

This great tool open an infinity of possibility for write apps. Here are a few of apps that implements a Stream Wrapper:

• filesnap : Stream wrapper to write and read snapshot files
• gFeed : Stream wrapper to read and write RSS feeds
• gHttp : Stream wrapper to send HTTP POST and GET requests
• MS-Excel Stream Handler : Stream wrapper to read and write MS Excel file.
• POP3 e-mail client : Access to e-mail mailboxes using the POP3 protocol.
• smb4php: Stream wrapper to access Windows shared files.

In the past week I’ve wrote an Stream Wrapper for access Amazon S3 Files. Supported functions are fopen, fread, fwrite, fclose, stat, mkdir, rmdir, unlink, opendir, readdir, rewinddir, closedir.

dirs are amazon “buckets”, here is an example.

<?php
set_time_limit(0);
include(“gs3.php“);
/* fake keys!, please put yours */
define(‘S3_KEY‘, ‘DA5S4D5A6S4D‘);
define(‘S3_PRIVATE‘,‘adsadasd‘); 

/* create a folder,and every one can read*/
mkdir(‘s3://cesar_gs3‘,_PUBLIC_READ);
/* create a file and any one can read*/
/*
 * r = read,
 * w= write, private
 * w+r = write, public read,
 * w+w=write, public write
 */
$f = fopen(‘s3://cesar_gs3/file.txt‘, ‘w+r‘);
        for($i=0; $i <= 1000; $i++)
            fwrite($f, “Line #$in“);
        rewind($f);
        fwrite($f, “Line #5n“);
fclose($f); 

/* displain the files contains in the folder */
$e = opendir(‘s3://cesar_gs3‘);
while($f = readdir($e) ) {
	echo $f.“<br/>“;
}
closedir($e);
/* deleting file */
unlink(‘s3://cesar_gs3/file.txt‘);
/* deleting foler */
rmdir(‘s3://cesar_gs3‘);
?>

DOWNLOAD The class.

Here is the online documentation is here and the project could be download from here

The project is protected under a BSD license, so you are free to use and modify for free.

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This entry was posted on Monday, September 24th, 2007 at 7:21 pm and is filed under PHP, servers, phpclasses. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.