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Using a stream wrapper to access CouchDb attachments with PHP

04.27.2011
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I’m still working in my filesystem with CouchDb. After creating a library to enable working with PHP and CouchDB (see the post here), and after using Monkey Patching to override standard PHP’s filesystem functions. I’ve created another solution now. Thanks to a comment in my last post (many thanks Benjamin) I’ve discovered that it’s possible to create a stream wrapper in PHP (I thought it was only available with a C extension).

It’s pretty straightforward to create the wrapper. Of course it’s only an approach. We can create more functionality to our stram wrapper but at least this example meets my needs.

namespace Nov\CouchDb\Fs;

class StreamWrapper {
    var $position;
    var $varname;
    /**
     * @var \Nov\CouchDb\Fs\Resource
     */
    var $fs;

    /**
     * @param string $path
     * @return \Nov\CouchDb\Fs
     */
    private static function _getFs($path, $_url)
    {
        return \Nov\CouchDb\Fs::factory(FSCDB, $_url['host']);
    }

    function stream_open($path, $mode, $options, &$opened_path)
    {
        $_url = parse_url($path);
        $_path = $_url['path'];
        $fs = self::_getFs($path, $_url);
        $_type = strtolower(substr($mode, 0, 1));
        switch ($_type) {
            case 'r':
                $this->fs = $fs->open($_path);
                break;
            case 'w':
                $this->fs = $fs->open($_path, true, true);
                break;
        }
        return true;
    }

    function stream_read($count=null)
    {
        if (is_null($count)) {
            return $this->fs->raw();
        } else {
            return $this->fs->raw(0, $count);
        }
    }

    function stream_write($data, $lenght=null)
    {
        if (is_null($lenght)) {
            $this->fs->write($data);
        } else {
            $this->fs->write(mb_substr($data, 0, $lenght));
        }
        return strlen($data);
    }

    public function unlink($path)
    {
        $_url = parse_url($path);
        $_path = $_url['path'];

        $fs = self::_getFs($path, $_url)->open($_path);
        $fs->delete();
    }

    public function url_stat($path , $flags)
    {
        $_url = parse_url($path);
        $_path = $_url['path'];
        $fs = self::_getFs($path, $_url)->open($_path);

        //tamaño en bytes
        $size = $fs->getLenght();
        $out[7] = $size;
        $out['size'] = $size;
        return $out;
    }

That’s very simple. It’s almost the same code than the Monkey Patching example.
And now if we want to use it:

use Nov\CouchDb;
use Nov\CouchDb\Fs;
require_once ("Nov/Loader.php");
Nov\Loader::init();
// I use FSCDB to set up the connection parameters to our couchDb database
define('FSCDB', \NovConf::CDB1);

stream_wrapper_register("novCouchDb", "Nov\CouchDb\Fs\StreamWrapper") or die("Failed to register protocol");
$file = "novCouchDb://fs/home/gonzalo/new.txt";

$f = fopen($file, 'w+');
fwrite($f, "***12345dkkydd678901");
fclose($f);

$f = fopen($file, 'r');
$a = fread($f, filesize($file));
fclose($f);

unlink($file);
echo $a;

As we can see the URI is:

novCouchDb://fs/home/gonzalo/new.txt.

That’s mean [protocol]://[database]/[path]

The behaviour of this example is exactly the same than Monkey Patching one but I preffer this one. It looks like more “clean” than Monkey Patching approach.

The full source code is available here. And the example: document_root/tests/couchdb/test7.php


References
Published at DZone with permission of Gonzalo Ayuso, author and DZone MVB. (source)

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