PHP build script for a Google Chrome browser extension

ChromePluginCompiler.php

<?php

class ChromePluginCompiler extends PluginCompiler
{
	// constants - set these in your subclass
	public $major_version = '5.0';
	public $browser = 'chrome';
	protected $output_mime_type = 'application/x-chrome-extension';
	protected $output_filename = 'ChromeExtension.crx';
	protected $build_dir = 'chrome';
	protected $private_key = "-----BEGIN PRIVATE KEY-----\n...\n-----END PRIVATE KEY-----";
	protected $public_key  = "-----BEGIN PUBLIC KEY-----\n...\n-----END PUBLIC KEY-----";
	protected $public_key_der_base64 = "...";
	
	protected $files = array(
		'manifest.json',
		'icon16.png',
		'icon64.png',
		'icon128.png',
		'_locales/en/messages.json',
		'content/jquery-1.5.1.js',
		'content/mtoolbar.js',
		'content/content.js',
		'content/signrequest.js',
		'content/background.html',
	);
	
	protected $tempdir;
	
	public function compile()
	{
		// create a temporary build directory
		$this->tempdir = tempnam($this->_tmpdir(), 'msg');
		unlink($this->tempdir);
		mkdir($this->tempdir);
		
		$dir = $this->tempdir.'/';
		$key = $this->build_path;
		$name = $this->build_dir;
		$crx = "$name.crx";
		$zip = "$name.zip";
		
		$this->tempfile = $dir.$zip;
		
		// data to insert into plugin files...
		$version = $this->version();
		$tags = array(
			'content/background.html' => array(
				'{{msg_secret}}' => Config::get('msg_secret'),
				'{{msg_api_endpoint}}' => Config::get('msg_api_endpoint'),
				'{{version}}' => $version,
				'{{distributor_id}}' => $this->distributor->pk(),
			),
			'manifest.json' => array(
				'{{version}}' => $version,
				'{{msg_api_endpoint}}' => Config::get('msg_api_endpoint'),
				'{{updateURL}}' => Config::get('msg_include_update_url')?
					'"update_url": "'.Config::get('msg_api_endpoint')."/download/crupdate.xml?distributor_id=".$this->distributor->pk().'",' :
					'',
			),
		);
		
		// Chrome plugins start with a zip archive...
		$z = new ZipArchiveImproved();
		if ($z->open($this->tempfile, ZIPARCHIVE::CREATE) !== TRUE)
		{
			throw new Exception("Cannot open $this->tempfile");
		}
		
		// add each file to the archive
		foreach ($this->files as $file)
		{
			if ($tags[$file])
			{
				$filecontents = str_replace(
					array_keys($tags[$file]),
					array_values($tags[$file]),
					file_get_contents($this->build_path.$file)
				);
				$z->addFromString($file, $filecontents);
			}
			else
			{
				$z->addFile($this->build_path.$file, $file);
			}
		}
		
		// build
		$z->close();
		
		// make a SHA1 signature using our private key
		$pk = openssl_pkey_get_private($this->private_key);
		openssl_sign(file_get_contents($this->tempfile), $signature, $pk, 'sha1');
		openssl_free_key($pk);
		
		// decode the public key
		$key = base64_decode($this->public_key_der_base64);
		
		// .crx package format:
		//
		//   magic number               char(4)
		//   crx format ver             byte(4)
		//   pub key lenth              byte(4)
		//   signature length           byte(4)
		//   public key                 string
		//   signature                  string
		//   package contents, zipped   string
		//
		// see http://code.google.com/chrome/extensions/crx.html
		//
		$fh = fopen($dir.$crx, 'wb');
		fwrite($fh, 'Cr24');                               // extension file magic number
		fwrite($fh, pack('V', 2));                         // crx format version
		fwrite($fh, pack('V', strlen($key)));              // public key length
		fwrite($fh, pack('V', strlen($signature)));        // signature length
		fwrite($fh, $key);                                 // public key
		fwrite($fh, $signature);                           // signature
		fwrite($fh, file_get_contents($this->tempfile));   // package contents, zipped
		fclose($fh);
		
		// clean up build files
		@unlink($this->tempfile); // zip file
		$this->tempfile = array_shift(explode('.', $dir)).'.crx'; // move the .crx file up one level
		if (@rename($dir.$crx, $this->tempfile))
		{
			// delete the temporary working dir
			@rmdir($dir);
		}
		else
		{
			// failsafe ('twas a nice thought!)
			$this->tempfile = $dir.$crx;
		}
		
		// return the path to the compiled plugin
		return $this->tempfile;
	}
}

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