Resume download in AIR via SOCKET

Here is a some set of source code which is demonstrace how to use SOCKET to implement resume download and how to write received data. Sample class is in attached archive.

_socket.addEventListener( Event.CLOSE, socketClose ); // === COMPLETE
_socket.addEventListener( Event.CONNECT, socketConnect );
_socket.addEventListener( IOErrorEvent.IO_ERROR, uStreamIOErrorHandler );
_socket.addEventListener( SecurityErrorEvent.SECURITY_ERROR, uStreamSecurityErrorHandler );
_socket.addEventListener( ProgressEvent.SOCKET_DATA, socketData ); // === PROGRESS

public function downloadFile ( $fileURL:String, $fileName:String, $pathToSave:String ) : void
{
    _isBusy            = true;
   
    // _pathToTarget is path to file on server
    // i.e. /getFile?myfile.jpg
    // NOTE it cant be an url or anything, depends on serve config
    _pathToTarget    = "/getFile?" + $fileURL.split( "/getFile?")[1];
    _host            = URLUtil.getServerName( $fileURL );

    var fl : File = new File().resolvePath( $pathToSave + File.separator + $fileName );

    // PATH TO YOU DOWNLOAD FILE
    var fl : File = new File().resolvePath( $pathToSave + File.separator + $fileName );

    if ( fl.exists )
    {
        // position from download will be started
        _downloadFromBytes    = fl.size;
       
        // indicates is headers from socket data wah removed or not
        _headerRemoved        = false;
       
        // creating file stream to append downloaded data
        _fileStream = new FileStream();
        _fileStream.open( fl, FileMode.APPEND );

        // check is socket is connected already
        if ( _socket.connected )
        {
            sendRequest();
        }
        else
        {
            // connecting to your host and port
            // i.e. host http://www.mydomain.com
            // i.e. post 80
            _socket.connect( _host, _port );
        }
    }
    else
    {
        // if file is not exist downloading file with bacis download method.
        _fileStream = new FileStream();
        _urlRequest = new URLRequest( $fileURL );

        _fileStream.open( fl, FileMode.WRITE );
        _urlStream.load( _urlRequest );
    }
}


private function socketConnect ( event:Event ) : void
{
    sendRequest();
}

 private function socketClose ( event:Event ) : void
{
    _fileStream.close();
}

 private function uStreamIOErrorHandler ( event:IOErrorEvent ) : void
{

    _fileStream.close();
}

 private function uStreamSecurityErrorHandler ( event:SecurityErrorEvent ) : void
{
    _fileStream.close();
}

 private function sendRequest () : void
{
    var request : String = "";
   
    // _pathToTarget is path to file on server
    // i.e. /getFile?myfile.jpg
    // NOTE it cant be an url or anything, depends on serve config
    request += "GET " + _pathToTarget + " HTTP/1.1" + "\n"
   
    // host where file is hosted
    // i.e. http://www.mydomain.com
    request += "Host: " + _host + "\n";
   
    // bytes from download will be started
    request += "Range: bytes=" + _downloadFromBytes + "- ";
    request += "\n\n";

    // sending this request
    sendMultiByte( request );
}


private function socketData ( event:ProgressEvent ) : void
{
    // creating holder for loaded bytes
    var _loadedBytes        : ByteArray = new ByteArray();
   
    // length of content to download from server
    var _contentLength        : Number = 0;
   
    // creating holder for bytes to APPEND to existed file on you HDD
    var _bytesToWrite        : ByteArray = new ByteArray();

    // if we have some data from socket
    if ( _socket.bytesAvailable )
    {
        // reading bytes
        _socket.readBytes( _loadedBytes, _prevBytesPosition );

        // checking if headers was removed
        // if not we must remove HTTP headers from socket data,
        // to avoid writing this HTTP headers in to file body on HDD
        if ( !_headerRemoved )
        {
            var loadedChars : String = "";
           
            // making loop to remove all HTTP headers
            for ( var i : int = 0; i < _loadedBytes.length; i++  )
            {
                if ( loadedChars.indexOf( "13101310" ) > -1 || loadedChars.indexOf( "1313" ) > -1 )
                {
                    _bytesToWrite.writeByte( _loadedBytes[ i ] );
                }
                else
                {
                    loadedChars += String( _loadedBytes[i] );
                }
            }
           
            var str                : String = _loadedBytes.toString();
            var httpStatus        : String;
            var headerEndIndex    : int = str.indexOf( "Content-Transfer-Encoding: binary\r\n\r\n" );

            // getting content length, it may be useful for progress calculation
            var _range            : String = StringUtil.trim( str.substr( str.indexOf( "Content-Range: bytes " ) + 21, str.indexOf( "Connection:" ) - ( str.indexOf( "Content-Range: bytes " ) + 21 ) ) )
            _contentLength = parseInt( _range.substr( _range.lastIndexOf( "/" ) + 1 ) );

            // setting headerRemoved flag to true, to avoid next time checking for "clear" content
            _headerRemoved = true;
        }
        else
        {
            _bytesToWrite = _loadedBytes;
        }
       
        // writing file data in to file on HDD
        _fileStream.writeBytes( _bytesToWrite );
    }

    _prevBytesPosition = _socket.bytesAvailable;

    event.bytesTotal = _contentLength;

    dispatchEvent( event );
}