try
        {
            writeln("Downloading: " ~ filename ~ " ...");
            auto sock = new TcpSocket(new InternetAddress(domain, 80));
            auto ss = new SocketStream(sock);
            scope(exit) sock.close(); // close the socket when quit the program
            ss.writeString("GET " ~ url ~ " HTTP/1.0\r\n"
                           "Host: " ~ domain ~ "\r\n"
                           "\r\n");
            // Skip Http header and fill the string who contain the original catalog
            while (true)
            {
                auto line = ss.readLine();
                if (!line.length) break;
            }

            ubyte[4096] buffer; // buffer size: 4kb
            while (!ss.eof())
            {
                int read = ss.readBlock(&buffer, buffer.length);
                content ~=  buffer[0..read];
            }
            writeln("Download finish: " ~ filename);
        }
        catch(Exception e)
        {
            writeln("fatal error in downloader thread (" ~ filename ~ "):\r\n" ~ e.toString());
            return;
        }