networking - Android - find a server in the network

Question

I am currently writing a client-server application and I ask myself if there is a better way to find a server in the local network then going trough all the available IP addresses and see if the correct answer is supplied?

Answer 1

You might want to look into UDP broadcasts, where your server announces itself and the phone listens for the broadcasts.

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There is an example from the Boxee remote project, quoted below.

Getting the Broadcast Address

You need to access the wifi manager to get the DHCP info and construct a broadcast address from that:

InetAddress getBroadcastAddress() throws IOException {
    WifiManager wifi = mContext.getSystemService(Context.WIFI_SERVICE);
    DhcpInfo dhcp = wifi.getDhcpInfo();
    // handle null somehow

    int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
    byte[] quads = new byte[4];
    for (int k = 0; k < 4; k++)
      quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
    return InetAddress.getByAddress(quads);
}

Sending and Receiving UDP Broadcast Packets

Having constructed the broadcast address, things work as normal. The following code would send the string data over broadcast and then wait for a response:

DatagramSocket socket = new DatagramSocket(PORT);
socket.setBroadcast(true);
DatagramPacket packet = new DatagramPacket(data.getBytes(), data.length(),
    getBroadcastAddress(), DISCOVERY_PORT);
socket.send(packet);

byte[] buf = new byte[1024];
DatagramPacket packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);

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You could also look into Bonjour/zeroconf, and there is a Java implementation that should work on Android.