udp forwarding to emulator

Issue

I have a java application on my host that sends UDP packets to a port: e.g. 8888.
And I have an Android application that listens to this port and simply displays the data.

This works fine with a real device (which is connected via WiFi to the same network), but I cannot get this working in the Emulator.

Some info:

• I am working on Ubuntu 16.10
• I have deactivated the Ubuntu firewall
• Start the Android emulator app via IntelliJ
  • the emulator has API level 25
• I use udp port forwarding as explained in the Android docs:
  telnet localhost 5554 redir add udp:8888:8888

the code in the Android app to connect to the port:

final DatagramSocket udpSocket = new DatagramSocket(8888);

here's the (pseudo) code of the server that sends the broadcast:

String data = "test";
InetAddress broadcastAddress = Inet4Address.getByName("255.255.255.255");
DatagramSocket udpSocket = new DatagramSocket();
udpSocket.setBroadcast(true);
byte[] dataBytes = data.getBytes();
DatagramPacket datagramPacket = new DatagramPacket(dataBytes, dataBytes.length, broadcastAddress, 8888);
udpSocket.send(datagramPacket);

What am I missing?

Solution

This does not work because of a bug in Android: Issue#207602: Emulator does not redirect UDP packets

Workaround:

• in a terminal:
  • get a list of your avds:
    emulator -list-avds
  • start the emulator with one of the avds and add the -engine classic parameter:
    emulator -avd Nexus_6_API_25_GER -engine classic
• then start your app in Android Studio:
  Run - Run 'app' and connect to the emulator that you have just started
• in the terminal (maybe another terminal) setup the udp port redirection:
  telnet localhost 5554 redir add udp:8888:8888
• note: I saw some problems in newer emulators when using the -engine classic (pixel launcher crashes), but my application worked and it received the UDP packets from the host

Answered By - TmTron