Android Question UDP networking: EADDRINUSE (Address already in use)

[peacemaker]

App that communicates itself by UDP, each side can send and receieve data async.
And connection is closed when the settings are needed (port or other).
And sometimes this error (Address already in use) - stops all the work

How to reuse the address that was firstly used successfully by the app automatically?

 

[Erel]

Use a different port for each app.

 

[peacemaker]

This means that the exact port setting is not needed for UDP ? Is it OK to choose "0" at init ?

 

[Erel]

It is important if you want to send to that socket. However two apps cannot use the same port.

 

[peacemaker]

Sorry, Erel, unclear
One device with single app is a sensor mode, another is data receiver mode (the same app) and remote calibration. So, each device must be able to send data. If different port numbers on both devices - no data exchange, for sure.

But if to disconnect the connection for settings or any other reason - at second connection try this error occurs. If stop\start again - somethimes it helps, but sometimes - no, this error is shown.

 

[Erel]

Is it possible that you initialize UDPSocket multiple times?

 

[peacemaker]

Hmm, i use this init sub

Sub Start_UDP
Try
    UDP.Close
Catch
    Log("Start_UDP.Close:" & LastException)
End Try
Try
    If UDP.IsInitialized = False Then
        UDP.Initialize("UDP", prefs.manager.GetString("PortNumber"),1000)
    End If
    timUDP.Enabled = True
Catch
    Dim a As ServerSocket
    a.Initialize(prefs.manager.GetString("PortNumber"), "")
    Dim s As String = "WiFi error: " & a.GetMyWifiIP & ": " & LastException
    others.Notif(s, False, True, Me, "")
    Log(s)
    ToastMessageShow(s, True)
End Try
End Sub

at Service.Start and at

Sub ph_ConnectivityChanged (NetworkType As String, State As String, Intent As Intent)
If State = "CONNECTED" Then
    others.Notif("Internet OK", False, False, Main, "")
    InternetConnected = True
    Start_UDP
Else    'NO INTERNET
    InternetConnected = False
    a = "Check WiFi-connection..."
    others.Notif(a, False, False, Main, "")
    ToastMessageShow(a, True)
    UDP.Close
End If
End Sub

 

[Erel]

Why are you closing the UDPSocket? Open it once in Starter.Service_Create and leave it open.

 

[peacemaker]

But if port is changed by user? Such setting is available, if this port is used by another apps on the phone.

Or if WiFi connection is broken ?

 

[Erel]

If the port is used by a different app then it will fail. However I'm pretty sure that it is not the case here.

You can try one port and if it fails switch to an alternative port. You will need to implement a similar solution in the client side.

App that communicates itself by UDP, each side can send and receieve data async

What do you mean? Are you communicating between two different devices?

Or if WiFi connection is broken ?

It doesn't matter. UDP is a connection-less protocol.

 

[peacemaker]

What do you mean? Are you communicating between two different devices?

Sure. My single app has setting: sensor or receiver, common the same port and these UDP subs above.
Sensor sends data, receiver gets. Receiver gives command to calibrate the sensor and gets delta values for calibration.

 

[Bert Oudshoorn]

Encountered a similar problem, and found this thread. Starting UDP in Starter.bas and keep it open works, but the UDP_PacketArrived can only be placed (works only) in Starter.bas. Now, I do an UDP-start in each module (in the Resume and an UDP-close in the Pause. Each module can transmit and receive it's data.
Assuming, I am the only Android client of my esp8266 server Details:

Sub Process_Globals : Public IPserver As String = "192.168.1.34"
Private UDPSock As UDPSocket : Private Packet As UDPPacket etc
Sub Activity_Resume : UDPSock.Initialize("UDP", 6000, 256) etc
Sub Activity_Pause (UserClosed As Boolean) : UDPSock.Close etc
Sub UDP_PacketArrived (Packetx As UDPPacket)
Msgbox(Packetx.Data(0) & etc

 

[Erel]

You should keep all the UDP related code in the starter service and use CallSub or CallSubDelayed to interact with the starter service.

 

[Bert Oudshoorn]

What a nice solution via Starter.bas, CallSub and CallSubDelayed. Better than the vb.net mechanism (with Delegate and InvokeRequired for a non-gui thread/backgroundworker). Thank you!