UDP SocketException - Only one usage of each socket address is normally permitted

Question

As much as there are many questions on here that are very similar, none of the supplied answers have helped me, which makes me sad :(

I've got a very large management system that I've been tasked to write some UDP packet sending/receiving for. I'd already written a prototype and all was well, so I started merging my code into said system. However, I've now got a (not show-stopping, but annoying) SocketException popping up:

System.Net.Sockets.SocketException occurred
  ErrorCode=10048
  Message=Only one usage of each socket address (protocol/network address/port) is normally permitted
  NativeErrorCode=10048
  Source=System
  StackTrace:
       at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, SocketAddress socketAddress)
       at System.Net.Sockets.Socket.Bind(EndPoint localEP)
       at System.Net.Sockets.UdpClient..ctor(Int32 port, AddressFamily family)
       at System.Net.Sockets.UdpClient..ctor(Int32 port)
       at Goose.Job.DeviceServerUDPReceiver.InitialiseReceiverClient() in C:\WORK\Trunk\GooseOrders\Classes\SheetCounter\DeviceServerUDPReceiver.vb:line 39

Here is the UDPReceiver class - Which is responsible for just sitting in a loop and waiting for responses from the Device Servers we've got dotted about the place.

Public Class DeviceServerUDPReceiver : Implements IDisposable
'///////////////////////////////////////////////////////////////////////////////
' CONSTANTS
'///////////////////////////////////////////////////////////////////////////////
Private Const TIBBO_DEVICE_REPLY_CMD_START As Integer = 0
Private Const TIBBO_DEVICE_REPLY_CMD_END As Integer = 3
Private Const TIBBO_MESSAGE_REPLY_DIVIDER As String = "_"
Private Const TIBBO_DEVICE_REPLY_OK As String = "OK"

'///////////////////////////////////////////////////////////////////////////////
' MEMBER VARIABLES
'///////////////////////////////////////////////////////////////////////////////
Public _ReceivingClient As System.Net.Sockets.UdpClient
Public _iReceivingPort As Integer = 2002
Public _thReceivingThread As System.Threading.Thread
Public _bClosing As Boolean

'///////////////////////////////////////////////////////////////////////////////
' EVENTS
'///////////////////////////////////////////////////////////////////////////////
Public Event GotDeviceResponse(ByVal sResponse As String)
Public Event FoundNewDevice(ByVal TibboObject As TibboDevice)

'///////////////////////////////////////////////////////////////////////////////
' METHODS
'///////////////////////////////////////////////////////////////////////////////
' Initialises the UDP receiver client on the specified port number. Then runs
' a listening thread constantly waiting to receive udp messages
Public Sub InitialiseReceiverClient()
    Try
        ' TODO - FIX SOCKET EXCEPTION HERE - NOT THREAD ISSUE - THIS IS DUE TO 
        ' THE SOCKET NOT BEING CLOSED. BUT SEEING HOW UDP IS CONNECTIONLESS .... ?!
        _ReceivingClient = New System.Net.Sockets.UdpClient(_iReceivingPort)
        Dim thStartThread As Threading.ThreadStart = New Threading.ThreadStart(AddressOf SitAndReceive)
        _thReceivingThread = New Threading.Thread(thStartThread)
        _thReceivingThread.IsBackground = True
        _thReceivingThread.Start()
    Catch ex As System.Net.Sockets.SocketException
        Console.WriteLine("Socket Exception: " & ex.Message)
    Finally

    End Try
End Sub

' The endless loop listener thread. Will sit and wait for udp packets to 
' process
Private Sub SitAndReceive()
    Dim epEndPoint As System.Net.IPEndPoint = New System.Net.IPEndPoint(System.Net.IPAddress.Any, _iReceivingPort)

    ' infinite loop to listen for udp messages
    While (_bClosing = False)
        Try
            Dim sMessage As String = ""
            Dim byData() As Byte

            byData = _ReceivingClient.Receive(epEndPoint)
            sMessage = System.Text.Encoding.ASCII.GetString(byData)
            Console.WriteLine(sMessage)

            ProcessIncomingUDPDataMessage(sMessage)

        Catch ex As System.Net.Sockets.SocketException
            Console.WriteLine(ex.Message)
        End Try
    End While
End Sub

' close the connection to the receiving udp socket
Public Sub Close()
    _bClosing = True
End Sub


' Processes incoming udp packets for answeres from the device servers
Private Sub ProcessIncomingUDPDataMessage(ByVal sMessage As String)

    ' UDP Data packet from Tibbo devices is set out as follows
    '
    ' CMD_ANSWER
    ' Where "CMD" = The command the device is replying too and
    ' "ANSWER" = It's reply
    Select Case sMessage.Substring(TIBBO_DEVICE_REPLY_CMD_START, TIBBO_DEVICE_REPLY_CMD_END)
        Case TibboDevice.DEVICE_COMMAND_ATO
            '/////////////////////////////////////////////////////////////////////////
            ' Any Tibbo's out there reply message 
            '/////////////////////////////////////////////////////////////////////////
            Dim s() As String = sMessage.Split(TIBBO_MESSAGE_REPLY_DIVIDER)
            Dim sMacAddress As String = s(2) ' the replying devices' mac address
            Dim sIpAddress As System.Net.IPAddress = System.Net.IPAddress.Parse(s(3)) ' ip
            Dim sNetBiosName As String = s(1) ' netbios name
            Dim iTibboStatus As TibboDevice.ETIIBO_DEVICE_STATE = TibboDevice.ETIIBO_DEVICE_STATE.TIBBO_DEVICE_STATE_BAD ' status

            ' set this device status depending on the reply
            If s(4) = TIBBO_DEVICE_REPLY_OK Then
                iTibboStatus = TibboDevice.ETIIBO_DEVICE_STATE.TIBBO_DEVICE_STATE_OK
            End If

            ' create a new tibbo device to pass back to the main form
            Dim Tibbo As TibboDevice = New TibboDevice(sMacAddress, sIpAddress, sNetBiosName, iTibboStatus)
            ' raise event to add this to our list
            RaiseEvent FoundNewDevice(Tibbo)


        Case TibboDevice.DEVICE_COMMAND_STS
            '//////////////////////////////////////////////////////////////////////////
            ' Status reply message
            '//////////////////////////////////////////////////////////////////////////
            Dim s() As String = sMessage.Split(TIBBO_MESSAGE_REPLY_DIVIDER)
            Dim sResult As String = ""

            ' format our string nicely
            sResult &= "Mac Address: " & vbTab & vbTab & s(1)
            sResult &= Environment.NewLine & "IP Address: " & vbTab & vbTab & s(2)
            sResult &= Environment.NewLine & "Device Name: " & vbTab & vbTab & s(3)
            sResult &= Environment.NewLine & "TiOS FW: " & vbTab & vbTab & s(4)
            sResult &= Environment.NewLine & "Goose SC FW: " & vbTab & vbTab & s(5)
            sResult &= Environment.NewLine & "System Uptime: " & vbTab & vbTab & s(6)
            sResult &= Environment.NewLine & "System Time: " & vbTab & vbTab & s(7)
            sResult &= Environment.NewLine & "System Status: " & vbTab & vbTab & s(8)

            RaiseEvent GotDeviceResponse(sResult)

        Case TibboDevice.DEVICE_COMMAND_ASC
            '////////////////////////////////////////////////////////////////////////////
            ' Average sheet count message
            '////////////////////////////////////////////////////////////////////////////
            Dim s() As String = sMessage.Split(TIBBO_MESSAGE_REPLY_DIVIDER)
            Dim sResult As String = ""

            RaiseEvent GotDeviceResponse(sResult)

        Case TibboDevice.DEVICE_COMMAND_NAM
            '////////////////////////////////////////////////////////////////////////////
            ' Changed device name reply message
            ' Device will reply NAM_[NEWNAME] - once it's set it's new name
            '////////////////////////////////////////////////////////////////////////////
            Dim s() As String = sMessage.Split(TIBBO_MESSAGE_REPLY_DIVIDER)
            Dim sResult As String = ""

            RaiseEvent GotDeviceResponse(sResult)

        Case TibboDevice.DEVICE_COMMAND_IDX
            '////////////////////////////////////////////////////////////////////////////
            ' Device responds with it's device id
            '////////////////////////////////////////////////////////////////////////////
            Dim s() As String = sMessage.Split(TIBBO_MESSAGE_REPLY_DIVIDER)
            Dim sResult As String = ""

            ' TODO - do something with the result

        Case TibboDevice.DEVICE_COMMAND_RBT
            '////////////////////////////////////////////////////////////////////////////
            ' Device is going down for a reboot - not much to do here, we have to wait
            '////////////////////////////////////////////////////////////////////////////

        Case TibboDevice.DEVICE_COMMAND_BUZ
            '////////////////////////////////////////////////////////////////////////////
            ' Device has played it's buzz sound - ignore
            '////////////////////////////////////////////////////////////////////////////

        Case TibboDevice.DEVICE_COMMAND_FSH
            '////////////////////////////////////////////////////////////////////////////
            ' Device flashed it's LEDs - ignore
            '////////////////////////////////////////////////////////////////////////////

        Case TibboDevice.DEVICE_COMMAND_AIP
            '////////////////////////////////////////////////////////////////////////////
            ' Device replies with it's actual ip address
            '////////////////////////////////////////////////////////////////////////////
            Dim s() As String = sMessage.Split(TIBBO_MESSAGE_REPLY_DIVIDER)
            Dim sResult As String = ""

            ' TODO - do something with the result

        Case TibboDevice.DEVICE_COMMAND_CBC
            '////////////////////////////////////////////////////////////////////////////
            ' Device replies with it's current box count
            '////////////////////////////////////////////////////////////////////////////
            Dim s() As String = sMessage.Split(TIBBO_MESSAGE_REPLY_DIVIDER)
            Dim sResult As String = ""

            ' TODO - do something with the result

        Case TibboDevice.DEVICE_COMMAND_STP
            '////////////////////////////////////////////////////////////////////////////
            ' Device has been stopped - won't reply. Only way to bring it back to life
            ' is to press the 'reset' button on the actual unit - ignore
            '////////////////////////////////////////////////////////////////////////////
    End Select

End Sub

Protected Overridable Overloads Sub Dispose(disposing As Boolean)
    If (disposing) Then
        ' free managed objects
        '_ReceivingClient = Nothing
        _bClosing = True
    End If
End Sub

Public Overloads Sub Dispose() Implements IDisposable.Dispose
    Dispose(True)
    GC.SuppressFinalize(Me)
End Sub


End Class

Now, all I'm doing in the main form, is: When my listener form is closed - I want to close the listener down (obviously)... For this, I'm using Dispose(). However, when someone wants to start it up again, said exception occurs on the byData = _ReceivingClient.Receive(epEndPoint) line in the SitAndReceive procedure.

Since UDP is transaction based and its sockets (possibly theoretically) can't be in a CLOSE_WAIT state, what is stopping me from closing it down and then immediately relaunching the listener?

I must admit I'm new to UDP sockets, so far however, I've found them a joy to work with and even though this exception wouldn't crash an end-users software (with a simple try/catch), it does have me intrigued and I'd like to understand why it's happening.

Any help is very much appreciated.

Answer 1

Managed to figure this out in the end. Apparently if you want to have more than one connection to a socket, you have to manually configure it, like so:

Dim endPoint = New System.Net.IPEndPoint(0, _iReceivingPort)
_ReceivingClient = New System.Net.Sockets.UdpClient()
_ReceivingClient.ExclusiveAddressUse = False
_ReceivingClient.Client.SetSocketOption(Net.Sockets.SocketOptionLevel.Socket, Net.Sockets.SocketOptionName.ReuseAddress, True)
 _ReceivingClient.Client.Bind(endPoint)

Works now, so I'm happy.