问题
I have a legacy (2008) Windows service application (using System.ServiceProcess.ServiceBase) that I need to utilize in a slightly different way to how it's working now. At the moment it starts up and creates a TCPLISTENER on a specific port, for a client app to connect to (which it does once) in order to send/receive requests to the listening port. This all works fine. However, the adaptation requires use of a web app to connect to the listener port, then send/rcv as normal but after the receive it must DISCONNECT(*)
(* - if the web app didn't have to disconnect from the listening socket after each test that'd be better, but how I might achieve this is beyond me. Can I keep a TCP connection in session state for re-use?)
Anyway, the adaptation all works fine for the first TWO connect/send/rcv/disconnect tests but on the THIRD the service throws an ArgumentException in the EndAccept of the Socket class.
I don't understand why it is failing on the 3rd test.
Here is the simple test client.
Public Class ConnectDisconnectTCP
Inherits System.Web.UI.Page
Private IP As String = "127.0.0.1"
Private port As Int32 = 10002
Private mTCP As System.Net.Sockets.TcpClient
Private netStrm As NetworkStream
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
End Sub
Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim oEnc As New ASCIIEncoding
Dim ScanText As String = "100000000093001X" + vbLf
Dim mTCP As System.Net.Sockets.TcpClient
'connect and create a tcpclient
mTCP = New System.Net.Sockets.TcpClient(IP, port)
netStrm = mTCP.GetStream()
netStrm.WriteAsync(oEnc.GetBytes(ScanText.ToString), 0, ScanText.ToString.Length)
If netStrm.CanRead Then
Dim myReadBuffer(1024) As Byte
Dim myCompleteMessage As StringBuilder = New StringBuilder()
Dim numberOfBytesRead As Integer = 0
' Incoming message may be larger than the buffer size.
Do
numberOfBytesRead = netStrm.Read(myReadBuffer, 0, myReadBuffer.Length)
myCompleteMessage.AppendFormat("{0}", Encoding.ASCII.GetString(myReadBuffer, 0, numberOfBytesRead))
Loop While netStrm.DataAvailable
End If
'CLOSE
netStrm.Close()
mTCP.Close() 'Disposes this TcpClient instance and requests that the underlying TCP connection be closed.
mTCP = Nothing
Label1.Text = "Closed"
End Sub End Class
And here is the TCPListener class on the service that does all the work
Imports System
Imports System.IO
Imports System.Net
Imports System.Net.Sockets
Imports System.Threading
Imports System.Text
Public Class TCPListenerPort
Private currentAsynchResult As IAsyncResult
Private cState As ClientState
Private servSock As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
Private m_connectionstate As Int32 = 0
Dim sData As String = String.Empty
'counters
Public cnt As Int32 = 0
Public rcvcnt As Int32 = 0
Public acccnt As Int32 = 0
Public sndcnt As Int32 = 0
Public sndcal As Int32 = 0
Public cncnt As Int32 = 0
'Public Events
Public Event ConnectionState(ByVal enmState As Int32)
Public Event DataArrived(ByVal strData As Object)
Public Sub New()
End Sub
Public Sub New(ByVal dr As DataRow)
End Sub
Protected Overrides Sub Finalize()
Try
If Not cState Is Nothing Then
cState.ClntSock.Close()
End If
If Not servSock Is Nothing Then
servSock.Close()
End If
Catch ex As Exception
Throw ex
Finally
MyBase.Finalize()
End Try
End Sub
Private Class ClientState
Public Const BUFSIZE As Integer = 1024
Public mrcvBuffer As Byte() = New Byte(BUFSIZE - 1) {}
Public mSendBuffer As Byte() = New Byte(BUFSIZE - 1) {}
Private mclntSock As Socket = Nothing
Public Sub New(ByRef clntSock As Socket)
mclntSock = clntSock
ReDim mrcvBuffer(BUFSIZE)
ReDim mSendBuffer(BUFSIZE)
End Sub
Public ReadOnly Property SckConnected() As Boolean
Get
SckConnected = mclntSock.Connected
End Get
End Property
Public ReadOnly Property RcvBuffer() As Byte()
Get
RcvBuffer = mrcvBuffer
End Get
End Property
Public ReadOnly Property SendBuffer() As Byte()
Get
SendBuffer = mSendBuffer
End Get
End Property
Public ReadOnly Property ClntSock() As Socket
Get
ClntSock = mclntSock
End Get
End Property
End Class
Public Sub Connect(ByVal TCPPort As Int32, ByVal Backlog As Int32)
Try
cState = New ClientState(servSock)
cState.ClntSock.Bind(New IPEndPoint(System.Net.IPAddress.Any, TCPPort))
cState.ClntSock.Listen(100) '5
While True
cncnt = cncnt + 1
System.Diagnostics.Debug.WriteLine("in connect WHILE " + cncnt.ToString)
currentAsynchResult = servSock.BeginAccept(New AsyncCallback(AddressOf AcceptCallback), cState)
currentAsynchResult.AsyncWaitHandle.WaitOne()
End While
Catch __unusedObjectDisposedException1__ As ObjectDisposedException
Catch e As Exception
End Try
End Sub
Private Sub AcceptCallback(ByVal asyncResult As IAsyncResult)
Try
acccnt = acccnt + 1
System.Diagnostics.Debug.WriteLine("AcceptCallback Start" + acccnt.ToString)
'obtain the Socket on which the connection attempt is being made
Dim servSock As ClientState = asyncResult.AsyncState 'Asyncstate gets a user defined object that qualifies or contains info about an async operation
Dim clntSock As Socket
clntSock = servSock.ClntSock.EndAccept(asyncResult)
System.Diagnostics.Debug.WriteLine(clntSock.RemoteEndPoint)
Dim cs As New ClientState(clntSock)
clntSock.BeginReceive(cs.RcvBuffer, 0, cs.RcvBuffer.Length, SocketFlags.None, New AsyncCallback(AddressOf ReceiveCallback), cs)
Catch ar As ArgumentException
'!!!!!Test 3 errors here with
'The IAsyncResult object was not returned from the corresponding asynchronous method on this class.
Catch ex As Exception
End Try
System.Diagnostics.Debug.WriteLine("AcceptCallback End " + acccnt.ToString)
End Sub
Private Sub ReceiveCallback(ByVal asyncResult As IAsyncResult)
rcvcnt = rcvcnt + 1
System.Diagnostics.Debug.WriteLine("ReceiveCallback In " + rcvcnt.ToString)
Dim cs As ClientState = asyncResult.AsyncState
Dim AE As New System.Text.ASCIIEncoding
Dim recvMsgSize As Int32 = 0
Dim strTmp As String = String.Empty
Dim strSend As String = String.Empty
Try
recvMsgSize = cs.ClntSock.EndReceive(asyncResult)
strTmp = Replace(AE.GetString(cs.RcvBuffer), vbNullChar, "")
If recvMsgSize > 0 Then
System.Diagnostics.Debug.WriteLine("ReceiveCallback receiveMsgSize " + recvMsgSize.ToString)
If Right(strTmp, 1) = vbLf Or Right(strTmp, 1) = vbCr Then
strSend = sData + strTmp
strSend = strSend.Replace(vbLf, "")
strSend = strSend.Replace(vbCr, "")
cState = cs
sData = String.Empty
RaiseEvent DataArrived(strSend)
Else
End If
Else
End If
Catch ex As Exception
Throw ex
End Try
System.Diagnostics.Debug.WriteLine("ReceiveCallback Exit " + rcvcnt.ToString)
End Sub
Public Function SendData(ByVal strData As Object) As Boolean
' Change the data to a byte array if necessary, then send it via the socket
Dim oEncoder As New System.Text.ASCIIEncoding
Dim bytes As Byte()
Dim Result As IAsyncResult
Try
Select Case strData.GetType().ToString
Case "System.String" ' Convert a string to a byte array
bytes = oEncoder.GetBytes(strData)
Case "System.Byte[]" ' Send a byte array directly
bytes = strData
Case Else ' And just send anything else as-is
bytes = strData
End Select
sndcnt = sndcnt + 1
Result = cState.ClntSock.BeginSend(bytes, 0, bytes.Length, SocketFlags.None, New AsyncCallback(AddressOf SendCallback), cState)
System.Diagnostics.Debug.WriteLine("SendData " + sndcnt + " " + Result.ToString)
Result.AsyncWaitHandle.WaitOne()
Catch ex As Exception
Throw ex
End Try
Return True
End Function
Private Sub SendCallback(ByVal asyncResult As IAsyncResult)
Dim cs As ClientState = asyncResult.AsyncState
Dim bytesSent As Int32 = 0
Try
bytesSent = cs.ClntSock.EndSend(asyncResult)
sndcal = sndcal + 1
cs.ClntSock.BeginReceive(cs.RcvBuffer, 0, cs.RcvBuffer.Length, SocketFlags.None, New AsyncCallback(AddressOf ReceiveCallback), cs)
System.Diagnostics.Debug.WriteLine("SendCallBack " + sndcal.ToString + " " + bytesSent.ToString)
Catch ex As Exception
Throw (ex)
End Try
End Sub
End Class
With .net trace on, plus the code's system diagnostics debug.write, here is a complete log of the TEST1, TEST2, TEST3/CRASH operation. Note the '<-- SCANTEXT RECEIVED' and '<-- RESPONSE RECEIVED' annotations. The 'in connect WHILE 4' annotation shows the arrival of the 3rd request attempt.
[12572] TcpClient#57416410::TcpClient(AddressFamily#2)
[12572] Socket#61940669::Socket(AddressFamily#2)
[12572] Exiting Socket#61940669::Socket()
[12572] Exiting TcpClient#57416410::TcpClient()
[12572] TcpClient#57416410::TcpClient()
[12572] Exiting TcpClient#57416410::TcpClient()
[12572] Socket#15193904::Socket(AddressFamily#2)
[12572] Exiting Socket#15193904::Socket()
[17872] Socket#40528290::Socket(AddressFamily#2)
[17872] Exiting Socket#40528290::Socket()
[17872] Socket#40528290::Bind(0.0.0.0:10002#10002)
[17872] Exiting Socket#40528290::Bind()
[17872] Socket#40528290::Listen(Int32#100)
[17872] Exiting Socket#40528290::Listen()
in connect WHILE 1
[17872] Socket#40528290::BeginAccept()
[17872] Exiting Socket#40528290::BeginAccept() -> AcceptAsyncResult#515737
The thread '1' (0x6674) has exited with code 0 (0x0).
The thread '<No Name>' (0x1df8) has exited with code 0 (0x0).
The thread '<No Name>' (0x5dac) has exited with code 0 (0x0).
[7984] Socket#49538252::Socket()
[7984] Exiting Socket#49538252::Socket()
in connect WHILE 2
AcceptCallback Start1
[17872] Socket#40528290::BeginAccept()
[7984] Socket#40528290::EndAccept(AcceptAsyncResult#515737)
[17872] Exiting Socket#40528290::BeginAccept() -> AcceptAsyncResult#27334100
System.Net.Sockets Information: 0 : [7984] Socket#49538252 - Accepted connection from 127.0.0.1:63817 to 127.0.0.1:10002.
[7984] Exiting Socket#40528290::EndAccept() -> Socket#49538252
127.0.0.1:63817
[7984] Socket#49538252::BeginReceive()
[7984] Exiting Socket#49538252::BeginReceive() -> OverlappedAsyncResult#62696216
AcceptCallback End 1
[22168] Data from Socket#49538252::PostCompletion
[22168] 00000000 : 32 30 30 30 30 30 30 30-30 30 38 33 30 30 31 58 : 100000000093001X <-- SCANTEXT RECEIVED, TEST1
[22168] 00000010 : 0A : .
ReceiveCallback In 1
[22168] Socket#49538252::EndReceive(OverlappedAsyncResult#62696216)
[22168] Exiting Socket#49538252::EndReceive() -> Int32#17
ReceiveCallback receiveMsgSize 17
[22168] Socket#49538252::BeginSend()
[22168] Exiting Socket#49538252::BeginSend() -> OverlappedAsyncResult#13462887
A first chance exception of type 'System.FormatException' occurred in Microsoft.VisualBasic.dll
[19228] Data from Socket#49538252::PostCompletion
[19228] 00000000 : 07 : . <-- RESPONSE RECEIVED, TEST1
[19228] Socket#49538252::EndSend(OverlappedAsyncResult#13462887)
[19228] Exiting Socket#49538252::EndSend() -> Int32#1
[19228] Socket#49538252::BeginReceive()
[19228] Exiting Socket#49538252::BeginReceive() -> OverlappedAsyncResult#25961440
SendCallBack 1 1
[7984] Data from Socket#49538252::PostCompletion
[7984] 00000000 : :
ReceiveCallback In 2
[7984] Socket#49538252::EndReceive(OverlappedAsyncResult#25961440)
[7984] Exiting Socket#49538252::EndReceive() -> Int32#0
ReceiveCallback Exit 2
ReceiveCallback Exit 2
[22168] Socket#31352595::Socket()
[22168] Exiting Socket#31352595::Socket()
AcceptCallback Start2
in connect WHILE 3
[17872] Socket#40528290::BeginAccept()
[22168] Socket#40528290::EndAccept(AcceptAsyncResult#27334100)
[17872] Exiting Socket#40528290::BeginAccept() -> AcceptAsyncResult#39421196
System.Net.Sockets Information: 0 : [22168] Socket#31352595 - Accepted connection from 127.0.0.1:63820 to 127.0.0.1:10002.
[22168] Exiting Socket#40528290::EndAccept() -> Socket#31352595
127.0.0.1:63820
[22168] Socket#31352595::BeginReceive()
[22168] Exiting Socket#31352595::BeginReceive() -> OverlappedAsyncResult#28002689
AcceptCallback End 2
[7984] Data from Socket#31352595::PostCompletion
[7984] 00000000 : 32 30 30 30 30 30 30 30-30 30 38 33 30 30 31 58 : 100000000093001X <-- SCANTEXT RECEIVED, TEST2
[7984] 00000010 : 0A : .
ReceiveCallback In 3
[7984] Socket#31352595::EndReceive(OverlappedAsyncResult#28002689)
[7984] Exiting Socket#31352595::EndReceive() -> Int32#17
ReceiveCallback receiveMsgSize 17
[7984] Socket#31352595::BeginSend()
[7984] Exiting Socket#31352595::BeginSend() -> OverlappedAsyncResult#31071611
[22168] Data from Socket#31352595::PostCompletion
A first chance exception of type 'System.FormatException' occurred in Microsoft.VisualBasic.dll
[22168] 00000000 : 07 : . <-- RESULT RECEIVED, TEST2
[22168] Socket#31352595::EndSend(OverlappedAsyncResult#31071611)
[22168] Exiting Socket#31352595::EndSend() -> Int32#1
[22168] Socket#31352595::BeginReceive()
[22168] Exiting Socket#31352595::BeginReceive() -> OverlappedAsyncResult#51673536
SendCallBack 2 1
[4640] Data from Socket#31352595::PostCompletion
[4640] 00000000 : :
ReceiveCallback Exit 3
The thread '<No Name>' (0x4b1c) has exited with code 0 (0x0).
ReceiveCallback In 4
[4640] Socket#31352595::EndReceive(OverlappedAsyncResult#51673536)
[4640] Exiting Socket#31352595::EndReceive() -> Int32#0
ReceiveCallback Exit 4
[4640] Socket#37088038::Socket()
[4640] Exiting Socket#37088038::Socket()
AcceptCallback Start3
[4640] Socket#49538252::EndAccept(AcceptAsyncResult#39421196)
in connect WHILE 4
[17872] Socket#40528290::BeginAccept()
[17872] Exiting Socket#40528290::BeginAccept() -> AcceptAsyncResult#8948635
//ERROR THROWN HERE
AcceptCallback End 3
Monitoring with netstat
When the service is started, this appears, indicating the service is listening on port 10002
TCP 0.0.0.0:10002 LON-WKS-ZER01:0 LISTENING
On the 1st and 2nd scans (ie successful) everything works fine. The test web app connects, sends 'scantext', various callback delegates are fired, and we get a good reply.
Netstat during the 1st test, after the connection is made :
TCP 0.0.0.0:10002 LON-WKS-ZER01:0 LISTENING
TCP 127.0.0.1:10002 apps:59574 ESTABLISHED
TCP 127.0.0.1:59574 apps:10002 ESTABLISHED
(then scan #1 is completed)
When testApp mTCP.Close() called, the status changes to CLOSE_WAIT and FIN_WAIT_2
TCP 0.0.0.0:10002 LON-WKS-ZER01:0 LISTENING
TCP 127.0.0.1:10002 apps:59574 CLOSE_WAIT
TCP 127.0.0.1:59574 apps:10002 FIN_WAIT_2
A few mins later, the CLOSE and FIN connections disappear but still have the LISTENER
TCP 0.0.0.0:10002 LON-WKS-ZER01:0 LISTENING
Next, send scan#2, it repeats the sequence as above, with a successful result.
On the third scan, when it attempts to make a new connection, the exception is thrown in AcceptCallback on this line :
clntSock = servSock.ClntSock.EndAccept(asyncResult)
Specifically, it's an ArgumentException, 'asyncResult was not created by a call to BeginAccept' (see EndAccept)
So, for reasons I can't quite fathom, the IASyncResult of the 3rd test is causing the EndAccept method to throw an ArgumentException.
To summarise the bug - the Connect call's BeginAccept sets up a delegate for AcceptCallback and passes an IASyncResult. The AcceptCallBacks EndAccept throws an ArgumentException
I realise the way things are being done are not very up to date and we'd be better off with something else, but with one thing and another (time, resource) I need to try and make the slight adaptation work. But I don't understand why (existing client app) CONNECT, scan,scan,scan,scan etc works, but (web app) CONNECT,scan,DISCONNECT, CONNECT, scan, DISCONNECT fails on the THIRD scan's CONNECT
Thanks in advance for any suggestions.
回答1:
There is a similar issue raised and answered here
... you are holding the socket object in a class-scoped variable. So, if somehow the socket gets disconnected while the ReadCallback is executing and you reconnect it (thereby changing the socket object) - now they don't match, you are trying to complete the Async request using the new object when the old one is the one actually completing.
In your case it is the variable cState. On Connect method, if you just declare a new instance of cState locally which holds the socket then the error may stops occuring.
Dim clientState As New ClientState(servSock)
clientState.ClntSock.Bind(New IPEndPoint(System.Net.IPAddress.Any, TCPPort))
clientState.ClntSock.Listen(Backlog)
While True
Dim result As IAsyncResult = servSock.BeginAccept(New AsyncCallback(AddressOf AcceptCallback), clientState)
result.AsyncWaitHandle.WaitOne()
End While
And also, mTCP should be disposed on the client side.
来源：https://stackoverflow.com/questions/49427831/exception-but-only-on-3rd-time-the-iasyncresult-object-was-not-returned-from