I am writing a TCP listener (server) that needs to receive messages and send back an acknowledgement. Pretty basic stuff. There are literally dozens of examples out there, including MSDN, from which I copied much of my code. I can receive the message no problem. The problem comes when I try to send back the response. The sending client (Corepoint HL7 engine) reports the following error:
The connection was closed before a response was received
I have tested my service with my own TCP sending test app (written using code copied from MSDN) and it works. But when I receive messages from Corepoint, the response does not go back.
Below is my code. Does anyone have any idea why the NetworkStream.Write method is not actually sending the data (or why the client is not receiving it)? I've tried every idea I've found in other posts that are similar to my problem, and nothing is working. Am I doing something wrong, or is something wrong in the configuration of Corepoint?
Sub Main()
listenThread.Start()
End Sub
Private serverSocket As TcpListener
Dim listenThread As New Thread(New ThreadStart(AddressOf ListenForClients))
Private Sub ListenForClients()
Dim port As Int32 = '(pick a port #)
Dim localIP As IPAddress = 'enter your IP
serverSocket = New TcpListener(localIP, port)
serverSocket.Start()
While True 'blocks until a client has connected to the server
Dim client As TcpClient
If serverSocket.Pending Then
client = serverSocket.AcceptTcpClient
'tried these 2 settings with no effect
'client.NoDelay = True
client.Client.NoDelay = True
ProcessIncomingMessageSocketTCPClient(client) 'I was doing this in a separate thread but temporarily kept it on this thread to eliminate threading as the possible cause (but no luck)
client.Close()
Else
Threading.Thread.Sleep(1000) 'wait 1 second and poll again
End If
End While
End Sub
Private Sub ProcessIncomingMessageSocketTCPClient(ByRef objClient As TcpClient)
Dim strMessageText As String
Dim clientStream As NetworkStream
Dim msgBuffer(4096) As Byte
Dim numberOfBytesRead As Integer
Dim strChunk As String
Dim strCompleteMessage As New Text.StringBuilder
Dim sendBytes As Byte()
clientStream = objClient.GetStream()
Do
numberOfBytesRead = clientStream.Read(msgBuffer, 0, msgBuffer.Length)
strChunk = Encoding.ASCII.GetString(msgBuffer, 0, numberOfBytesRead)
strCompleteMessage.AppendFormat("{0}", strChunk)
Loop While clientStream.DataAvailable
strMessageText = strCompleteMessage.ToString
sendBytes = Encoding.ASCII.GetBytes("I received a message from you")
clientStream.Write(sendBytes, 0, sendBytes.Length)
objClient.Close() 'tried it with and without this line
End Sub
It turns out that nothing is wrong with my code. The TCP was and is working correctly. This application is an HL7 listener and I was missing the MLP wrapping around my ACK. As soon as I added that, the sending application accepted my ACK and all is good.
Related
So at the moment I am hosting some HTML code on my localhost using a httplistener in VB.NET. Here is the code for that:
Shared httpListener As HttpListener = New HttpListener()
Private Shared Sub Main()
Debug.WriteLine("Starting server...")
httpListener.Prefixes.Add("localhost:5000/")
httpListener.Start()
Debug.WriteLine("Server started.")
Dim _responseThread As Thread = New Thread(AddressOf ResponseThread)
_responseThread.Start()
End Sub
Private Shared Sub ResponseThread()
While True
Dim context As HttpListenerContext = httpListener.GetContext()
Dim responseArray As Byte() = Encoding.UTF8.GetBytes("<html><script src=""https://www.google.com/recaptcha/api.js"">async defer</script><div class=""g-recaptcha"" data-sitekey=""sitekey""></div></html>")
context.Response.OutputStream.Write(responseArray, 0, responseArray.Length)
context.Response.KeepAlive = False
context.Response.Close()
Debug.WriteLine("Respone given to a request.")
End While
End Sub
Now this works perfectly and notifies me whenever a request is made to the localhost, but I want to be able to receive response data when a user (me) does the recaptcha. I am not sure how to do this and have looked everywhere. So any help is appreciated, I tried seeing if I could get responses using the httplistenerresponse but had no look and even looked into TCP clients and listeners. There is probably an easier way to do this, and any help is appreciated.
Fiddler is a prime example of what I need my program to do, but just listen to the response after completing the captcha.
Thanks!
I’m after some help with a problem i have been working on for the past few days but i can't seem to get it to work correctly.
I have multiple clients connecting to a server, the server needs to keep a list of connected clients and remove them from the list if the client disconnects, I have this bit working correctly.
Once a client is connected the server may call upon the client for some information about its state by sending a few bytes of data to which the client responds with 2 bytes of data. Based on this response the server will complete any one of number of different tasks.
I have had this working synchronously, though now I am trying to make the function asynchronous and I’m running in to an issue. The best I can tell my function that request the information from the client is completing before the client responds and is returning incorrect data, if I print the data received from the client I can see it is the correct information.
This is my 1st time working with asynchronous functions and connections so it’s highly likely I’ve got it completely wrong, I have looked at lots of example code but I can seem to find any that sheads any light on my issue.
This is what I have at the moment:
'create the collection instance to store connected clients
Private clients As New List(Of TcpClient)
'declare a variable to hold the listener instance
Private listener As TcpListener
'declare a variable to hold the cancellation token source instance
Private tokenSource As CancellationTokenSource
Private recvTsk As Task
Private Rreply As New List(Of Byte)
Private Async Sub startTCPListenerServer()
'get port from ini file
Dim netPort = SettingsIniFile.GetString("Setup", "NetworkPort", "")
While True
'create a new cancellation token source instance
tokenSource = New CancellationTokenSource
'create a new listener instance bound to the desired address and port
listener = New TcpListener(IPAddress.Any, netPort)
'start the listener
listener.Start()
While True
Try
Dim client As TcpClient = Await listener.AcceptTcpClientAsync
clients.Add(client)
Dim clientIP As String = client.Client.RemoteEndPoint.ToString
ListBox1.Items.Add(clientIP)
Try
'begin reading from the client's data stream
Using stream As NetworkStream = client.GetStream
Dim buffer(client.ReceiveBufferSize - 1) As Byte
Dim read As Integer = 1
'if read is 0 client has disconnected
While read > 0
recvTsk = New Task(Sub()
For i = 0 To read - 1
'data recived at this point is correct
Rreply.Add(buffer(i))
Next
End Sub, tokenSource.Token)
read = Await stream.ReadAsync(buffer, 0, buffer.Length, tokenSource.Token)
recvTsk.Start()
End While
'client gracefully closed the connection on the remote end
End Using
Catch ocex As OperationCanceledException
'the expected exception if this routines's async method calls honor signaling of the cancelation token
'*NOTE: NetworkStream.ReadAsync() will not honor the cancelation signal
Catch odex As ObjectDisposedException
'server disconnected client while reading
Catch ioex As IOException
'client terminated (remote application terminated without socket close) while reading
Finally
'ensure the client is closed - this is typically a redundant call, but in the
'case of an unhandled exception it may be necessary
'remove the client from the list of connected clients
clients.Remove(client)
client.Close()
ListBox1.Items.Remove(clientIP)
'remove the client's task from the list of running tasks
'clientTasks.Remove(client.Task)
End Try
Catch odex As ObjectDisposedException
'listener stopped, so server is shutting down
Exit While
End Try
End While
For i As Integer = clients.Count - 1 To 0 Step -1
clients(i).Close()
Next
tokenSource.Dispose()
End While
'signal any processing of current clients to cancel (if listening)
tokenSource.Cancel()
'abort the current listening operation/prevent any new connections
listener.Stop()
'End If
End Sub
Async Function sendToPod(message() As Byte, podNum As Integer) As Task(Of Byte)
If clients.Count = 0 Then
Else
Dim podIP As String
'get ip address as string from ini file
podIP = SettingsIniFile.GetString("NetworkSettings", "Pod" & podNum & "IP", "")
Dim currentClient As TcpClient = Nothing
For Each client As TcpClient In clients
Dim clientIP As String = (CType(client.Client.RemoteEndPoint, IPEndPoint).Address.ToString())
If clientIP = podIP Then
currentClient = client
End If
Next
If currentClient IsNot Nothing Then
'get the current client, stream, and data to write
Dim stream As NetworkStream = currentClient.GetStream
Dim buffer() As Byte = message
'wait for the data to be sent to the remote
Await stream.WriteAsync(buffer, 0, buffer.Length)
recvTsk.Wait()
Return Rreply(1)
End If
End If
End Function
Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Try
Me.TextBox1.Text = Await sendToPod({"&HAB", "&HAD", "&HFF", "&HFF"}, 1)
Catch
End Try
End Sub
End Class
I'm developing some software that listens for events from another program via TCP.
The events come in a string formatted like this: "value1;value2;value3"
The problem is that sometimes a single character from value1 gets read onto the previous event so i get something like this:
value1;value2;value3v
alue1;value2;value3
How can i make it know where each message begins and ends?
Here is the code:
Dim client As New TcpClient()
Sub listen()
Dim networkStream As Stream = client.GetStream()
While True
Dim bytes(client.ReceiveBufferSize) As Byte
Dim size As Integer = 0
size = networkStream.Read(bytes, 0, CInt(client.ReceiveBufferSize))
'process event here
End While
End Sub
This is all done on a thread of it's own.
Sender has to included the length of each data its sending so at receiver you will receive upto the provided length. Easier option would be to include NULL termination so that you can read it as individual string at receiver end.
I am not a software programmer but I have a task to create a TCP Server (a program that is listening on its network card interfaces for incoming data streams).
I have searched on the internet and I found that I can use two methods: Socket or TCPListener class.
I have created an example for the Socket class, but I was wondering how I can test it?
If another computer in the network sends some string data to the listener computer, then the message should be displayed.
Here is the example from Microsoft that I am using for the TCP server using a Socket:
Public Shared Sub Main()
' Data buffer for incoming data.
Dim data = nothing
Dim bytes() As Byte = New [Byte](1024) {}
Dim ipAddress As IPAddress = ipAddress.Any
Dim localEndPoint As New IPEndPoint(ipAddress, 0)
Dim intI As Integer = 0
'Display the NIC interfaces from the listener
For Each ipAddress In ipHostInfo.AddressList
Console.WriteLine("The NIC are {0}", ipHostInfo.AddressList(intI))
intI += 1
Next
Console.WriteLine("You are listening on {0}",localEndPoint)
' Create a TCP/IP socket.
Dim listener As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
' Bind the socket to the local endpoint and
' listen for incoming connections.
Try
listener.Bind(localEndPoint)
listener.Listen(200)
Catch e As SocketException
Console.WriteLine("An application is alreading using that combination of ip adress/port", e.ErrorCode.ToString)
End Try
' Start listening for connections.
While True
Console.WriteLine("Waiting for a connection...")
' Program is suspended while waiting for an incoming connection.
Dim handler As Socket = listener.Accept()
data = Nothing
' An incoming connection needs to be processed.
While True
bytes = New Byte(1024) {}
Dim bytesRec As Integer = handler.Receive(bytes)
data += Encoding.ASCII.GetString(bytes, 0, bytesRec)
Console.WriteLine("The string captured is {0}", data)
If data.IndexOf("something") > -1 Then
Exit While
End If
End While
' Show the data on the console.
Console.WriteLine("Text received : {0}", data)
' Echo the data back to the client.
Dim msg As Byte() = Encoding.ASCII.GetBytes(data)
handler.Shutdown(SocketShutdown.Both)
handler.Close()
End While
End Sub
End Class
Am I on the right lead?
Thanks
Later Edit:
I have used that code in a Console Application created with Visual Studio and I want to check the scenario when a device is sending some string message through the network.
E.g:
I have two devices :Computer A, computer B connected through LAN
I have tried this command : telnet computerA port ( from computer B) but nothing is displayed in the TCP server running from computer A.
telnet 192.168.0.150 3232
I also made a TCP client for testing (derived from the Microsoft example):
Public Class SynchronousSocketClient
Public Shared Sub Main()
' Data buffer for incoming data.
Dim bytes(1024) As Byte
Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName())
Dim ipAddress As IPAddress = ipHostInfo.AddressList(0)
Dim remoteEP As New IPEndPoint(ipAddress, 11000)
' Create a TCP/IP socket.
Dim sender As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)
' Connect the socket to the remote endpoint.
sender.Connect(remoteEP)
Console.WriteLine("Socket connected to {0}", _
sender.RemoteEndPoint.ToString())
' Encode the data string into a byte array.
Dim msg As Byte() = _
Encoding.ASCII.GetBytes("This is a test<EOF>")
' Send the data through the socket.
Dim bytesSent As Integer = sender.Send(msg)
' Receive the response from the remote device.
Dim bytesRec As Integer = sender.Receive(bytes)
Console.WriteLine("Echoed test = {0}", _
Encoding.ASCII.GetString(bytes, 0, bytesRec))
' Release the socket.
sender.Shutdown(SocketShutdown.Both)
sender.Close()
Console.ReadLine()
End Sub
End Class 'SynchronousSocketClient
But it does not work because of the PORT setting.
If in the TCP Server I have "Dim localEndPoint As New IPEndPoint(ipAddress, 0)" then the client crashes, but if I change the port from any (0) to 11000 for example, the client works fine.
Do you know why?
Later edit 2:
Maybe I should have started with this question: Which method is recommended for my scope - asynchronous or synchronous method?
Yes, you are on the right path.
The next thing to do is to introduce message detection since TCP is stream based and not message based like UDP. This means that TCP might decide to send two of your messages in the same packet (so that one socket.Recieve will get two messages) or that it will split up your message into two packets (thus requiring you to use two socket.Recieve to get it).
The two most common ways to create message detection is:
Create a fixed size header which includes message size
Create a delimiter which is appended to all messages.
Your "server" isn't listening on a set port, so you'll need to pay attention to the "You are listening on" message that appears. Then, from another machine on the network, telnet the.ip.add.ress port. (This may require installing "telnet client", or enabling it in the Programs and Features stuff, or whatever.)
Side note...if you actually intend for this to be a server of some sort, you'll want to decide what port you want to use, so that other computers can find your service. Most people won't be able to read your screen to figure out where to connect. :)
As for your "client"...when you connect to another computer, you don't just "pick a port" (which is what a port number of 0 means in an endpoint). You need to know what port the server uses. (Reread what i said in the previous paragraph. A program running on another computer has no idea what port to use to connect to the server -- any server could be running on any port.) You need to pick a port number for the server (say, 11000...good as any, really) rather than letting it use port 0.
I'm using HttpListener as a simple http server. I've been benchmarking req/sec performance by having HttpListener return the string "OK" to each request - this has hit a limit at 16,000 requests per second. Based on the following code, is there anything that I can do to further optimize performance? Or are we hitting the limits of Windows Http.sys?
Image uploading isn't working, here's a link to the Visual Studio performance trace:
VS Performance Trace
Public Class HTTPServer
Shared Listener As HttpListener = New HttpListener
Public Shared Sub Start()
ServicePointManager.DefaultConnectionLimit = 500
ServicePointManager.Expect100Continue = False
ServicePointManager.MaxServicePoints = 500
Listener.Prefixes.Add("http://localhost/")
Listener.Start()
For i As Integer = 1 To (System.Environment.ProcessorCount * 2)
Dim NewThread As New System.Threading.Thread(AddressOf ListenerThread)
NewThread.Priority = ThreadPriority.Normal
NewThread.IsBackground = True
NewThread.Start()
Next
End Sub
Private Shared Sub ListenerThread()
Dim SyncResult As IAsyncResult
While True
SyncResult = Listener.BeginGetContext(New AsyncCallback(AddressOf ListenerCallback), Listener)
SyncResult.AsyncWaitHandle.WaitOne()
End While
End Sub
Private Shared Sub ListenerCallback(ByVal StateObject As IAsyncResult)
Dim Listener As HttpListener = DirectCast(StateObject.AsyncState, HttpListener)
Dim Context As HttpListenerContext = Listener.EndGetContext(StateObject)
Dim Request As HttpListenerRequest = Context.Request
Dim Response As HttpListenerResponse = Context.Response
Dim ResponseString As String = "OK"
Dim Buffer As Byte() = System.Text.Encoding.UTF8.GetBytes(ResponseString)
Response.ContentLength64 = Buffer.Length
Dim OutputStream As System.IO.Stream = Response.OutputStream
OutputStream.Write(Buffer, 0, Buffer.Length)
OutputStream.Close()
OutputStream.Dispose()
End Sub
End Class
Well one thing you can do is only call Encoding.UTF8.GetBytes("OK") once, instead of on every request. I doubt that it'll make much difference, but if you're doing exactly the same thing on every request, you might as well have that response in the form you need it.
I would also use a Using statement rather than calling Close and Dispose explicitly. That's not a performance thing - just general good practice to avoid problems with unclosed streams when there are exceptions.
Realistically, do you need to hit more than 16K QPS? Have you worked out whether you're being CPU-bound or IO-bound? As soon as your program needs to actually do some real work on each request, I would imagine that will dwarf any micro-optimizations you make here anyway.