The New Brew-CQ Synchronous Sockets and Threading

Transcription

1 The New Brew-CQ Synchronous Sockets and Threading Server Topology: The Brew-CQ server is an application written in the new.net compilers from Microsoft. The language of choice is Visual Basic. The purpose of this application is to demonstrate how a chat server (such as MSN Messenger and Brew-CQ) works.there are a couple of things that the server must do. Firstly, it should monitor all client connections, accepting and closing, maintaining a list of all logged on client. It must maintain an up to date list of logged on client on each of the logged on client applications. Hence, when a client first logs on to the server his name must be added to the list, then the up to date list must be distributed to all clients. Conversely, when a client logs off the server the list must be updated and then distributed to all clients still logged on to the server. The second thing that the server provides is a message relay from client to client. This is different from some chat programs in that they have server/client applications, where we are using a straight server. So, we accept one clients message and send it to the appropriate other client. In the next sections I discuss some of the specific programming used to accomplish this application. Listen to the Music: The main differnce from a server and a client is that the server listens for client trying to connect to it and then either accept or reject the connection request. The server uses a listening synchronous socket which prompts us to write a thread to constantly keep the server listening while allowing the applilcation to providing other services. The listen instruction once executed sits and waits for an attempt to connect. Once an connection is initiated by a client the thread continues execution. Within the listening thread a lot of things have to take place. Firstly, a new socket instance must be created and accept the connection. Then the list of clients has to be updated and then distributed to the all of the clients. The connecting client first must send the username for the client the list can then be updated. A small protocol had to implemented to dicern between a message or the list of names being sent to a client. Simply we tack on "names@" to the beginning of the namelist and "username@" at the beginnig of the message. Once the namelist has been created we can now send the list. The last thing to do is to create a thread for the new client to receive messages from that client. A thread is executed for each client connected. it was found we can run multiple instances of the thread procedure and they run independantly of the others. We suspend the execution of the listen thread for 200 milliseconds to allow the creation of the new thread and get its values before the listen thread changes these values. Finally, we loop back and start to listen for the next client that wishes to connect. Communication Breakdown: The server constantly polls all connections to see if they are still alive. If the connection exists and is currently OK the connection thread does nothing. However, if the connection does not respond the server kills the thread associated with that client. It also updates the connection list and ditributes the new list to all still connected client. Sounds great, But! This method wish in previous versions of Visual Studio could be accomplished. In.Net however, the Poll method return the status of the socket and no combination of its returned results can tell you if the remote socket diconnects. The Poll method would continually drop the connection because the thread that is polling the connection would pick up the selectread as true and the bytesavailable as zero as soon as the receiving thread had read all of the message, this is the closest combination to tell if the connection had been dropped. The other method to monitor the connection is with the Connected property, which is true when connected and false when disconnected. Wow, problem solved! Well,

2 not quite. The Connected property is updated after a socket IO event, which means you always lose your last message before the property is updated. Too bad the Poll method is not an IO event. Solution, error trapping and sending disconnect messages. Each client thread and the listening thread have on error commands to trap errors that occur. Are You Receiving Me: Each client when connected has a thread created for it that is constantly ready to receive messages. The thread is created within the listening thread and is aborted in the connection thread. This thread monitors a specific client connection and waits until a message has been sent. The server receives the message and reads the first bit of the message to find the destination client. Once it has determined what the destination it looks up the socket instance of that client and sends the message off to the appropriate client. It then continues to listen for another message. Form Layout: The layout of the form is simple. There are two list boxes, one for the names of the connected clients, the other the corresponding list of ip addresses of each client. One of these list boxes are redundant, but it was a debugging tool more than anything. The only other component on the page is the exit button which aborts all running threads and terminates the application. The list boxes are called conlist and namelist, the exit button is called exitbutton. This program written for ENG3553 Networking by Bruce Misner 2004 Demonstrates synchronous sockets and threading This is the Server Application Imports System Imports System.Object Imports System.Net Imports System.Net.Sockets Imports System.Net.SocketAddress Imports System.Threading Imports System.IO Imports System.Text Public Class Form1 Inherits System.Windows.Forms.Form #Region " Windows Form Designer generated code " My Global Variables

3 by Brew-C Dim listenthread As Thread Dim conthread As Thread Dim clithread(50) As Thread Dim ipaddress As ipaddress Dim newcon As Integer Dim tester As Boolean Dim ssock(50) As Socket Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load conlist.items.clear() listenthread = New Thread(New ThreadStart(AddressOf Me.listenproc)) listenthread.isbackground = True listenthread.start() tester = False Public Sub cliproc() Dim clientno As Integer clientno = newcon Declare variables Dim i As Integer Dim j As Integer Dim data As String = Nothing Dim newdata As String = Nothing Dim bytesrec As Integer Dim destination As String Dim fromwho As String Dim towho As String Dim bytes = New Byte(1024) {} Dim lendata As Integer Dim curlen As Integer call to error handler

4 On Error GoTo clihandler Set up the from who header portion fromwho = namelist.items.item(clientno) + "@" wait for data arriving from this client recvnext: Do While ssock(clientno).available = 0 Loop read the data bytesrec = ssock(clientno).receive(bytes) convert to string data = Encoding.ASCII.GetString(bytes, 0, bytesrec) - 1)) pick out the length of data sent from client lendata = Val(Microsoft.VisualBasic.Left(data, InStr(data, "@") set byte counter curlen = bytesrec keep receiving the whole message Do While lendata > curlen bytesrec = ssock(clientno).receive(bytes) data = data + Encoding.ASCII.GetString(bytes, 0, bytesrec) curlen = curlen + bytesrec Loop convert message to string

5 data = Microsoft.VisualBasic.Right(data, Len(data) - InStr(data, find who the message is destined to If InStr(data, "@") > 0 Then towho = Microsoft.VisualBasic.Left (data, InStr(data, "@")) check if the message is to be sent If InStr(data, "@") > 0 And towho <> "bye@" Then destination = Microsoft.VisualBasic.Left(data, InStr(data, "@") - 1) newdata = Nothing assemble message with new header newdata = fromwho + Microsoft.VisualBasic.Right(data, Len (data) - Len(destination) - 1) convert to byte array bytes = Encoding.ASCII.GetBytes(newdata) find destination For i = 0 To 49 If (namelist.items.item(i) = destination) Then ssock(i).send(bytes) newdata = "" bytesrec = 0 Next i see if client is diconnecting ElseIf InStr(data, "@") > 0 And towho = "bye@" Then handle disconnection conlist.items.item(clientno) = "No Connection" namelist.items.item(clientno) = "" ssock(clientno).shutdown(socketshutdown.both) ssock(clientno).close() update connected client list

6 data = "names@" For j = 0 To 49 If namelist.items.item(j) <> "" Then data += namelist.items.item(j) + "@" Next j convert to byte array bytes = Encoding.ASCII.GetBytes(data) send to all connected clients For j = 0 To 49 If namelist.items.item(j) <> "" Then ssock(j).send(bytes) Next j kill that clients thread clithread(clientno).abort() GoTo recvnext clihandler: MessageBox.Show(Err.Description + " " + Str$(i)) Thread code for the synchronous listener Public Sub listenproc() Const portnumber As Integer = 13 Dim address As String Initialize listbox entries conlist.items.clear() namelist.items.clear() Dim x As Integer

7 For x = 0 To 49 conlist.items.add("no Connection") namelist.items.add("") Next x server name address = "newdig1" Create listener instance Dim tcplist As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) Dim endpoint As New IPEndPoint(Dns.Resolve(address).AddressList (0), 13) keeplistening: This makes it syncronous tcplist.blocking = True tcplist.bind(endpoint) Waits for client to initiate connection tcplist.listen(10) Find free listbox entry newcon = 0 Do While (conlist.items.item(newcon) <> "No Connection") newcon = newcon + 1 Loop Accept client connection ssock(newcon) = tcplist.accept()

8 Dim bytes = New Byte(1024) {} Dim data As String = Nothing Dim bytesrec As Integer conlist.items.item(newcon) = ssock (newcon).remoteendpoint.serialize().item(4).tostring() + "." _ + ssock(newcon).remoteendpoint.serialize().item(5).tostring () + "." _ + ssock(newcon).remoteendpoint.serialize().item(6).tostring () + "." _ + ssock(newcon).remoteendpoint.serialize().item(7).tostring () bytesrec = ssock(newcon).receive(bytes) data = Encoding.ASCII.GetString(bytes, 0, bytesrec) namelist.items.item(newcon) = data Dim i As Integer data = "names@" Create up to date client list to be sent to all connected clients For i = 0 To 49 If namelist.items.item(i) <> "" Then data += namelist.items.item(i) + "@" Next i bytes = Encoding.ASCII.GetBytes(data) Send name list to all Clients For i = 0 To 49 If namelist.items.item(i) <> "" Then ssock(i).send(bytes) Next i

9 Create Thread for connecting client clithread(newcon) = New Thread(New ThreadStart(AddressOf Me.cliproc)) clithread(newcon).isbackground = True clithread(newcon).start() Pause for Thread to be Created listenthread.sleep(200) GoTo keeplistening Private Sub exitbutton_click(byval sender As System.Object, ByVal e As System.EventArgs) Handles exitbutton.click Closes all running threads and connected sockets by Brew-C listenthread.abort() Dim i As Integer For i = 0 To 49 If conlist.items.item(i) <> "No Connection" Then clithread (i).abort() If conlist.items.item(i) <> "No Connection" Then ssock(i).send(encoding.ascii.getbytes("bye@")) ssock(i).shutdown(socketshutdown.both) ssock(i).close() Next End the Program End

10 Private Sub namelist_doubleclick(byval sender As Object, ByVal e As System.EventArgs) Handles namelist.doubleclick This routine allows the server to forcefully disconnect any client currently logged in Dim i As Integer Dim bytes = New Byte(1024) {} Dim data As String = Nothing find which name was double clicked i = namelist.selectedindex conlist.items.item(i) = "No Connection" get rid of the client clithread(i).abort() namelist.items.item(i) = "" ssock(i).send(encoding.ascii.getbytes("bye@")) ssock(i).shutdown(socketshutdown.both) ssock(i).close() data = "names@" Create up to date client list to be sent to all connected clients For i = 0 To 49 If namelist.items.item(i) <> "" Then data += namelist.items.item(i) + "@" Next i bytes = Encoding.ASCII.GetBytes(data)

11 Send name list to all Clients For i = 0 To 49 If namelist.items.item(i) <> "" Then ssock(i).send(bytes) Next i Private Sub Form1_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing This routine covers other exits from the program besides a click of the exit button Abort all threads and close all sockets, sending bye first listenthread.abort() Dim i As Integer For i = 0 To 49 If conlist.items.item(i) <> "No Connection" Then clithread (i).abort() If conlist.items.item(i) <> "No Connection" Then ssock(i).send(encoding.ascii.getbytes("bye@")) ssock(i).shutdown(socketshutdown.both) ssock(i).close() Next i End Class Client Application The client application is your interface to chat. There are several things the client app. has to do. Firstly, the client has to connect to the server and establish a connection. It should also be able to disconnect from the server as well. The client must be able to list all connected clients on the server so you can select who you wish to send a message to. The client must have a place to type your message you wish to send and a way to invoke the message send off. The client must also have a place to display received messages. Form Layout The client form has more to display so is a little more complicated. From top down we start with the username textbox and the connect button. First when you start the client app. you must provide a username for yourself and click the connect button to "loggin" to the server. Once the

12 connection has been established the server returns a list of all other clients that are logged on. From the list of connected people you can select whom you wish to send a message to. You must also have a message to send to that user, hence, a textbox that is for the message you wish to send. Once the message is ready to send a click of the send button beneath the textbox with your message will send the message to the other user via the server. The other textbox is for received messages, as well as, a clear button. When the textbox is too full you can click the clear button and will start the textbox anew. The Code This is the Client Applilcation Imports System Imports System.Net Imports System.Net.Sockets Imports System.Text Imports System.Threading Imports System.Object Public Class Form1 Inherits System.Windows.Forms.Form #Region " Windows Form Designer generated code " My Global Variables Dim csock As Socket Dim recthread As thread Dim endpoint As IPEndPoint Dim conthread As Thread #End Region Form Load Event Code Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

13 endpoint = New IPEndPoint(Dns.Resolve("newdig1").AddressList(0), 13) Receive thread code Public Sub recproc() declare local variables Dim bytes = New Byte(1024) {} Dim data As String Dim recbytes As Integer Dim cr As String Dim crbyte(2) As Byte crbyte(0) = 13 crbyte(1) = 10 error trap On Error GoTo handler carriage return linefeed define cr = Encoding.ASCII.GetString(crbyte) wait for data available recvnext: Do While csock.available = 0 Loop receive data and convert to string recbytes = csock.receive(bytes) data = Encoding.ASCII.GetString(bytes) are we receiving an updated namelist If Microsoft.VisualBasic.Left(data, InStr(data, "@")) = "names@" Then Dim tpoint As Integer tpoint = 7 theirnames.items.clear() Dim npoint As Integer

14 npoint = 1 pull out individual names and populate the listbox Do While tpoint < recbytes npoint = InStr(tpoint, data, "@") If npoint = 0 Then npoint = recbytes theirnames.items.add(mid$(data, tpoint, npoint - tpoint)) tpoint = npoint + 1 Loop bytes = New Byte(1024) {} GoTo recvnext is the server disconnecting ElseIf Microsoft.VisualBasic.Left(data, InStr(data, "@")) = "bye@" Then close socket and reset form to disconnected conditions csock.shutdown(socketshutdown.both) csock.close() theirnames.items.clear() cbut.text = "Connect" MessageBox.Show("Server has left") recthread.abort() receive message Else recbox.appendtext("received this from: " + Microsoft.VisualBasic.Left(data, InStr(data, "@") - 1) _ + cr) recbox.appendtext(microsoft.visualbasic.right(data, Len (data) - InStr(data, "@"))) recbox.appendtext(cr + cr) redeclare bytes to expunge old message bytes = New Byte(1024) {}

15 GoTo recvnext error handler handler: show what you got then terminate receiving thread MessageBox.Show(data) recthread.abort() Connect Button Click event Private Sub cbut_click(byval sender As System.Object, ByVal e As System.EventArgs) Handles cbut.click Dim bytes = New Byte(1024) {} Dim data As String Dim recbytes As Integer check if you have entered a username If yourname.text = "" Then MessageBox.Show("You must specify your username") Exit Sub check if connected If (cbut.text = "Connect") And (yourname.text <> "") Then if not connected On Error GoTo handler create socket instance and connect csock = New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp)

16 csock.connect(endpoint) send your username to server bytes = Encoding.ASCII.GetBytes(yourname.Text) csock.send(bytes) bytes = Nothing cbut.text = "Disconnect" start receiving thread recthread = New Thread(New ThreadStart(AddressOf recproc)) recthread.isbackground = True recthread.start() ElseIf cbut.text = "Disconnect" Then if currently connected csock.send(encoding.ascii.getbytes("6@bye@")) csock.shutdown(socketshutdown.both) csock.close() theirnames.items.clear() recthread.abort() cbut.text = "Connect" handler: skiphandler: GoTo skiphandler MessageBox.Show("Can not connect") Run this code when the Send Button is Clicked Private Sub sendbut_click(byval sender As System.Object, ByVal e As System.EventArgs) Handles sendbut.click declare local variables

17 Dim data As String Dim lendata As String Dim lendataint As Integer setup on error trap On Error GoTo sendhandler check to see if a destination user has been selected If theirnames.selectedindex = -1 Then if no selection MessageBox.Show("No destination user specified") Exit Sub define local variables Dim bytes = New Byte(1024) {} build string to send string starts with length of data then destination user then message text all signs in between data = theirnames.items.item(theirnames.selectedindex) + "@" + sendbox.text lendata = Str$(Len(data)) + "@" lendataint = Len(lendata) + Len(data) data = Str$(lendataint) + "@" + data convert to binary and send message bytes = Encoding.ASCII.GetBytes(data) csock.send(bytes) sendbox.text = "" sendhandler: GoTo skipsendhandler

18 If the client can not send message to server run this code MessageBox.Show("Server Problems. Your message was lost") csock.close() theirnames.items.clear() recthread.abort() cbut.text = "Connect" skipsendhandler: This code clears the received textbox Private Sub clearbut_click(byval sender As System.Object, ByVal e As System.EventArgs) Handles clearbut.click End Class Summary recbox.text = "" I would like to clean up a few odds and ends. First when it comes to threads there is another document you should see. However, what is not mentioned there is the fact you can create a collection of threads by defining them as an array. You can run the same thread code multiple times at once and they will run independantly of each other. The Poll method is an unreliable means of checking for existing connections, too many other events satisfy conditions that signal a diconnect event. Despite the above mentioned problem with the Poll method this prgram is quite stable and seems to run well. More error trapping could be worked on to make it a more than useable chat program.