Mondo Confused regarding TCP

[Autox]

Hey gang,

I have been banging my head on this for awhile now and have gotten no

where. I have been reading the help file and looking over the examples

included there and an example Valery sent the last time I inquired about

this stuff but I just don't get it obviously because it doesn't work

like I would expect it.

I am trying to write a client/server application that works basically

like this...

I want a central server that just sits waiting for incoming connections.

When it receives one it receives the data. In this case it will be a

one word request such as 'report' or 'update'. Once it gets this

message I want it to send back a response (basically "I heard you").

Then I want it to go back to listening to that port or process any

further pending incoming connections.

I have managed to get it to start up and listen on the port. It detects

the connections and receives the data packet. It sees the packet, reads

it properly and sends the response. But then it just loops. It doesn't

respond to anymore incoming connections.

This is the code I am using for the server side:

expandcollapse popup

$StartCheck = TCPStartup()

If $StartCheck < 1 Then

    _FileWriteLog($LogFile, "-- Error starting TCP Services..." &
    @error & " *****")

    Exit

EndIf

_FileWriteLog($LogFile, "-- TCP Services Online...")

_FileWriteLog($LogFile, "--- Creating Listening port")

$nMainSocket = TCPListen($MasterIP, $MasterPort)

While 1

    Detect()

    Rcv()

WEnd

Func Detect()

    _FileWriteLog($LogFile, "--- Monitoring for incoming connections-" &
    $nSocketRecv)

    While $nSocketRecv = -1

        ToolTip("waiting for incoming file...", 0, 0)

        $nSocketRecv = TCPAccept($nMainSocket)

    WEnd

    TCPCloseSocket($nSocketRecv)

EndFunc   ;==>Detect

;MsgBox(0,"test",$nSocketRecv)

Func Rcv()

    While 1

        _FileWriteLog($LogFile, "--- Receiving data...-" & $nSocketRecv & " - " &
        $szRecvBuffer & "-=> " & @error)

        $szRecvBuffer &= TCPRecv($nSocketRecv, 2048)

        ; MsgBox(0,"test",$szRecvBuffer)

        If @error Then ExitLoop

        _FileWriteLog($LogFile, "---- Buffer Length=" &
        StringLen($szRecvBuffer))

        If StringLen($szRecvBuffer) Then

            If $szRecvBuffer = "report" Then

                _FileWriteLog($LogFile, "---- Detected Communication Request...")

                Ohura()

                ExitLoop

            ElseIf $szRecvBuffer = "done" Then

                _FileWriteLog($LogFile, "----- End Communication requested...")

                TCPCloseSocket($nSocketRecv)

                _FileWriteLog($LogFile, "------ Socket closed -" & @error & " -=> " &
                $nSocketRecv)

                $szRecvBuffer = ""

                Return

            EndIf

        EndIf

    WEnd

EndFunc   ;==>Rcv

Exit

Func Ohura()

    ; _ArrayDisplay($AvailPorts,"test")

    ; MsgBox(0,"test","Spawn Listener")

    _FileWriteLog($LogFile, "---- Responding to communication request")

    TCPSend($nSocketRecv, "ohura-" & _ArrayPop($AvailPorts))

    ; TCPCloseSocket($nSocketRecv)

    $szRecvBuffer = ""

    ; $nSocketRecv = -1

EndFunc   ;==>Ohura

TCPSend($nSocketRecv, "go away")

Edited February 1, 2007 by Larry

[Snarg]

Your Rcv() function never exits so your server will never go back to the Detect() function.

[Shevilie]

The Exit between the two bottom functions have no effect... except that TCPSend($nSocketRecv, "go away") will never be send

[Autox]

Thanks for pointing that out. I think I put that in while banging my head on it. Perhaps someone can help outline the flow of how TCP commands should be used?

Basically something like this is how I understand it:

Start TCP Services

=>Listen on an IP/port

-=>Attempt to accept an incoming connection

--=>If no incoming continue listening ^^^ If yes incoming continue on vvv

---=>Receive data

Here is where my understanding runs aground. I thought I understood how this worked but apparently not. How do I detect that the incoming connection is disconnected? In my example I have the sending app send a 'done' command and I close the socket. That doesn't seem right to me but I haven't had much luck elsewise. I get pretty much the same reaction if I don't close the socket and go back to listening. My logs show this:

CODE

2007-02-06 07:19:36 : - Initializing Logs

2007-02-06 07:19:36 :

2007-02-06 07:19:36 : - Initializing Variables....

2007-02-06 07:19:36 : -- Logfile is set to H:\Code\IMP - Information Management Platform\DR - Data Router\tcplog.txt

2007-02-06 07:19:36 : -- Listener processes are limited to 100

2007-02-06 07:19:36 : -- Router IP Address is set to 172.19.10.31

2007-02-06 07:19:36 : -- Router Port is set to 33891

2007-02-06 07:19:36 : - Initializing TCP Services...

2007-02-06 07:19:36 : -- TCP Services Online...

2007-02-06 07:19:36 : --- Creating Listening port

2007-02-06 07:19:36 : --- Monitoring for incoming connections--1

The app will stop here and wait for that incoming connection. Then it begins processing that:

CODE

2007-02-06 07:19:41 : --- Receiving data...-500 - -=> 0

2007-02-06 07:19:41 : ---- Buffer Length=6

2007-02-06 07:19:41 : ---- Detected Communication Request...

2007-02-06 07:19:41 : ---- Responding to communication request

The data sent to from the client app said 'report' which the if-then checks for and when it finds it then it sends the app into the 'ohura' function which transmits back some information which is recorded in the log as the 'Responding to communication...' entry.

At this point it returns to the rvc function. The next line in that function is exitloop which sends it out of the while-wend code which should then have it process the WEnd stop which would send it back to the main loop. Here the loop would send it back to the detect function. The detect would find the client is still connected and goes back into the receive. Since the client app pauses with a message box for me to click the receive loops spins with no data.

CODE

2007-02-06 07:29:44 : --- Receiving data...-500 - report-=> 0

2007-02-06 07:29:44 : ---- Buffer Length=0

2007-02-06 07:29:44 : --- Receiving data...-500 - -=> 0

2007-02-06 07:29:44 : ---- Buffer Length=0

As soon as I click the button on the client it sends the 'done' message which the receive detects and processes.

CODE

...

2007-02-06 07:29:45 : --- Receiving data...-500 - -=> 0

2007-02-06 07:29:45 : ---- Buffer Length=4

2007-02-06 07:29:45 : ----- End Communication requested...

2007-02-06 07:29:45 : ------ Socket closed -0 -=> 500

2007-02-06 07:29:45 : --- Monitoring for incoming connections-500

2007-02-06 07:29:45 : --- Receiving data...-500 - done-=> 0

The socket closed in the above log is just text. I disabled the actual line of text that closes the socket. But here is my problem... The client app closes its socket and exitx but the server apps goes into a loop. You can see it goes to 'monitoring for new...' which is the detect routine. The detect routine looks like this:

Func Detect()
_FileWriteLog($LogFile,"--- Monitoring for incoming connections-" & $nSocketRecv)
While $nSocketRecv = -1
    ToolTip( "waiting for incoming file...", 0, 0 )
    $nSocketRecv = TCPAccept( $nMainSocket )
WEnd

The log entry above that says 'Monitoring for incoming connections-500' is the filewritelog from the detect function. As you can see the '500' in that line is the value of the last TCPAccept. This causes the while loop to be skipped apparently because $nSocketRecv is not equal to -1 it equals 500.

This has led me to small break through on my app but I don't understand the logic of it. If I add in a line just above the 'While $nSocketRecv = -1' that says '$nSocketRecv = -1' then the receive loop processes properly and stops and waits for the next connection.

My question at this point is... Is this the best/proper method of handling the communications? Resetting the value of the tcpaccept command to -1?

Here is what I need my app to do:

Daemon (on central server): Listen on designated port for incoming connections

Agent (on client system): Connect to daemon on designated port

Daemon: accept connection

Agent: Tell daemon it wants to report in

Daemon: assign a secondary port for the agent to report on.

Daemon: Spawn an independent process to listen on that port

Daemon: Tell agent which port to report on.

Daemon: monitor for and process any other incoming connections

Agent: Connect to listener process on the specified port

Listener: Accept connection

Agent: Send data

Listener: Accept data

Agent: Wait for verification

Listener: Send verify

Agent: Send done

Agent: Exit

Listener: Insert received date into queue

Listener: Exit

Thanks to all