COM Interface: Planning Both Sides

[Dan Gin zel]

Greetings! Tonight I'm inquring if anyone has any input regarding building a basic COM interface between two programs where I'm in control of both sides and where two-way communications (mostly simple strings) are required on each side, assuming COM is even the best mechanism.

This is my first need for COM and have reviewed many of the examples on the board. All that I've discovered relate to controlling Excel, Word or some other application, and most of which I've been able to make work. However, I have not encountered any examples of a COM "server" in PowerBasic, supposing it can even be done.

Are there any limitations or common mistakes made when building ones first COM interface? Any tip, suggestions and (hopefully) even a COM server code clip would be greatly appreciated.

Also, I am very much open to alternate methods of inter-application communication where I can pass strings between them.

Thanks,
Dan

[Knuth Konrad]

PB doesn't provide, as of yet, the ability to create COM servers. That's why you dont' find examples here. If you really like to go the COM way, I guess José Roca's forums would eb agood place to look at.

That said, exchanging "strings" could easily be done via TCP communication. Look at the Echoserver (client/server) in you PB examples folder.

[Michael Mattias]

There are many, many ways to exchange info between cooperating applications on the same computer...

- Memory Mappped file objects
- Window messages, eg WM_COPYDATA
- Regular disk files
- Pipes and Mailslots

I'm sure I've forgotten some. Try a seach here on "interprocess communications."

[Edwin Knoppert]

Com servers behave much better than sendmessages and such.
using sm you can lock up both apps.

[Bob Zale]

An EXE and a DLL.

[Cliff Nichols]

An EXE and a DLL.

Not to mention, the DLL can have its own "Windows/Dialog/etc"

[Dan Gin zel]

First, I want to thank everyone for the input. That's exactly what I needed to get the cognitive processes moving again.

And now, for the winning entry:

That said, exchanging "strings" could easily be done via TCP communication. Look at the Echoserver (client/server) in you PB examples folder.

The beauty of this solution is that I can use it between more than process, use it for multiple instance detection and here's the key: to use it between computers on a LAN. The latter opens up a whole new realm of possibilities that I had not before considered!

I've been doing searches looking for existing code as I have little TCP/IP communications experience. Lots to learn by Friday (Demo Day.)

(Now if someone has any tips or thoughts in this direction, I'm all ears!)

Thanks again to all! Y'alls input is most appreciated!

Dan

[Edwin Knoppert]

http://planetsquires.com/support/index.php?board=23.0

It is a tcp server using sqlite database..

[John Petty]

Dan
Here is a very simple TCP server DLL that allows control of and reporting on a VB6 program. The VB6 program just calls StartTCP passing a Callback address. The StartTCP Sub just starts a MODELESS (most important for a TCP server) hidden Dialog, the TCP and returns to VB6. When the VB6 prog is closing down it just calls CloseTCP which closes the Dialog and TCP server.
External program (over Internet or LAN) simply connect to the TCP server and send a brief message. Depending on the message it either sends a control code back to the VB6 prog Callback or returns info to the caller.
The port number you use is your own choice, preferably not a commonly used one.

#PBFORMS CREATED V1.51
#COMPILE DLL
#DIM ALL

#PBFORMS BEGIN INCLUDES
#IF NOT %DEF(%WINAPI)
    #INCLUDE "WIN32API.INC"
#ENDIF
#PBFORMS END INCLUDES

#PBFORMS BEGIN CONSTANTS
%Bqt     = 1002
%Dtcp    =  101
%Tmess   = 1001
#PBFORMS END CONSTANTS

GLOBAL Htcp AS LONG
GLOBAL LoggedIn AS LONG
GLOBAL ManualLogout AS LONG
GLOBAL LastAct AS STRING
GLOBAL LastOrd AS STRING
GLOBAL CurrentMonth AS STRING
GLOBAL Cfg() AS STRING
GLOBAL VBAdd AS DWORD
GLOBAL WHndl AS DWORD

DECLARE CALLBACK FUNCTION ShowDtcpProc()
'DECLARE FUNCTION ShowDtcp(BYVAL hParent AS DWORD) AS LONG
#PBFORMS DECLARATIONS
DECLARE SUB GiveAction(BYVAL DoThis AS LONG)

SUB StartTCP(BYVAL VBAddress AS DWORD) EXPORT
    LOCAL hDlg  AS DWORD
    LOCAL fi AS LONG
    LOCAL a AS LONG
    LOCAL s AS STRING
    LOCAL t AS STRING
    VBAdd = VBAddress
    fi = FREEFILE
    OPEN "c:\jiwamcaord.cfg" FOR INPUT AS fi
    WHILE EOF(fi) = 0
        LINE INPUT #fi, t
        a = INSTR(t, "=")
        IF a THEN
            s = UCASE$(TRIM$(LEFT$(t, a - 1)))
            t = TRIM$(RIGHT$(t, LEN(t) - a))
            SELECT CASE s
                CASE "PERIOD START"
                    CurrentMonth = t
            END SELECT
        END IF
    WEND
    CLOSE fi
    DIALOG NEW %HWND_DESKTOP, "Hidden Dialog", 247, 162, 201, 121, TO hDlg
    CONTROL ADD TEXTBOX, hDlg, %Tmess, "", 5, 5, 190, 90, %WS_CHILD OR _
        %WS_VISIBLE OR %WS_VSCROLL OR %ES_LEFT OR %ES_MULTILINE OR _
        %ES_AUTOHSCROLL OR %ES_AUTOVSCROLL OR %ES_READONLY, _
        %WS_EX_CLIENTEDGE OR %WS_EX_LEFT OR %WS_EX_LTRREADING OR _
        %WS_EX_RIGHTSCROLLBAR
    CONTROL ADD BUTTON,  hDlg, %Bqt, "Exit", 76, 100, 50, 15
#PBFORMS END DIALOG
    TCP OPEN SERVER PORT 1122 AS #2    'create a TCP server to handle action requests
    TCP NOTIFY #2, ACCEPT TO hdlg AS 889    'and have it notify when a session is requested
    WHndl = hDlg
    DIALOG SHOW STATE hDlg, %sw_hide
    DIALOG SHOW MODELESS hDlg, CALL ShowDtcpProc
END SUB

SUB StopTCP() EXPORT
    TCP CLOSE #2
    DIALOG END WHndl
END SUB

SUB SaveState(Lact AS STRING, LIn AS LONG, MLOut AS LONG) EXPORT
    LoggedIn = Lin
    ManualLogout = MLOut
    LastAct = Lact
END SUB

SUB OrderDet(Lord AS STRING) EXPORT
    LastOrd = Lord
END SUB


CALLBACK FUNCTION ShowDtcpProc()
    LOCAL buffer AS STRING
    LOCAL s AS STRING
    LOCAL fi AS LONG
    LOCAL a AS LONG

    SELECT CASE AS LONG CBMSG
        CASE %WM_INITDIALOG

        CASE %WM_NCACTIVATE
            STATIC hWndSaveFocus AS DWORD
            IF ISFALSE CBWPARAM THEN
                hWndSaveFocus = GetFocus()
            ELSEIF hWndSaveFocus THEN
                SetFocus(hWndSaveFocus)
                hWndSaveFocus = 0
            END IF

        CASE 889    'a new query session has been started
            htcp = FREEFILE
            TCP ACCEPT 2 AS htcp
            TCP NOTIFY htcp, RECV CLOSE TO CBHNDL AS 890
            SLEEP 500

        CASE 890    'the requesting packet has been received
            SELECT CASE CBLPARAM
                CASE 1  '%FD_READ
                    TCP RECV htcp, 512, buffer    'the incoming packet will never be more than 512 bytes
                    buffer = TRIM$(buffer)
                    SELECT CASE buffer
                        CASE "Return Status"
                            s = LastAct + $CRLF
                            IF LoggedIn THEN
                                s = s + "Logged in to Jiwa" + $CRLF
                            ELSE
                                IF ManualLogout THEN
                                    s = s + " Manually "
                                END IF
                                s = s + "Logged out of Jiwa" + $CRLF
                            END IF
                            s = s + "Current period start date " + CurrentMonth + $CRLF
                            s = s + LastOrd
                            TCP SEND htcp, s 'send the reply back
                        CASE "Log Out"
                            CALL DWORD VBAdd USING GiveAction(2)
                            TCP SEND htcp, "Done" 'send the reply back
                        CASE "Send Log"
                            CALL DWORD VBAdd USING GiveAction(1)
                            TCP SEND htcp, "Done" 'send the reply back
                        CASE "Shutdown"
                            CALL DWORD VBAdd USING GiveAction(3)
                            TCP SEND htcp, "Done" 'send the reply back
                        CASE ELSE
                            IF INSTR(buffer, "Log In") THEN
                                a = INSTR(buffer, "New Month")
                                IF a THEN
                                    CurrentMonth = TRIM$(RIGHT$(buffer, LEN(buffer) - a - 9))
                                    REDIM cfg(0)
                                    fi = FREEFILE
                                    OPEN "c:\jiwamcaord.cfg" FOR INPUT AS fi
                                    WHILE EOF(fi) = 0
                                        LINE INPUT #fi, cfg(UBOUND(cfg))
                                        a = INSTR(cfg(UBOUND(cfg)) , "=")
                                        IF a THEN
                                            s = UCASE$(TRIM$(LEFT$(cfg(UBOUND(cfg)) , a - 1)))
                                            IF TRIM$(s) = "PERIOD START" THEN
                                                cfg(UBOUND(cfg)) = "PERIOD START" + " = " + CurrentMonth
                                            END IF
                                        END IF
                                        REDIM PRESERVE cfg(UBOUND(cfg) + 1)
                                    WEND
                                    CLOSE fi
                                    fi = FREEFILE
                                    OPEN "c:\jiwamcaord.cfg" FOR OUTPUT AS fi
                                    FOR a = 0 TO UBOUND(cfg) - 1
                                        PRINT #fi, cfg(a)
                                    NEXT
                                    CLOSE fi
                                    CALL DWORD VBAdd USING GiveAction(5)
                                ELSE
                                    CALL DWORD VBAdd USING GiveAction(4)
                                END IF
                                TCP SEND htcp, "Done" 'send the reply back
                            END IF

                    END SELECT
                    SLEEP 500
                CASE &H20   'and close the session %FD_CLOSE
                    TCP CLOSE htcp
            END SELECT
        CASE %WM_COMMAND
            SELECT CASE AS LONG CBCTL
                CASE %Tmess

                CASE %Bqt
                    IF CBCTLMSG = %BN_CLICKED OR CBCTLMSG = 1 THEN
                        TCP CLOSE #2
                        DIALOG END CBHNDL
                    END IF

            END SELECT
    END SELECT
END FUNCTION

[Dan Gin zel]

Well, here's the latest.

I discovered that one of the third-party programs that I'll be working with already uses 34000 for UDP communications! Therefore the direction is now set!

Here is a very simple TCP server DLL that allows control of and reporting on a VB6 program. The VB6 program just calls StartTCP passing a Callback address. The StartTCP Sub just starts a MODELESS (most important for a TCP server) hidden Dialog, the TCP and returns to VB6. When the VB6 prog is closing down it just calls CloseTCP which closes the Dialog and TCP server.
External program (over Internet or LAN) simply connect to the TCP server and send a brief message. Depending on the message it either sends a control code back to the VB6 prog Callback or returns info to the caller.
The port number you use is your own choice, preferably not a commonly used one.

Well, that looks like as good of a starting point as any. I'll spend some time this weekend to digest it and reorganize it --that's how I learn how things work. I'll then rework it for UDP and use that as the basis for the final version. I do appreciate you taking the time to post the example as it will be most helpful!

Thank you to everyone for your comments and assistance!

Dan

[John Petty]

Hi Dan
Working with UDP is somewhat different as it is connectionless, which apart from meaning delivery is not guaranteed means you just can’t send a reply like the TCP server can. However it does give you the IP address of the sending computer so if you want to send information back then you just do a UDP Send. To illustrate here are some fragments from a private network DNS server I wrote a few years ago.

‘ union for converting long IP to dotted IP
UNION LtoB
    l AS LONG
    b(3) AS BYTE
END UNION

‘ set up the window to receive messages
    DIALOG SHOW MODELESS hdlg, CALL GotUdt 'create a window to receive messages
    UDP OPEN PORT 13000 AS #1           'open a udp port to receive registrations
    UDP NOTIFY #1, RECV TO hdlg AS 888  'and have it notify when a message is received

‘ receive a message and reset for next
CALLBACK FUNCTION GotUdt()
    SELECT CASE CBMSG
        CASE 888
            UDP RECV #1, FROM ip.l, pnumvar&, MyName$   'receive a registration
            'and extract the senders IP from the packet header and convert to dotted notation adding to registration string
            NewText$ = MyName$ + " " + FORMAT$(ip.b(0)) + "." + FORMAT$(ip.b(1)) + "." + FORMAT$(ip.b(2)) + "." + FORMAT$(ip.b(3))
            y& = INSTR(MyName$," on ")
            t$ = LEFT$(MyName$, y& - 1) 'extract the name from the string which also contains date etc
            l& = LEN(t$)
            FOR y& = 0 TO ccnt - 1
                IF LEFT$(comps(y&),l&) = t$ THEN EXIT FOR   'check if name already registered
                'note this test is case sensitive as it assumes you will never change the name
                'being transmitted by the registration program
            NEXT
            IF y& < ccnt THEN
                comps(y&) = newtext$    'yes so just replace current reg with new
            ELSE
                comps(ccnt) = newtext$  'no so create a new registration
                ccnt = ccnt + 1
                REDIM PRESERVE comps(ccnt)
            END IF
            LISTBOX RESET hdlg, 1
            FOR y& = 0 TO ccnt - 1
                LISTBOX ADD hdlg, 1, comps(y&)
            NEXT
            UDP CLOSE #1
            SLEEP 500
            UDP OPEN PORT 13000 AS #1
            UDP NOTIFY #1, RECV TO hdlg AS 888

‘*********** the sending program just sends it data at a regular period
    UDP OPEN AS #1
    EndlessLoop:
        Stext$ = compnme$ + " on " + DATE$ + " at " + TIME$ 
        “the sending IP number is by the name server
        'when it receives the packet
        UDP SEND #1, AT ip.l, 13000, stext$
	'note ip.l is a long not dotted format
        'I use port 13000, you can choose any port number that is not already used on the
        'computer running the name server, of course you need to set your name server
        'to receive on that port
        SLEEP tme&
    GOTO EndlessLoop
    UDP CLOSE #1
‘ *******************