How test if an UDP client is alway online ?

How test if an UDP client is alway online ? an idea ?

One possible way:

Have the client send out and ACK every 2 seconds, and have the server show client online if the ACK is received.

Once server shows client online and doesn't get ACK within four seconds show Client NOT online. Adjust times to suit your purpose.

B3D Sample code:

;
; Sample UDP communications program (Client/Server same machine)
; --- Now with client heartbeat ---

; Author: W.Gray  Last updated: 1/5/4
; Comment: Free code no restrictions, use at your own risk.
;
; Instructions:
; Start program, select mode, your IP will be displayed, enter destination IP , type.

; Testing client and server on same machine, run server with 127.0.0.1, and run client with 127.0.0.1


Print "Sample UDP Communications"

; Ask for mode

Print "1-Server"
Print "2-Client"
Mode$=Input$(">")

Select Mode$
	Case "1"
	Udp_Port=4000 ; I/O Port
	Dest_Port=4001
	AppTitle "Server on UDP Port "+Str(Udp_Port)
	
	Case "2"
	Udp_Port=4001 ; I/O Port
	Dest_Port=4000
	AppTitle "Client on UDP Port "+Str(Udp_Port)
	
	Default 
	Udp_Port=4000 ; I/O Port
	Dest_Port=4001
	AppTitle "Server on UDP Port "+Str(Udp_Port)
End Select


; Display all local user IP's
;
Print "Local IPs:"
For i=1 To CountHostIPs(GetEnv("localhost"))
    Print DottedIP(HostIP(i))
Next

Print "Enter Destination IP#: xxx.xxx.xxx.xxx"
Dest_IP$=Input$(">")

; Convert to integer IP
IP= Int_IP(Dest_IP$)

Print
Print "Starting Chat <esc> to quit"

; Allocate ports, get stream id's
udp_stream=CreateUDPStream(Udp_Port) ; Read Stream


.loop
t1=t0
t0=MilliSecs()

Elapsed_Time=Elapsed_Time+(t0-t1)

; Poll Keyboard for Keypress.
byte1=GetKey()

; transmit each key press.
If byte1>0 Then
	; If 'Enter' pressed force new line locally, and send it.
    	If Byte1=13 Then 
        Print
	; put character in stream buffer.
        WriteByte(udp_stream,byte1)
	; send all characters in the stream buffer.
        SendUDPMsg udp_stream,IP,Dest_Port
    Else
	; Show character before we send it.
        Write Chr(Byte1)
	; put character in stream buffer.
        WriteByte(udp_stream,byte1)
	; send all characters in the stream buffer.
        SendUDPMsg udp_stream,IP,Dest_Port
    EndIf
EndIf

;Client Sends Heart Beat every 2 sec (2000ms)
If Elapsed_Time>2000 And mode$="2" Then 
	; Ack Character
	Byte1=6
	; put character in stream buffer.
    WriteByte(udp_stream,byte1)
	; send all characters in the stream buffer.
    SendUDPMsg udp_stream,IP,Dest_Port
	; reset time
	Elapsed_Time=0
EndIf

; Load UDP message into stream
IP_rd=RecvUDPMsg(udp_stream)

; Test for messages in stream
If IP_rd <> 0 Then    

;Get number of bytes in UDP stream
    Buflen=ReadAvail(udp_stream)
    If Buflen > 0 Then
    
; Get received character and print to display
        byte1=ReadByte(udp_stream)
		If byte1=6 Then
			If online=False Then
				AppTitle "Server on UDP Port "+Str(Udp_Port)+" Client Online"
				online=True
			EndIf
			Elapsed_Time=0
		Else
; Translate <enter> key    
	        If byte1=13 Then
	            Print
	        Else
	            Write Chr$(byte1)
	        EndIf
        EndIf
    EndIf
    
EndIf

; Look for <escape>
If KeyDown(1) Then
    Goto quit
EndIf

; Show client NOT online if no ack within 4 sec
If Elapsed_Time>4000 And mode$="1" And online=True Then
	AppTitle "Server on UDP Port "+Str(Udp_Port)
	online=False
	Elapsed_Time=0
EndIf

Goto loop

; Cleanup and terminate
.quit
CloseUDPStream udp_stream



;--------------------------------------
; FUNCTION: INT_IP(IP$)
; 
; Returns integer value of a IP Address string
; IP$ Format n.n.n.n

Function Int_IP(IP$)
a1=val(Left(IP$,Instr(IP$,".")-1)):IP$=Right(IP$,Len(IP$)-Instr(IP$,"."))
a2=val(Left(IP$,Instr(IP$,".")-1)):IP$=Right(IP$,Len(IP$)-Instr(IP$,"."))
a3=val(Left(IP$,Instr(IP$,".")-1)):IP$=Right(IP$,Len(IP$)-Instr(IP$,"."))
a4=val(IP$)
Return (a1 Shl 24) + (a2 Shl 16) + (a3 Shl 8 ) +a4
End Function


;--------------------------------------
; FUNCTION: VAL(STRING$)
; 
; Returns integer value of a string

Function val(String$) 
ac=String$
Return String$
End Function

Filax

Thanks very much for this really good example !