OPENHOST

The _OPENHOST function opens a Host which listens for new connections and returns a Host status handle.

Syntax: host_handle = _OPENHOST("TCP/IP:8080")

• Creates an ILLEGAL FUNCTION CALL if called with a string argument of the wrong syntax.
• The port used in the syntax example is 8080.
• Valid handles are usually negative number values.
• If the syntax is correct but they fail to begin/connect a handle of 0 is returned. * Always check if the handle returned is 0 (failed) before continuing.
• CLOSE host_handle closes the host. A failed handle value of 0 does not need to be closed.

Example: Chat program that attempts to connect as a Client. If not it attempts to become the Host.

PRINT "Mini Messenger"

LOCATE , , 1 ' display the print cursor for INKEY$

client = _OPENCLIENT("TCP/IP:7319:localhost") ' Attempt to connect to local host as a client

IF client THEN

PRINT "[connected to " + _CONNECTIONADDRESS(client) + "]"

_TITLE "Client - Mini Messenger"

INPUT "Enter your name: ", myname$

PRINT #client, myname$ + " connected!"

DO

GetMessage client

SendMessage myname$, mymessage$, client ' display current input on screen

_DELAY 0.01 ' reduce CPU usage

LOOP

ELSE ' "if client" alternative to open a new Host

PRINT "[No existing host found]"

host = _OPENHOST("TCP/IP:7319") ' no host found, so begin new host

IF host THEN

_TITLE "Host - Mini Messenger"

PRINT "[Beginning new host chat session!]"

DIM Chatters(1 to 1000) ' array to hold other client info

numclients = 0

client = _OPENCLIENT("TCP/IP:7319:localhost")

IF client = 0 THEN PRINT "ERROR: could not attach host's personal client to host!"

INPUT "Enter your name:", myname$

PRINT #client, myname$ + " connected!"

PRINT "[Chat session active!]"

DO ' host main loop

newclient = _OPENCONNECTION(host) ' receive any new connection

IF newclient THEN

numclients = numclients + 1

Chatters(numclients) = newclient

PRINT #Chatters(numclients),"Welcome!"

END IF

FOR i = 1 TO numclients ' distribute incoming messages to all clients

IF Chatters(i) THEN

INPUT #Chatters(i), message$

IF message$ <> "" THEN

FOR p = 1 TO numclients

IF Chatters(p) THEN PRINT #Chatters(p), message$

NEXT p

END IF

END IF

NEXT i

GetMessage client ' allow host to get messages and chat also

SendMessage myname$, mymessage$, client

_DELAY 0.01 ' reduce CPU usage

LOOP

END IF ' host

PRINT "ERROR: Could not begin new host!"

END IF ' if client from start

SLEEP

SYSTEM

'.................... END OF MAIN PROGRAM ................

SUB GetMessage (client) ' get & display any new message

INPUT #client, newmessage$

IF newmessage$ <> "" THEN

VIEW PRINT 1 TO 23

LOCATE 23,1

PRINT newmessage$

VIEW PRINT 1 TO 24

END IF

END SUB

SUB SendMessage (myname$, mymessage$, client) ' simple input handler

k$ = INKEY$$

IF LEN(k$) THEN

IF k$ = CHR$(8) AND LEN(mymessage$) <> 0 THEN

mymessage$ = LEFT$(mymessage$, LEN(mymessage$) - 1)

ELSE

IF LEN(k$) = 1 and ASC(k$) >= 32 THEN mymessage$ = mymessage$ + k$

END IF

END IF

LOCATE 24, 1: PRINT SPACE$(80); ' erase previous display

LOCATE 24, 1: PRINT myname$ + ": ";mymessage$;

IF k$ = CHR$(13) THEN ' [Enter] sends the message

IF mymessage$ = "" THEN SYSTEM ' [Enter] with no message ends program

PRINT #client, myname$ + ": " + mymessage$

mymessage$ = ""

END IF

IF k$ = CHR$(27) THEN SYSTEM ' [Esc] key ends program

END SUB

Explanation: The SendMessage SUB program controls the program exit unless both Client and Host fail. Entering no message and hitting [Enter] or pressing the [Esc]] key closes the program. Both SUB programs allow a Client or Host to communicate with others simply. ::INPUT # is used to read messages and PRINT # is used to send messages. The client handle value is used as the port number. Keep in mind that this is just an example. A lot could be added like recording IP addresses!

See also: _OPENCONNECTION, _OPENCLIENT, _CONNECTED, _CONNECTIONADDRESS

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