Implementing a TCP socket channel

The base.Channel class provides methods to implement basic TCP client and server programs. Consider character set encodings when designing such programs: No implicit character set conversion is done by the runtime system. Both client and server must use the same character set and length semantics.

The following code example implements a client program connecting to a TCP port, using the openClientSocket() method:

MAIN
  DEFINE ch base.Channel,
         time DATETIME HOUR TO SECOND,
         data STRING
  LET ch = base.Channel.create()
  CALL ch.openClientSocket("localhost",99999,"u",3)
  CALL ch.writeLine("get_time")
  LET time = ch.readLine()
  DISPLAY "client 1: ", time
  CALL ch.writeLine("get_string")
  LET data = ch.readLine()
  DISPLAY "client 2: ", data
  CALL ch.writeLine("disconnect")
  CALL ch.close()
END MAIN

The next code example implements the server program that can be used with the above client program. The server program uses the openServerSocket() and readLine() methods to listen to a given TCP interface/port. Note that the connection with a client must be ended by sending an EOF character (ASCII 26) to the client, the next readLine() call will wait for a new client connection, or select a pending client connection:

MAIN
  DEFINE ch base.Channel,
         cmd, data STRING
  LET ch = base.Channel.create()
  DISPLAY "starting server..."
  CALL ch.openServerSocket(null, 99999, "u")
  WHILE TRUE
      LET cmd = ch.readLine()
      IF ch.isEof() THEN
        DISPLAY "Connection ended by client..."
        EXIT WHILE
      END IF
      DISPLAY "cmd: ", cmd
      IF cmd == "get_time" THEN
        CALL ch.writeLine(CURRENT HOUR TO SECOND)
      END IF
      IF cmd == "get_string" THEN
        LET data = "This is a string..."
        CALL ch.writeLine(data)
      END IF
      IF cmd == "disconnect" THEN
         CALL ch.writeLine(ASCII 26) -- EOF
      END IF
  END WHILE
  DISPLAY "end of server..."
END MAIN