Sockets

STK defines sockets, on systems which support them, as first class objects. Sockets permits processes to communicate even if they are on different machines. Sockets are useful for creating client-server applications.





`=̀13`(ndexfile(index-entry "make-client-socket" "tt" main )make-client-sockethostname port-number)
procedure
ndexfile(index-entry "make-client-socket" "tt" aux )make-client-socket returns a new socket object. This socket establishes a link between the running application listening on port port-number of hostname.





`=̀13`(ndexfile(index-entry "socket?" "tt" main )socket?socket)
procedure
Returns #t if socket is a socket, otherwise returns #f.





`=̀13`(ndexfile(index-entry "socket-host-name" "tt" main )socket-host-namesocket)
procedure
Returns a string which contains the name of the distant host attached to socket. If socket has been created with ndexfile(index-entry "make-client-socket" "tt" aux )make-client-socket this procedure returns the official name of the distant machine used for connection. If socket has been created with ndexfile(index-entry "make-server-socket" "tt" aux )make-server-socket, this function returns the official name of the client connected to the socket. If no client has used yet the socket, this function returns #f.





`=̀13`(ndexfile(index-entry "socket-host-address" "tt" main )socket-host-addresssocket)
procedure
Returns a string which contains the IPndexfile(index-entry "IP number" "rm" main ) number of the distant host attached to socket. If socket has been created with ndexfile(index-entry "make-client-socket" "tt" aux )make-client-socket this procedure returns the IP number of the distant machine used for connection. If socket has been created with ndexfile(index-entry "make-server-socket" "tt" aux )make-server-socket, this function returns the address of the client connected to the socket. If no client has used yet the socket, this function returns #f.





`=̀13`(ndexfile(index-entry "socket-local-address" "tt" main )socket-local-addresssocket)
procedure
Returns a string which contains the IPndexfile(index-entry "IP number" "rm" main ) number of the local host attached to socket.





`=̀13`(ndexfile(index-entry "socket-port-number" "tt" main )socket-port-numbersocket)
procedure
Returns the integer number of the port used for socket.





`=̀13`(ndexfile(index-entry "socket-input" "tt" main )socket-inputsocket)
procedure
`=̀13`(ndexfile(index-entry "socket-output" "tt" main )socket-outputsocket)
procedure
Returns the file port associated for reading or writing with the program connected with socket. If no connection has already been established, these functions return #f.

The following example shows how to make a client socket. Here we create a socket on port 13 of the machine ``kaolin.unice.fr''4: $\Longrightarrow$
$\Longrightarrow$ unspecified error makeotherˆ`=̀13`


          gobblecr(let ((s (make-client-socket "kaolin.unice.fr" 13)))  (format #t  "Time is: ~A\n" (read-line (socket-input s)))  (socket-shutdown  s))





`=̀13`(ndexfile(index-entry "make-server-socket" "tt" main )make-server-socket)
procedure
`=̀13`(ndexfile(index-entry "make-server-socket" "tt" main )make-server-socketport-number)
procedure
ndexfile(index-entry "make-server-socket" "tt" aux )make-server-socket returns a new socket object. If port-number is specified, the socket is listening on the specified port; otherwise, the communication port is choosen by the system.





`=̀13`(ndexfile(index-entry "socket-accept-connection" "tt" main )socket-accept-connectionsocket)
procedure
ndexfile(index-entry "socket-accept-connection" "tt" aux )socket-accept-connection waits for a client connection on the given socket. If no client is already waiting for a connection, this procedure blocks its caller; otherwise, the first connection request on the queue of pending connections is connected to socket. This procedure must be called on a server socket created with ndexfile(index-entry "make-server-socket" "tt" aux )make-server-socket. The result of ndexfile(index-entry "socket-accept-connection" "tt" aux )socket-accept-connection is undefined.

The following exemple is a simple server which waits for a connection on the port 12345. Once the connection with the distant program is established, we read a line on the input port associated to the socket and we write the length of this line on its output port. $\Longrightarrow$
$\Longrightarrow$ unspecified error makeotherˆ`=̀13`


          gobblecr(let ((s (make-server-socket 1234)))  (socket-accept-connection s)  (let ((l (read-line (socket-input s))))    (format (socket-output s) "Length is: ~A\n" (string-length l))    (flush (socket-output s)))  (socket-shutdown s))





`=̀13`(ndexfile(index-entry "socket-shutdown" "tt" main )socket-shutdownsocket)
procedure
`=̀13`(ndexfile(index-entry "socket-shutdown" "tt" main )socket-shutdownsocket close)
procedure
ndexfile(index-entry "Socket-shutdown" "tt" aux )Socket-shutdown shutdowns the connection associated to socket. Close is a boolean; it indicates if the socket must be close or not, when the connection is dstroyed. Closing the socket forbids further connections on the same port with the ndexfile(index-entry "socket-accept-connection" "tt" aux )socket-accept-connection procedure. Omitting a value for close implies the closing of socket. The result of ndexfile(index-entry "socket-shutdown" "tt" aux )socket-shutdown is undefined.

The following example shows a simple server: when there is a new connection on the port number 1234, the server displays the first line sent to it by the client, discards the others and go back waiting for further client connections. $\Longrightarrow$
$\Longrightarrow$ unspecified error makeotherˆ`=̀13`


          gobblecr(let ((s (make-server-socket 1234)))  (let loop ()    (socket-accept-connection s)    (format #t "I've read: ~A\n" (read-line (socket-input s)))    (socket-shutdown s #f)    (loop)))





`=̀13`(ndexfile(index-entry "socket-down?" "tt" main )socket-down?socket)
procedure
Returns #t if socket has been previously closed with ndexfile(index-entry "socket-shutdown" "tt" aux )socket-shutdown. It returns #f otherwise.





`=̀13`(ndexfile(index-entry "socket-dup" "tt" main )socket-dupsocket)
procedure
Returns a copy of socket. The original and the copy socket can be used interchangeably. However, if a new connection is accepted on one socket, the characters exchanged on this socket are not visible on the other socket. Duplicating a socket is useful when a server must accept multiple simultaneous connections. The following example creates a server listening on port 1234. This server is duplicated and, once two clients are present, a message is sent on both connections. $\Longrightarrow$
$\Longrightarrow$ unspecified error makeotherˆ`=̀13`


          gobblecr(define s1 (make-server-socket 1234))(define s2 (socket-dup s1))(socket-accept-connection s1)(socket-accept-connection s2);; blocks until two clients are present(display "Hello,\n" (socket-output s1))(display "world\n"  (socket-output s2))(flush (socket-output s1))(flush (socket-output s2))





`=̀13`(ndexfile(index-entry "when-socket-ready" "tt" main )when-socket-readysocket handler)
procedure
`=̀13`(ndexfile(index-entry "when-socket-ready" "tt" main )when-socket-readysocket)
procedure
Defines a handler for socket. The handler is a thumk which is executed when a connection is available on socket. If the special value #f is provided as handler, the current handler for socket is deleted. If a handler is provided, the value returned by ndexfile(index-entry "when-socket-ready" "tt" aux )when-socket-ready is undefined. Otherwise, it returns the handler currently associated to socket.

This procedure, in conjonction with ndexfile(index-entry "socket-dup" "tt" aux )socket-dup permits to build multiple-clients servers which work asynchronously. Such a server is shown below. $\Longrightarrow$
$\Longrightarrow$ unspecified error makeotherˆ`=̀13`


          gobblecr(define p (make-server-socket 1234))(when-socket-ready p                   (let ((count 0))                    (lambda ()                      (set! count (+ count 1))                      (register-connection (socket-dup p) count))))

(define register-connection (let ((sockets '())) (lambda (s cnt) ;; Accept connection (socket-accept-connection s) ;; Save socket somewhere to avoid GC problems (set! sockets (cons s sockets)) ;; Create a handler for reading inputs from this new connection (let ((in (socket-input s)) (out (socket-output s))) (when-port-readable in (lambda () (let ((l (read-line in))) (if (eof-object? l) ;; delete current handler (when-port-readable in #f) ;; Just write the line read on the socket (begin (format out "On #~A –> ~A\n" cnt l) (flush out))))))))))