14.3 Networking
14.3.1 TCP
14.3.2 UDP
On this page:
udp-open-socket
udp-bind!
udp-connect!
udp-send-to
udp-send
udp-send-to*
udp-send*
udp-send-to/ enable-break
udp-send/ enable-break
udp-receive!
udp-receive!*
udp-receive!/ enable-break
udp-close
udp?
udp-bound?
udp-connected?
udp-send-ready-evt
udp-receive-ready-evt
udp-send-to-evt
udp-send-evt
udp-receive!-evt
Version: 4.2.1
14.3.2 UDP

The bindings documented in this section are provided by the scheme/udp and scheme libraries, but not scheme/base.

For information about UDP in general, see TCP/IP Illustrated, Volume 1 by W. Richard Stevens.

(udp-open-socket [family-hostname    
  family-port-no])  udp?
  family-hostname : (or/c string? #f) = #f
  family-port-no : (or/c string? #f) = #f
Creates and returns a UDP socket to send and receive datagrams (broadcasting is allowed). Initially, the socket is not bound or connected to any address or port.

If family-hostname or family-port-no is not #f, then the socket’s protocol family is determined from these arguments. The socket is not bound to the hostname or port number. For example, the arguments might be the hostname and port to which messages will be sent through the socket, which ensures that the socket’s protocol family is consistent with the destination. Alternately, the arguments might be the same as for a future call to udp-bind!, which ensures that the socket’s protocol family is consistent with the binding. If neither family-hostname nor family-port-no is non-#f, then the socket’s protocol family is IPv4.

(udp-bind! udp-socket    
  hostname-string    
  port-no)  void?
  udp-socket : udp?
  hostname-string : (or/c string? #f)
  port-no : 
(and/c exact-nonnegative-integer?
       (integer-in 1 65535))
Binds an unbound udp-socket to the local port number port-no.

If hostname-string is #f, then the socket accepts connections to all of the listening machine’s IP addresses at port-no. Otherwise, the socket accepts connections only at the IP address associated with the given name. For example, providing "127.0.0.1" as hostname-string typically creates a listener that accepts only connections to "127.0.0.1" from the local machine.

A socket cannot receive datagrams until it is bound to a local address and port. If a socket is not bound before it is used with a sending procedure udp-send, udp-send-to, etc., the sending procedure binds the socket to a random local port. Similarly, if an event from udp-send-evt or udp-send-to-evt is chosen for a synchronization (see Events), the socket is bound; if the event is not chosen, the socket may or may not become bound.

The binding of a bound socket cannot be changed, with one exception: on some systems, if the socket is bound automatically when sending, if the socket is disconnected via udp-connect!, and if the socket is later used again in a send, then the later send may change the socket’s automatic binding.

If udp-socket is already bound or closed, the exn:fail:network exception is raised.

(udp-connect! udp-socket    
  hostname-string    
  port-no)  void?
  udp-socket : udp?
  hostname-string : (or/c string? #f)
  port-no : 
(or/c (and/c exact-nonnegative-integer?
             (integer-in 1 65535))
      #f)
Connects the socket to the indicated remote address and port if hostname-string is a string and port-no is an exact integer.

If hostname-string is #f, then port-no also must be #f, and the port is disconnected (if connected). If one of hostname-string or port-no is #f and the other is not, the exn:fail:contract exception is raised.

A connected socket can be used with udp-send (not udp-send-to), and it accepts datagrams only from the connected address and port. A socket need not be connected to receive datagrams. A socket can be connected, re-connected, and disconnected any number of times.

If udp-socket is closed, the exn:fail:network exception is raised.

(udp-send-to udp-socket    
  hostname    
  port-no    
  bstr    
  [start-pos    
  end-pos])  void
  udp-socket : udp?
  hostname : string?
  port-no : 
(and/c exact-nonnegative-integer?
       (integer-in 1 65535))
  bstr : bytes?
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Sends (subbytes bytes start-pos end-pos) as a datagram from the unconnected udp-socket to the socket at the remote machine hostname-address on the port port-no. The udp-socket need not be bound or connected; if it is not bound, udp-send-to binds it to a random local port. If the socket’s outgoing datagram queue is too full to support the send, udp-send-to blocks until the datagram can be queued.

If start-pos is greater than the length of bstr, or if end-pos is less than start-pos or greater than the length of bstr, the exn:fail:contract exception is raised.

If udp-socket is closed or connected, the exn:fail:network exception is raised.

(udp-send udp-socket bstr [start-pos end-pos])  void
  udp-socket : udp?
  bstr : bytes?
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Like udp-send-to, except that udp-socket must be connected, and the datagram goes to the connection target. If udp-socket is closed or unconnected, the exn:fail:network exception is raised.

(udp-send-to* udp-socket    
  hostname    
  port-no    
  bstr    
  [start-pos    
  end-pos])  boolean?
  udp-socket : udp?
  hostname : string?
  port-no : 
(and/c exact-nonnegative-integer?
       (integer-in 1 65535))
  bstr : bytes?
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Like udp-send-to, but never blocks; if the socket’s outgoing queue is too full to support the send, #f is returned, otherwise the datagram is queued and the result is #t.

(udp-send* udp-socket bstr [start-pos end-pos])  boolean?
  udp-socket : udp?
  bstr : bytes?
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Like udp-send, except that (like udp-send-to) it never blocks and returns #f or #t.

(udp-send-to/enable-break udp-socket    
  hostname    
  port-no    
  bstr    
  [start-pos    
  end-pos])  void
  udp-socket : udp?
  hostname : string?
  port-no : 
(and/c exact-nonnegative-integer?
       (integer-in 1 65535))
  bstr : bytes?
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Like udp-send-to, but breaking is enabled (see Breaks) while trying to send the datagram. If breaking is disabled when udp-send-to/enable-break is called, then either the datagram is sent or the exn:break exception is raised, but not both.

(udp-send/enable-break udp-socket    
  bstr    
  [start-pos    
  end-pos])  void
  udp-socket : udp?
  bstr : bytes?
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Like udp-send, except that breaks are enabled like udp-send-to/enable-break.

(udp-receive! udp-socket    
  bstr    
  [start-pos    
  end-pos])  
exact-nonnegative-integer?
string?
(integer-in 1 65535)
  udp-socket : udp?
  bstr : (and/c bytes? (not immutable?))
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Accepts up to end-pos-start-pos bytes of udp-socket’s next incoming datagram into bstr, writing the datagram bytes starting at position start-pos within bstr. The udp-socket must be bound to a local address and port (but need not be connected). If no incoming datagram is immediately available, udp-receive! blocks until one is available.

Three values are returned: the number of received bytes (between 0 and end-pos-start-pos, a hostname string indicating the source address of the datagram, and an integer indicating the source port of the datagram. If the received datagram is longer than end-pos-start-pos bytes, the remainder is discarded.

If start-pos is greater than the length of bstr, or if end-pos is less than start-pos or greater than the length of bstr, the exn:fail:contract exception is raised.

(udp-receive!* udp-socket 
  bstr 
  [start-pos 
  end-pos]) 
  
(or/c exact-nonnegative-integer? #f)
(or/c string? #f)
(or/c (integer-in 1 65535) #f)
  udp-socket : udp?
  bstr : (and/c bytes? (not immutable?))
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Like udp-receive!, except that it never blocks. If no datagram is available, the three result values are all #f.

(udp-receive!/enable-break udp-socket 
  bstr 
  [start-pos 
  end-pos]) 
  
exact-nonnegative-integer?
string?
(integer-in 1 65535)
  udp-socket : udp?
  bstr : (and/c bytes? (not immutable?))
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Like udp-receive!, but breaking is enabled (see Breaks) while trying to receive the datagram. If breaking is disabled when udp-receive!/enable-break is called, then either a datagram is received or the exn:break exception is raised, but not both.

(udp-close udp-socket)  void?
  udp-socket : udp?
Closes udp-socket, discarding unreceived datagrams. If the socket is already closed, the exn:fail:network exception is raised.

(udp? v)  boolean?
  v : any/c
Returns #t if v is a socket created by udp-open-socket, #f otherwise.

(udp-bound? udp-socket)  boolean?
  udp-socket : udp?
Returns #t if udp-socket is bound to a local address and port, #f otherwise.

(udp-connected? udp-socket)  boolean?
  udp-socket : udp?
Returns #t if udp-socket is connected to a remote address and port, #f otherwise.

(udp-send-ready-evt udp-socket)  evt?
  udp-socket : udp?
Returns a synchronizable event (see Events) that is in a blocking state when udp-send-to on udp-socket would block.

(udp-receive-ready-evt udp-socket)  evt?
  udp-socket : udp?
Returns a synchronizable event (see Events) that is in a blocking state when udp-receive! on udp-socket would block.

(udp-send-to-evt udp-socket    
  hostname    
  port-no    
  bstr    
  [start-pos    
  end-pos])  evt?
  udp-socket : udp?
  hostname : string?
  port-no : 
(and/c exact-nonnegative-integer?
       (integer-in 1 65535))
  bstr : bytes?
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Returns a synchronizable event. The event is in a blocking state when udp-send-to on udp-socket would block. Otherwise, if the event is chosen in a synchronization, data is sent as for (udp-send-to udp-socket hostname-address port-no bstr start-pos end-pos), and the synchronization result is #<void>. (No bytes are sent if the event is not chosen.)

(udp-send-evt udp-socket    
  bstr    
  [start-pos    
  end-pos])  evt?
  udp-socket : udp?
  bstr : bytes?
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Returns a synchronizable event. The event is in a blocking state when udp-send on udp-socket would block. Otherwise, if the event is chosen in a synchronization, data is sent as for (udp-send-to udp-socket bstr start-pos end-pos), and the synchronization result is #<void>. (No bytes are sent if the event is not chosen.) If udp-socket is closed or unconnected, the exn:fail:network exception is raised during a synchronization attempt.

(udp-receive!-evt udp-socket    
  bstr    
  [start-pos    
  end-pos])  evt?
  udp-socket : udp?
  bstr : (and/c bytes? (not immutable?))
  start-pos : exact-nonnegative-integer? = 0
  end-pos : exact-nonnegative-integer? = (bytes-length bstr)
Returns a synchronizable event. The event is in a blocking state when udp-receive on udp-socket would block. Otherwise, if the event is chosen in a synchronization, data is received into bstr as for (udp-receive! udp-socket bytes start-pos end-pos), and the synchronization result is a list of three values, corresponding to the three results from udp-receive!. (No bytes are received and the bstr content is not modified if the event is not chosen.)