14.3.2 UDP
For information about UDP in general, see TCP/IP Illustrated,
Volume 1 by W. Richard Stevens.
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.
Binds an unbound
udp-socket to the local port number
port-no. If
port-no is 0 the
udp-socket is
bound to an ephemeral port, which can be determined by calling
udp-addresses.
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.
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.
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.
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.
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.
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.
Like
udp-receive!, except that it never blocks. If no
datagram is available, the three result values are all
#f.
Closes
udp-socket, discarding unreceived datagrams. If the
socket is already closed, the
exn:fail:network exception is raised.
Returns #t if udp-socket is bound to a local address
and port, #f otherwise.
Returns #t if udp-socket is connected to a remote
address and port, #f otherwise.
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.)
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.
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.)
Returns two strings when
port-numbers? is
#f (the
default). The first string is the Internet address for the local
machine a viewed by the given
UDP socket’s connection. (For most
machines, the answer corresponds to the current machine’s only
Internet address, but when a machine serves multiple addresses, the
result is connection-specific.) The second string is the Internet
address for the other end of the connection.
If port-numbers? is true, then four results are returned: a
string for the local machine’s address, an exact integer between
1 and 65535 for the local machine’s port number, a
string for the remote machine’s address, and an exact integer between
1 and 65535 for the remote machine’s port number.
If the given port has been closed, the exn:fail:network exception is raised.