Datagram channels are a mild abstraction of UDP sockets. They are a disjoint type.
In the following descriptions, interface and host are strings, which may be IPv4 dotted-decimal addresses, IPv6 colon-hexadecimal addresses if supported by the operating system, or host names to be looked up according to whatever operating system conventions exist, if any. Appropriate strings may refer to broadcast or multicast addresses.
(make-datagram-channel [[interface] port])
Returns a new datagram channel suitable for sending and receiving datagrams. If port is omitted, the channel will receive datagrams that are sent to a unused port assigned by the operating system over any local interface. If port is present but interface is omitted, the channel will receive datagrams that are sent to port over any local interface. Otherwise, the channel will only receive datagrams sent to the specified interface and port. (Note that if there is exactly one argument, it is port, as this is the more common case.)
(make-output-only-datagram-channel)
Returns a new datagram channel only suitable for sending datagrams. It is not bound to any port.
(datagram-channel? obj)
Returns #t if obj is a datagram channel and #f otherwise.
(datagram-channel-interface channel)
Returns the interface on which channel receives datagrams, or #f if there is none. The value returned need not be the same as the value passed to make-i/o-datagram-channel.
(datagram-channel-port channel)
Returns the port number on which channel receives datagrams, or #f if there is none.
(datagram-channel-send-to channel host port blob [start [end]])
Send the portion of blob defined by start (inclusive) and end (exclusive) to the endpoint specified by host and port using channel. If end is omitted, it is the length of blob plus one; if start is omitted, it is 0. Returns undefined values.
(datagram-channel-receive-from channel blob [start [end]])
Receives a datagram from channel into the portion of blob defined by start (inclusive) and end (exclusive). If end is omitted, it is the length of blob plus one; if start is omitted, it is 0. Returns three values: the sending host, the sending port, and #t if the datagram was complete or #f if it was truncated. It is an error to invoke this procedure on an output-only datagram channel.
(datagram-channel-connect! channel host port)
Connects channel to a remote endpoint specified by host and port. Datagrams can be sent to this endpoint using datagram-channel-send, but it is still possible to send datagrams to other endpoints using datagram-channel-send-to. When connected, a datagram channel will receive datagrams only from the specified remote endpoint. Returns undefined values.
(datagram-channel-disconnect! channel)
Disconnects channel. Returns undefined values.
(datagram-channel-connected-host channel)
Returns the host to which channel is connected, or #f if there is none. The value returned need not be the same as the value passed to datagram-channel-connect!.
(datagram-channel-connected-port channel)
Returns the port to which channel is connected, or #f if there is none.
(datagram-channel-send channel blob [start [end]])
Send the portion of blob defined by start (inclusive) and end (exclusive) to the connected endpoint of channel. If end is omitted, it is the length of blob plus one; if start is omitted, it is 0. It is an error if channel is not connected. Returns undefined values.
These names are very verbose, but I couldn't think of a better term than datagram-channel, which is borrowed from java.nio.channels.DatagramChannel. This API is more powerful than Java's, though.
Should the end arguments be replaced by length arguments?
The name "blob" is subject to change.