gen_udp_sketch

License: MIT

This is a sketch of a simple generic Erlang UDP listener. It’s used as follows:

{ok, Pid} = gus:start_link(Opts).

Where Opts are:

• {module, Module} - A module implementing gus_handle_msg/5 that accepts
  the following arguments:
  • Ref - detailed below
  • Socket - gen_udp socket
  • LocalAddr - a tuple pair of the local address and port
  • RemoteAddr - a tuple pair of the remote address and port
  • Msg - a binary payload
• {ref, Ref} - Ref will be passed verbatim to the callback outlined above
• {payload_min, N} - Minimum useful payload size
• {payload_max, N} - Maximum useful payload size
• {worker_count, N} - Number of workers to process requests
• {worker_queue_max, N} - Maximum number of messages to queue with a worker
• {listener_count, N} - Number of sockets to open if the kernel supports[1]
  balancing between multiple sockets.
• {ip, IP} - IP to listen on
• {port, N} - Port to listen on
• {active, once | true | {N, once | true} | N}
  • once - listener(s) should accept one datagram at a time.
    (inet:setopts(S,[{active,once}]).)
  • true - listener(s) will set the socket into active mode until a message
    is received, then put it into passive mode until the mailbox is drained of
    datagrams.
    (inet:setopts(S,[{active,true}]) -> inet:setopts(S,[{active,once}]).)
  • {N, once | true} - if {active,N} is available[2], set the socket to
    receive up to N datagrams, process those datagrams, then set the option
    again. Falls back to once or true if {active,N} is unavailable.
    (inet:setopts(S,[{active,N}]).)
  • N - same behaviour as previous option with no fallback.

See gus.erl for defaults.

Example echo server:

gus:start_link([{module,gus_echo},{ip,{127,0,0,1}},{port,5030}]).

1: At the time of writing, that’s Linux 3.9 or later only and Dragonfly, but
I’ve only added support for Linux. The FreeBSD networking folks seem to
think it’s a good idea but have not implemented it yet.

2: https://github.com/erlang/otp/pull/66