Module Tcp.Keepalive

TCP keepalives.

A TCP implementation may send "keep-alives" (empty TCP ACKs with the sequence number set to one less than the current sequence number for the connection) in order to provoke the peer to respond with an ACK of the current sequence number. If the peer doesn't recognise the connection (e.g. because the connection state has been dropped) then it will return a RST; if the peer (or the network in-between) fails to respond to a configured number of repeated probes then the connection is assumed to be lost.

type action = [
  1. | `SendProbe
    (*

    we should send a keep-alive now

    *)
  2. | `Wait of Duration.t
    (*

    sleep for a given number of nanoseconds

    *)
  3. | `Close
    (*

    connection should be closed

    *)
]

An I/O action to perform

type state

State of a current connection

val alive : state

An alive connection

val next : configuration:Tcpip.Tcp.Keepalive.t -> ns:int64 -> state -> action * state

next ~configuration ~ns state returns the action we should take given that we last received a packet ns nanoseconds ago and the new state of the connection

type t

A keep-alive timer

val create : Tcpip.Tcp.Keepalive.t -> ([ `SendProbe | `Close ] -> unit Lwt.t) -> t

create configuration f clock returns a keep-alive timer which will call f in future depending on both the configuration and any calls to refresh

val refresh : t -> unit

refresh t marks the connection t as alive. This should be called when packets are received.