package async_kernel

A connection, perhaps embellished with additional information upon connection.

The error type of the provided connect function. Use S if this is going to be Error.t

create ~server_name ~on_event ~retry_delay get_address returns a persistent connection to a server whose host and port are obtained via get_address every time we try to connect. For example, get_address might look up a server's host and port in catalog at a particular path to which multiple redundant copies of a service are publishing their location. If one copy dies, we get the address of the another one when looking up the address afterwards.

All connection events (see the type above) are passed to the on_event callback, if given. When this callback becomes determined, we move on to the next step in our connection attempt (e.g. we won't actually attempt to connect until on_event Attempting_to_connect is finished). Note that on_event Disconnected will only be called once on_event (Connected conn) finishes even if the connection goes down during that callback.

`Failed_to_connect error and `Obtained_address addr events are only reported if they are distinct from the most recent event of the same type that has taken place since the most recent `Attempting_to_connect event.

Connection is by default retried after Time.Span.randomize ~percent:(Percent.of_mult 0.3) (retry_delay ()). The default for retry_delay is const (sec 10.). Note that what this retry delay actually throttles is the delay between two connection attempts, so when a long-lived connection dies, connection is usually immediately retried, and if that failed, wait for another retry delay and retry.

The random_state and time_source arguments are there to make persistent connection code more deterministically testable. They default to `State Random.State.default and Time_source.wall_clock (), respectively. If random_state is set to `Non_random, retry_delay will be used directly.

connected returns the first available connection from the time it is called. When currently connected, the returned deferred is already determined. If closed has been called, then the returned deferred is never determined.

event returns a bus which is written to whenever an event happens. Since the 'address used in create is not exposed as a parameter of the t type, we replace it with ().

connected_or_failed_to_connect is immediately determined as Ok _ if t is already connected. Otherwise it becomes determined the next time t becomes connected or fails to connect or when t is closed.

The current connection, if any.

close t closes the connection. The returned deferred becomes determined once any resources needed to maintain the connection have been released.

is_closed t returns true if close has ever been called (even if the returned deferred has not yet been fulfilled).

Note that some modules implementing Closable may call close internally upon noticing that the connection was closed by the other side. The interface of such a module ought to say that this is the case.

close_finished t becomes determined at the same time as the result of the first call to close. close_finished differs from close in that it does not have the side effect of initiating a close.

close_when_current_connection_is_closed t causes the persistent connection to not reconnect if the current connection closes or if it is not currently connected. It does not close any active connection.