### Parameters

`Conn : T`

### Signature

`type t`````
`type address``= Conn.Address.t```

The address of a service to which one can connect. E.g. `Host_and_port.t` is a reasonable choice when making a TCP connection.

`type conn``= Conn.t```

A connection, perhaps embellished with additional information upon connection.

`module Event : sig ... end`
`val create : server_name:string ‑> ?⁠on_event:(Event.t ‑> unit Async_kernel.Deferred.t) ‑> ?⁠retry_delay:(unit ‑> Core_kernel.Time_ns.Span.t) ‑> connect:(address ‑> conn Core_kernel.Or_error.t Async_kernel.Deferred.t) ‑> (unit ‑> address Core_kernel.Or_error.t Async_kernel.Deferred.t) ‑> 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 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.

`val connected : t ‑> conn Async_kernel.Deferred.t`

`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.

`val current_connection : t ‑> conn option`

The current connection, if any.

`close t` closes the current connection and stops it from trying to reconnect. After the deferred it returns becomes determined, the last connection has been closed and no others will be attempted.

Note: no `close` calls are ever generated internally in response to the connection being closed by the other side.

`include Closable with type t := t`
`type t`````

a connection type

`val close : t ‑> unit Async_kernel.Deferred.t`

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

`val is_closed : t ‑> bool`

`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.

`val close_finished : t ‑> unit Async_kernel.Deferred.t`

`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.