# `Broadway.Acknowledger`
[🔗](https://github.com/dashbitco/broadway/blob/v1.3.0/lib/broadway/acknowledger.ex#L1)

A behaviour used to acknowledge that the received messages
were successfully processed or failed.

When implementing a new connector for Broadway, you should
implement this behaviour and consider how the technology
you're working with handles message acknowledgement.

The `c:ack/3` callback must be implemented in order to notify
the origin of the data that a message can be safely removed
after been successfully processed and published. In case of
failed messages or messages without acknowledgement, depending
on the technology chosen, the messages can be either moved back
in the queue or, alternatively, moved to a *dead-letter queue*.

# `ack`

```elixir
@callback ack(
  ack_ref :: term(),
  successful :: [Broadway.Message.t()],
  failed :: [Broadway.Message.t()]
) ::
  :ok
```

Invoked to acknowledge successful and failed messages.

  * `ack_ref` is a term that uniquely identifies how messages
    should be grouped and sent for acknowledgement. Imagine
    you have a scenario where messages are coming from
    different producers. Broadway will use this information
    to correctly identify the acknowledger and pass it among
    with the messages so you can properly communicate with
    the source of the data for acknowledgement. `ack_ref` is
    part of `t:Broadway.Message.acknowledger/0`.

  * `successful` is the list of messages that were
    successfully processed and published.

  * `failed` is the list of messages that, for some reason,
    could not be processed or published.

# `configure`
*optional* 

```elixir
@callback configure(ack_ref :: term(), ack_data :: term(), options :: keyword()) ::
  {:ok, new_ack_data :: term()}
```

Configures the acknowledger with new `options`.

Every acknowledger can decide how to incorporate the given `options` into its
`ack_data`. The `ack_data` is the current acknowledger's data. The return value
of this function is `{:ok, new_ack_data}` where `new_ack_data` is the updated
data for the acknowledger.

Note that `options` are different for every acknowledger, as the acknowledger
is what specifies what are the supported options. Check the documentation for the
acknowledger you're using to see the supported options.

`ack_ref` and `ack_data` are part of `t:Broadway.Message.acknowledger/0`.

---

*Consult [api-reference.md](api-reference.md) for complete listing*