@callback chunk(payload(), body :: Plug.Conn.body()) ::
  :ok | {:ok, sent_body :: binary(), payload()} | {:error, term()}

Sends a chunk in the chunked response.

If the request has method "HEAD", the adapter should not send the response to the client.

Webservers are advised to return :ok and not modify any further state for each chunk. However, the test implementation returns the actual body and payload so it can be used during testing.

@callback get_http_protocol(payload()) :: http_protocol()

Returns the HTTP protocol and its version.

@callback get_peer_data(payload()) :: peer_data()

Returns peer information such as the address, port and ssl cert.

@callback inform(payload(), status :: Plug.Conn.status(), headers :: Keyword.t()) ::
  :ok | {:error, term()}

Send an informational response to the client.

If the adapter does not support inform, then {:error, :not_supported} should be returned.

@callback push(payload(), path :: String.t(), headers :: Keyword.t()) ::
  :ok | {:error, term()}

Push a resource to the client.

If the adapter does not support server push then {:error, :not_supported} should be returned.

@callback read_req_body(payload(), options :: Keyword.t()) ::
  {:ok, data :: binary(), payload()}
  | {:more, data :: binary(), payload()}
  | {:error, term()}

Reads the request body.

Read the docs in Plug.Conn.read_body/2 for the supported options and expected behaviour.

@callback send_chunked(
  payload(),
  status :: Plug.Conn.status(),
  headers :: Plug.Conn.headers()
) ::
  {:ok, sent_body :: binary() | nil, payload()}

Sends the given status, headers as the beginning of a chunked response to the client.

Webservers are advised to return nil as the sent_body, as the body can no longer be manipulated. However, the test implementation returns the actual body so it can be used during testing.

@callback send_file(
  payload(),
  status :: Plug.Conn.status(),
  headers :: Plug.Conn.headers(),
  file :: binary(),
  offset :: integer(),
  length :: integer() | :all
) :: {:ok, sent_body :: binary() | nil, payload()}

Sends the given status, headers and file as a response back to the client.

If the request has method "HEAD", the adapter should not send the response to the client.

Webservers are advised to return nil as the sent_body, as the body can no longer be manipulated. However, the test implementation returns the actual body so it can be used during testing.

@callback send_resp(
  payload(),
  status :: Plug.Conn.status(),
  headers :: Plug.Conn.headers(),
  body :: Plug.Conn.body()
) :: {:ok, sent_body :: binary() | nil, payload()}

Sends the given status, headers and body as a response back to the client.

If the request has method "HEAD", the adapter should not send the response to the client.

Webservers are advised to return nil as the sent_body, as the body can no longer be manipulated. However, the test implementation returns the actual body so it can be used during testing.