= gun_event(3)

== Name

gun_event - Events

== Description

The `gun_event` module provides the callback interface
and types for implementing event handlers.

== Callbacks

Event handlers implement the following interface.
Because types are tied to specific events, they
are documented alongside them. All event types
are exported and can be referred to as `gun_event:Type()`.

The events are ordered by the order they are likely
to be triggered, with the most frequent events listed
first.

=== init

[source,erlang]
----
init_event() :: #{
    owner := pid(),
    transport := tcp | tls,
    origin_scheme := binary(),
    origin_host := inet:hostname() | inet:ip_address(),
    origin_port := inet:port_number(),
    opts := gun:opts()
}

init(init_event(), State) -> State
----

Gun is initializing.

=== domain_lookup_start

[source,erlang]
----
domain_lookup_event() :: #{
    host := inet:hostname() | inet:ip_address(),
    port := inet:port_number(),
    tcp_opts := [gen_tcp:connect_option()],
    timeout := timeout(),
    lookup_info => gun_tcp:lookup_info(),
    error => any()
}

domain_lookup_start(domain_lookup_event(), State) -> State
----

Gun is starting to resolve the host address.

The `lookup_info` and `error` keys are never set
for this event.

=== domain_lookup_end

[source,erlang]
----
domain_lookup_end(domain_lookup_event(), State) -> State
----

Gun has finished resolving the host address.

The `lookup_info` key is only set when the lookup is
successful. The `error` key is set otherwise.

=== connect_start

[source,erlang]
----
connect_event() :: #{
    lookup_info := gun_tcp:lookup_info(),
    timeout := timeout(),
    socket => inet:socket(),
    protocol => http | http2 | socks | raw,
    error => any()
}

connect_start(connect_event(), State) -> State
----

Gun is starting to connect to the host address and port.

The `socket`, `protocol` and `error` keys are never set
for this event.

=== connect_end

[source,erlang]
----
connect_end(connect_event(), State) -> State
----

Gun has finished connecting to the host address and port.

The `socket` key is set on connect success. The `error`
key is set otherwise.

The `protocol` key is only set when the transport is
`tcp` and the connection is successful. The protocol
is only known in the `tls_handshake_end` event otherwise.

=== tls_handshake_start

[source,erlang]
----
tls_handshake_event() :: #{
    stream_ref => gun:stream_ref(),
    reply_to => pid(),
    socket := inet:socket() | ssl:sslsocket() | pid(), %% The socket before/after will be different.
    tls_opts := [ssl:tls_client_option()],
    timeout := timeout(),
    protocol => http | http2 | socks | raw,
    error => any()
}

tls_handshake_start(tls_handshake_event(), State) -> State
----

Gun has started a TLS handshake.

This and the `tls_handshake_end` event only occur when
connecting to a TLS server or when upgrading the connection
or a stream to use TLS, for example when using CONNECT or
when connecting to a secure SOCKS server.

The `stream_ref` and `reply_to` keys are only set when the
TLS handshake occurs as a result of a CONNECT request or
inside an existing CONNECT tunnel.

The `protocol` and `error` keys are never set for this event.

=== tls_handshake_end

[source,erlang]
----
tls_handshake_end(tls_handshake_event(), State) -> State
----

Gun has finished a TLS handshake.

The `protocol` key is set on TLS handshake success. The
`error` key is set otherwise.

=== request_start

[source,erlang]
----
request_start_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    function := headers | request | ws_upgrade | connect,
    method := iodata(),
    scheme => binary(),
    authority := iodata(),
    path => iodata(),
    headers := [{binary(), iodata()}]
}

request_start(request_start_event(), State) -> State
----

Gun is starting to send a request.

The `scheme` and `path` keys are never set when the `function`
is set to `connect`.

=== request_headers

[source,erlang]
----
request_headers(request_start_event(), State) -> State
----

Gun has finished sending the request headers.

=== request_end

[source,erlang]
----
request_end_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid()
}

request_end(request_end_event(), State) -> State
----

Gun has finished sending the request.

=== push_promise_start

[source,erlang]
----
push_promise_start_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid()
}

push_promise_start(push_promise_start_event(), State) -> State
----

Gun has begun receiving a promised request (server push).

=== push_promise_end

[source,erlang]
----
push_promise_end_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    promised_stream_ref => gun:stream_ref(),
    method := binary(),
    uri := binary(),
    headers := [{binary(), iodata()}]
}

push_promise_end(push_promise_end_event(), State) -> State
----

Gun has finished receiving a promised request (server push).
Promised requests never include a body.

Promised requests received during the graceful shutdown of the
connection get canceled immediately.

// @todo The cancel event should probably trigger as well.

=== response_start

[source,erlang]
----
response_start_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid()
}

response_start(response_start_event(), State) -> State
----

Gun has begun receiving a response.

=== response_inform

[source,erlang]
----
response_headers_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    status := non_neg_integer(),
    headers := [{binary(), binary()}]
}

response_inform(response_headers_event(), State) -> State
----

Gun has received an informational response (1xx status code).

A `status` with value 101 indicates that the response has
concluded as the stream will be upgraded to a new protocol.

=== response_headers

[source,erlang]
----
response_headers(response_headers_event(), State) -> State
----

Gun has finished receiving response headers.

=== response_trailers

[source,erlang]
----
response_trailers_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    headers := [{binary(), binary()}]
}

response_trailers(response_trailers_event(), State) -> State
----

Gun has received response trailers.

=== response_end

[source,erlang]
----
response_end_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid()
}

response_end(response_end_event(), State) -> State
----

Gun has finished receiving a response.

=== ws_upgrade

[source,erlang]
----
ws_upgrade_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    opts := gun:ws_opts()
}

ws_upgrade(ws_upgrade_event(), State) -> State
----

A Websocket upgrade was requested.

Success is indicated by a response (101 informational
if HTTP/1.1, 2xx if HTTP/2) followed by a `protocol_changed`
event.

=== ws_recv_frame_start

[source,erlang]
----
ws_recv_frame_start_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    frag_state := cow_ws:frag_state(),
    extensions := cow_ws:extensions()
}

ws_recv_frame_start(ws_recv_frame_start_event(), State) -> State
----

Gun has begun receiving a Websocket frame.

=== ws_recv_frame_header

[source,erlang]
----
ws_recv_frame_header_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    frag_state := cow_ws:frag_state(),
    extensions := cow_ws:extensions(),
    type := cow_ws:frame_type(),
    rsv := cow_ws:rsv(),
    len := non_neg_integer(),
    mask_key := cow_ws:mask_key()
}

ws_recv_frame_header(ws_recv_frame_header_event(), State) -> State
----

Gun has received the header part of a Websocket frame.

It will be immediately be followed by the frame's payload.

=== ws_recv_frame_end

[source,erlang]
----
ws_recv_frame_end_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    extensions := cow_ws:extensions(),
    close_code := undefined | cow_ws:close_code(),
    payload := binary()
}

ws_recv_frame_end(ws_recv_frame_end_event(), State) -> State
----

Gun has finished receiving a Websocket frame.

=== ws_send_frame_start

[source,erlang]
----
ws_send_frame_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    extensions := cow_ws:extensions(),
    frame := gun:ws_frame()
}

ws_send_frame_start(ws_send_frame_event(), State) -> State
----

Gun has started sending a Websocket frame.

=== ws_send_frame_end

[source,erlang]
----
ws_send_frame_end(ws_send_frame_event(), State) -> State
----

Gun has finished sending a Websocket frame.

=== protocol_changed

[source,erlang]
----
protocol_changed_event() :: #{
    stream_ref := gun:stream_ref(),
    protocol := http | http2 | socks | raw | ws
}

protocol_changed(protocol_changed_event(), State) -> State
----

The protocol has changed for either the entire Gun connection
or for a specific stream.

The `stream_ref` key is only set when the protocol has
changed for a specific stream or inside a CONNECT tunnel.

This event occurs during successful Websocket upgrades,
as a result of successful CONNECT requests or after a
SOCKS tunnel was successfully established.

=== origin_changed

[source,erlang]
----
origin_changed_event() :: #{
    stream_ref => gun:stream_ref(),
    type := connect | socks5,
    origin_scheme := binary(),
    origin_host := inet:hostname() | inet:ip_address(),
    origin_port := inet:port_number()
}

origin_changed(origin_changed_event(), State) -> State
----

The origin server has changed for either the Gun connection
or for a specific stream.

The `stream_ref` key is only set when the origin has
changed for a specific stream or inside a CONNECT tunnel.

=== cancel

[source,erlang]
----
cancel_event() :: #{
    stream_ref := gun:stream_ref(),
    reply_to := pid(),
    endpoint := local | remote,
    reason := atom()
}

cancel(cancel_event(), State) -> State
----

A stream has been canceled.

HTTP/1.1 streams can't be canceled at the protocol level. In
this case Gun will silence the stream for the user but events
may still occur.

HTTP/2 streams can be canceled both by the client and the
server. Events may still occur for a short time after the
stream has been canceled.

=== disconnect

[source,erlang]
----
disconnect_event() :: #{
    reason := normal | closed | {error, any()}
}

disconnect(disconnect_event(), State) -> State
----

Gun has been disconnected from the server.

=== terminate

[source,erlang]
----
terminate_event() :: #{
    state := not_connected
        | domain_lookup | connecting | initial_tls_handshake | tls_handshake
        | connected | connected_data_only | connected_ws_only,
    reason := normal | shutdown | {shutdown, any()} | any()
}

terminate(terminate_event(), State) -> State
----

Gun is terminating.

== Changelog

* *2.0*: Module introduced.

== See also

link:man:gun(7)[gun(7)],
link:man:gun(3)[gun(3)]