Graceful shutdown

Note: This commit makes cowboy depend on cowlib master.

Graceful shutdown for HTTP/2:

1. A GOAWAY frame with the last stream id set to 2^31-1 is sent and a
   timer is started (goaway_initial_timeout, default 1000ms), to wait
   for any in-flight requests sent by the client, and the status is set
   to 'closing_initiated'. If the client responds with GOAWAY and closes
   the connection, we're done.
2. A second GOAWAY frame is sent with the actual last stream id and the
   status is set to 'closing'. If no streams exist, the connection
   terminates. Otherwise a second timer (goaway_complete_timeout,
   default 3000ms) is started, to wait for the streams to complete. New
   streams are not accepted when status is 'closing'.
3. If all streams haven't completed after the second timeout, the
   connection is forcefully terminated.

Graceful shutdown for HTTP/1.x:

1. If a request is currently being handled, it is waited for and the
   response is sent back to the client with the header "Connection:
   close". Then, the connection is closed.
2. If the current request handler is not finished within the time
   configured in transport option 'shutdown' (default 5000ms), the
   connection process is killed by its supervisor (ranch).

Implemented for HTTP/1.x and HTTP/2 in the following scenarios:

* When receiving exit signal 'shutdown' from the supervisor (e.g. when
  cowboy:stop_listener/3 is called).
* When a connection process is requested to terminate using
  sys:terminate/2,3.

LH: Edited tests a bit and added todos for useful tests to add.

1 files changed, 12 insertions, 0 deletions

diff --git a/doc/src/manual/cowboy_http2.asciidoc b/doc/src/manual/cowboy_http2.asciidoc
index c61bfe6..de632be 100644
--- a/doc/src/manual/cowboy_http2.asciidoc
+++ b/doc/src/manual/cowboy_http2.asciidoc
@@ -22,6 +22,8 @@ opts() :: #{
     connection_window_margin_size  => 0..16#7fffffff,
     connection_window_update_threshold => 0..16#7fffffff,
     enable_connect_protocol        => boolean(),
+    goaway_initial_timeout         => timeout(),
+    goaway_complete_timeout        => timeout(),
     idle_timeout                   => timeout(),
     inactivity_timeout             => timeout(),
     initial_connection_window_size => 65535..16#7fffffff,
@@ -92,6 +94,16 @@ Whether to enable the extended CONNECT method to allow
 protocols like Websocket to be used over an HTTP/2 stream.
 This option is experimental and disabled by default.
 
+goaway_initial_timeout (1000)::
+
+Time in ms to wait for any in-flight stream creations before stopping to accept
+new streams on an existing connection during a graceful shutdown.
+
+goaway_complete_timeout (3000)::
+
+Time in ms to wait for ongoing streams to complete before closing the connection
+during a graceful shutdown.
+
 idle_timeout (60000)::
 
 Time in ms with no data received before Cowboy closes the connection.