cowboy_http2 - HTTP/2


The module cowboy_http2 implements HTTP/2 as a Ranch protocol.


opts() :: #{
    connection_type                => worker | supervisor,
    enable_connect_protocol        => boolean(),
    env                            => cowboy_middleware:env(),
    inactivity_timeout             => timeout(),
    initial_connection_window_size => 65535..16#7fffffff,
    initial_stream_window_size     => 0..16#7fffffff,
    max_concurrent_streams         => non_neg_integer() | infinity,
    max_decode_table_size          => non_neg_integer(),
    max_encode_table_size          => non_neg_integer(),
    max_frame_size_received        => 16384..16777215,
    max_frame_size_sent            => 16384..16777215 | infinity,
    middlewares                    => [module()],
    preface_timeout                => timeout(),
    settings_timeout               => timeout(),
    shutdown_timeout               => timeout(),
    stream_handlers                => [module()]

Configuration for the HTTP/2 protocol.

This configuration is passed to Cowboy when starting listeners using cowboy:start_clear/3 or cowboy:start_tls/3 functions.

It can be updated without restarting listeners using the Ranch functions ranch:get_protocol_options/1 and ranch:set_protocol_options/2.

The default value is given next to the option name:

connection_type (supervisor)

Whether the connection process also acts as a supervisor.

enable_connect_protocol (false)

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.

env (#{})

Middleware environment.

inactivity_timeout (300000)

Time in ms with nothing received at all before Cowboy closes the connection.

initial_connection_window_size (65535)

Initial window size for the connection. This is the total amount of data (from request bodies for example) that may be buffered by the connection across all streams before the user code explicitly requests it.

Note that this value cannot be lower than the default.

initial_stream_window_size (65535)

Initial window size for new streams. This is the total amount of data (from request bodies for example) that may be buffered by a single stream before the user code explicitly requests it.

max_concurrent_streams (infinity)

Maximum number of concurrent streams allowed on the connection.

max_decode_table_size (4096)

Maximum header table size used by the decoder. This is the value advertised to the client. The client can then choose a header table size equal or lower to the advertised value.

max_encode_table_size (4096)

Maximum header table size used by the encoder. The server will compare this value to what the client advertises and choose the smallest one as the encoder's header table size.

max_frame_size_received (16384)

Maximum size of the frames received by the server. This value is advertised to the remote endpoint which can then decide to use any value lower or equal for its frame sizes.

max_frame_size_sent (infinity)

Maximum size of the frames sent by the server. This option allows setting an upper limit to the frame sizes instead of blindly following the client's advertised maximum.

Note that actual frame sizes may be lower than the limit when there is not enough space left in the flow control window.

middlewares ([cowboy_router, cowboy_handler])

Middlewares to run for every request.

preface_timeout (5000)

Time in ms Cowboy is willing to wait for the connection preface.

settings_timeout (5000)

Time in ms Cowboy is willing to wait for a SETTINGS ack.

shutdown_timeout (5000)

Time in ms Cowboy will wait for child processes to shut down before killing them.

stream_handlers ([cowboy_stream_h])

Ordered list of stream handlers that will handle all stream events.


  • 2.4: Add the options initial_connection_window_size, initial_stream_window_size, max_concurrent_streams, max_decode_table_size, max_encode_table_size, max_frame_size_received, max_frame_size_sent and settings_timeout to configure HTTP/2 SETTINGS and related behavior.
  • 2.4: Add the experimental option enable_connect_protocol.
  • 2.0: Protocol introduced.

See also

cowboy(7), cowboy_http(3), cowboy_websocket(3)

Cowboy 2.5 Function Reference


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