cowboy:start_clear - Listen for connections using plain TCP


start_clear(Name          :: ranch:ref(),
            TransportOpts :: ranch_tcp:opts(),
            ProtocolOpts  :: opts())
    -> {ok, ListenerPid :: pid()}
     | {error, any()}

Start listening for connections over a clear TCP channel.

Both HTTP/1.1 and HTTP/2 are supported on this listener. HTTP/2 has two methods of establishing a connection over a clear TCP channel. Both the upgrade and the prior knowledge methods are supported.



The listener name is used to refer to this listener in future calls, for example when stopping it or when updating the routes defined.

It can be any Erlang term. An atom is generally good enough, for example api, my_app_clear or my_app_tls.


The transport options are where the TCP options, including the listener's port number, are defined. Transport options are provided as a list of keys and values, for example [{port, 8080}].

The available options are documented in the ranch_tcp(3) manual.


The protocol options are in a map containing all the options for the different protocols that may be involved when connecting to the listener, including HTTP/1.1 and HTTP/2.

The HTTP/1.1 options are documented in the cowboy_http(3) manual; and the HTTP/2 options in cowboy_http2(3).

Return value

An ok tuple is returned on success. It contains the pid of the top-level supervisor for the listener.

An error tuple is returned on error. The error reason may be any Erlang term.

A common error is eaddrinuse. It indicates that the port configured for Cowboy is already in use.


  • 2.0: HTTP/2 support added.
  • 2.0: Function introduced. Replaces cowboy:start_http/4.


Start a listener
Dispatch = cowboy_router:compile([
    {'_', [
        {"/", toppage_h, []}

{ok, _} = cowboy:start_clear(example, [{port, 8080}], #{
    env => #{dispatch => Dispatch}
Start a listener on a random port
Name = example,

{ok, _} = cowboy:start_clear(Name, [], #{
    env => #{dispatch => Dispatch}

Port = ranch:get_port(Name).

See also

cowboy(3), cowboy:start_tls(3), cowboy:stop_listener(3), ranch(3)

Cowboy 2.7 Function Reference


Version select

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