Cowmachine

Webmachine for Zotonic and Cowboy

This is an adaptation of https://github.com/webmachine/webmachine for the Cowboy web server.

Cowmachine is a request handler for Cowboy.

Main differences with Basho’s Webmachine are:

• Use cowboy instead of mochiweb for the http server
• Separate dispatching
• Simplified callbacks
• Single process/4 callback for all http methods
• Caching of some callbacks (like modified)
• More streaming options for returned data
• Better support for range requests

Installation

Cowmachine is at Hex, in your rebar.config file use:

{deps, [
    cowmachine
]}.

You can also use the direct Git url and use the development version:

{deps, [
    {cowmachine, {git, "https://github.com/zotonic/cowmachine.git", {branch, "master"}}}
]}.

Calling Cowmachine

Cowmachine can be called from your Cowboy middleware:

-spec execute(Req, Env) -> {ok, Req, Env} | {stop, Req}
    when Req::cowboy_req:req(), Env::cowboy_middleware:env().
execute(Req, Env) ->
    % Replace below with your own controller module and optionally wrap
    % the request in your own request-context record or map.
    EnvController = Env#{
        cowmachine_controller => mycontroller
    },
    RequestContext = cowmachine_req:init_context(Req, EnvController, #{}),
    % Set options for the cowmachine
    Options = #{
        on_welformed =>
            fun(Ctx) ->
                % Perform anything after well-formedness check of your request
                % Examples are parsing the query args, or authentication
            end
    },
    % Handle the request, returns updated Req and Env for next Cowboy middleware
    cowmachine:request(RequestContext, Options).

Or just use the default Cowmachine middleware:

    #{
        middlewares => [
            % ... add your dispatcher middlware
            cowmachine
        ],
        request_timeout => 60000,
        env => #{
            % If no dispatcher, default to `mycontroller` as the cowmachine
            % controller.
            cowmachine_controller => mycontroller
        }
    }.

Dispatching

You can use the Zotonic Dispatch Compiler to match your controller paths against the request.

Controller

The controller provides the callbacks to handle the request.

The controller is an Erlang module implementing callback functions, only functions that return some non-default value need to be implemented.

For the controller callbacks and more documentation, check the wiki pages.