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Cowboy routes on steroids!

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If you find any bugs or have a problem while using this library, please open an issue in this repo (or a pull request 😄).

And you can check out all of our open-source projects at

Why Cowboy Trails?

Cowboy-Trails enables you to:

  • add information to cowboy routes, which can later be used to interact with the server in a higher abstraction level,
  • define the server routes directly within the module that implements them.

How to Use it?

The most common use case for cowboy_trails is to compile cowboy routes.

Normally with cowboy you compile routes in the following way:

Routes = [{'_',
           [ {"/resource1", resource1_handler, []}
           , {"/resource2/[:id]", resource2_handler, []}

Trails is fully compatible with cowboy routes, so you can pass the same routes in order to be processed by Trails:


So far it seems like there's no difference, right? But most of the time, with cowboy, you usually work with only a single host, but you're required to keep defining the host parameter within the routes ([{'_', [...]}]).

Well, with Trails you have another useful function to compile single host routes:

%% You only define the routes/paths
Routes = [ {"/resource1", resource1_handler, []}
         , {"/resource2/[:id]", resource2_handler, []}

Now, let's suppose you want to add metadata to cowboy routes related with the semantics of each HTTP method.

You'd do something like:

Metadata = #{put => #{description => "PUT method"},
             post => #{description => "POST method"},
             get => #{description => "GET method"}},
Trail = trails:trail("/",
                     {private_file, "index2.html"},
%% You can later retrieve the metadata:
Metadata = trails:metadata(Trail),

This can then be used to generate documentation related to each endpoint.

Also, when you work with cowboy, you have to define all routes in one place:

Routes =
    [ {"/", cowboy_static, {file, "www/index.html"}}
    , {"/favicon.ico", cowboy_static, {file, "www/assets/favicon.ico"}}
    , {"/assets/[...]", cowboy_static, {dir, "www/assets"}}
    , {"/game/:game_id", cowboy_static, {file, "www/game.html"}}
    , {"/api/status", spts_status_handler,  []}
    , {"/api/games", spts_games_handler, []}
    , {"/api/games/:game_id", spts_single_game_handler, []}
    , {"/api/games/:game_id/serpents", spts_serpents_handler, []}
    , { "/api/games/:game_id/serpents/:token"
      , spts_single_serpent_handler, []
    , {"/api/games/:game_id/news", lasse_handler, [spts_news_handler]}
Dispatch = cowboy_router:compile(Routes),

But now, with trails, you're able to define the routes on each of your resource handlers, separately. These handlers must implement callback trails/0 or trails/1 and return the specific routes that define them. For a better understanding, you can check out the examples in the test folder (trails_test_handler).

Once you have implemented the trails/0 or trails/1 callback on your handlers, you can do something like this:

Handlers =
  [ spts_status_handler
  , spts_games_handler
  , spts_single_game_handler
  , spts_serpents_handler
  , spts_single_serpent_handler
  , spts_news_handler
  , {support_params_handler, #{key => value}}
Trails =
  [ {"/", cowboy_static, {file, "www/index.html"}}
  , {"/favicon.ico", cowboy_static, {file, "www/assets/favicon.ico"}}
  , {"/assets/[...]", cowboy_static, {dir, "www/assets"}}
  , {"/game/:game_id", cowboy_static, {file, "www/game.html"}}
  | trails:trails(Handlers)

This way each handler maintains their own routes, as it should be, and you can merge them easily.


For more information about cowboy_trails, how to use it and the different functions that it exposes, please check this example.