Combo.Router (combo v0.8.0)

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Defines a router.

The router provides a set of macros for generating routes that dispatch to specific controllers and actions. Those macros are named after HTTP verbs. For example:

defmodule MyApp.Web.Router do
  use Combo.Router

  get "/pages/:page", MyApp.Web.PageController, :show
end

Combo's router is extremely efficient, as it relies on pattern matching for matching routes.

Routing

get/3, post/3, put/3, and other macros named after HTTP verbs are used to create routes.

The route:

get "/pages", PageController, :index

matches a GET request to /pages and dispatches it to the index action in PageController.

get "/pages/:page", PageController, :show

matches /pages/hello and dispatches to the show action in PageController with %{"page" => "hello"} in params.

defmodule PageController do
  def show(conn, params) do
    # %{"page" => "hello"} == params
  end
end

Partial and multiple segments can be matched. For example:

get "/api/v:version/pages/:id", PageController, :show

matches /api/v1/pages/2 and puts %{"version" => "1", "id" => "2"} in params. Only the trailing part of a segment can be captured.

Routes are matched from top to bottom. The second route here:

get "/pages/:page", PageController, :show
get "/pages/hello", PageController, :hello

will never match /pages/hello because /pages/:page matches that first.

Routes can use glob-like patterns to match trailing segments.

get "/pages/*page", PageController, :show

matches /pages/hello/world and puts the globbed segments in params["page"].

GET /pages/hello/world
%{"page" => ["hello", "world"]} = params

Globs cannot have prefixes nor suffixes, but can be mixed with variables:

get "/pages/he:page/*rest", PageController, :show

matches

GET /pages/hello
%{"page" => "llo", "rest" => []} = params

GET /pages/hey/there/world
%{"page" => "y", "rest" => ["there" "world"]} = params

Why the macros?

Combo does its best to keep the usage of macros low. You may have noticed, however, that the Combo.Router relies heavily on macros. Why is that?

We use macros for one purposes:

  • To be faster. They define the routing engine, used on every request, to choose which controller to dispatch the request to. Thanks to macros, Combo compiles all of your routes to a single case-statement with pattern matching rules, which is heavily optimized by the Erlang VM.

Route helpers

Combo generates a module Helpers for your routes, which contains named helpers to help you generate and keep your routes up to date.

Helpers are automatically generated based on the controller name. For example, the route:

get "/pages/:page", PageController, :show

will generate the following named helper:

MyApp.Web.Router.Helpers.page_path(conn, :show, "hello")
"/pages/hello"

MyApp.Web.Router.Helpers.page_path(conn, :show, "hello", some: "query")
"/pages/hello?some=query"

MyApp.Web.Router.Helpers.page_url(conn, :show, "hello")
"http://example.com/pages/hello"

MyApp.Web.Router.Helpers.page_url(conn, :show, "hello", some: "query")
"http://example.com/pages/hello?some=query"

If the route contains glob-like patterns, parameters for those have to be given as list:

MyApp.Web.Router.Helpers.page_path(conn, :show, ["hello", "world"])
"/pages/hello/world"

The named helper can also be customized with the :as option. Given the route:

get "/pages/:page", PageController, :show, as: :special_page

the named helper will be:

MyApp.Web.Router.Helpers.special_page_path(conn, :show, "hello")
"/pages/hello"

See the Combo.Router.Helpers for more information.

Scopes and Resources

It is very common to namespace routes under a scope. For example:

scope "/", MyApp.Web do
  get "/pages/:id", PageController, :show
end

The route above will dispatch to MyApp.Web.PageController. This syntax is convenient to use, since you don't have to repeat MyApp.Web. prefix on all routes.

Like all paths, you can define dynamic segments that will be applied as parameters in the controller. For example:

scope "/api/:version", MyApp.Web do
  get "/pages/:id", PageController, :show
end

The route above will match on the path "/api/v1/pages/1" and in the controller the params argument be a map like %{"version" => "v1", "id" => "1"}.

Combo also provides a resources/4 macro that allows to generate "RESTful" routes to a given resource:

defmodule MyApp.Web.Router do
  use Combo.Router

  resources "/pages", PageController, only: [:show]
  resources "/users", UserController, except: [:delete]
end

Check scope/2 and resources/4 for more information.

Listing routes

Combo ships with a mix combo.routes task that formats all routes in a given router. We can use it to verify all routes included in the router.

Pipelines and plugs

Once a request arrives at the Combo router, it performs a series of transformations through pipelines until the request is dispatched to a desired route.

Such transformations are defined via plugs, as defined in the Plug specification.

Once a pipeline is defined, it can be piped through per scope.

For example:

defmodule MyApp.Web.Router do
  use Combo.Router

  import Combo.Controller
  import Plug.Conn

  pipeline :browser do
    plug :accepts, ["html"]
    plug :fetch_session
  end

  scope "/" do
    pipe_through :browser

    # browser related routes
    # ...
  end
end

In the example above, we also imports Combo.Controller and Plug.Conn to help defining plugins. accepts/2 comes from Combo.Controller, while fetch_session/2 comes from Plug.Conn.

Note that router pipelines are only invoked after a route is found. No plug is invoked in case no matches were found.

Summary

Reflection

route_info(router, method, path, host)

Returns the compile-time route info and runtime path params for a request.

scoped_alias(router_module, alias)

Returns the full alias with the current scope's aliased prefix.

scoped_path(router_module, path)

Returns the full path with the current scope's path prefix.

Functions

connect(path, plug, plug_opts, options \\ [])

Defines a route to handle a connect request to the given path.

delete(path, plug, plug_opts, options \\ [])

Defines a route to handle a delete request to the given path.

forward(path, plug, plug_opts \\ [], router_opts \\ [])

Forwards a request at the given path to a plug.

get(path, plug, plug_opts, options \\ [])

Defines a route to handle a get request to the given path.

head(path, plug, plug_opts, options \\ [])

Defines a route to handle a head request to the given path.

match(verb, path, plug, plug_opts, options \\ [])

Defines a route based on an arbitrary HTTP method.

options(path, plug, plug_opts, options \\ [])

Defines a route to handle a options request to the given path.

patch(path, plug, plug_opts, options \\ [])

Defines a route to handle a patch request to the given path.

pipe_through(pipes)

Defines a list of plugs (and pipelines) to send the connection through.

pipeline(name, list)

Defines a plug pipeline.

plug(plug, opts \\ [])

Defines a plug inside a pipeline.

post(path, plug, plug_opts, options \\ [])

Defines a route to handle a post request to the given path.

put(path, plug, plug_opts, options \\ [])

Defines a route to handle a put request to the given path.

resources(path, controller)

See resources/4.

resources(path, controller, opts)

See resources/4.

resources(path, controller, opts, list)

Defines "RESTful" routes for a resource.

routes(router)

Returns all routes information from the given router.

scope(options, list)

Defines a scope in which routes can be nested.

scope(path, options, list)

Define a scope with the given path.

scope(path, alias, options, list)

Defines a scope with the given path and alias.

trace(path, plug, plug_opts, options \\ [])

Defines a route to handle a trace request to the given path.

Reflection

route_info(router, method, path, host)

Returns the compile-time route info and runtime path params for a request.

The path can be either a string or the path_info segments.

A map of metadata is returned with the following keys:

  • :log - the configured log level, such as :debug.
  • :path_params - the map of runtime path params.
  • :pipe_through - the list of pipelines for the route's scope, such as [:browser].
  • :plug - the plug to dispatch the route to, such as MyApp.Web.PostController.
  • :plug_opts - the options to pass when calling the plug, such as :index.
  • :route - the string route pattern, such as "/posts/:id".

Examples

iex> Combo.Router.route_info(MyApp.Web.Router, "GET", "/posts/123", "myhost")
%{
  log: :debug,
  path_params: %{"id" => "123"},
  pipe_through: [:browser],
  plug: MyApp.Web.PostController,
  plug_opts: :show,
  route: "/posts/:id",
}

iex> Combo.Router.route_info(MyRouter, "GET", "/not-exists", "myhost")
:error

scoped_alias(router_module, alias)

Returns the full alias with the current scope's aliased prefix.

Useful for applying the same short-hand alias handling to other values besides the second argument in route definitions.

Examples

scope "/", MyPrefix do
  get "/", ProxyPlug, controller: scoped_alias(__MODULE__, MyController)
end

scoped_path(router_module, path)

Returns the full path with the current scope's path prefix.

Functions

connect(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a connect request to the given path.

connect "/events/:id", EventController, :action

See match/5 for options.

delete(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a delete request to the given path.

delete "/events/:id", EventController, :action

See match/5 for options.

forward(path, plug, plug_opts \\ [], router_opts \\ [])

(macro)

Forwards a request at the given path to a plug.

This is commonly used to forward all subroutes to another Plug. For example:

forward "/admin", SomeLib.AdminDashboard

The above will allow SomeLib.AdminDashboard to handle /admin, /admin/foo, /admin/bar/baz, and so on. Furthermore, SomeLib.AdminDashboard does not to be aware of the prefix it is mounted in. From its point of view, the routes above are simply handled as /, /foo, and /bar/baz.

A common use case for forward is for sharing a router between applications or breaking a big router into smaller ones. However, in other for route generation to route accordingly, you can only forward to a given Combo.Router once.

The router pipelines will be invoked prior to forwarding the connection.

Examples

scope "/", MyApp do
  pipe_through [:browser, :admin]

  forward "/admin", SomeLib.AdminDashboard
  forward "/api", ApiRouter
end

get(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a get request to the given path.

get "/events/:id", EventController, :action

See match/5 for options.

head(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a head request to the given path.

head "/events/:id", EventController, :action

See match/5 for options.

Compatibility with Plug.Head

By default, Combo apps include Plug.Head in their endpoint, which converts HEAD requests into regular GET requests. Therefore, if you intend to use head/4 in your router, you need to move Plug.Head to inside your router in a way it does not conflict with the paths given to head/4.

match(verb, path, plug, plug_opts, options \\ [])

(macro)

Defines a route based on an arbitrary HTTP method.

Useful for defining routes not included in the built-in macros.

The catch-all verb, :*, may also be used to match all HTTP methods.

Options

  • :as - the named helper. If nil, does not generate a helper.
  • :alias - if the scope alias should be applied to the route. Defaults to true.
  • :log - the level to log the route dispatching under, may be set to false. Defaults to :debug. Route dispatching contains information about how the route is handled (which controller action is called, what parameters are available and which pipelines are used) and is separate from the plug level logging. To alter the plug log level, please see https://hexdocs.pm/combo/Combo.Logger.html#module-dynamic-log-level.
  • :private - a map of private data to merge into the connection when a a route matches.
  • :assigns - a map of data to merge into the connection when a route matches.
  • :metadata - a map of metadata used by the telemetry events and returned by route_info/4. The :mfa field is used by telemetry to print logs and by the router to emit compile time checks. Custom fields may be added.

Examples

match :move, "/events/:id", EventController, :move

match :*, "/any", CatchAllController, :any

options(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a options request to the given path.

options "/events/:id", EventController, :action

See match/5 for options.

patch(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a patch request to the given path.

patch "/events/:id", EventController, :action

See match/5 for options.

pipe_through(pipes)

(macro)

Defines a list of plugs (and pipelines) to send the connection through.

Plugs are specified using the atom name of any imported 2-arity function which takes a Plug.Conn struct and options and returns a Plug.Conn struct. For example, :require_authenticated_user.

Pipelines are defined in the router, see pipeline/2 for more information.

pipe_through [:require_authenticated_user, :my_browser_pipeline]

Multiple invocations

pipe_through/1 can be invoked multiple times within the same scope. Each invocation appends new plugs and pipelines to run, which are applied to all routes after the pipe_through/1 invocation. For example:

scope "/" do
  pipe_through [:browser]
  get "/", HomeController, :index

  pipe_through [:require_authenticated_user]
  get "/settings", UserController, :edit
end

In the example above, / pipes through browser only, while /settings pipes through both browser and require_authenticated_user. Therefore, to avoid confusion, we recommend a single pipe_through at the top of each scope:

scope "/" do
  pipe_through [:browser]
  get "/", HomeController, :index
end

scope "/" do
  pipe_through [:browser, :require_authenticated_user]
  get "/settings", UserController, :edit
end

pipeline(name, list)

(macro)

Defines a plug pipeline.

Pipelines are defined at the router root and can be used from any scope.

Examples

pipeline :api do
  plug :token_authentication
  plug :dispatch
end

A scope may then use this pipeline as:

scope "/" do
  pipe_through :api
end

Every time pipe_through/1 is called, the new pipelines are appended to the ones previously given.

plug(plug, opts \\ [])

(macro)

Defines a plug inside a pipeline.

See pipeline/2 for more information.

post(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a post request to the given path.

post "/events/:id", EventController, :action

See match/5 for options.

put(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a put request to the given path.

put "/events/:id", EventController, :action

See match/5 for options.

resources(path, controller)

(macro)

See resources/4.

resources(path, controller, opts)

(macro)

See resources/4.

resources(path, controller, opts, list)

(macro)

Defines "RESTful" routes for a resource.

The given definition:

resources "/users", UserController

will include routes to the following actions:

  • GET /users => :index
  • GET /users/new => :new
  • POST /users => :create
  • GET /users/:id => :show
  • GET /users/:id/edit => :edit
  • PATCH /users/:id => :update
  • PUT /users/:id => :update
  • DELETE /users/:id => :delete

Options

This macro accepts a set of options:

  • :only - a list of actions to generate routes for, for example: [:show, :edit]
  • :except - a list of actions to exclude generated routes from, for example: [:delete]
  • :param - the name of the parameter for this resource, defaults to "id"
  • :name - the prefix for this resource. This is used for the named helper and as the prefix for the parameter in nested resources. The default value is automatically derived from the controller name, i.e. UserController will have name "user".
  • :as - configures the named helper. If nil, does not generate a helper.
  • :singleton - defines routes for a singleton resource. Read below for more information.

Singleton resources

When a resource needs to be looked up without referencing an ID, because it contains only a single entry in the given context, the :singleton option can be used to generate a set of routes that are specific to such single resource:

  • GET /user/new => :new
  • POST /user => :create
  • GET /user => :show
  • GET /user/edit => :edit
  • PATCH /user => :update
  • PUT /user => :update
  • DELETE /user => :delete

Usage example:

resources "/account", AccountController, only: [:show], singleton: true

Nested Resources

This macro also supports passing a nested block of route definitions. This is helpful for nesting children resources within their parents to generate nested routes.

The given definition:

resources "/users", UserController do
  resources "/posts", PostController
end

will include the following routes:

user_post_path  GET     /users/:user_id/posts           PostController :index
user_post_path  GET     /users/:user_id/posts/new       PostController :new
user_post_path  POST    /users/:user_id/posts           PostController :create
user_post_path  GET     /users/:user_id/posts/:id       PostController :show
user_post_path  GET     /users/:user_id/posts/:id/edit  PostController :edit
user_post_path  PATCH   /users/:user_id/posts/:id       PostController :update
                PUT     /users/:user_id/posts/:id       PostController :update
user_post_path  DELETE  /users/:user_id/posts/:id       PostController :delete

routes(router)

Returns all routes information from the given router.

scope(options, list)

(macro)

Defines a scope in which routes can be nested.

Examples

scope path: "/api/v1", alias: API.V1 do
  get "/pages/:id", PageController, :show
end

The generated route above will match on the path "/api/v1/pages/:id" and will dispatch to :show action in API.V1.PageController. A named helper api_v1_page_path will also be generated.

Options

The supported options are:

  • :path - a string containing the path scope.
  • :as - a string or atom containing the named helper scope. When set to false, it resets the nested helper scopes. Has no effect when using verified routes exclusively
  • :alias - an alias (atom) containing the controller scope. When set to false, it resets all nested aliases.
  • :host - a string or list of strings containing the host scope, or prefix host scope, ie "foo.bar.com", "foo."
  • :private - a map of private data to merge into the connection when a route matches
  • :assigns - a map of data to merge into the connection when a route matches
  • :log - the level to log the route dispatching under, may be set to false. Defaults to :debug. Route dispatching contains information about how the route is handled (which controller action is called, what parameters are available and which pipelines are used) and is separate from the plug level logging. To alter the plug log level, please see https://hexdocs.pm/combo/Combo.Logger.html#module-dynamic-log-level.

scope(path, options, list)

(macro)

Define a scope with the given path.

This function is a shortcut for:

scope path: path do
  ...
end

Examples

scope "/v1", host: "api." do
  get "/pages/:id", PageController, :show
end

scope(path, alias, options, list)

(macro)

Defines a scope with the given path and alias.

This function is a shortcut for:

scope path: path, alias: alias do
  ...
end

Examples

scope "/v1", API.V1, host: "api." do
  get "/pages/:id", PageController, :show
end

trace(path, plug, plug_opts, options \\ [])

(macro)

Defines a route to handle a trace request to the given path.

trace "/events/:id", EventController, :action

See match/5 for options.