A DSL to define a routing algorithm that works with Plug.
It provides a set of macros to generate routes. For example:
defmodule AppRouter do use Plug.Router plug :match plug :dispatch get "/hello" do send_resp(conn, 200, "world") end match _ do send_resp(conn, 404, "oops") end end
Each route receives a conn
variable containing a Plug.Conn
struct and it needs to return a connection, as per the Plug spec. A catch-all match
is recommended to be defined as in the example above, otherwise routing fails with a function clause error.
The router is itself a plug, which means it can be invoked as:
AppRouter.call(conn, AppRouter.init([]))
Each Plug.Router
has a plug pipeline, defined by Plug.Builder
, and by default it requires two plugs: :match
and :dispatch
. :match
is responsible for finding a matching route which is then forwarded to :dispatch
. This means users can easily hook into the router mechanism and add behaviour before match, before dispatch, or after both. All of the options given to use Plug.Router
are forwarded to Plug.Builder
. See the Plug.Builder
module for more information on the plug
macro and on the available options.
get "/hello" do send_resp(conn, 200, "world") end
In the example above, a request will only match if it is a GET
request and the route is "/hello". The supported HTTP methods are get
, post
, put
, patch
, delete
and options
.
A route can also specify parameters which will then be available in the function body:
get "/hello/:name" do send_resp(conn, 200, "hello #{name}") end
The :name
parameter will also be available in the function body as conn.params["name"]
and conn.path_params["name"]
.
Routes allow for globbing which will match the remaining parts of a route and can be available as a parameter in the function body. Also note that a glob can't be followed by other segments:
get "/hello/*_rest" do send_resp(conn, 200, "matches all routes starting with /hello") end get "/hello/*glob" do send_resp(conn, 200, "route after /hello: #{inspect glob}") end
Finally, a general match
function is also supported:
match "/hello" do send_resp(conn, 200, "world") end
A match
will match any route regardless of the HTTP method. Check match/3
for more information on how route compilation works and a list of supported options.
Handling request data can be done through the Plug.Parsers
plug. It provides support for parsing URL-encoded, form-data, and JSON data as well as providing a behaviour that others parsers can adopt.
Here is an example of Plug.Parsers
can be used in a Plug.Router
router to parse the JSON-encoded body of a POST request:
defmodule AppRouter do use Plug.Router plug :match plug Plug.Parsers, parsers: [:json], pass: ["application/json"], json_decoder: Jason plug :dispatch post "/hello" do IO.inspect conn.body_params # Prints JSON POST body send_resp(conn, 200, "Success!") end end
It is important that Plug.Parsers
is placed before the :dispatch
plug in the pipeline, otherwise the matched clause route will not receive the parsed body in its Plug.Conn
argument when dispatched.
Plug.Parsers
can also be plugged between :match
and :dispatch
(like in the example above): this means that Plug.Parsers
will run only if there is a matching route. This can be useful to perform actions such as authentication before parsing the body, which should only be parsed if a route matches afterwards.
In case something goes wrong in a request, the router by default will crash, without returning any response to the client. This behaviour can be configured in two ways, by using two different modules:
Plug.ErrorHandler
- allows the developer to customize exactly which page is sent to the client via the handle_errors/2
function;
Plug.Debugger
- automatically shows debugging and request information about the failure. This module is recommended to be used only in a development environment.
Here is an example of how both modules could be used in an application:
defmodule AppRouter do use Plug.Router if Mix.env == :dev do use Plug.Debugger end use Plug.ErrorHandler plug :match plug :dispatch get "/hello" do send_resp(conn, 200, "world") end defp handle_errors(conn, %{kind: _kind, reason: _reason, stack: _stack}) do send_resp(conn, conn.status, "Something went wrong") end end
It is also possible to assign data to the Plug.Conn
that will be available to any plug invoked after the :match
plug. This is very useful if you want a matched route to customize how later plugs will behave.
You can use :assigns
(which contains user data) or :private
(which contains library/framework data) for this. For example:
get "/hello", assigns: %{an_option: :a_value} do send_resp(conn, 200, "world") end
In the example above, conn.assigns[:an_option]
will be available to all plugs invoked after :match
. Such plugs can read from conn.assigns
(or conn.private
) to configure their behaviour based on the matched route.
All routes are compiled to a match function that receives three arguments: the method, the request path split on /
and the connection. Consider this example:
match "/foo/bar", via: :get do send_resp(conn, 200, "hello world") end
It is compiled to:
defp match("GET", ["foo", "bar"], conn) do send_resp(conn, 200, "hello world") end
This means guards can be given to match
:
match "/foo/bar/:baz" when size(baz) <= 3, via: :get do send_resp(conn, 200, "hello world") end
After a match is found, the block given as do/end
is stored as a function in the connection. This function is then retrieved and invoked in the dispatch
plug.
Sometimes you may want to customize how a route behaves during dispatch. This can be done by accessing the opts
variable inside the route:
defmodule AppRouter do use Plug.Router plug :match plug :dispatch, content: "hello world" get "/hello" do send_resp(conn, 200, opts[:content]) end match _ do send_resp(conn, 404, "oops") end end
This is particularly useful when used with Plug.Builder.builder_opts/0
. builder_opts/0
allows us to pass options received when initializing AppRouter
to a specific plug, such as dispatch itself. So if instead of:
plug :dispatch, content: "hello world"
we do:
plug :dispatch, builder_opts()
now the content can be given when starting the router, like this:
Plug.Cowboy.http AppRouter, [content: "hello world"]
Or as part of a pipeline like this:
plug AppRouter, content: "hello world"
In a nutshell, builder_opts()
allows us to pass the options given when initializing the router to a dispatch
.
The router emits the following telemetry events:
[:plug, :router_dispatch, :start]
- dispatched before dispatching to a matched route
%{system_time: System.system_time}
%{conn: Plug.Conn.t, route: binary, router: module}
[:plug, :router_dispatch, :exception]
- dispatched after exceptions on dispatching a route
%{duration: native_time}
%{conn: Plug.Conn.t, route: binary, router: module}
[:plug, :router_dispatch, :stop]
- dispatched after successfully dispatching a matched route
%{duration: native_time}
%{conn: Plug.Conn.t, route: binary, router: module}
Dispatches to the path only if the request is a DELETE request. See match/3
for more examples.
Forwards requests to another Plug. The path_info
of the forwarded connection will exclude the portion of the path specified in the call to forward
. If the path contains any parameters, those will be available in the target Plug in conn.params
and conn.path_params
.
Dispatches to the path only if the request is a GET request. See match/3
for more examples.
Dispatches to the path only if the request is a HEAD request. See match/3
for more examples.
Main API to define routes.
Returns the path of the route that the request was matched to.
Dispatches to the path only if the request is an OPTIONS request. See match/3
for more examples.
Dispatches to the path only if the request is a PATCH request. See match/3
for more examples.
Dispatches to the path only if the request is a POST request. See match/3
for more examples.
Dispatches to the path only if the request is a PUT request. See match/3
for more examples.
Dispatches to the path only if the request is a DELETE request. See match/3
for more examples.
Forwards requests to another Plug. The path_info
of the forwarded connection will exclude the portion of the path specified in the call to forward
. If the path contains any parameters, those will be available in the target Plug in conn.params
and conn.path_params
.
forward
accepts the following options:
:to
- a Plug the requests will be forwarded to.:init_opts
- the options for the target Plug.:host
- a string representing the host or subdomain, exactly like in match/3
.:private
- values for conn.private
, exactly like in match/3
.:assigns
- values for conn.assigns
, exactly like in match/3
.If :init_opts
is undefined, then all remaining options are passed to the target plug.
forward "/users", to: UserRouter
Assuming the above code, a request to /users/sign_in
will be forwarded to the UserRouter
plug, which will receive what it will see as a request to /sign_in
.
forward "/foo/:bar/qux", to: FooPlug
Here, a request to /foo/BAZ/qux
will be forwarded to the FooPlug
plug, which will receive what it will see as a request to /
, and conn.params["bar"]
will be set to "BAZ"
.
Some other examples:
forward "/foo/bar", to: :foo_bar_plug, host: "foobar." forward "/baz", to: BazPlug, init_opts: [plug_specific_option: true]
Dispatches to the path only if the request is a GET request. See match/3
for more examples.
Dispatches to the path only if the request is a HEAD request. See match/3
for more examples.
Main API to define routes.
It accepts an expression representing the path and many options allowing the match to be configured.
The route can dispatch either to a function body or a Plug module.
match "/foo/bar", via: :get do send_resp(conn, 200, "hello world") end match "/baz", to: MyPlug, init_opts: [an_option: :a_value]
match/3
and the other route macros accept the following options:
:host
- the host which the route should match. Defaults to nil
, meaning no host match, but can be a string like "example.com" or a string ending with ".", like "subdomain." for a subdomain match.
:private
- assigns values to conn.private
for use in the match
:assigns
- assigns values to conn.assigns
for use in the match
:via
- matches the route against some specific HTTP method(s) specified as an atom, like :get
or :put
, or a list, like [:get, :post]
.
:do
- contains the implementation to be invoked in case the route matches.
:to
- a Plug that will be called in case the route matches.
:init_opts
- the options for the target Plug given by :to
.
A route should specify only one of :do
or :to
options.
match_path(Plug.Conn.t()) :: String.t()
Returns the path of the route that the request was matched to.
Dispatches to the path only if the request is an OPTIONS request. See match/3
for more examples.
Dispatches to the path only if the request is a PATCH request. See match/3
for more examples.
Dispatches to the path only if the request is a POST request. See match/3
for more examples.
Dispatches to the path only if the request is a PUT request. See match/3
for more examples.
© 2013 Plataformatec
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/plug/Plug.Router.html