Plug v1.8.1 Plug.Router View Source
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.
Routes
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.
Parameter Parsing
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.
Error handling
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 thehandle_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
Passing data between routes and plugs
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.
Routes compilation
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.
Routes options
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
.
Link to this section Summary
Functions
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
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
Link to this section Functions
delete(path, options, contents \\ []) View Source (macro)
Dispatches to the path only if the request is a DELETE request.
See match/3
for more examples.
forward(path, options) View Source (macro)
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
.
Options
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 inmatch/3
.:private
- values forconn.private
, exactly like inmatch/3
.:assigns
- values forconn.assigns
, exactly like inmatch/3
.
If :init_opts
is undefined, then all remaining options are passed
to the target plug.
Examples
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]
get(path, options, contents \\ []) View Source (macro)
Dispatches to the path only if the request is a GET request.
See match/3
for more examples.
match(path, options, contents \\ []) View Source (macro)
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.
Examples
match "/foo/bar", via: :get do
send_resp(conn, 200, "hello world")
end
match "/baz", to: MyPlug, init_opts: [an_option: :a_value]
Options
match/3
and the other route macros accept the following options:
:host
- the host which the route should match. Defaults tonil
, 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 toconn.private
for use in the match:assigns
- assigns values toconn.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(conn)
View Source
match_path(Plug.Conn.t()) :: String.t()
match_path(Plug.Conn.t()) :: String.t()
Returns the path of the route that the request was matched to.
options(path, options, contents \\ []) View Source (macro)
Dispatches to the path only if the request is an OPTIONS request.
See match/3
for more examples.
patch(path, options, contents \\ []) View Source (macro)
Dispatches to the path only if the request is a PATCH request.
See match/3
for more examples.
post(path, options, contents \\ []) View Source (macro)
Dispatches to the path only if the request is a POST request.
See match/3
for more examples.
put(path, options, contents \\ []) View Source (macro)
Dispatches to the path only if the request is a PUT request.
See match/3
for more examples.