Controllers are used to group common functionality in the same (pluggable) module.
For example, the route:
get "/users/:id", MyAppWeb.UserController, :show
will invoke the show/2
action in the MyAppWeb.UserController
:
defmodule MyAppWeb.UserController do use MyAppWeb, :controller def show(conn, %{"id" => id}) do user = Repo.get(User, id) render(conn, "show.html", user: user) end end
An action is a regular function that receives the connection and the request parameters as arguments. The connection is a Plug.Conn
struct, as specified by the Plug library.
When used, the controller supports the following options:
:namespace
- sets the namespace to properly inflect the layout view. By default it uses the base alias in your controller name
:log
- the level to log. When false, disables controller logging
:put_default_views
- controls whether the default view and layout should be set or not
A controller by default provides many convenience functions for manipulating the connection, rendering templates, and more.
Those functions are imported from two modules:
Plug.Conn
- a collection of low-level functions to work with the connection
Phoenix.Controller
- functions provided by Phoenix to support rendering, and other Phoenix specific behaviour
If you want to have functions that manipulate the connection without fully implementing the controller, you can import both modules directly instead of use Phoenix.Controller
.
As with routers, controllers also have their own plug pipeline. However, different from routers, controllers have a single pipeline:
defmodule MyAppWeb.UserController do use MyAppWeb, :controller plug :authenticate, usernames: ["jose", "eric", "sonny"] def show(conn, params) do # authenticated users only end defp authenticate(conn, options) do if get_session(conn, :username) in options[:usernames] do conn else conn |> redirect(to: "/") |> halt() end end end
The :authenticate
plug will be invoked before the action. If the plug calls Plug.Conn.halt/1
(which is by default imported into controllers), it will halt the pipeline and won't invoke the action.
plug/2
in controllers supports guards, allowing a developer to configure a plug to only run in some particular action:
plug :authenticate, [usernames: ["jose", "eric", "sonny"]] when action in [:show, :edit] plug :authenticate, [usernames: ["admin"]] when not action in [:index]
The first plug will run only when action is show or edit. The second plug will always run, except for the index action.
Those guards work like regular Elixir guards and the only variables accessible in the guard are conn
, the action
as an atom and the controller
as an alias.
Like routers, controllers are plugs, but they are wired to dispatch to a particular function which is called an action.
For example, the route:
get "/users/:id", UserController, :show
will invoke UserController
as a plug:
UserController.call(conn, :show)
which will trigger the plug pipeline and which will eventually invoke the inner action plug that dispatches to the show/2
function in the UserController
.
As controllers are plugs, they implement both init/1
and call/2
, and it also provides a function named action/2
which is responsible for dispatching the appropriate action after the plug stack (and is also overridable).
action/2
for custom arguments Phoenix injects an action/2
plug in your controller which calls the function matched from the router. By default, it passes the conn and params. In some cases, overriding the action/2
plug in your controller is a useful way to inject arguments into your actions that you would otherwise need to repeatedly fetch off the connection. For example, imagine if you stored a conn.assigns.current_user
in the connection and wanted quick access to the user for every action in your controller:
def action(conn, _) do args = [conn, conn.params, conn.assigns.current_user] apply(__MODULE__, action_name(conn), args) end def index(conn, _params, user) do videos = Repo.all(user_videos(user)) # ... end def delete(conn, %{"id" => id}, user) do video = Repo.get!(user_videos(user), id) # ... end
One of the main features provided by controllers is the ability to perform content negotiation and render templates based on information sent by the client. Read render/3
to learn more.
It is also important not to confuse Phoenix.Controller.render/3
with Phoenix.View.render/3
. The former expects a connection and relies on content negotiation while the latter is connection-agnostic and typically invoked from your views.
Performs content negotiation based on the available formats.
Registers the plug to call as a fallback to the controller action.
Returns the action name as an atom, raises if unavailable.
A plug that may convert a JSON response into a JSONP one.
Clears all flash messages.
Returns the controller module as an atom, raises if unavailable.
Returns the current request path with its default query parameters
Returns the current path with the given query parameters.
Returns the current request url with its default query parameters
Returns the current request URL with query params.
Deletes the CSRF token from the process dictionary.
Returns the endpoint module as an atom, raises if unavailable.
Fetches the flash storage.
Gets or generates a CSRF token.
Returns a map of previously set flash messages or an empty map.
Returns a message from flash by key
(or nil
if no message is available for key
).
Returns the request format, such as "json", "html".
Sends html response.
Sends JSON response.
Retrieves the current layout.
Retrieves current layout formats.
Merges a map into the flash.
Enables CSRF protection.
Persists a value in flash.
Puts the format in the connection.
Stores the layout for rendering.
Sets which formats have a layout when rendering.
Stores the layout for rendering if one was not stored yet.
Stores the view for rendering if one was not stored yet.
Stores the root layout for rendering.
Puts the url string or %URI{}
to be used for route generation.
Put headers that improve browser security.
Puts the URL or %URI{}
to be used for the static url generation.
Stores the view for rendering.
Sends redirect response to the given url.
Render the given template or the default template specified by the current action with the given assigns.
Renders the given template
and assigns
based on the conn
information.
Retrieves the current root layout.
Returns the router module as an atom, raises if unavailable.
Scrubs the parameters from the request.
Sends the given file or binary as a download.
Generates a status message from the template name.
Sends text response.
Retrieves the current view.
Returns the template name rendered in the view as a string (or nil if no template was rendered).
accepts(Plug.Conn.t(), [binary()]) :: Plug.Conn.t() | no_return()
Performs content negotiation based on the available formats.
It receives a connection, a list of formats that the server is capable of rendering and then proceeds to perform content negotiation based on the request information. If the client accepts any of the given formats, the request proceeds.
If the request contains a "_format" parameter, it is considered to be the format desired by the client. If no "_format" parameter is available, this function will parse the "accept" header and find a matching format accordingly.
This function is useful when you may want to serve different content-types (such as JSON and HTML) from the same routes. However, if you always have distinct routes, you can also disable content negotiation and simply hardcode your format of choice in your route pipelines:
plug :put_format, "html"
It is important to notice that browsers have historically sent bad accept headers. For this reason, this function will default to "html" format whenever:
the accepted list of arguments contains the "html" format
the accept header specified more than one media type preceded or followed by the wildcard media type "*/*
"
This function raises Phoenix.NotAcceptableError
, which is rendered with status 406, whenever the server cannot serve a response in any of the formats expected by the client.
accepts/2
can be invoked as a function:
iex> accepts(conn, ["html", "json"])
or used as a plug:
plug :accepts, ["html", "json"] plug :accepts, ~w(html json)
It is possible to add custom media types to your Phoenix application. The first step is to teach Plug about those new media types in your config/config.exs
file:
config :mime, :types, %{ "application/vnd.api+json" => ["json-api"] }
The key is the media type, the value is a list of formats the media type can be identified with. For example, by using "json-api", you will be able to use templates with extension "index.json-api" or to force a particular format in a given URL by sending "?_format=json-api".
After this change, you must recompile plug:
$ mix deps.clean mime --build $ mix deps.get
And now you can use it in accepts too:
plug :accepts, ["html", "json-api"]
Registers the plug to call as a fallback to the controller action.
A fallback plug is useful to translate common domain data structures into a valid %Plug.Conn{}
response. If the controller action fails to return a %Plug.Conn{}
, the provided plug will be called and receive the controller's %Plug.Conn{}
as it was before the action was invoked along with the value returned from the controller action.
defmodule MyController do use Phoenix.Controller action_fallback MyFallbackController def show(conn, %{"id" => id}, current_user) do with {:ok, post} <- Blog.fetch_post(id), :ok <- Authorizer.authorize(current_user, :view, post) do render(conn, "show.json", post: post) end end end
In the above example, with
is used to match only a successful post fetch, followed by valid authorization for the current user. In the event either of those fail to match, with
will not invoke the render block and instead return the unmatched value. In this case, imagine Blog.fetch_post/2
returned {:error, :not_found}
or Authorizer.authorize/3
returned {:error, :unauthorized}
. For cases where these data structures serve as return values across multiple boundaries in our domain, a single fallback module can be used to translate the value into a valid response. For example, you could write the following fallback controller to handle the above values:
defmodule MyFallbackController do use Phoenix.Controller def call(conn, {:error, :not_found}) do conn |> put_status(:not_found) |> put_view(MyErrorView) |> render(:"404") end def call(conn, {:error, :unauthorized}) do conn |> put_status(403) |> put_view(MyErrorView) |> render(:"403") end end
action_name(Plug.Conn.t()) :: atom()
Returns the action name as an atom, raises if unavailable.
allow_jsonp(Plug.Conn.t(), Keyword.t()) :: Plug.Conn.t()
A plug that may convert a JSON response into a JSONP one.
In case a JSON response is returned, it will be converted to a JSONP as long as the callback field is present in the query string. The callback field itself defaults to "callback", but may be configured with the callback option.
In case there is no callback or the response is not encoded in JSON format, it is a no-op.
Only alphanumeric characters and underscore are allowed in the callback name. Otherwise an exception is raised.
# Will convert JSON to JSONP if callback=someFunction is given plug :allow_jsonp # Will convert JSON to JSONP if cb=someFunction is given plug :allow_jsonp, callback: "cb"
Clears all flash messages.
controller_module(Plug.Conn.t()) :: atom()
Returns the controller module as an atom, raises if unavailable.
Returns the current request path with its default query parameters:
iex> current_path(conn) "/users/123?existing=param"
See current_path/2
to override the default parameters.
Returns the current path with the given query parameters.
You may also retrieve only the request path by passing an empty map of params.
iex> current_path(conn) "/users/123?existing=param" iex> current_path(conn, %{new: "param"}) "/users/123?new=param" iex> current_path(conn, %{filter: %{status: ["draft", "published"}) "/users/123?filter[status][]=draft&filter[status][]=published" iex> current_path(conn, %{}) "/users/123"
Returns the current request url with its default query parameters:
iex> current_url(conn) "https://www.example.com/users/123?existing=param"
See current_url/2
to override the default parameters.
Returns the current request URL with query params.
The path will be retrieved from the currently requested path via current_path/1
. The scheme, host and others will be received from the URL configuration in your Phoenix endpoint. The reason we don't use the host and scheme information in the request is because most applications are behind proxies and the host and scheme may not actually reflect the host and scheme accessed by the client. If you want to access the url precisely as requested by the client, see Plug.Conn.request_url/1
.
iex> current_url(conn) "https://www.example.com/users/123?existing=param" iex> current_url(conn, %{new: "param"}) "https://www.example.com/users/123?new=param" iex> current_url(conn, %{}) "https://www.example.com/users/123"
In some cases, you'll need to generate a request's URL, but using a different scheme, different host, etc. This can be accomplished in two ways.
If you want to do so in a case-by-case basis, you can define a custom function that gets the endpoint URI configuration and changes it accordingly. For example, to get the current URL always in HTTPS format:
def current_secure_url(conn, params \\ %{}) do cur_uri = MyAppWeb.Endpoint.struct_url() cur_path = Phoenix.Controller.current_path(conn, params) MyAppWeb.Router.Helpers.url(%URI{cur_uri | scheme: "https"}) <> cur_path end
However, if you want all generated URLs to always have a certain schema, host, etc, you may use put_router_url/2
.
Deletes the CSRF token from the process dictionary.
Note: The token is deleted only after a response has been sent.
endpoint_module(Plug.Conn.t()) :: atom()
Returns the endpoint module as an atom, raises if unavailable.
Fetches the flash storage.
Gets or generates a CSRF token.
If a token exists, it is returned, otherwise it is generated and stored in the process dictionary.
Returns a map of previously set flash messages or an empty map.
iex> get_flash(conn) %{} iex> conn = put_flash(conn, :info, "Welcome Back!") iex> get_flash(conn) %{"info" => "Welcome Back!"}
Returns a message from flash by key
(or nil
if no message is available for key
).
iex> conn = put_flash(conn, :info, "Welcome Back!") iex> get_flash(conn, :info) "Welcome Back!"
Returns the request format, such as "json", "html".
This format is used when rendering a template as an atom. For example, render(conn, :foo)
will render "foo.FORMAT"
where the format is the one set here. The default format is typically set from the negotiation done in accepts/2
.
html(Plug.Conn.t(), iodata()) :: Plug.Conn.t()
Sends html response.
iex> html(conn, "<html><head>...")
json(Plug.Conn.t(), term()) :: Plug.Conn.t()
Sends JSON response.
It uses the configured :json_library
under the :phoenix
application for :json
to pick up the encoder module.
iex> json(conn, %{id: 123})
layout(Plug.Conn.t()) :: {atom(), String.t() | atom()} | false
Retrieves the current layout.
layout_formats(Plug.Conn.t()) :: [String.t()]
Retrieves current layout formats.
Merges a map into the flash.
Returns the updated connection.
iex> conn = merge_flash(conn, info: "Welcome Back!") iex> get_flash(conn, :info) "Welcome Back!"
Enables CSRF protection.
Currently used as a wrapper function for Plug.CSRFProtection
and mainly serves as a function plug in YourApp.Router
.
Check get_csrf_token/0
and delete_csrf_token/0
for retrieving and deleting CSRF tokens.
Persists a value in flash.
Returns the updated connection.
iex> conn = put_flash(conn, :info, "Welcome Back!") iex> get_flash(conn, :info) "Welcome Back!"
Puts the format in the connection.
This format is used when rendering a template as an atom. For example, render(conn, :foo)
will render "foo.FORMAT"
where the format is the one set here. The default format is typically set from the negotiation done in accepts/2
.
See get_format/1
for retrieval.
put_layout( Plug.Conn.t(), {atom(), binary() | atom()} | atom() | binary() | false ) :: Plug.Conn.t()
Stores the layout for rendering.
The layout must be a tuple, specifying the layout view and the layout name, or false. In case a previous layout is set, put_layout
also accepts the layout name to be given as a string or as an atom. If a string, it must contain the format. Passing an atom means the layout format will be found at rendering time, similar to the template in render/3
. It can also be set to false
. In this case, no layout would be used.
iex> layout(conn) false iex> conn = put_layout conn, {AppView, "application.html"} iex> layout(conn) {AppView, "application.html"} iex> conn = put_layout conn, "print.html" iex> layout(conn) {AppView, "print.html"} iex> conn = put_layout conn, :print iex> layout(conn) {AppView, :print}
Raises Plug.Conn.AlreadySentError
if conn
is already sent.
put_layout_formats(Plug.Conn.t(), [String.t()]) :: Plug.Conn.t()
Sets which formats have a layout when rendering.
iex> layout_formats(conn) ["html"] iex> put_layout_formats(conn, ["html", "mobile"]) iex> layout_formats(conn) ["html", "mobile"]
Raises Plug.Conn.AlreadySentError
if conn
is already sent.
put_new_layout(Plug.Conn.t(), {atom(), binary() | atom()} | false) :: Plug.Conn.t()
Stores the layout for rendering if one was not stored yet.
Raises Plug.Conn.AlreadySentError
if conn
is already sent.
put_new_view(Plug.Conn.t(), atom()) :: Plug.Conn.t()
Stores the view for rendering if one was not stored yet.
Raises Plug.Conn.AlreadySentError
if conn
is already sent.
put_root_layout( Plug.Conn.t(), {atom(), binary() | atom()} | atom() | binary() | false ) :: Plug.Conn.t()
Stores the root layout for rendering.
Like put_layout/2
, the layout must be a tuple, specifying the layout view and the layout name, or false.
In case a previous layout is set, put_root_layout
also accepts the layout name to be given as a string or as an atom. If a string, it must contain the format. Passing an atom means the layout format will be found at rendering time, similar to the template in render/3
. It can also be set to false
. In this case, no layout would be used.
iex> root_layout(conn) false iex> conn = put_root_layout conn, {AppView, "root.html"} iex> root_layout(conn) {AppView, "root.html"} iex> conn = put_root_layout conn, "bare.html" iex> root_layout(conn) {AppView, "bare.html"} iex> conn = put_root_layout conn, :bare iex> root_layout(conn) {AppView, :bare}
Raises Plug.Conn.AlreadySentError
if conn
is already sent.
Puts the url string or %URI{}
to be used for route generation.
This function overrides the default URL generation pulled from the %Plug.Conn{}
's endpoint configuration.
Imagine your application is configured to run on "example.com" but after the user signs in, you want all links to use "some_user.example.com". You can do so by setting the proper router url configuration:
def put_router_url_by_user(conn) do put_router_url(conn, get_user_from_conn(conn).account_name <> ".example.com") end
Now when you call Routes.some_route_url(conn, ...)
, it will use the router url set above. Keep in mind that, if you want to generate routes to the current domain, it is preferred to use Routes.some_route_path
helpers, as those are always relative.
Put headers that improve browser security.
It sets the following headers:
x-frame-options
- set to SAMEORIGIN to avoid clickjacking through iframes unless in the same originx-content-type-options
- set to nosniff. This requires script and style tags to be sent with proper content typex-xss-protection
- set to "1; mode=block" to improve XSS protection on both Chrome and IEx-download-options
- set to noopen to instruct the browser not to open a download directly in the browser, to avoid HTML files rendering inline and accessing the security context of the application (like critical domain cookies)x-permitted-cross-domain-policies
- set to none to restrict Adobe Flash Player’s access to datacross-origin-window-policy
- set to deny to avoid window control attacksA custom headers map may also be given to be merged with defaults. It is recommended for custom header keys to be in lowercase, to avoid sending duplicate keys in a request. Additionally, responses with mixed-case headers served over HTTP/2 are not considered valid by common clients, resulting in dropped responses.
Puts the URL or %URI{}
to be used for the static url generation.
Using this function on a %Plug.Conn{}
struct tells static_url/2
to use the given information for URL generation instead of the the %Plug.Conn{}
's endpoint configuration (much like put_router_url/2
but for static URLs).
put_view(Plug.Conn.t(), atom()) :: Plug.Conn.t()
Stores the view for rendering.
Raises Plug.Conn.AlreadySentError
if conn
is already sent.
Sends redirect response to the given url.
For security, :to
only accepts paths. Use the :external
option to redirect to any URL.
The response will be sent with the status code defined within the connection, via Plug.Conn.put_status/2
. If no status code is set, a 302 response is sent.
iex> redirect(conn, to: "/login") iex> redirect(conn, external: "http://elixir-lang.org")
render(Plug.Conn.t(), Keyword.t() | map() | binary() | atom()) :: Plug.Conn.t()
Render the given template or the default template specified by the current action with the given assigns.
See render/3
for more information.
render( Plug.Conn.t(), binary() | atom(), Keyword.t() | map() | binary() | atom() ) :: Plug.Conn.t()
Renders the given template
and assigns
based on the conn
information.
Once the template is rendered, the template format is set as the response content type (for example, an HTML template will set "text/html" as response content type) and the data is sent to the client with default status of 200.
conn
- the Plug.Conn
struct
template
- which may be an atom or a string. If an atom, like :index
, it will render a template with the same format as the one returned by get_format/1
. For example, for an HTML request, it will render the "index.html" template. If the template is a string, it must contain the extension too, like "index.json"
assigns
- a dictionary with the assigns to be used in the view. Those assigns are merged and have higher precedence than the connection assigns (conn.assigns
)
defmodule MyAppWeb.UserController do use Phoenix.Controller def show(conn, _params) do render(conn, "show.html", message: "Hello") end end
The example above renders a template "show.html" from the MyAppWeb.UserView
and sets the response content type to "text/html".
In many cases, you may want the template format to be set dynamically based on the request. To do so, you can pass the template name as an atom (without the extension):
def show(conn, _params) do render(conn, :show, message: "Hello") end
In order for the example above to work, we need to do content negotiation with the accepts plug before rendering. You can do so by adding the following to your pipeline (in the router):
plug :accepts, ["html"]
By default, Controllers render templates in a view with a similar name to the controller. For example, MyAppWeb.UserController
will render templates inside the MyAppWeb.UserView
. This information can be changed any time by using the put_view/2
function:
def show(conn, _params) do conn |> put_view(MyAppWeb.SpecialView) |> render(:show, message: "Hello") end
put_view/2
can also be used as a plug:
defmodule MyAppWeb.UserController do use Phoenix.Controller plug :put_view, MyAppWeb.SpecialView def show(conn, _params) do render(conn, :show, message: "Hello") end end
Templates are often rendered inside layouts. By default, Phoenix will render layouts for html requests. For example:
defmodule MyAppWeb.UserController do use Phoenix.Controller def show(conn, _params) do render(conn, "show.html", message: "Hello") end end
will render the "show.html" template inside an "app.html" template specified in MyAppWeb.LayoutView
. put_layout/2
can be used to change the layout, similar to how put_view/2
can be used to change the view.
layout_formats/1
and put_layout_formats/2
can be used to configure which formats support/require layout rendering (defaults to "html" only).
root_layout(Plug.Conn.t()) :: {atom(), String.t() | atom()} | false
Retrieves the current root layout.
router_module(Plug.Conn.t()) :: atom()
Returns the router module as an atom, raises if unavailable.
scrub_params(Plug.Conn.t(), String.t()) :: Plug.Conn.t()
Scrubs the parameters from the request.
This process is two-fold:
required_key
is presentrequired_key
(recursively) to nilsThis function is useful for removing empty strings sent via HTML forms. If you are providing an API, there is likely no need to invoke scrub_params/2
.
If the required_key
is not present, it will raise Phoenix.MissingParamError
.
iex> scrub_params(conn, "user")
Sends the given file or binary as a download.
The second argument must be {:binary, contents}
, where contents
will be sent as download, or{:file, path}
, where path
is the filesystem location of the file to be sent. Be careful to not interpolate the path from external parameters, as it could allow traversal of the filesystem.
The download is achieved by setting "content-disposition" to attachment. The "content-type" will also be set based on the extension of the given filename but can be customized via the :content_type
and :charset
options.
:filename
- the filename to be presented to the user as download:content_type
- the content type of the file or binary sent as download. It is automatically inferred from the filename extension:disposition
- specifies dispositon type (:attachment
or :inline
). If :attachment
was used, user will be prompted to save the file. If :inline
was used, the browser will attempt to open the file. Defaults to :attachment
.:charset
- the charset of the file, such as "utf-8". Defaults to none:offset
- the bytes to offset when reading. Defaults to 0
:length
- the total bytes to read. Defaults to :all
:encode
- encodes the filename using URI.encode_www_form/1
. Defaults to true
. When false
, disables encoding. If you disable encoding, you need to guarantee there are no special characters in the filename, such as quotes, newlines, etc. Otherwise you can expose your application to security attacksTo send a file that is stored inside your application priv directory:
path = Application.app_dir(:my_app, "priv/prospectus.pdf") send_download(conn, {:file, path})
When using {:file, path}
, the filename is inferred from the given path but may also be set explicitly.
To allow the user to download contents that are in memory as a binary or string:
send_download(conn, {:binary, "world"}, filename: "hello.txt")
See Plug.Conn.send_file/3
and Plug.Conn.send_resp/3
if you would like to access the low-level functions used to send files and responses via Plug.
Generates a status message from the template name.
iex> status_message_from_template("404.html") "Not Found" iex> status_message_from_template("whatever.html") "Internal Server Error"
text(Plug.Conn.t(), String.Chars.t()) :: Plug.Conn.t()
Sends text response.
iex> text(conn, "hello") iex> text(conn, :implements_to_string)
view_module(Plug.Conn.t()) :: atom()
Retrieves the current view.
view_template(Plug.Conn.t()) :: binary() | nil
Returns the template name rendered in the view as a string (or nil if no template was rendered).
© 2014 Chris McCord
Licensed under the MIT License.
https://hexdocs.pm/phoenix/Phoenix.Controller.html