View Source Phoenix.Controller (Phoenix v1.7.18)

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, 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.

Then we invoke render/3, passing the connection, the template to render (typically named after the action), and the user: user as assigns. We will explore all of those concepts next.

Connection

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.

Rendering and layouts

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.

There are two ways to render content in a controller. One option is to invoke format-specific functions, such as html/2 and json/2.

However, most commonly controllers invoke custom modules called views. Views are modules capable of rendering a custom format. This is done by specifying the option :formats when defining the controller:

use Phoenix.Controller,
  formats: [:html, :json]

Now, when invoking render/3, a controller named MyAppWeb.UserController will invoke MyAppWeb.UserHTML and MyAppWeb.UserJSON respectively when rendering each format:

def show(conn, %{"id" => id}) do
  user = Repo.get(User, id)
  # Will invoke UserHTML.show(%{user: user}) for html requests
  # Will invoke UserJSON.show(%{user: user}) for json requests
  render(conn, :show, user: user)
end

Some formats are also handy to have layouts, which render content shared across all pages. We can also specify layouts on use:

use Phoenix.Controller,
  formats: [:html, :json],
  layouts: [html: MyAppWeb.Layouts]

You can also specify formats and layouts to render by calling put_view/2 and put_layout/2 directly with a connection. The line above can also be written directly in your actions as:

conn
|> put_view(html: MyAppWeb.UserHTML, json: MyAppWeb.UserJSON)
|> put_layout(html: MyAppWeb.Layouts)

Backwards compatibility

In previous Phoenix versions, a controller you always render MyApp.UserView. This behaviour can be explicitly retained by passing a suffix to the formats options:

use Phoenix.Controller,
  formats: [html: "View", json: "View"],
  layouts: [html: MyAppWeb.Layouts]

Options

When used, the controller supports the following options to customize template rendering:

  • :formats - the formats this controller will render by default. For example, specifying formats: [:html, :json] for a controller named MyAppWeb.UserController will invoke MyAppWeb.UserHTML and MyAppWeb.UserJSON when respectively rendering each format. If :formats is not set, the default view is set to MyAppWeb.UserView

  • :layouts - which layouts to render for each format, for example: [html: DemoWeb.Layouts]

Deprecated options:

  • :namespace - sets the namespace for the layout. Use :layouts instead

  • :put_default_views - controls whether the default view and layout should be set or not. Set formats: [] and layouts: [] instead

Plug pipeline

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.

Guards

plug/2 in controllers supports guards, allowing a developer to configure a plug to only run in some particular action.

plug :do_something when action in [:show, :edit]

Due to operator precedence in Elixir, if the second argument is a keyword list, we need to wrap the keyword in [...] when using when:

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.

Controllers are plugs

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 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).

Overriding 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

Summary

Types

layout()
view()

Functions

accepts(conn, accepted)

Performs content negotiation based on the available formats.

action_fallback(plug)

Registers the plug to call as a fallback to the controller action.

action_name(conn)

Returns the action name as an atom, raises if unavailable.

allow_jsonp(conn, opts \\ [])

A plug that may convert a JSON response into a JSONP one.

clear_flash(conn)

Clears all flash messages.

controller_module(conn)

Returns the controller module as an atom, raises if unavailable.

current_path(conn)

Returns the current request path with its default query parameters

current_path(conn, params)

Returns the current path with the given query parameters.

current_url(conn)

Returns the current request url with its default query parameters

current_url(conn, params)

Returns the current request URL with query params.

delete_csrf_token()

Deletes the CSRF token from the process dictionary.

endpoint_module(conn)

Returns the endpoint module as an atom, raises if unavailable.

fetch_flash(conn, opts \\ [])

Fetches the flash storage.

get_csrf_token()

Gets or generates a CSRF token.

get_flash(conn) deprecated

Returns a map of previously set flash messages or an empty map.

get_flash(conn, key) deprecated

Returns a message from flash by key (or nil if no message is available for key).

get_format(conn)

Returns the request format, such as "json", "html".

html(conn, data)

Sends html response.

json(conn, data)

Sends JSON response.

layout(conn, format \\ nil)

Retrieves the current layout for the given format.

layout_formats(conn) deprecated

Retrieves current layout formats.

merge_flash(conn, enumerable)

Merges a map into the flash.

protect_from_forgery(conn, opts \\ [])

Enables CSRF protection.

put_flash(conn, key, message)

Persists a value in flash.

put_format(conn, format)

Puts the format in the connection.

put_layout(conn, layout)

Stores the layout for rendering.

put_layout_formats(conn, formats) deprecated

Sets which formats have a layout when rendering.

put_new_layout(conn, layout)

Stores the layout for rendering if one was not stored yet.

put_new_view(conn, formats)

Stores the view for rendering if one was not stored yet.

put_root_layout(conn, layout)

Stores the root layout for rendering.

put_router_url(conn, uri)

Puts the url string or %URI{} to be used for route generation.

put_secure_browser_headers(conn, headers \\ %{})

Put headers that improve browser security.

put_static_url(conn, uri)

Puts the URL or %URI{} to be used for the static url generation.

put_view(conn, formats)

Stores the view for rendering.

redirect(conn, opts)

Sends redirect response to the given url.

render(conn, template_or_assigns \\ [])

Render the given template or the default template specified by the current action with the given assigns.

render(conn, template, assigns)

Renders the given template and assigns based on the conn information.

root_layout(conn, format \\ nil)

Retrieves the current root layout for the given format.

router_module(conn)

Returns the router module as an atom, raises if unavailable.

scrub_params(conn, required_key)

Scrubs the parameters from the request.

send_download(conn, kind, opts \\ [])

Sends the given file or binary as a download.

status_message_from_template(template)

Generates a status message from the template name.

text(conn, data)

Sends text response.

view_module(conn, format \\ nil)

Retrieves the current view for the given format.

view_template(conn)

Returns the template name rendered in the view as a string (or nil if no template was rendered).

Types

layout()

@type layout() :: {module(), layout_name :: atom()} | atom() | false

view()

@type view() :: atom()

Functions

accepts(conn, accepted)

@spec accepts(Plug.Conn.t(), [binary()]) :: Plug.Conn.t()

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.

Examples

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)

Custom media types

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"]

action_fallback(plug)

(macro)

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.

Examples 

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(:forbidden)
    |> put_view(MyErrorView)
    |> render(:"403")
  end
end

action_name(conn)

@spec action_name(Plug.Conn.t()) :: atom()

Returns the action name as an atom, raises if unavailable.

allow_jsonp(conn, opts \\ [])

@spec 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.

Examples 

# 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"

clear_flash(conn)

Clears all flash messages.

controller_module(conn)

@spec controller_module(Plug.Conn.t()) :: atom()

Returns the controller module as an atom, raises if unavailable.

current_path(conn)

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.

The path is normalized based on the conn.script_name and conn.path_info. For example, "/foo//bar/" will become "/foo/bar". If you want the original path, use conn.request_path instead.

current_path(conn, params)

Returns the current path with the given query parameters.

You may also retrieve only the request path by passing an empty map of params.

Examples 

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"

The path is normalized based on the conn.script_name and conn.path_info. For example, "/foo//bar/" will become "/foo/bar". If you want the original path, use conn.request_path instead.

current_url(conn)

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.

current_url(conn, params)

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.

Examples 

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"

Custom URL Generation

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
  current_uri = MyAppWeb.Endpoint.struct_url()
  current_path = Phoenix.Controller.current_path(conn, params)
  Phoenix.VerifiedRoutes.unverified_url(%URI{current_uri | scheme: "https"}, current_path)
end

However, if you want all generated URLs to always have a certain schema, host, etc, you may use put_router_url/2.

delete_csrf_token()

Deletes the CSRF token from the process dictionary.

Note: The token is deleted only after a response has been sent.

endpoint_module(conn)

@spec endpoint_module(Plug.Conn.t()) :: atom()

Returns the endpoint module as an atom, raises if unavailable.

fetch_flash(conn, opts \\ [])

Fetches the flash storage.

get_csrf_token()

Gets or generates a CSRF token.

If a token exists, it is returned, otherwise it is generated and stored in the process dictionary.

get_flash(conn)

This function is deprecated. get_flash/1 is deprecated. Use the @flash assign provided by the :fetch_flash plug.

Returns a map of previously set flash messages or an empty map.

Examples 

iex> get_flash(conn)
%{}

iex> conn = put_flash(conn, :info, "Welcome Back!")
iex> get_flash(conn)
%{"info" => "Welcome Back!"}

get_flash(conn, key)

This function is deprecated. get_flash/2 is deprecated. Use Phoenix.Flash.get(@flash, key) instead.

Returns a message from flash by key (or nil if no message is available for key).

Examples 

iex> conn = put_flash(conn, :info, "Welcome Back!")
iex> get_flash(conn, :info)
"Welcome Back!"

get_format(conn)

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(conn, data)

@spec html(Plug.Conn.t(), iodata()) :: Plug.Conn.t()

Sends html response.

Examples 

iex> html(conn, "<html><head>...")

json(conn, data)

@spec 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.

Examples 

iex> json(conn, %{id: 123})

layout(conn, format \\ nil)

@spec layout(Plug.Conn.t(), binary() | nil) :: {atom(), String.t() | atom()} | false

Retrieves the current layout for the given format.

If no format is given, takes the current one from the connection.

layout_formats(conn)

This function is deprecated. layout_formats/1 is deprecated, pass a keyword list to put_layout/put_root_layout instead. 
@spec layout_formats(Plug.Conn.t()) :: [String.t()]

Retrieves current layout formats.

merge_flash(conn, enumerable)

Merges a map into the flash.

Returns the updated connection.

Examples 

iex> conn = merge_flash(conn, info: "Welcome Back!")
iex> Phoenix.Flash.get(conn.assigns.flash, :info)
"Welcome Back!"

protect_from_forgery(conn, opts \\ [])

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.

put_flash(conn, key, message)

Persists a value in flash.

Returns the updated connection.

Examples 

iex> conn = put_flash(conn, :info, "Welcome Back!")
iex> Phoenix.Flash.get(conn.assigns.flash, :info)
"Welcome Back!"

put_format(conn, format)

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(conn, layout)

@spec put_layout(Plug.Conn.t(), [{format :: atom(), layout()}] | false) ::
  Plug.Conn.t()

Stores the layout for rendering.

The layout must be given as keyword list where the key is the request format the layout will be applied to (such as :html) and the value is one of:

  • {module, layout} with the module the layout is defined and the name of the layout as an atom

  • layout when the name of the layout. This requires a layout for the given format in the shape of {module, layout} to be previously given

  • false which disables the layout

If false is given without a format, all layouts are disabled.

Examples 

iex> layout(conn)
false

iex> conn = put_layout(conn, html: {AppView, :application})
iex> layout(conn)
{AppView, :application}

iex> conn = put_layout(conn, html: :print)
iex> layout(conn)
{AppView, :print}

Raises Plug.Conn.AlreadySentError if conn is already sent.

put_layout_formats(conn, formats)

This function is deprecated. put_layout_formats/2 is deprecated, pass a keyword list to put_layout/put_root_layout instead. 
@spec put_layout_formats(Plug.Conn.t(), [String.t()]) :: Plug.Conn.t()

Sets which formats have a layout when rendering.

Examples 

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(conn, layout)

@spec put_new_layout(Plug.Conn.t(), [{format :: atom(), layout()}] | layout()) ::
  Plug.Conn.t()

Stores the layout for rendering if one was not stored yet.

See put_layout/2 for more information.

Raises Plug.Conn.AlreadySentError if conn is already sent.

put_new_view(conn, formats)

@spec put_new_view(Plug.Conn.t(), [{format :: atom(), view()}] | view()) ::
  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(conn, layout)

@spec put_root_layout(Plug.Conn.t(), [{format :: atom(), layout()}] | false) ::
  Plug.Conn.t()

Stores the root layout for rendering.

The layout must be given as keyword list where the key is the request format the layout will be applied to (such as :html) and the value is one of:

  • {module, layout} with the module the layout is defined and the name of the layout as an atom

  • layout when the name of the layout. This requires a layout for the given format in the shape of {module, layout} to be previously given

  • false which disables the layout

Examples 

iex> root_layout(conn)
false

iex> conn = put_root_layout(conn, html: {AppView, :root})
iex> root_layout(conn)
{AppView, :root}

iex> conn = put_root_layout(conn, html: :bare)
iex> root_layout(conn)
{AppView, :bare}

Raises Plug.Conn.AlreadySentError if conn is already sent.

put_router_url(conn, uri)

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.

Examples

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_secure_browser_headers(conn, headers \\ %{})

Put headers that improve browser security.

It sets the following headers:

  • referrer-policy - only send origin on cross origin requests
  • x-frame-options - set to SAMEORIGIN to avoid clickjacking through iframes unless in the same origin
  • x-content-type-options - set to nosniff. This requires script and style tags to be sent with proper content type
  • x-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 data

A 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.

put_static_url(conn, uri)

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 %Plug.Conn{}'s endpoint configuration (much like put_router_url/2 but for static URLs).

put_view(conn, formats)

@spec put_view(Plug.Conn.t(), [{format :: atom(), view()}] | view()) :: Plug.Conn.t()

Stores the view for rendering.

Raises Plug.Conn.AlreadySentError if conn is already sent.

Examples 

# Use single view module
iex> put_view(conn, AppView)

# Use multiple view module for content negotiation
iex> put_view(conn, html: AppHTML, json: AppJSON)

redirect(conn, opts)

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.

Examples 

iex> redirect(conn, to: "/login")

iex> redirect(conn, external: "https://elixir-lang.org")

render(conn, template_or_assigns \\ [])

@spec 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(conn, template, assigns)

@spec render(Plug.Conn.t(), binary() | atom(), Keyword.t() | map()) :: 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.

Arguments

  • 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)

Examples 

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"]

Views

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, html: MyAppWeb.SpecialView

  def show(conn, _params) do
    render(conn, :show, message: "Hello")
  end
end

Layouts

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.

root_layout(conn, format \\ nil)

@spec root_layout(Plug.Conn.t(), binary() | nil) ::
  {atom(), String.t() | atom()} | false

Retrieves the current root layout for the given format.

If no format is given, takes the current one from the connection.

router_module(conn)

@spec router_module(Plug.Conn.t()) :: atom()

Returns the router module as an atom, raises if unavailable.

scrub_params(conn, required_key)

@spec scrub_params(Plug.Conn.t(), String.t()) :: Plug.Conn.t()

Scrubs the parameters from the request.

This process is two-fold:

  • Checks to see if the required_key is present
  • Changes empty parameters of required_key (recursively) to nils

This 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.

Examples 

iex> scrub_params(conn, "user")

send_download(conn, kind, opts \\ [])

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.

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 disposition 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/2. 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 attacks

Examples

To 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.

status_message_from_template(template)

Generates a status message from the template name.

Examples 

iex> status_message_from_template("404.html")
"Not Found"
iex> status_message_from_template("whatever.html")
"Internal Server Error"

text(conn, data)

@spec text(Plug.Conn.t(), String.Chars.t()) :: Plug.Conn.t()

Sends text response.

Examples 

iex> text(conn, "hello")

iex> text(conn, :implements_to_string)

view_module(conn, format \\ nil)

@spec view_module(Plug.Conn.t(), binary() | nil) :: atom()

Retrieves the current view for the given format.

If no format is given, takes the current one from the connection.

view_template(conn)

@spec 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).