Specs

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.

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"]

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

Specs

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

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

Specs

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"

Clears all flash messages.

Specs

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.

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"

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.

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
  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.

Specs

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.

Examples

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).

Examples

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.

Specs

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

Sends html response.

Examples

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

Specs

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})

Specs

layout(Plug.Conn.t()) :: {atom(), String.t() | atom()} | false

Retrieves the current layout.

Specs

layout_formats(Plug.Conn.t()) :: [String.t()]

Retrieves current layout formats.

Merges a map into the flash.

Returns the updated connection.

Examples

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.

Examples

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.

Specs

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.

Examples

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.

Specs

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.

Specs

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.

Specs

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.

Specs

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.

Examples

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.

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 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 origin
• x-content-type-options - set to nosniff. This requires script and style tags to be sent with proper content type
• x-xss-protection - set to "1; mode=block" to improve XSS protection on both Chrome and IE
• 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
• cross-origin-window-policy - set to deny to avoid window control attacks

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.

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).

Specs

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.

Examples

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

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

Specs

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.

Specs

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.

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, 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.

layout_formats/1 and put_layout_formats/2 can be used to configure which formats support/require layout rendering (defaults to "html" only).

Specs

root_layout(Plug.Conn.t()) :: {atom(), String.t() | atom()} | false

Retrieves the current root layout.

Specs

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

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

Specs

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")

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 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 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.

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"

Specs

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

Sends text response.

Examples

iex> text(conn, "hello")

iex> text(conn, :implements_to_string)

Specs

view_module(Plug.Conn.t()) :: atom()

Retrieves the current view.

Specs

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).