Plug v1.7.1 Plug behaviour View Source

The plug specification.

There are two kind of plugs: function plugs and module plugs.

Function plugs

A function plug is any function that receives a connection and a set of options and returns a connection. Its type signature must be:

(Plug.Conn.t, Plug.opts) :: Plug.Conn.t

Module plugs

A module plug is an extension of the function plug. It is a module that must export:

  • a call/2 function with the signature defined above
  • an init/1 function which takes a set of options and initializes it.

The result returned by init/1 is passed as second argument to call/2. Note that init/1 may be called during compilation and as such it must not return pids, ports or values that are not specific to the runtime.

The API expected by a module plug is defined as a behaviour by the Plug module (this module).

Examples

Here’s an example of a function plug:

def json_header_plug(conn, opts) do
  Plug.Conn.put_resp_content_type(conn, "application/json")
end

Here’s an example of a module plug:

defmodule JSONHeaderPlug do
  import Plug.Conn

  def init(opts) do
    opts
  end

  def call(conn, _opts) do
    put_resp_content_type(conn, "application/json")
  end
end

The Plug pipeline

The Plug.Builder module provides conveniences for building plug pipelines.

Link to this section Summary

Link to this section Types

Link to this type opts() View Source
opts() ::
  binary()
  | tuple()
  | atom()
  | integer()
  | float()
  | [opts()]
  | %{optional(opts()) => opts()}

Link to this section Callbacks