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Plug behaviour

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
  conn |> put_resp_content_type("application/json")
end

Here’s an example of a module plug:

defmodule JSONHeaderPlug do
  def init(opts) do
    opts
  end

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

The Plug pipeline

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

Summary

Types

opts()

Callbacks

call(arg0, opts)
init(opts)

Types

opts()

opts ::
  binary |
  tuple |
  atom |
  integer |
  float |
  [opts] |
  %{optional(opts) => opts}

Callbacks

call(arg0, opts)

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

init(opts)

init(opts) :: opts

© 2013 Plataformatec
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/plug/1.3.0/Plug.html