Plug v1.7.2 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.