Plug behaviour

The plug specification.

There are two kind of plugs: function plugs and module 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

A module plug is an extension of the function plug. It must export a call/2 function, with the signature defined above, but it must also provide an init/1 function, for initialization of the options.

The result returned by init/1 is the one given as second argument to call/2. Note 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).

The Plug stack

The Plug.Builder module provides conveniences for stacking many plugs into a single module.