View Source Plug behaviour (Plug v1.13.6)
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 specific to the runtime.
The API expected by a module plug is defined as a behaviour by the
Plug
module (this module).
examples
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 pipeline
The Plug.Builder
module provides conveniences for building plug
pipelines.
Link to this section Summary
Functions
Forwards requests to another Plug setting the connection to a trailing subpath of the request.
Run a series of Plugs at runtime.
Link to this section Types
Link to this section Callbacks
@callback call(conn :: Plug.Conn.t(), opts()) :: Plug.Conn.t()
Link to this section Functions
@spec forward(Plug.Conn.t(), [String.t()], atom(), opts()) :: Plug.Conn.t()
Forwards requests to another Plug setting the connection to a trailing subpath of the request.
The path_info
on the forwarded connection will only include the trailing segments
of the request path supplied to forward, while conn.script_name
will
retain the correct base path for e.g. url generation.
example
Example
defmodule Router do
def init(opts), do: opts
def call(conn, opts) do
case conn do
# Match subdomain
%{host: "admin." <> _} ->
AdminRouter.call(conn, opts)
# Match path on localhost
%{host: "localhost", path_info: ["admin" | rest]} ->
Plug.forward(conn, rest, AdminRouter, opts)
_ ->
MainRouter.call(conn, opts)
end
end
end
@spec run( Plug.Conn.t(), [{module(), opts()} | (Plug.Conn.t() -> Plug.Conn.t())], Keyword.t() ) :: Plug.Conn.t()
Run a series of Plugs at runtime.
The plugs given here can be either a tuple, representing a module plug and their options, or a simple function that receives a connection and returns a connection.
If any of the plugs halt, the remaining plugs are not invoked. If the given connection was already halted, none of the plugs are invoked either.
While Plug.Builder
works at compile-time, this is a straight-forward
alternative that works at runtime.
examples
Examples
Plug.run(conn, [{Plug.Head, []}, &IO.inspect/1])
options
Options
:log_on_halt
- a log level to be used if a Plug halts