View Source Plug.ErrorHandler behaviour (Plug v1.14.0)

A module to be used in your existing plugs in order to provide error handling.

defmodule AppRouter do
  use Plug.Router
  use Plug.ErrorHandler

  plug :match
  plug :dispatch

  get "/hello" do
    send_resp(conn, 200, "world")

  @impl Plug.ErrorHandler
  def handle_errors(conn, %{kind: _kind, reason: _reason, stack: _stack}) do
    send_resp(conn, conn.status, "Something went wrong")

Once this module is used, a callback named handle_errors/2 should be defined in your plug. This callback will receive the connection already updated with a proper status code for the given exception. The second argument is a map containing:

  • the exception kind (:throw, :error or :exit),
  • the reason (an exception for errors or a term for others)
  • the stacktrace

After the callback is invoked, the error is re-raised.

It is advised to do as little work as possible when handling errors and avoid accessing data like parameters and session, as the parsing of those is what could have led the error to trigger in the first place.

Also notice that these pages are going to be shown in production. If you are looking for error handling to help during development, consider using Plug.Debugger.

Note: If this module is used with Plug.Debugger, it must be used after Plug.Debugger.

Link to this section Summary


Handle errors from plugs.

Link to this section Callbacks

@callback handle_errors(Plug.Conn.t(), %{
  kind: :error | :throw | :exit,
  reason: Exception.t() | term(),
  stack: Exception.stacktrace()
}) :: no_return()

Handle errors from plugs.

Called when an exception is raised during the processing of a plug.