Timber v0.1.4 Timber.Plug

Automatically captures context information about HTTP requests and responses in Plug-based frameworks like Phoenix.

Whether you use Plug by itself or as part of a framework like Phoenix, adding this plug to your pipeline will automatically add context information about HTTP requests and responses to your log statements.

Adding the Plug

Timber.Plug can be added to your plug pipeline using the standard Plug.Builder.plug/2 macro. The point at which you place it determines what state Timber will receive the connection in, therefore it’s recommended you place it as close to the origin of the request as possible.

Plug (Standalone or Plug.Router)

If you are using Plug without a framework, your setup will vary depending on your architecture. The call to plug Plug.Timber should be grouped with any other plugs you call prior to performing business logic.

Timber expects query paramters to have already been fetched on the connection using Plug.Conn.fetch_query_params/2.

Phoenix

Phoenix’s flexibility means there are multiple points in the plug pipeline where the Timber.Plug can be inserted. The recommended place is in a :logging pipeline in your router, but if you have more complex needs you can also place the plug in an endpoint or a controller.

defmodule MyApp.Router do
  use MyApp.Web, :router

  pipeline :logging do
    plug Timber.Plug
  end

  scope "/api", MyApp do
    pipe_through :logging
  end
end

If you place the plug call in your endpoint, you will need to make sure that it appears after Plug.RequestId (if you are using it) but before the call to your router.

Request ID

Timber does its best to track the request ID for every HTTP request in order to help you filter your logs responsibly. If you are calling the Plug.RequestId plug in your pipeline, you should make sure that Timber.Plug appears after that plug so that it can pick up the correct ID.

By default, Timber expects your request ID to be stored using the header name “X-Request-ID” (casing irrelevant), but that may not fit all needs. If you use a custom header name for your request ID, you can pass that name as an option to the plug:

plug Timber.Plug, request_id_header: "req-id"

Issues with Plug.ErrorHandler

If you are using Plug.ErrorHandler, you will lose any context regarding the response if an exception is raised. This is because of how the error handler works in practice. In order to capture information about the response, Timber registers a callback to be used before Plug actually sends the response. Plug stores this context information on the connection struct. When an exception is raised, the methodology used by the error handler will reset the conn to the state it was first accepted. This means the conn loses any changes made to it by your plug pipeline, including the callback Timber registered.

Summary

Functions

Adds contextual data about the request and response for this conn to Timber’s context stack

Prepares the given options for use in a plug pipeline

Functions

call(conn, opts)

Adds contextual data about the request and response for this conn to Timber’s context stack

When this plug is called, information about the request is immediately added to the stack.

init(opts)
init(Plug.opts) :: Plug.opts

Prepares the given options for use in a plug pipeline

When the Plug.Builder.plug/2 macro is called, it will use this function to prepare options. Any resulting options will be passed on to the plug on every call. The options accepted by this function are the same as defined by call/2.