feat(request_id): add custom Logger's metadata option

lib/plug/request_id.ex

@@ -20,7 +20,8 @@ defmodule Plug.RequestId do
  config :logger, :default_formatter, metadata: [:request_id]
 
  We recommend to include this metadata configuration in your production
- configuration file.
+ configuration file. You can also configure a custom metadata key using 
+ `:metadata_as` (see below).
 
  > #### Programmatic access to the request ID {: .tip}
  >
@@ -47,6 +48,12 @@ defmodule Plug.RequestId do
 
  plug Plug.RequestId, assign_as: :plug_request_id
 
+ * `:metadata_as` - The key to use when storing the request ID in Logger metadata.
+ Default value is `:request_id`.
+
+ plug Plug.RequestId, metadata_as: :correlation_id
+
+
  """
 
  require Logger
@@ -57,15 +64,16 @@ defmodule Plug.RequestId do
  def init(opts) do
  {
  Keyword.get(opts, :http_header, "x-request-id"),
+ Keyword.get(opts, :metadata_as, :request_id),
  Keyword.get(opts, :assign_as)
  }
  end
 
  @impl true
- def call(conn, {header, assign_as}) do
+ def call(conn, {header, metadata_as, assign_as}) do
  request_id = get_request_id(conn, header)
 
- Logger.metadata(request_id: request_id)
+ Logger.metadata([{metadata_as, request_id}])
  conn = if assign_as, do: Conn.assign(conn, assign_as, request_id), else: conn
 
  Conn.put_resp_header(conn, header, request_id)

test/plug/request_id_test.exs

@@ -81,6 +81,20 @@ defmodule Plug.RequestIdTest do
  assert res_request_id == meta_request_id
  end
 
+ test "uses the custom Logger metadata if it was given" do
+ request_id = "existingidthatislongenough"
+
+ conn =
+ conn(:get, "/")
+ |> put_req_header("x-request-id", request_id)
+ |> call(metadata_as: :correlation_id)
+
+ [res_request_id] = get_resp_header(conn, "x-request-id")
+ meta_request_id = Logger.metadata()[:correlation_id]
+ assert res_request_id == request_id
+ assert res_request_id == meta_request_id
+ end
+
  defp generated_request_id?(request_id) do
  Regex.match?(~r/\A[A-Za-z0-9-_]+\z/, request_id)
  end