Update the adapter spec to included telemetry events

.gitignore

@@ -1,4 +1,5 @@
 /_build
+/cover
 /deps
 /docs
 /doc

lib/plug/conn/adapter.ex

@@ -1,6 +1,10 @@
 defmodule Plug.Conn.Adapter do
   @moduledoc """
-  Specification of the connection adapter API implemented by webservers
+  Specification of the connection adapter API implemented by webservers.
+
+  All adapters are required to emit the proper `plug_adapter.request.start`,
+  `plug_adapter.request.stop` and `plug_adapter.request.failure` telemetry
+  events on every request.
   """
   alias Plug.Conn
 

lib/plug/telemetry.ex

@@ -13,9 +13,9 @@ defmodule Plug.Telemetry do
   In the example above, two events will be emitted:
 
     * `[:my, :plug, :start]` - emitted when the plug is invoked.
-      The event carries no measurement.  The metadata is the whole
-      `Plug.Conn` under the `:conn` key and any leftover options
-      given to the plug under `:options`.
+      The event carries the `system_time` as measurement. The metadata
+      is the whole `Plug.Conn` under the `:conn` key and any leftover
+      options given to the plug under `:options`.
 
     * `[:my, :plug, :stop]` - emitted right before the request is sent.
       The event carries a single measurement, `:duration`,  which is the
@@ -72,7 +72,8 @@ defmodule Plug.Telemetry do
   @impl true
   def call(conn, {start_event, stop_event, opts}) do
     start_time = System.monotonic_time()
-    :telemetry.execute(start_event, %{time: start_time}, %{conn: conn, options: opts})
+    metadata = %{conn: conn, options: opts}
+    :telemetry.execute(start_event, %{system_time: System.system_time()}, metadata)
 
     Plug.Conn.register_before_send(conn, fn conn ->
       duration = System.monotonic_time() - start_time

test/plug/telemetry_test.exs

@@ -60,8 +60,8 @@ defmodule Plug.TelemetryTest do
 
     assert_received {:event, [:pipeline, :start], measurements, metadata}
     assert map_size(measurements) == 1
-    assert %{time: time} = measurements
-    assert is_integer(time)
+    assert %{system_time: system_time} = measurements
+    assert is_integer(system_time) and system_time > 0
     assert map_size(metadata) == 2
     assert %{conn: %Plug.Conn{}, options: [extra_options: :hello]} = metadata