Add support for sending telemetry events on throws and exits (#443)

lib/bandit/telemetry.ex

@@ -80,7 +80,8 @@ defmodule Bandit.Telemetry do
         the conn
       * `plug`: The Plug which is being used to serve this request. Specified as `{plug_module, plug_opts}`
       * `kind`: The kind of unexpected condition, typically `:exit`
-      * `exception`: The exception which caused this unexpected termination
+      * `exception`: The exception which caused this unexpected termination. May be an exception
+        or an arbitrary value when the event was an uncaught throw or an exit
       * `stacktrace`: The stacktrace of the location which caused this unexpected termination
 
   ## `[:bandit, :websocket, *]`
@@ -195,22 +196,20 @@ defmodule Bandit.Telemetry do
 
   @spec span_exception(t(), Exception.kind(), Exception.t() | term(), Exception.stacktrace()) ::
           :ok
-  def span_exception(span, :error, reason, stacktrace) when is_exception(reason) do
+  def span_exception(span, kind, reason, stacktrace) do
+    # Using :exit for backwards-compatibility with Bandit =< 1.5.7
+    kind = if kind == :error, do: :exit, else: kind
+
     metadata =
       Map.merge(span.start_metadata, %{
-        # Using :exit for backwards-compatibility with Bandit =< 1.5.7
-        kind: :exit,
+        kind: kind,
         exception: reason,
         stacktrace: stacktrace
       })
 
     span_event(span, :exception, %{}, metadata)
   end
 
-  def span_exception(_span, _kind, _reason, _stacktrace) do
-    :ok
-  end
-
   @doc false
   @spec span_event(t(), span_name(), :telemetry.event_measurements(), :telemetry.event_metadata()) ::
           :ok

test/bandit/http1/request_test.exs

@@ -2330,21 +2330,49 @@ defmodule HTTP1RequestTest do
     end
 
     @tag :capture_log
-    test "it should not send `exception` events for throwing requests", context do
+    test "it should send `exception` events for throwing requests", context do
       Req.get!(context.req, url: "/uncaught_throw")
 
-      refute_receive {:telemetry, [:bandit, :request, :stop], _, _}
+      assert_receive {:telemetry, [:bandit, :request, :exception], measurements, metadata}, 500
+
+      assert measurements
+             ~> %{monotonic_time: integer()}
+
+      assert metadata
+             ~> %{
+               connection_telemetry_span_context: reference(),
+               telemetry_span_context: reference(),
+               conn: struct_like(Plug.Conn, []),
+               plug: {__MODULE__, []},
+               kind: :throw,
+               exception: "thrown",
+               stacktrace: list()
+             }
     end
 
     def uncaught_throw(_conn) do
       throw("thrown")
     end
 
     @tag :capture_log
-    test "it should not send `exception` events for exiting requests", context do
+    test "it should send `exception` events for exiting requests", context do
       Req.get!(context.req, url: "/uncaught_exit")
 
-      refute_receive {:telemetry, [:bandit, :request, :exception], _, _}
+      assert_receive {:telemetry, [:bandit, :request, :exception], measurements, metadata}, 500
+
+      assert measurements
+             ~> %{monotonic_time: integer()}
+
+      assert metadata
+             ~> %{
+               connection_telemetry_span_context: reference(),
+               telemetry_span_context: reference(),
+               conn: struct_like(Plug.Conn, []),
+               plug: {__MODULE__, []},
+               kind: :exit,
+               exception: "exited",
+               stacktrace: list()
+             }
     end
 
     def uncaught_exit(_conn) do

test/bandit/http2/plug_test.exs

@@ -1012,21 +1012,47 @@ defmodule HTTP2PlugTest do
     end
 
     @tag :capture_log
-    test "it should not send `exception` events for throwing requests", context do
+    test "it should send `exception` events for throwing requests", context do
       Req.get!(context.req, url: "/uncaught_throw")
 
-      refute_receive {:telemetry, [:bandit, :request, :exception], _, _}
+      assert_receive {:telemetry, [:bandit, :request, :exception], measurements, metadata}, 500
+
+      assert measurements ~> %{monotonic_time: integer()}
+
+      assert metadata
+             ~> %{
+               connection_telemetry_span_context: reference(),
+               telemetry_span_context: reference(),
+               conn: struct_like(Plug.Conn, []),
+               plug: {__MODULE__, []},
+               kind: :throw,
+               exception: "thrown",
+               stacktrace: list()
+             }
     end
 
     def uncaught_throw(_conn) do
       throw("thrown")
     end
 
     @tag :capture_log
-    test "it should not send `exception` events for exiting requests", context do
+    test "it should send `exception` events for exiting requests", context do
       Req.get!(context.req, url: "/uncaught_exit")
 
-      refute_receive {:telemetry, [:bandit, :request, :exception], _, _}
+      assert_receive {:telemetry, [:bandit, :request, :exception], measurements, metadata}, 500
+
+      assert measurements ~> %{monotonic_time: integer()}
+
+      assert metadata
+             ~> %{
+               connection_telemetry_span_context: reference(),
+               telemetry_span_context: reference(),
+               conn: struct_like(Plug.Conn, []),
+               plug: {__MODULE__, []},
+               kind: :exit,
+               exception: "exited",
+               stacktrace: list()
+             }
     end
 
     def uncaught_exit(_conn) do