Add ServerTimings API

src/api/routes/route.py

@@ -184,23 +184,28 @@ def api_function(track_in_diagnostics: bool = True,
                     if random.random() * 100 < int(api.config["API_ROULETTE_MODE"]):
                         raise ApiClientException(random.choice(ALL_ERRORS_RANDOM))
 
-                start_time = time.time()
+                start_time = time.time_ns()
                 result = func(*args, **kwargs)
+                stop_time = time.time_ns()
                 if call_time_counter is not None:
-                    call_time_counter.trigger(int((time.time() - start_time) * 1000))
+                    call_time_counter.trigger(int((stop_time - start_time) / 1000000))
 
                 if isinstance(result, Response):
-                    return result
+                    resp = result
                 elif isinstance(result, ApiResponse):
-                    return result.build_response()
+                    resp = result.build_response()
                 elif result is None:
-                    return ApiResponse(None, HTTP_200_OK, None).build_response()
+                    resp = ApiResponse(None, HTTP_200_OK, None).build_response()
                 elif isinstance(result, dict):
-                    return ApiResponse(result).build_response()
+                    resp = ApiResponse(result).build_response()
                 elif isinstance(result, tuple) and len(result) == 2:
-                    return ApiResponse(result[0], result[1]).build_response()
+                    resp = ApiResponse(result[0], result[1]).build_response()
                 else:  # pragma: no cover
                     raise Exception(f"Api route {truncate_string(request.path)} returned result of unknown type: {str(result)}")
+
+                if call_time_counter is not None:  # i.e. diagnostics are enabled
+                    resp.headers["Server-Timing"] = f"api;dur={(stop_time - start_time) / 1000000}"
+                return resp
             except ApiClientException as e:
                 return api_on_error(e.error)
             except (TransactionConflictError, NoAvailableConnectionError) as e: