Propagate request start/end lazily

esrally/client/context.py

@@ -37,21 +37,19 @@ async def __aenter__(self):
 
     @property
     def request_start(self):
-        return self.ctx["request_start"]
+        return self.ctx.get("request_start")
 
     @property
     def request_end(self):
-        return self.ctx["request_end"]
+        return self.ctx.get("request_end")
 
     async def __aexit__(self, exc_type, exc_val, exc_tb):
-        # propagate earliest request start and most recent request end to parent
-        request_start = self.request_start
-        request_end = self.request_end
         self.ctx_holder.restore_context(self.token)
         # don't attempt to restore these values on the top-level context as they don't exist
         if self.token.old_value != contextvars.Token.MISSING:
-            self.ctx_holder.update_request_start(request_start)
-            self.ctx_holder.update_request_end(request_end)
+            # propagate earliest request start and most recent request end to parent
+            self.ctx_holder.update_request_start(self.request_start)
+            self.ctx_holder.update_request_end(self.request_end)
         self.token = None
         return False
 

tests/client/factory_test.py

@@ -427,6 +427,19 @@ def test_client_cert(self, tmp_path_factory: pytest.TempPathFactory):
 
 
 class TestRequestContextManager:
+    @pytest.mark.asyncio
+    async def test_does_not_propagates_empty_toplevel_context(self):
+        test_client = client.RequestContextHolder()
+        async with test_client.new_request_context() as top_level_ctx:
+            # Simulate that we started a request context but did not issue a request.
+            # This can happen when a runner throws an exception before it issued an
+            # API request. The most typical case is that a mandatory parameter is
+            # missing.
+            pass
+
+        assert top_level_ctx.request_start is None
+        assert top_level_ctx.request_end is None
+
     @pytest.mark.asyncio
     async def test_propagates_nested_context(self):
         test_client = client.RequestContextHolder()