Fix UnboundLocalError local variable 'start' referenced before assign…

…ment (open-telemetry#1889)

Co-authored-by: Pablo Collins <pablo.collins@gmail.com>

CHANGELOG.md

@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Fixed
+
+- `opentelemetry-instrumentation-asgi` Fix UnboundLocalError local variable 'start' referenced before assignment 
+  ([#1889](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1889))
+
 ## Version 1.19.0/0.40b0 (2023-07-13)
 - `opentelemetry-instrumentation-asgi` Add `http.server.request.size` metric
   ([#1867](https://github.com/open-telemetry/opentelemetry-python-contrib/pull/1867))

instrumentation/opentelemetry-instrumentation-asgi/src/opentelemetry/instrumentation/asgi/__init__.py

@@ -538,6 +538,7 @@ async def __call__(self, scope, receive, send):
             receive: An awaitable callable yielding dictionaries
             send: An awaitable callable taking a single dictionary as argument.
         """
+        start = default_timer()
         if scope["type"] not in ("http", "websocket"):
             return await self.app(scope, receive, send)
 
@@ -591,7 +592,6 @@ async def __call__(self, scope, receive, send):
                     send,
                     duration_attrs,
                 )
-                start = default_timer()
 
                 await self.app(scope, otel_receive, otel_send)
         finally:

instrumentation/opentelemetry-instrumentation-asgi/tests/test_asgi_middleware.py

@@ -14,6 +14,7 @@
 
 # pylint: disable=too-many-lines
 
+import asyncio
 import sys
 import unittest
 from timeit import default_timer
@@ -796,5 +797,38 @@ async def wrapped_app(scope, receive, send):
         )
 
 
+class TestAsgiApplicationRaisingError(AsgiTestBase):
+    def tearDown(self):
+        pass
+
+    @mock.patch(
+        "opentelemetry.instrumentation.asgi.collect_custom_request_headers_attributes",
+        side_effect=ValueError("whatever"),
+    )
+    def test_asgi_issue_1883(
+        self, mock_collect_custom_request_headers_attributes
+    ):
+        """
+        Test that exception UnboundLocalError local variable 'start' referenced before assignment is not raised
+        See https://github.com/open-telemetry/opentelemetry-python-contrib/issues/1883
+        """
+        app = otel_asgi.OpenTelemetryMiddleware(simple_asgi)
+        self.seed_app(app)
+        self.send_default_request()
+        try:
+            asyncio.get_event_loop().run_until_complete(
+                self.communicator.stop()
+            )
+        except ValueError as exc_info:
+            self.assertEqual(exc_info.args[0], "whatever")
+        except Exception as exc_info:  # pylint: disable=W0703
+            self.fail(
+                "expecting ValueError('whatever'), received instead: "
+                + str(exc_info)
+            )
+        else:
+            self.fail("expecting ValueError('whatever')")
+
+
 if __name__ == "__main__":
     unittest.main()