Falcon: handle env vars locally vs globally (open-telemetry#650)

All instrumentations read most env vars today at module level. This has
a few disadvantages.

- harder to test.
- code executed on import even if instrumentation is not used.
- forces to use global vars.

This commit fixes the Falcon instrumentation to handle env vars locally
during instrumentor initialization and considerably simplifies testing.
Other instrumentations should receive similar treatment.

Author: owais

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

@@ -124,8 +124,6 @@ def response_hook(span, req, resp):
 _ENVIRON_EXC = "opentelemetry-falcon.exc"
 
 
-_excluded_urls = get_excluded_urls("FALCON")
-_traced_request_attrs = get_traced_request_attrs("FALCON")
 _response_propagation_setter = FuncSetter(falcon.Response.append_header)
 
 
@@ -159,17 +157,21 @@ def __init__(self, *args, **kwargs):
 
         trace_middleware = _TraceMiddleware(
             self._tracer,
-            kwargs.pop("traced_request_attributes", _traced_request_attrs),
+            kwargs.pop(
+                "traced_request_attributes", get_traced_request_attrs("FALCON")
+            ),
             kwargs.pop("request_hook", None),
             kwargs.pop("response_hook", None),
         )
         middlewares.insert(0, trace_middleware)
         kwargs["middleware"] = middlewares
+
+        self._excluded_urls = get_excluded_urls("FALCON")
         super().__init__(*args, **kwargs)
 
     def __call__(self, env, start_response):
         # pylint: disable=E1101
-        if _excluded_urls.url_disabled(env.get("PATH_INFO", "/")):
+        if self._excluded_urls.url_disabled(env.get("PATH_INFO", "/")):
             return super().__call__(env, start_response)
 
         start_time = _time_ns()

instrumentation/opentelemetry-instrumentation-falcon/tests/test_falcon.py

@@ -26,20 +26,13 @@
 from opentelemetry.semconv.trace import SpanAttributes
 from opentelemetry.test.test_base import TestBase
 from opentelemetry.trace import StatusCode, format_span_id, format_trace_id
-from opentelemetry.util.http import get_excluded_urls, get_traced_request_attrs
 
 from .app import make_app
 
 
 class TestFalconBase(TestBase):
     def setUp(self):
         super().setUp()
-        FalconInstrumentor().instrument(
-            request_hook=getattr(self, "request_hook", None),
-            response_hook=getattr(self, "response_hook", None),
-        )
-        self.app = make_app()
-        # pylint: disable=protected-access
         self.env_patch = patch.dict(
             "os.environ",
             {
@@ -48,20 +41,12 @@ def setUp(self):
             },
         )
         self.env_patch.start()
-        self.exclude_patch = patch(
-            "opentelemetry.instrumentation.falcon._excluded_urls",
-            get_excluded_urls("FALCON"),
-        )
-        middleware = self.app._middleware[0][  # pylint:disable=W0212
-            0
-        ].__self__
-        self.traced_patch = patch.object(
-            middleware,
-            "_traced_request_attrs",
-            get_traced_request_attrs("FALCON"),
+
+        FalconInstrumentor().instrument(
+            request_hook=getattr(self, "request_hook", None),
+            response_hook=getattr(self, "response_hook", None),
         )
-        self.exclude_patch.start()
-        self.traced_patch.start()
+        self.app = make_app()
 
     def client(self):
         return testing.TestClient(self.app)
@@ -71,8 +56,6 @@ def tearDown(self):
         with self.disable_logging():
             FalconInstrumentor().uninstrument()
         self.env_patch.stop()
-        self.exclude_patch.stop()
-        self.traced_patch.stop()
 
 
 class TestFalconInstrumentation(TestFalconBase):