Added ability to extract span attributes from falcon request objects.

OTEL_PYTHON_FALCON_TRACED_REQUEST_ATTRS env var can be set to a command
separated list of attributes names that will be extracted from Falcon's
request object and set as attributes on spans.

Author: owais

Diff for: instrumentation/opentelemetry-instrumentation-falcon/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Added support for `OTEL_PYTHON_FALCON_TRACED_REQUEST_ATTRS` ([#1158](https://github.com/open-telemetry/opentelemetry-python/pull/1158))
+
 ## Version 0.13b0
 
 Released 2020-09-17

Diff for: instrumentation/opentelemetry-instrumentation-falcon/README.rst

@@ -31,6 +31,21 @@ For example,
 
 will exclude requests such as ``https://site/client/123/info`` and ``https://site/xyz/healthcheck``.
 
+Request attributes
+********************
+To extract certain attributes from Falcon's request object and use them as span attributes, set the environment variable ``OTEL_PYTHON_FALCON_TRACED_REQUEST_ATTRS`` to a comma
+delimited list of request attribute names. 
+
+For example,
+
+::
+
+    export OTEL_PYTHON_FALCON_TRACED_REQUEST_ATTRS='query_string,uri_template'
+
+will extract path_info and content_type attributes from every traced request and add them as span attritbues.
+
+Falcon Request object reference: https://falcon.readthedocs.io/en/stable/api/request_and_response.html#id1
+
 References
 ----------
 

Diff for: instrumentation/opentelemetry-instrumentation-falcon/src/opentelemetry/instrumentation/falcon/__init__.py

@@ -50,6 +50,7 @@ def on_get(self, req, resp):
 
 import opentelemetry.instrumentation.wsgi as otel_wsgi
 from opentelemetry import configuration, context, propagators, trace
+from opentelemetry.configuration import Configuration
 from opentelemetry.instrumentation.falcon.version import __version__
 from opentelemetry.instrumentation.instrumentor import BaseInstrumentor
 from opentelemetry.instrumentation.utils import http_status_to_canonical_code
@@ -92,13 +93,16 @@ def _uninstrument(self, **kwargs):
 
 class _InstrumentedFalconAPI(falcon.API):
     def __init__(self, *args, **kwargs):
-        mw = kwargs.pop("middleware", [])
-        if not isinstance(mw, (list, tuple)):
-            mw = [mw]
+        middlewares = kwargs.pop("middleware", [])
+        if not isinstance(middlewares, (list, tuple)):
+            middlewares = [middlewares]
 
         self._tracer = trace.get_tracer(__name__, __version__)
-        mw.insert(0, _TraceMiddleware(self._tracer))
-        kwargs["middleware"] = mw
+        trace_middleware = _TraceMiddleware(
+            self._tracer, kwargs.get("traced_request_attributes")
+        )
+        middlewares.insert(0, trace_middleware)
+        kwargs["middleware"] = middlewares
         super().__init__(*args, **kwargs)
 
     def __call__(self, env, start_response):
@@ -144,8 +148,24 @@ def _start_response(status, response_headers, *args, **kwargs):
 class _TraceMiddleware:
     # pylint:disable=R0201,W0613
 
-    def __init__(self, tracer=None):
+    def __init__(self, tracer=None, traced_request_attrs=None):
         self.tracer = tracer
+        self._traced_request_attrs = traced_request_attrs or [
+            attr.strip()
+            for attr in (
+                Configuration().FALCON_TRACED_REQUEST_ATTRS or ""
+            ).split(",")
+        ]
+
+    def process_request(self, req, resp):
+        span = req.env.get(_ENVIRON_SPAN_KEY)
+        if not span:
+            return
+
+        for attr in self._traced_request_attrs:
+            value = getattr(req, attr, None)
+            if value is not None:
+                span.set_attribute(attr, str(value))
 
     def process_resource(self, req, resp, resource, params):
         span = req.env.get(_ENVIRON_SPAN_KEY)

Diff for: instrumentation/opentelemetry-instrumentation-falcon/tests/test_falcon.py

@@ -171,3 +171,20 @@ def test_exclude_lists(self):
         self.client().simulate_get(path="/hello")
         span_list = self.memory_exporter.get_finished_spans()
         self.assertEqual(len(span_list), 1)
+
+    def test_traced_request_attributes(self):
+        self.client().simulate_get(path="/hello?q=abc")
+        span = self.memory_exporter.get_finished_spans()[0]
+        self.assertNotIn("query_string", span.attributes)
+        self.memory_exporter.clear()
+
+        middleware = self.app._middleware[0][  # pylint:disable=W0212
+            0
+        ].__self__
+        with patch.object(
+            middleware, "_traced_request_attrs", ["query_string"]
+        ):
+            self.client().simulate_get(path="/hello?q=abc")
+            span = self.memory_exporter.get_finished_spans()[0]
+            self.assertIn("query_string", span.attributes)
+            self.assertEqual(span.attributes["query_string"], "q=abc")