Added ability to extract span attributes from django request objects.

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

Author: owais

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

@@ -3,6 +3,7 @@
 ## Unreleased
 
 - Changed span name extraction from request to comply semantic convention ([#992](https://github.com/open-telemetry/opentelemetry-python/pull/992)) 
+- Added support for `OTEL_PYTHON_DJANGO_TRACED_REQUEST_ATTRS` ([#1154](https://github.com/open-telemetry/opentelemetry-python/pull/1154))
 
 ## Version 0.13b0
 

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

@@ -30,6 +30,19 @@ For example,
 
 will exclude requests such as ``https://site/client/123/info`` and ``https://site/xyz/healthcheck``.
 
+Request attributes
+********************
+To extract certain attributes from Django's request object and use them as span attributes, set the environment variable ``OTEL_PYTHON_DJANGO_TRACED_REQUEST_ATTRS`` to a comma
+delimited list of request attribute names. 
+
+For example,
+
+::
+
+    export OTEL_PYTHON_DJANGO_TRACED_REQUEST_ATTRS='path_info,content_type'
+
+will extract path_info and content_type attributes from every traced request and add them as span attritbues.
+
 References
 ----------
 

Diff for: instrumentation/opentelemetry-instrumentation-django/src/opentelemetry/instrumentation/django/middleware.py

@@ -58,6 +58,13 @@ class _DjangoMiddleware(MiddlewareMixin):
     else:
         _excluded_urls = ExcludeList(_excluded_urls)
 
+    _traced_request_attrs = [
+        attr.strip()
+        for attr in (Configuration().DJANGO_TRACED_REQUEST_ATTRS or "").split(
+            ","
+        )
+    ]
+
     @staticmethod
     def _get_span_name(request):
         try:
@@ -95,6 +102,11 @@ def process_request(self, request):
         tracer = get_tracer(__name__, __version__)
 
         attributes = collect_request_attributes(environ)
+        for attr in self._traced_request_attrs:
+            if hasattr(request, attr):
+                value = str(getattr(request, attr))
+                if value:
+                    attributes[attr] = value
 
         span = tracer.start_span(
             self._get_span_name(request),

Diff for: instrumentation/opentelemetry-instrumentation-django/tests/test_middleware.py

@@ -174,3 +174,30 @@ def test_span_name_404(self):
 
         span = span_list[0]
         self.assertEqual(span.name, "HTTP GET")
+
+    def test_traced_request_attrs(self):
+        with patch(
+            "opentelemetry.instrumentation.django.middleware._DjangoMiddleware._traced_request_attrs",
+            [],
+        ):
+            Client().get("/span_name/1234/", CONTENT_TYPE="test/ct")
+            span_list = self.memory_exporter.get_finished_spans()
+            self.assertEqual(len(span_list), 1)
+
+            span = span_list[0]
+            self.assertNotIn("path_info", span.attributes)
+            self.assertNotIn("content_type", span.attributes)
+            self.memory_exporter.clear()
+
+        with patch(
+            "opentelemetry.instrumentation.django.middleware._DjangoMiddleware._traced_request_attrs",
+            ["path_info", "content_type", "non_existing_variable"],
+        ):
+            Client().get("/span_name/1234/", CONTENT_TYPE="test/ct")
+            span_list = self.memory_exporter.get_finished_spans()
+            self.assertEqual(len(span_list), 1)
+
+            span = span_list[0]
+            self.assertEqual(span.attributes["path_info"], "/span_name/1234/")
+            self.assertEqual(span.attributes["content_type"], "test/ct")
+            self.assertNotIn("non_existing_variable", span.attributes)