ext/requests - apply custom attributes callback (open-telemetry#656)

Implement passing an optional span_callback callback when instrumenting requests.

The callback will be called just before returning the result and will be invoked with the span and the result (type of requests.Response).

This mimics the same functionality as the js http plugin.

ext/opentelemetry-ext-requests/src/opentelemetry/ext/requests/__init__.py

@@ -55,7 +55,7 @@
 
 
 # pylint: disable=unused-argument
-def _instrument(tracer_provider=None):
+def _instrument(tracer_provider=None, span_callback=None):
     """Enables tracing of all requests calls that go through
       :code:`requests.session.Session.request` (this includes
       :code:`requests.get`, etc.)."""
@@ -101,6 +101,8 @@ def instrumented_request(self, method, url, *args, **kwargs):
             span.set_status(
                 Status(_http_status_to_canonical_code(result.status_code))
             )
+            if span_callback is not None:
+                span_callback(span, result)
 
             return result
 
@@ -156,8 +158,22 @@ def _http_status_to_canonical_code(code: int, allow_redirect: bool = True):
 
 
 class RequestsInstrumentor(BaseInstrumentor):
+    """An instrumentor for requests
+    See `BaseInstrumentor`
+    """
+
     def _instrument(self, **kwargs):
-        _instrument(tracer_provider=kwargs.get("tracer_provider"))
+        """Instruments requests module
+
+        Args:
+            **kwargs: Optional arguments
+                ``tracer_provider``: a TracerProvider, defaults to global
+                ``span_callback``: An optional callback invoked before returning the http response. Invoked with Span and requests.Response
+        """
+        _instrument(
+            tracer_provider=kwargs.get("tracer_provider"),
+            span_callback=kwargs.get("span_callback"),
+        )
 
     def _uninstrument(self, **kwargs):
         _uninstrument()

ext/opentelemetry-ext-requests/tests/test_requests_integration.py

@@ -183,6 +183,37 @@ def test_distributed_context(self):
         finally:
             propagators.set_global_httptextformat(previous_propagator)
 
+    def test_span_callback(self):
+        RequestsInstrumentor().uninstrument()
+
+        def span_callback(span, result: requests.Response):
+            span.set_attribute(
+                "http.response.body", result.content.decode("utf-8")
+            )
+
+        RequestsInstrumentor().instrument(
+            tracer_provider=self.tracer_provider, span_callback=span_callback,
+        )
+
+        result = requests.get(self.URL)
+        self.assertEqual(result.text, "Hello!")
+
+        span_list = self.memory_exporter.get_finished_spans()
+        self.assertEqual(len(span_list), 1)
+        span = span_list[0]
+
+        self.assertEqual(
+            span.attributes,
+            {
+                "component": "http",
+                "http.method": "GET",
+                "http.url": self.URL,
+                "http.status_code": 200,
+                "http.status_text": "OK",
+                "http.response.body": "Hello!",
+            },
+        )
+
     def test_custom_tracer_provider(self):
         resource = resources.Resource.create({})
         result = self.create_tracer_provider(resource=resource)