fix(sampling): sentry-trace should take precedence over baggage

sentry_sdk/tracing_utils.py

@@ -1575,20 +1575,6 @@ def add_sentry_baggage_to_headers(
     )
 
 
-def _get_effective_sample_rate(
-    client: "Any", propagation_context: "PropagationContext"
-) -> "Union[float, bool]":
-    if propagation_context.parent_sampled is not None:
-        propagation_context_sample_rate = propagation_context._sample_rate()
-
-        if propagation_context_sample_rate is not None:
-            return propagation_context_sample_rate
-        else:
-            return propagation_context.parent_sampled
-    else:
-        return client.options["traces_sample_rate"]
-
-
 def _make_sampling_decision(
     name: str,
     attributes: "Optional[Attributes]",
@@ -1651,13 +1637,15 @@ def _make_sampling_decision(
                 "[Tracing] traces_sampler raised; falling back to parent sample rate or traces_sample_rate",
                 exc_info=True,
             )
-            sample_rate = _get_effective_sample_rate(
-                client=client, propagation_context=propagation_context
-            )
+            if propagation_context.parent_sampled is not None:
+                sample_rate = propagation_context.parent_sampled
+            else:
+                sample_rate = client.options["traces_sample_rate"]
     else:
-        sample_rate = _get_effective_sample_rate(
-            client=client, propagation_context=propagation_context
-        )
+        if propagation_context.parent_sampled is not None:
+            sample_rate = propagation_context.parent_sampled
+        else:
+            sample_rate = client.options["traces_sample_rate"]
 
     # Validate whether the sample_rate we got is actually valid. Since
     # traces_sampler is user-provided, it could return anything.

tests/integrations/stdlib/test_httplib.py

@@ -318,7 +318,7 @@ def getresponse(self, *args, **kwargs):
         expected_outgoing_baggage = (
             "sentry-trace_id=771a43a4192642f0b136d5159a501700,"
             "sentry-public_key=49d0f7386ad645858ae85020e393bef3,"
-            "sentry-sample_rate=0.01337,"
+            "sentry-sample_rate=1.0,"
             "sentry-user_id=Am%C3%A9lie,"
             "sentry-sample_rand=0.000005,"
             "sentry-sampled=true"
@@ -345,8 +345,6 @@ def getresponse(self, *args, **kwargs):
             sampled=1,
         )
 
-        # Note: the sample rate here is actually wrong. It's fixed in the
-        # streaming path
         expected_outgoing_baggage = (
             "sentry-trace_id=771a43a4192642f0b136d5159a501700,"
             "sentry-public_key=49d0f7386ad645858ae85020e393bef3,"

tests/tracing/test_span_streaming.py

@@ -988,10 +988,67 @@ def test_outgoing_traceparent_and_baggage_incoming_trace(
                 traceparent == f"{trace_id}-{span_id}-{'1' if parent_sampled else '0'}"
             )
 
-        # As we've received incoming baggage, we mustn't modify it ourselves and
-        # have to propagate it as-is
         baggage = sentry_sdk.get_baggage()
         baggage_items = dict(tuple(item.split("=")) for item in baggage.split(","))
+
+        # As we've received incoming baggage, we shouldn't modify it ourselves
+        # and should propagate it as-is. However, in the case where our
+        # effective sample rate overrides the parent sample rate, we update the
+        # sample rate in the baggage as a consequence of updating the sample rate
+        # in the DSC.
+        if traces_sample_rate is not None:
+            incoming_baggage["sentry-sample_rate"] = str(float(parent_sampled))
+
+        assert baggage_items == incoming_baggage
+
+
+def test_outgoing_traceparent_and_baggage_inconsistent_incoming_trace(
+    sentry_init,
+):
+    # We correctly propagate even if we get a sample_rate/sample_rand/sampled
+    # baggage combination from upstream that doesn't align with the parent
+    # sampling decision
+    sentry_init(
+        traces_sample_rate=1.0,
+        trace_lifecycle="stream",
+    )
+
+    trace_id = "0af7651916cd43dd8448eb211c80319c"
+    parent_span_id = "b7ad6b7169203331"
+
+    # Baggage says sampled, sentry-trace says unsampled. sentry-trace takes
+    # precedence
+    incoming_sentry_trace = f"{trace_id}-{parent_span_id}-0"
+    incoming_baggage = {
+        "sentry-trace_id": trace_id,
+        "sentry-sample_rate": "0.75",
+        "sentry-sample_rand": "0.500000",
+        "sentry-sampled": "true",
+    }
+
+    sentry_sdk.traces.continue_trace(
+        {
+            "sentry-trace": incoming_sentry_trace,
+            "baggage": ",".join(
+                sorted([f"{k}={v}" for k, v in incoming_baggage.items()])
+            ),
+        }
+    )
+
+    with sentry_sdk.traces.start_span(name="span") as span:
+        assert span.sampled is False
+
+        traceparent = sentry_sdk.get_traceparent()
+
+        span_id = span.span_id
+        assert traceparent == f"{trace_id}-{span_id}-0"
+
+        # We shouldn't be updating incoming baggage, but in the case where our
+        # effective sample rate overrides the parent sample rate, we do this as
+        # a consequence of updating the sample rate in the DSC.
+        baggage = sentry_sdk.get_baggage()
+        baggage_items = dict(tuple(item.split("=")) for item in baggage.split(","))
+        incoming_baggage["sentry-sample_rate"] = "0.0"
         assert baggage_items == incoming_baggage