fix(tracing): drop trailing comma when serializing baggage without third-party items

sentry_sdk/tracing_utils.py

@@ -973,7 +973,7 @@ def serialize(self, include_third_party: bool = False) -> str:
                 item = Baggage.SENTRY_PREFIX + quote(key) + "=" + quote(str(val))
                 items.append(item)
 
-        if include_third_party:
+        if include_third_party and self.third_party_items:
             items.append(self.third_party_items)
 
         return ",".join(items)

tests/integrations/celery/test_update_celery_task_headers.py

@@ -15,6 +15,12 @@
     "custom=value"
 )
 
+SENTRY_ONLY_BAGGAGE_VALUE = (
+    "sentry-trace_id=771a43a4192642f0b136d5159a501700,"
+    "sentry-public_key=49d0f7386ad645858ae85020e393bef3,"
+    "sentry-sample_rate=0.1337"
+)
+
 SENTRY_TRACE_VALUE = "771a43a4192642f0b136d5159a501700-1234567890abcdef-1"
 
 
@@ -124,6 +130,28 @@ def test_span_with_transaction_custom_headers(sentry_init):
             )
 
 
+def test_span_with_transaction_custom_headers_without_third_party_baggage(
+    sentry_init,
+):
+    sentry_init(traces_sample_rate=1.0)
+    headers = {
+        "baggage": SENTRY_ONLY_BAGGAGE_VALUE,
+        "sentry-trace": SENTRY_TRACE_VALUE,
+    }
+
+    with sentry_sdk.start_transaction(name="test_transaction"):
+        with sentry_sdk.start_span(op="test_span") as span:
+            outgoing_headers = _update_celery_task_headers(headers, span, False)
+
+            for baggage in (
+                outgoing_headers["baggage"],
+                outgoing_headers["headers"]["baggage"],
+            ):
+                assert baggage.startswith("sentry-")
+                assert not baggage.endswith(",")
+                assert "custom=" not in baggage
+
+
 @pytest.mark.parametrize("monitor_beat_tasks", [True, False])
 def test_celery_trace_propagation_default(sentry_init, monitor_beat_tasks):
     """

tests/tracing/test_baggage.py

@@ -67,6 +67,30 @@ def test_mixed_baggage():
     )
 
 
+def test_serialize_no_trailing_comma_without_third_party_items():
+    # With Sentry items but no third-party items, include_third_party=True must not
+    # append an empty segment, which would leave a trailing comma in the header.
+    header = (
+        "sentry-trace_id=771a43a4192642f0b136d5159a501700,"
+        "sentry-public_key=49d0f7386ad645858ae85020e393bef3,"
+        "sentry-sample_rate=0.01337"
+    )
+    baggage = Baggage.from_incoming_header(header)
+
+    assert baggage.third_party_items == ""
+
+    serialized = baggage.serialize(include_third_party=True)
+
+    assert not serialized.endswith(",")
+    # with no third-party items, include_third_party should change nothing
+    assert serialized == baggage.serialize()
+    assert serialized == (
+        "sentry-trace_id=771a43a4192642f0b136d5159a501700,"
+        "sentry-public_key=49d0f7386ad645858ae85020e393bef3,"
+        "sentry-sample_rate=0.01337"
+    )
+
+
 def test_malformed_baggage():
     header = ","