tracing: forward the action journey on SDK calls

campus_python/tracing.py

@@ -28,6 +28,11 @@
 TRACE_ID_HEADER = "X-Request-ID"
 PARENT_SPAN_ID_HEADER = "X-Parent-Span-ID"
 
+# Mirror of campus.audit.middleware.journeys.ACTION_JOURNEY_HEADER
+# (campus#828): forwarded so a child service's span joins the caller's
+# action journey. Keep the two in lockstep.
+JOURNEY_ID_HEADER = "X-Journey-ID"
+
 # Same marker attribute as campus.audit.middleware.tracing so a session
 # instrumented by either implementation is left alone by the other.
 _INSTRUMENTED_ATTR = "_campus_trace_instrumented"
@@ -58,17 +63,30 @@ def current_context() -> tuple[str, str] | None:
 def propagation_headers() -> dict[str, str]:
     """Headers to attach to an outbound SDK call from the active request.
 
-    Empty outside a traced host request. The receiving campus service's
-    tracing middleware turns these into a child span of the caller's
-    span (#794, campus#816).
+    Empty outside a request context. The receiving campus service's
+    tracing middleware turns the trace headers into a child span of the
+    caller's span (#794, campus#816); the journeys middleware adopts
+    X-Journey-ID so the child span joins the caller's action journey
+    (campus#828). The two are independent: trace headers require span
+    state on flask.g (tracing middleware ran), the journey header only
+    requires an active journey.
     """
-    context = current_context()
-    if context is None:
-        return {}
-    return {
-        TRACE_ID_HEADER: context[0],
-        PARENT_SPAN_ID_HEADER: context[1],
-    }
+    headers: dict[str, str] = {}
+    try:
+        import flask
+    except ImportError:  # pragma: no cover - host without flask
+        return headers
+    if not flask.has_request_context():
+        return headers
+    trace_id = getattr(flask.g, "trace_id", None)
+    span_id = getattr(flask.g, "span_id", None)
+    if trace_id and span_id:
+        headers[TRACE_ID_HEADER] = trace_id
+        headers[PARENT_SPAN_ID_HEADER] = span_id
+    journey_id = getattr(flask.g, "journey_id", None)
+    if journey_id:
+        headers[JOURNEY_ID_HEADER] = journey_id
+    return headers
 
 
 def instrument_requests_session(session: requests.Session) -> bool:

tests/unit/test_trace_propagation.py

@@ -126,5 +126,60 @@ def test_instrumentation_is_idempotent(self):
         self.assertEqual(captured["headers"].get("X-Request-ID"), TRACE_ID)
 
 
+class TestJourneyForwarding(unittest.TestCase):
+    """Action-journey forwarding on SDK calls (campus#828).
+
+    When the host request carries an action journey (stashed as
+    flask.g.journey_id by the journeys middleware), SDK calls forward it
+    as X-Journey-ID so child services' spans join the same journey.
+    """
+
+    def test_journey_forwarded_inside_traced_request(self):
+        app = flask.Flask(__name__)
+        client = _make_client()
+        captured = _capture_send(client)
+
+        with app.test_request_context("/"):
+            flask.g.trace_id = TRACE_ID
+            flask.g.span_id = SPAN_ID
+            flask.g.journey_id = "uid-journey-abc123"
+            client.get("/ping")
+
+        self.assertEqual(
+            captured["headers"].get("X-Journey-ID"), "uid-journey-abc123"
+        )
+        self.assertEqual(captured["headers"].get("X-Request-ID"), TRACE_ID)
+
+    def test_no_journey_no_header(self):
+        """A traced request without a journey emits no journey header."""
+        app = flask.Flask(__name__)
+        client = _make_client()
+        captured = _capture_send(client)
+
+        with app.test_request_context("/"):
+            flask.g.trace_id = TRACE_ID
+            flask.g.span_id = SPAN_ID
+            client.get("/ping")
+
+        self.assertNotIn("X-Journey-ID", captured["headers"])
+
+    def test_journey_header_outside_trace_context(self):
+        """A journey without an active span still forwards (the journeys
+        middleware can adopt journeys on hosts where span tracing is off;
+        the trace headers are simply absent)."""
+        app = flask.Flask(__name__)
+        client = _make_client()
+        captured = _capture_send(client)
+
+        with app.test_request_context("/"):
+            flask.g.journey_id = "uid-journey-abc123"
+            client.get("/ping")
+
+        self.assertEqual(
+            captured["headers"].get("X-Journey-ID"), "uid-journey-abc123"
+        )
+        self.assertNotIn("X-Request-ID", captured["headers"])
+
+
 if __name__ == "__main__":
     unittest.main()