Expose opentracing trace id in response headers

changelog.d/10199.misc

@@ -0,0 +1 @@
+Expose opentracing trace id in response headers.

synapse/federation/transport/server.py

@@ -344,6 +344,12 @@ async def new_func(request, *args, **kwargs):
                     "incoming-federation-request", tags=request_tags
                 )
 
+            if hasattr(scope, "span"):
+                # include the trace id in the response headers.
+                request.responseHeaders.addRawHeader(
+                    "Synapse-Trace-Id", f"{scope.span.context.trace_id:x}"
+                )
+
             with scope:
                 if origin and self.RATELIMIT:
                     with ratelimiter.ratelimit(origin) as d:

synapse/logging/opentracing.py

@@ -842,6 +842,11 @@ def trace_servlet(request: "SynapseRequest", extract_context: bool = False):
     else:
         scope = start_active_span(request_name)
 
+    # include the trace id in the response headers.
+    request.responseHeaders.addRawHeader(
+        "Synapse-Trace-Id", f"{scope.span.context.trace_id:x}"
+    )
+
     with scope:
         try:
             yield