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agents,lib,src,test: add traceSampleRate support #430

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agents,lib,src,test: add traceSampleRate support #430

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1 change: 1 addition & 0 deletions agents/grpc/proto/reconfigure.proto
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ message ReconfigureBody {
optional uint32 tracingModulesBlacklist = 11;
optional bool contCpuProfile = 12;
optional bool assetsEnabled = 13;
optional double traceSampleRate = 14;
}

message ReconfigureEvent {
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4 changes: 4 additions & 0 deletions agents/grpc/src/grpc_agent.cc
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Expand Up @@ -1758,6 +1758,10 @@ void GrpcAgent::reconfigure(const grpcagent::CommandRequest& request) {
out["assetsEnabled"] = body.assetsenabled();
}

if (body.has_tracesamplerate()) {
out["traceSampleRate"] = body.tracesamplerate();
}
Comment on lines +1761 to +1763
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@coderabbitai coderabbitai bot Mar 3, 2026

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⚠️ Potential issue | 🟠 Major

traceSampleRate is accepted but not returned in reconfigure event body.

Lines 1761-1763 map inbound updates, but PopulateReconfigureEvent does not set body.traceSampleRate. This makes reconfigure responses incomplete even when the update is applied.

💡 Suggested fix 
diff --git a/agents/grpc/src/grpc_agent.cc b/agents/grpc/src/grpc_agent.cc
@@ void PopulateReconfigureEvent(grpcagent::ReconfigureEvent* reconfigure_event,
   it = config.find("assetsEnabled");
   if (it != config.end()) {
     body->set_assetsenabled(*it);
   }
+  it = config.find("traceSampleRate");
+  if (it != config.end()) {
+    body->set_tracesamplerate(*it);
+  }
 }
🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@agents/grpc/src/grpc_agent.cc` around lines 1761 - 1763,
PopulateReconfigureEvent currently omits the traceSampleRate field when building
the outgoing reconfigure event body; update PopulateReconfigureEvent to set
body.traceSampleRate from the internal config so the outgoing event mirrors
inbound updates (i.e., when you previously read body.tracesamplerate() on
incoming updates, ensure PopulateReconfigureEvent calls the corresponding setter
to populate body.traceSampleRate in the event). Locate the
PopulateReconfigureEvent function in grpc_agent.cc and add the traceSampleRate
assignment using the same source/field used for other mapped settings so
reconfigure responses include traceSampleRate.


DebugJSON("Reconfigure out: \n%s\n", out);

UpdateConfig(out.dump());
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83 changes: 52 additions & 31 deletions agents/grpc/src/proto/reconfigure.pb.cc
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56 changes: 49 additions & 7 deletions agents/grpc/src/proto/reconfigure.pb.h
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11 changes: 8 additions & 3 deletions lib/internal/otel/trace.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

const {
JSONStringify,
MathRandom,
SafeMap,
Uint8Array,
} = primordials;
Expand Down Expand Up @@ -278,10 +279,14 @@ class Tracer {
}

const internalId = newInternalSpanId();
// Follow parent, root always sampled.
let flags = api.TraceFlags.SAMPLED;
if (parentContext)
// Root spans make the sampling decision, child spans inherit parent flags.
let flags;
if (!parentContext) {
const sampled = MathRandom() < binding.trace_sample_rate[0];
flags = sampled ? api.TraceFlags.SAMPLED : api.TraceFlags.NONE;
} else {
flags = parentContext.traceFlags;
}
const spanContext = new SpanContext(internalId,
spanId,
flags,
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