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rpc: extract OpenTelemetry trace context from request headers #33599

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Merged
lightclient merged 2 commits into from
Jan 14, 2026
Merged

rpc: extract OpenTelemetry trace context from request headers #33599

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b7c3df5
rpc: extract opentelemetry trace context from request headers
jrhea Jan 13, 2026
5465410
rpc: add test for http propagator
lightclient Jan 14, 2026
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6 changes: 6 additions & 0 deletions rpc/http.go
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,9 @@ import (
"strconv"
"sync"
"time"

"go.opentelemetry.io/otel"
"go.opentelemetry.io/otel/propagation"
)

const (
Expand Down Expand Up @@ -334,6 +337,9 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
ctx := r.Context()
ctx = context.WithValue(ctx, peerInfoContextKey{}, connInfo)

// Extract trace context from incoming headers.
ctx = otel.GetTextMapPropagator().Extract(ctx, propagation.HeaderCarrier(r.Header))

// All checks passed, create a codec that reads directly from the request body
// until EOF, writes the response to w, and orders the server to process a
// single request.
Expand Down
36 changes: 34 additions & 2 deletions rpc/tracing_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,7 +21,9 @@ import (
"net/http/httptest"
"testing"

"go.opentelemetry.io/otel"
"go.opentelemetry.io/otel/attribute"
"go.opentelemetry.io/otel/propagation"
sdktrace "go.opentelemetry.io/otel/sdk/trace"
"go.opentelemetry.io/otel/sdk/trace/tracetest"
)
Expand Down Expand Up @@ -60,16 +62,33 @@ func newTracingServer(t *testing.T) (*Server, *sdktrace.TracerProvider, *tracete

// TestTracingHTTP verifies that RPC spans are emitted when processing HTTP requests.
func TestTracingHTTP(t *testing.T) {
t.Parallel()
// Not parallel: this test modifies the global otel TextMapPropagator.

// Set up a propagator to extract W3C Trace Context headers.
originalPropagator := otel.GetTextMapPropagator()
otel.SetTextMapPropagator(propagation.TraceContext{})
t.Cleanup(func() { otel.SetTextMapPropagator(originalPropagator) })

server, tracer, exporter := newTracingServer(t)
httpsrv := httptest.NewServer(server)
t.Cleanup(httpsrv.Close)

// Define the expected trace and span IDs for context propagation.
const (
traceID = "4bf92f3577b34da6a3ce929d0e0e4736"
parentSpanID = "00f067aa0ba902b7"
traceparent = "00-" + traceID + "-" + parentSpanID + "-01"
)

client, err := DialHTTP(httpsrv.URL)
if err != nil {
t.Fatalf("failed to dial: %v", err)
}
t.Cleanup(client.Close)

// Set trace context headers.
client.SetHeader("traceparent", traceparent)

// Make a successful RPC call.
var result echoResult
if err := client.Call(&result, "test_echo", "hello", 42, &echoArgs{S: "world"}); err != nil {
Expand All @@ -92,8 +111,10 @@ func TestTracingHTTP(t *testing.T) {
}
}
if rpcSpan == nil {
t.Fatalf("jsonrpc.test/echo span not found.")
t.Fatalf("jsonrpc.test/echo span not found")
}

// Verify span attributes.
attrs := attributeMap(rpcSpan.Attributes)
if attrs["rpc.system"] != "jsonrpc" {
t.Errorf("expected rpc.system=jsonrpc, got %v", attrs["rpc.system"])
Expand All @@ -107,6 +128,17 @@ func TestTracingHTTP(t *testing.T) {
if _, ok := attrs["rpc.jsonrpc.request_id"]; !ok {
t.Errorf("expected rpc.jsonrpc.request_id attribute to be set")
}

// Verify the span's parent matches the traceparent header values.
if got := rpcSpan.Parent.TraceID().String(); got != traceID {
t.Errorf("parent trace ID mismatch: got %s, want %s", got, traceID)
}
if got := rpcSpan.Parent.SpanID().String(); got != parentSpanID {
t.Errorf("parent span ID mismatch: got %s, want %s", got, parentSpanID)
}
if !rpcSpan.Parent.IsRemote() {
t.Error("expected parent span context to be marked as remote")
}
}

// TestTracingBatchHTTP verifies that RPC spans are emitted for batched JSON-RPC calls over HTTP.
Expand Down