tracing: Add `spanID` field to access logs and `http.vars.span_id` placeholder (#6646)

* logging: Add spanID field to access logs when tracing is enabled

Signed-off-by: YifanYang6 <[email protected]>

* tracing: add `http.vars.span_id` placeholder when tracing is enabled

Signed-off-by: YifanYang6 <[email protected]>

---------

Signed-off-by: YifanYang6 <[email protected]>

2 files changed, 11 insertions, 4 deletions

diff --git a/modules/caddyhttp/server_test.go b/modules/caddyhttp/server_test.go
index 2c8033d45..53f35368f 100644
--- a/modules/caddyhttp/server_test.go
+++ b/modules/caddyhttp/server_test.go
@@ -69,12 +69,13 @@ func TestServer_LogRequest(t *testing.T) {
 	}`, buf.String())
 }
 
-func TestServer_LogRequest_WithTraceID(t *testing.T) {
+func TestServer_LogRequest_WithTrace(t *testing.T) {
 	s := &Server{}
 
 	extra := new(ExtraLogFields)
 	ctx := context.WithValue(context.Background(), ExtraLogFieldsCtxKey, extra)
 	extra.Add(zap.String("traceID", "1234567890abcdef"))
+	extra.Add(zap.String("spanID", "12345678"))
 
 	req := httptest.NewRequest(http.MethodGet, "/", nil).WithContext(ctx)
 	rec := httptest.NewRecorder()
@@ -93,7 +94,8 @@ func TestServer_LogRequest_WithTraceID(t *testing.T) {
 		"msg":"handled request", "level":"info", "bytes_read":0,
 		"duration":"50ms", "resp_headers": {}, "size":0,
 		"status":0, "user_id":"",
-		"traceID":"1234567890abcdef"
+		"traceID":"1234567890abcdef",
+		"spanID":"12345678"
 	}`, buf.String())
 }
 
@@ -144,12 +146,13 @@ func BenchmarkServer_LogRequest_NopLogger(b *testing.B) {
 	}
 }
 
-func BenchmarkServer_LogRequest_WithTraceID(b *testing.B) {
+func BenchmarkServer_LogRequest_WithTrace(b *testing.B) {
 	s := &Server{}
 
 	extra := new(ExtraLogFields)
 	ctx := context.WithValue(context.Background(), ExtraLogFieldsCtxKey, extra)
 	extra.Add(zap.String("traceID", "1234567890abcdef"))
+	extra.Add(zap.String("spanID", "12345678"))
 
 	req := httptest.NewRequest(http.MethodGet, "/", nil).WithContext(ctx)
 	rec := httptest.NewRecorder()
diff --git a/modules/caddyhttp/tracing/tracer.go b/modules/caddyhttp/tracing/tracer.go
index 89c617bf4..261952aa6 100644
--- a/modules/caddyhttp/tracing/tracer.go
+++ b/modules/caddyhttp/tracing/tracer.go
@@ -88,11 +88,15 @@ func (ot *openTelemetryWrapper) serveHTTP(w http.ResponseWriter, r *http.Request
 	spanCtx := trace.SpanContextFromContext(ctx)
 	if spanCtx.IsValid() {
 		traceID := spanCtx.TraceID().String()
+		spanID := spanCtx.SpanID().String()
 		// Add a trace_id placeholder, accessible via `{http.vars.trace_id}`.
 		caddyhttp.SetVar(ctx, "trace_id", traceID)
-		// Add the trace id to the log fields for the request.
+		// Add a span_id placeholder, accessible via `{http.vars.span_id}`.
+		caddyhttp.SetVar(ctx, "span_id", spanID)
+		// Add the traceID and spanID to the log fields for the request.
 		if extra, ok := ctx.Value(caddyhttp.ExtraLogFieldsCtxKey).(*caddyhttp.ExtraLogFields); ok {
 			extra.Add(zap.String("traceID", traceID))
+			extra.Add(zap.String("spanID", spanID))
 		}
 	}
 	next := ctx.Value(nextCallCtxKey).(*nextCall)