Fix tracing module sampling option should default to 1.0 when not set (…

…#3231)

This commit ensures that if the `sampling` option of the tracing
module's client is not provided by user, the Client defaults to
sample 100% of the request.

cmd/tests/tracing_module_test.go

@@ -154,6 +154,58 @@ func TestTracingModuleClient_HundredPercentSampling(t *testing.T) {
 	assertHasTraceIDMetadata(t, jsonResults, 100, tb.Replacer.Replace("HTTPBIN_IP_URL/tracing"))
 }
 
+func TestTracingModuleClient_NoSamplingSetShouldAlwaysSample(t *testing.T) {
+	t.Parallel()
+	tb := httpmultibin.NewHTTPMultiBin(t)
+
+	var gotRequests int64
+	var gotSampleFlags int64
+
+	tb.Mux.HandleFunc("/tracing", func(w http.ResponseWriter, r *http.Request) {
+		atomic.AddInt64(&gotRequests, 1)
+
+		traceparent := r.Header.Get("traceparent")
+		require.NotEmpty(t, traceparent)
+		require.Len(t, traceparent, 55)
+
+		if traceparent[54] == '1' {
+			atomic.AddInt64(&gotSampleFlags, 1)
+		}
+	})
+
+	script := tb.Replacer.Replace(`
+		import http from "k6/http";
+		import { check } from "k6";
+		import tracing from "k6/experimental/tracing";
+
+		export const options = {
+			// 100 iterations to make sure we get 100% sampling
+			iterations: 100,
+		}
+
+		// We do not set the sampling option, thus the default
+		// behavior should be to always sample.
+		const instrumentedHTTP = new tracing.Client({
+			propagator: "w3c",
+		})
+
+		export default function () {
+			instrumentedHTTP.get("HTTPBIN_IP_URL/tracing");
+		};
+	`)
+
+	ts := getSingleFileTestState(t, script, []string{"--out", "json=results.json"}, 0)
+	cmd.ExecuteWithGlobalState(ts.GlobalState)
+
+	assert.Equal(t, int64(100), atomic.LoadInt64(&gotSampleFlags))
+	assert.Equal(t, int64(100), atomic.LoadInt64(&gotRequests))
+
+	jsonResults, err := fsext.ReadFile(ts.FS, "results.json")
+	require.NoError(t, err)
+
+	assertHasTraceIDMetadata(t, jsonResults, 100, tb.Replacer.Replace("HTTPBIN_IP_URL/tracing"))
+}
+
 func TestTracingModuleClient_ZeroPercentSampling(t *testing.T) {
 	t.Parallel()
 	tb := httpmultibin.NewHTTPMultiBin(t)

js/modules/k6/experimental/tracing/module.go

@@ -93,7 +93,7 @@ func (mi *ModuleInstance) newClient(cc goja.ConstructorCall) *goja.Object {
 //
 // When used in the context of a k6 script, it will automatically replace
 // the imported http module's methods with instrumented ones.
-func (mi *ModuleInstance) instrumentHTTP(options options) {
+func (mi *ModuleInstance) instrumentHTTP(options goja.Value) {
 	rt := mi.vu.Runtime()
 
 	if mi.vu.State() != nil {
@@ -109,10 +109,17 @@ func (mi *ModuleInstance) instrumentHTTP(options options) {
 		common.Throw(rt, err)
 	}
 
+	// Parse the options instance from the JS value.
+	// This will also validate the options, and set the sampling
+	// rate to 1.0 if the option was not set.
+	opts, err := newOptions(rt, options)
+	if err != nil {
+		common.Throw(rt, fmt.Errorf("unable to parse options object; reason: %w", err))
+	}
+
 	// Initialize the tracing module's instance default client,
 	// and configure it using the user-supplied set of options.
-	var err error
-	mi.Client, err = NewClient(mi.vu, options)
+	mi.Client, err = NewClient(mi.vu, opts)
 	if err != nil {
 		common.Throw(rt, err)
 	}

js/modules/k6/experimental/tracing/options.go

@@ -38,7 +38,7 @@ func newOptions(rt *goja.Runtime, from goja.Value) (options, error) {
 	}
 
 	fromSamplingValue := from.ToObject(rt).Get("sampling")
-	if fromSamplingValue == nil || common.IsNullish(fromSamplingValue) {
+	if common.IsNullish(fromSamplingValue) {
 		opts.Sampling = defaultSamplingRate
 	}