Expose the tracing client publicly as k6/experimental/tracing.Client

This commit exposes the Client constructor publicly as part of the
k6/experimental/tracing module. From this point forward users will be
able to instantiate the Client, and perform instrumented HTTP requests
using it.

This commit also adds a bunch of integration tests covering the expected
behavior of the module's API.

cmd/tests/tracing_module_test.go

@@ -0,0 +1,140 @@
+package tests
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.k6.io/k6/cmd"
+	"go.k6.io/k6/lib/testutils/httpmultibin"
+)
+
+func TestTracingModuleClient(t *testing.T) {
+	t.Parallel()
+	tb := httpmultibin.NewHTTPMultiBin(t)
+
+	gotRequests := 0
+
+	tb.Mux.HandleFunc("/tracing", func(w http.ResponseWriter, r *http.Request) {
+		gotRequests++
+		assert.NotEmpty(t, r.Header.Get("traceparent"))
+		assert.Len(t, r.Header.Get("traceparent"), 55)
+	})
+
+	script := tb.Replacer.Replace(`
+		import http from "k6/http";
+		import { check } from "k6";
+		import tracing from "k6/experimental/tracing";
+
+		const instrumentedHTTP = new tracing.Client({
+			propagator: "w3c",
+		})
+
+		export default function () {
+			instrumentedHTTP.del("HTTPBIN_IP_URL/tracing");
+			instrumentedHTTP.get("HTTPBIN_IP_URL/tracing");
+			instrumentedHTTP.head("HTTPBIN_IP_URL/tracing");
+			instrumentedHTTP.options("HTTPBIN_IP_URL/tracing");
+			instrumentedHTTP.patch("HTTPBIN_IP_URL/tracing");
+			instrumentedHTTP.post("HTTPBIN_IP_URL/tracing");
+			instrumentedHTTP.put("HTTPBIN_IP_URL/tracing");
+			instrumentedHTTP.request("GET", "HTTPBIN_IP_URL/tracing");
+		};
+	`)
+
+	ts := getSingleFileTestState(t, script, []string{"--out", "json=results.json"}, 0)
+	cmd.ExecuteWithGlobalState(ts.GlobalState)
+
+	assert.Equal(t, 8, gotRequests)
+
+	jsonResults, err := afero.ReadFile(ts.FS, "results.json")
+	require.NoError(t, err)
+
+	gotHTTPDataPoints := false
+
+	for _, jsonLine := range bytes.Split(jsonResults, []byte("\n")) {
+		if len(jsonLine) == 0 {
+			continue
+		}
+
+		var line sampleEnvelope
+		require.NoError(t, json.Unmarshal(jsonLine, &line))
+
+		if line.Type != "Point" {
+			continue
+		}
+
+		// Filter metric samples which are not related to http
+		if !strings.HasPrefix(line.Metric, "http_") {
+			continue
+		}
+
+		gotHTTPDataPoints = true
+
+		anyTraceID, hasTraceID := line.Data.Metadata["trace_id"]
+		require.True(t, hasTraceID)
+
+		traceID, gotTraceID := anyTraceID.(string)
+		require.True(t, gotTraceID)
+
+		assert.Len(t, traceID, 32)
+	}
+
+	assert.True(t, gotHTTPDataPoints)
+}
+
+func TestTracingClient_DoesNotInterfereWithHTTPModule(t *testing.T) {
+	t.Parallel()
+	tb := httpmultibin.NewHTTPMultiBin(t)
+
+	gotRequests := 0
+	gotInstrumentedRequests := 0
+
+	tb.Mux.HandleFunc("/tracing", func(w http.ResponseWriter, r *http.Request) {
+		gotRequests++
+
+		if r.Header.Get("traceparent") != "" {
+			gotInstrumentedRequests++
+			assert.Len(t, r.Header.Get("traceparent"), 55)
+		}
+	})
+
+	script := tb.Replacer.Replace(`
+		import http from "k6/http";
+		import { check } from "k6";
+		import tracing from "k6/experimental/tracing";
+
+		const instrumentedHTTP = new tracing.Client({
+			propagator: "w3c",
+		})
+
+		export default function () {
+			instrumentedHTTP.get("HTTPBIN_IP_URL/tracing");
+			http.get("HTTPBIN_IP_URL/tracing");
+			instrumentedHTTP.head("HTTPBIN_IP_URL/tracing");
+		};
+	`)
+
+	ts := getSingleFileTestState(t, script, []string{"--out", "json=results.json"}, 0)
+	cmd.ExecuteWithGlobalState(ts.GlobalState)
+
+	assert.Equal(t, 3, gotRequests)
+	assert.Equal(t, 2, gotInstrumentedRequests)
+}
+
+// sampleEnvelope is a trimmed version of the struct found
+// in output/json/wrapper.go
+// TODO: use the json output's wrapper struct instead if it's ever exported
+type sampleEnvelope struct {
+	Metric string `json:"metric"`
+	Type   string `json:"type"`
+	Data   struct {
+		Value    float64                `json:"value"`
+		Metadata map[string]interface{} `json:"metadata"`
+	} `json:"data"`
+}

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

@@ -2,6 +2,11 @@
 package tracing
 
 import (
+	"errors"
+	"fmt"
+
+	"github.com/dop251/goja"
+	"go.k6.io/k6/js/common"
 	"go.k6.io/k6/js/modules"
 )
 
@@ -38,5 +43,29 @@ func (*RootModule) NewModuleInstance(vu modules.VU) modules.Instance {
 // Exports implements the modules.Instance interface and returns
 // the exports of the JS module.
 func (mi *ModuleInstance) Exports() modules.Exports {
-	return modules.Exports{}
+	return modules.Exports{
+		Named: map[string]interface{}{
+			"Client": mi.newClient,
+		},
+	}
+}
+
+// NewClient is the JS constructor for the tracing.Client
+//
+// It expects a single configuration object as argument, which
+// will be used to instantiate an `Object` instance internally,
+// and will be used by the client to configure itself.
+func (mi *ModuleInstance) newClient(cc goja.ConstructorCall) *goja.Object {
+	rt := mi.vu.Runtime()
+
+	if len(cc.Arguments) < 1 {
+		common.Throw(rt, errors.New("Client constructor expects a single configuration object as argument; none given"))
+	}
+
+	var opts options
+	if err := rt.ExportTo(cc.Arguments[0], &opts); err != nil {
+		common.Throw(rt, fmt.Errorf("unable to parse options object; reason: %w", err))
+	}
+
+	return rt.ToValue(NewClient(mi.vu, opts)).ToObject(rt)
 }

samples/experimental/tracing-client.js

@@ -0,0 +1,46 @@
+import http from "k6/http";
+import { check } from "k6";
+import tracing from "k6/experimental/tracing";
+
+// Explicitly instantiating a tracing client allows to distringuish
+// instrumented from non-instrumented HTTP calls, by keeping APIs separate.
+// It also allows for finer-grained configuration control, by letting
+// users changing the tracing configuration on the fly during their
+// script's execution.
+let instrumentedHTTP = new tracing.Client({
+	propagator: "w3c",
+});
+
+const testData = { name: "Bert" };
+
+export default () => {
+	// Using the tracing client instance, HTTP calls will have
+	// their trace context headers set.
+	let res = instrumentedHTTP.request("GET", "http://httpbin.org/get", null, {
+		headers: {
+			"X-Example-Header": "instrumented/request",
+		},
+	});
+	check(res, {
+		"status is 200": (r) => r.status === 200,
+	});
+
+	// The tracing client offers more flexibility over
+	// the `instrumentHTTP` function, as it leaves the
+	// imported standard http module untouched. Thus,
+	// one can still perform non-instrumented HTTP calls
+	// using it.
+	res = http.post("http://httpbin.org/post", JSON.stringify(testData), {
+		headers: { "X-Example-Header": "noninstrumented/post" },
+	});
+	check(res, {
+		"status is 200": (r) => r.status === 200,
+	});
+
+	res = instrumentedHTTP.del("http://httpbin.org/delete", null, {
+		headers: { "X-Example-Header": "instrumented/delete" },
+	});
+	check(res, {
+		"status is 200": (r) => r.status === 200,
+	});
+};