http: add support for metrics

pkg/agent/protocol/http/proxy.go

@@ -44,6 +44,7 @@ type proxy struct {
 	config     ProxyConfig
 	disruption Disruption
 	srv        *http.Server
+	metrics    protocol.MetricMap
 }
 
 // NewProxy return a new Proxy for HTTP requests
@@ -85,6 +86,7 @@ type httpHandler struct {
 	upstreamURL url.URL
 	disruption  Disruption
 	client      httpClient
+	metrics     *protocol.MetricMap
 }
 
 // isExcluded checks whether a request should be proxied through without any kind of modification whatsoever.
@@ -145,7 +147,10 @@ func (h *httpHandler) fault(rw http.ResponseWriter, wait <-chan time.Time) {
 }
 
 func (h *httpHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	h.metrics.Inc(protocol.MetricRequests)
+
 	if h.isExcluded(req) {
+		h.metrics.Inc(protocol.MetricRequestsExcluded)
 		//nolint:contextcheck // Unclear which context the linter requires us to propagate here.
 		h.proxy(rw, req, time.After(0))
 		return
@@ -160,6 +165,7 @@ func (h *httpHandler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	responseTimer := time.After(delay)
 
 	if h.disruption.ErrorRate > 0 && rand.Float32() <= h.disruption.ErrorRate {
+		h.metrics.Inc(protocol.MetricRequestsFaulted)
 		h.fault(rw, responseTimer)
 		return
 	}
@@ -179,6 +185,7 @@ func (p *proxy) Start() error {
 		upstreamURL: *upstreamURL,
 		disruption:  p.disruption,
 		client:      http.DefaultClient,
+		metrics:     &p.metrics,
 	}
 
 	p.srv = &http.Server{
@@ -203,7 +210,7 @@ func (p *proxy) Stop() error {
 
 // Metrics returns runtime metrics for the proxy.
 func (p *proxy) Metrics() map[string]uint {
-	return nil
+	return p.metrics.Map()
 }
 
 // Force stops the proxy without waiting for connections to drain

pkg/agent/protocol/http/proxy_test.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/grafana/xk6-disruptor/pkg/agent/protocol"
 )
 
 // fakeHTTPClient mocks the execution of a request returning the predefines
@@ -415,3 +416,71 @@ func Test_ProxyHandler(t *testing.T) {
 		})
 	}
 }
+
+// TODO: This test covers metrics generated by the handler, but not the proxy. The reason for this is that the proxy is
+// currently not easily testable, as it coupled with `http.ListenAndServe`.
+func Test_Metrics(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name            string
+		config          Disruption
+		endpoints       []string
+		expectedMetrics map[string]uint
+	}{
+		{
+			name:            "no requests",
+			expectedMetrics: map[string]uint{},
+		},
+		{
+			name: "requests",
+			config: Disruption{
+				Excluded:  []string{"/excluded"},
+				ErrorRate: 1.0,
+				ErrorCode: http.StatusTeapot,
+			},
+			endpoints: []string{"/included", "/excluded"},
+			expectedMetrics: map[string]uint{
+				protocol.MetricRequests:         2,
+				protocol.MetricRequestsExcluded: 1,
+				protocol.MetricRequestsFaulted:  1,
+			},
+		},
+	} {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			upstreamServer := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+				rw.WriteHeader(http.StatusOK)
+			}))
+
+			upstreamURL, err := url.Parse(upstreamServer.URL)
+			if err != nil {
+				t.Fatalf("error parsing httptest url")
+			}
+
+			metrics := protocol.MetricMap{}
+
+			handler := &httpHandler{
+				upstreamURL: *upstreamURL,
+				disruption:  tc.config,
+				client:      http.DefaultClient,
+				metrics:     &metrics,
+			}
+
+			proxyServer := httptest.NewServer(handler)
+
+			for _, endpoint := range tc.endpoints {
+				_, err = http.Get(proxyServer.URL + endpoint)
+				if err != nil {
+					t.Fatalf("requesting %s: %v", endpoint, err)
+				}
+			}
+
+			if diff := cmp.Diff(tc.expectedMetrics, metrics.Map()); diff != "" {
+				t.Fatalf("expected metrics do not match output:\n%s", diff)
+			}
+		})
+	}
+}