Bake UserAgent into http.Clients (#92)

cmd/fastly-exporter/main.go

@@ -221,10 +221,16 @@ func main() {
 		apiLogger = log.With(logger, "component", "api.fastly.com")
 	}
 
+	var userAgent string
+	{
+		userAgent = `Fastly-Exporter (` + programVersion + `)`
+	}
+
 	var apiClient *http.Client
 	{
 		apiClient = &http.Client{
-			Timeout: apiTimeout,
+			Timeout:   apiTimeout,
+			Transport: userAgentTransport(http.DefaultTransport, userAgent),
 		}
 	}
 
@@ -289,11 +295,10 @@ func main() {
 	{
 		var (
 			rtLogger          = log.With(logger, "component", "rt.fastly.com")
-			rtClient          = &http.Client{Timeout: rtTimeout}
+			rtClient          = &http.Client{Timeout: rtTimeout, Transport: userAgentTransport(http.DefaultTransport, userAgent)}
 			subscriberOptions = []rt.SubscriberOption{
 				rt.WithLogger(rtLogger),
 				rt.WithMetadataProvider(serviceCache),
-				rt.WithUserAgent(`Fastly-Exporter (` + programVersion + `)`),
 			}
 		)
 		manager = rt.NewManager(serviceCache, rtClient, token, registry, subscriberOptions, rtLogger)

cmd/fastly-exporter/transport.go

@@ -0,0 +1,14 @@
+package main
+
+import "net/http"
+
+type roundTripperFunc func(*http.Request) (*http.Response, error)
+
+func (f roundTripperFunc) RoundTrip(req *http.Request) (*http.Response, error) { return f(req) }
+
+func userAgentTransport(next http.RoundTripper, userAgent string) http.RoundTripper {
+	return roundTripperFunc(func(req *http.Request) (*http.Response, error) {
+		req.Header.Set("User-Agent", userAgent)
+		return next.RoundTrip(req)
+	})
+}

cmd/fastly-exporter/transport_test.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestUserAgentTransport(t *testing.T) {
+	c := make(chan string, 1)
+	handler := func(_ http.ResponseWriter, r *http.Request) { c <- r.Header.Get("User-Agent") }
+	server := httptest.NewServer(http.HandlerFunc(handler))
+	defer server.Close()
+
+	userAgent := "something"
+	transport := userAgentTransport(http.DefaultTransport, userAgent)
+	client := &http.Client{Transport: transport}
+	if _, err := client.Get(server.URL); err != nil {
+		t.Fatal(err)
+	}
+
+	if want, have := userAgent, <-c; want != have {
+		t.Fatalf("want %q, have %q", want, have)
+	}
+}

pkg/rt/subscriber.go

@@ -32,7 +32,6 @@ type MetadataProvider interface {
 // It emits the received real-time stats data to Prometheus.
 type Subscriber struct {
 	client      HTTPClient
-	userAgent   string
 	token       string
 	serviceID   string
 	provider    MetadataProvider
@@ -44,12 +43,6 @@ type Subscriber struct {
 // SubscriberOption provides some additional behavior to a subscriber.
 type SubscriberOption func(*Subscriber)
 
-// WithUserAgent sets the User-Agent supplied to rt.fastly.com.
-// By default, the DefaultUserAgent is used.
-func WithUserAgent(ua string) SubscriberOption {
-	return func(s *Subscriber) { s.userAgent = ua }
-}
-
 // WithMetadataProvider sets the resolver used to look up service names and
 // versions. By default, a no-op metadata resolver is used, which causes each
 // service to have its name set to its service ID, and its version set to
@@ -71,16 +64,11 @@ func WithPostprocess(f func()) SubscriberOption {
 	return func(s *Subscriber) { s.postprocess = f }
 }
 
-// DefaultUserAgent passed to rt.fastly.com.
-// To change, use the WithUserAgent option.
-const DefaultUserAgent = "Fastly-Exporter (unknown version)"
-
 // NewSubscriber returns a ready-to-use subscriber.
 // Run must be called to update the metrics.
 func NewSubscriber(client HTTPClient, token, serviceID string, metrics *gen.Metrics, options ...SubscriberOption) *Subscriber {
 	s := &Subscriber{
 		client:      client,
-		userAgent:   DefaultUserAgent,
 		token:       token,
 		serviceID:   serviceID,
 		metrics:     metrics,
@@ -147,7 +135,6 @@ func (s *Subscriber) query(ctx context.Context, ts uint64) (currentName string,
 		return name, apiResultError, 0, ts, fmt.Errorf("error constructing real-time stats API request: %w", err)
 	}
 
-	req.Header.Set("User-Agent", s.userAgent)
 	req.Header.Set("Fastly-Key", s.token)
 	req.Header.Set("Accept", "application/json")
 	resp, err := s.client.Do(req.WithContext(ctx))

pkg/rt/subscriber_test.go

@@ -79,25 +79,6 @@ func TestSubscriberNoData(t *testing.T) {
 	assertMetricOutput(t, want, have)
 }
 
-func TestUserAgent(t *testing.T) {
-	var (
-		client      = newMockRealtimeClient(`{}`)
-		userAgent   = "Some user agent string"
-		metrics     = gen.NewMetrics("ns", "ss", filter.Filter{}, prometheus.NewRegistry())
-		processed   = make(chan struct{})
-		postprocess = func() { close(processed) }
-		options     = []rt.SubscriberOption{rt.WithUserAgent(userAgent), rt.WithPostprocess(postprocess)}
-		subscriber  = rt.NewSubscriber(client, "token", "service_id", metrics, options...)
-	)
-	go subscriber.Run(context.Background())
-
-	<-processed
-
-	if want, have := userAgent, client.lastUserAgent; want != have {
-		t.Errorf("User-Agent: want %q, have %q", want, have)
-	}
-}
-
 func TestBadTokenNoSpam(t *testing.T) {
 	var (
 		client     = &countingRealtimeClient{code: 403, response: `{"Error": "unauthorized"}`}