http: allow custom User-Agent for outgoing HTTP requests

internal/backend/http_transport.go

@@ -28,6 +28,9 @@ type TransportOptions struct {
 
 	// Skip TLS certificate verification
 	InsecureTLS bool
+
+	// Specify Custom User-Agent for the http Client
+	HTTPUserAgent string
 }
 
 // readPEMCertKey reads a file and returns the PEM encoded certificate and key
@@ -132,6 +135,13 @@ func Transport(opts TransportOptions) (http.RoundTripper, error) {
 	}
 
 	rt := http.RoundTripper(tr)
+
+	// if the userAgent is set in the Transport Options, wrap the
+	// http.RoundTripper
+	if opts.HTTPUserAgent != "" {
+		rt = newCustomUserAgentRoundTripper(rt, opts.HTTPUserAgent)
+	}
+
 	if feature.Flag.Enabled(feature.BackendErrorRedesign) {
 		rt = newWatchdogRoundtripper(rt, 120*time.Second, 128*1024)
 	}

internal/backend/httpuseragent_roundtripper.go

@@ -0,0 +1,25 @@
+package backend
+
+import "net/http"
+
+// httpUserAgentRoundTripper is a custom http.RoundTripper that modifies the User-Agent header
+// of outgoing HTTP requests.
+type httpUserAgentRoundTripper struct {
+	userAgent string
+	rt        http.RoundTripper
+}
+
+func newCustomUserAgentRoundTripper(rt http.RoundTripper, userAgent string) *httpUserAgentRoundTripper {
+	return &httpUserAgentRoundTripper{
+		rt:        rt,
+		userAgent: userAgent,
+	}
+}
+
+// RoundTrip modifies the User-Agent header of the request and then delegates the request
+// to the underlying RoundTripper.
+func (c *httpUserAgentRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	req = req.Clone(req.Context())
+	req.Header.Set("User-Agent", c.userAgent)
+	return c.rt.RoundTrip(req)
+}

internal/backend/httpuseragent_roundtripper_test.go

@@ -0,0 +1,50 @@
+package backend
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestCustomUserAgentTransport(t *testing.T) {
+	// Create a mock HTTP handler that checks the User-Agent header
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		userAgent := r.Header.Get("User-Agent")
+		if userAgent != "TestUserAgent" {
+			t.Errorf("Expected User-Agent: TestUserAgent, got: %s", userAgent)
+		}
+		w.WriteHeader(http.StatusOK)
+	})
+
+	// Create a test server with the mock handler
+	server := httptest.NewServer(handler)
+	defer server.Close()
+
+	// Create a custom user agent transport
+	customUserAgent := "TestUserAgent"
+	transport := &httpUserAgentRoundTripper{
+		userAgent: customUserAgent,
+		rt:        http.DefaultTransport,
+	}
+
+	// Create an HTTP client with the custom transport
+	client := &http.Client{
+		Transport: transport,
+	}
+
+	// Make a request to the test server
+	resp, err := client.Get(server.URL)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	defer func() {
+		if err := resp.Body.Close(); err != nil {
+			t.Log("failed to close response body")
+		}
+	}()
+
+	// Check the response status code
+	if resp.StatusCode != http.StatusOK {
+		t.Errorf("Expected status code: %d, got: %d", http.StatusOK, resp.StatusCode)
+	}
+}