feat: add custom User-Agent header (goperf/<version>)

cmd/run.go

@@ -107,6 +107,7 @@ Latency Percentiles:
 			u := config.ParsedTarget
 
 			httpCfg := config.ToHTTPConfig()
+			httpCfg.Version = cmd.Root().Version
 			if outputFormat != "json" {
 				httpCfg.Stderr = cmd.ErrOrStderr()
 			}

internal/httpclient/client.go

@@ -35,6 +35,7 @@ type Config struct {
 	Body        string
 	Headers     []string
 	Verbose     bool
+	Version     string
 	Stderr      io.Writer
 }
 
@@ -74,6 +75,10 @@ func MakeRequest(ctx context.Context, client HTTPDoer, cfg Config) (statusCode i
 		}
 	}
 
+	if req.Header.Get("User-Agent") == "" {
+		req.Header.Set("User-Agent", fmt.Sprintf("goperf/%s", cfg.Version))
+	}
+
 	if cfg.Body != "" && req.Header.Get("Content-Type") == "" {
 		req.Header.Set("Content-Type", "application/json")
 	}

internal/httpclient/client_test.go

@@ -57,6 +57,54 @@ func TestMakeRequestSuccess(t *testing.T) {
 	}
 }
 
+func TestMakeRequest_DefaultUserAgent(t *testing.T) {
+	var gotUA string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotUA = r.Header.Get("User-Agent")
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	_, _, err := MakeRequest(context.Background(), &http.Client{}, Config{
+		Target:  server.URL,
+		Timeout: testTimeout,
+		Method:  "GET",
+		Version: "1.2.3",
+	})
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if gotUA != "goperf/1.2.3" {
+		t.Errorf("expected User-Agent 'goperf/1.2.3', got %q", gotUA)
+	}
+}
+
+func TestMakeRequest_UserAgentOverride(t *testing.T) {
+	var gotUAValues []string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotUAValues = r.Header.Values("User-Agent")
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	_, _, err := MakeRequest(context.Background(), &http.Client{}, Config{
+		Target:  server.URL,
+		Timeout: testTimeout,
+		Method:  "GET",
+		Version: "1.2.3",
+		Headers: []string{"User-Agent: custom-agent/9.9"},
+	})
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if len(gotUAValues) != 1 {
+		t.Errorf("expected exactly 1 User-Agent value (no duplicates), got %v", gotUAValues)
+	}
+	if gotUAValues[0] != "custom-agent/9.9" {
+		t.Errorf("expected User-Agent 'custom-agent/9.9', got %q", gotUAValues[0])
+	}
+}
+
 func TestMakeRequest_Errors(t *testing.T) {
 	tests := []struct {
 		name          string