fix(server): serve the Admin SPA at / when dist exists (#346)

go-admin registered its welcome page on GET / in every non-prod mode, so a
reverse proxy that forwarded / to the server showed 「GO-ADMIN欢迎您」
instead of the Admin (happened after the 2026-09-28 server migration).
When dist/index.html exists, / now returns it; without a dist (vite
development) the previous welcome/prod behaviour is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NTDbDcwbDw1TSAcE6wfh2F

server/app/admin/router/spa.go

@@ -25,12 +25,8 @@ const SPADirEnv = "GOAUTO_WEB_DIST"
 // dist; a NoRoute handler installed anyway would turn every genuine 404 into
 // an HTML page, which is far more confusing than a plain 404.
 func InitSPARouter(engine *gin.Engine) {
-	dist := strings.TrimSpace(os.Getenv(SPADirEnv))
-	if dist == "" {
-		dist = "dist"
-	}
-	index := filepath.Join(dist, "index.html")
-	if _, err := os.Stat(index); err != nil {
+	dist, index, ok := spaIndex()
+	if !ok {
 		return
 	}
 
@@ -56,6 +52,38 @@ func InitSPARouter(engine *gin.Engine) {
 	})
 }
 
+// spaIndex resolves the built frontend directory and reports whether its
+// index.html exists.
+func spaIndex() (dist, index string, ok bool) {
+	dist = strings.TrimSpace(os.Getenv(SPADirEnv))
+	if dist == "" {
+		dist = "dist"
+	}
+	index = filepath.Join(dist, "index.html")
+	if _, err := os.Stat(index); err != nil {
+		return dist, index, false
+	}
+	return dist, index, true
+}
+
+// registerRootRoute decides what `GET /` returns (#346).
+//
+// `[必须]` When the built frontend exists, `/` must be the Admin SPA. go-admin's
+// welcome page used to own `/` in every non-prod mode, so any reverse proxy
+// that forwarded `/` to this server (instead of serving dist itself) showed
+// "GO-ADMIN欢迎您" instead of the Admin — which is exactly what happened after
+// the 2026-09-28 server migration. The welcome page is kept only for
+// development without a dist, where the frontend runs under vite.
+func registerRootRoute(r gin.IRoutes, mode string, welcome gin.HandlerFunc) {
+	if _, index, ok := spaIndex(); ok {
+		r.GET("/", func(c *gin.Context) { c.File(index) })
+		return
+	}
+	if mode != "prod" {
+		r.GET("/", welcome)
+	}
+}
+
 // isAPIPath reports whether a path belongs to the server rather than the SPA.
 func isAPIPath(path string) bool {
 	for _, prefix := range []string{"/api/", "/swagger/", "/static/", "/form-generator/", "/ws/", "/wslogout/", "/info"} {

server/app/admin/router/spa_test.go

@@ -91,3 +91,46 @@ func TestWithoutDistNoFallbackIsInstalled(t *testing.T) {
 		t.Fatalf("没有 dist 时接口仍应正常: %d", response.Code)
 	}
 }
+
+// #346: with a built frontend, `/` must be the Admin SPA — never go-admin's
+// welcome page, even in non-prod modes where the welcome page used to own `/`.
+func TestRootServesSPAWhenDistExists(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	dist := filepath.Join(t.TempDir(), "dist")
+	if err := os.MkdirAll(dist, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dist, "index.html"), []byte("<!doctype html>SPA"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv(SPADirEnv, dist)
+	for _, mode := range []string{"dev", "test", "prod"} {
+		engine := gin.New()
+		registerRootRoute(engine, mode, func(c *gin.Context) { c.String(http.StatusOK, "GO-ADMIN欢迎您") })
+		InitSPARouter(engine)
+		response := do(engine, http.MethodGet, "/")
+		if response.Code != http.StatusOK || response.Body.String() != "<!doctype html>SPA" {
+			t.Fatalf("mode=%s: / should serve index.html, got %d %q", mode, response.Code, response.Body.String())
+		}
+	}
+}
+
+// Without a dist (development under vite) the previous behaviour is kept:
+// welcome page outside prod, nothing registered in prod.
+func TestRootWithoutDistKeepsPreviousBehaviour(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	t.Setenv(SPADirEnv, filepath.Join(t.TempDir(), "missing-dist"))
+	welcome := func(c *gin.Context) { c.String(http.StatusOK, "GO-ADMIN欢迎您") }
+
+	dev := gin.New()
+	registerRootRoute(dev, "dev", welcome)
+	if response := do(dev, http.MethodGet, "/"); response.Code != http.StatusOK || response.Body.String() != "GO-ADMIN欢迎您" {
+		t.Fatalf("dev without dist should keep the welcome page, got %d %q", response.Code, response.Body.String())
+	}
+
+	prod := gin.New()
+	registerRootRoute(prod, "prod", welcome)
+	if response := do(prod, http.MethodGet, "/"); response.Code != http.StatusNotFound {
+		t.Fatalf("prod without dist should not register /, got %d", response.Code)
+	}
+}

server/app/admin/router/sys_router.go

@@ -40,9 +40,7 @@ func sysBaseRouter(r *gin.RouterGroup) {
 	go ws.WebsocketManager.SendService()
 	go ws.WebsocketManager.SendAllService()
 
-	if config.ApplicationConfig.Mode != "prod" {
-		r.GET("/", apis.GoAdmin)
-	}
+	registerRootRoute(r, config.ApplicationConfig.Mode, apis.GoAdmin)
 	r.GET("/info", handler.Ping)
 }