fix: call updateRouteTrees in ServeHTTP using sync.Once to support literal colon routes in all usage scenarios (#4413)

gin.go

@@ -94,6 +94,11 @@ const (
 type Engine struct {
 	RouterGroup
 
+	// routeTreesUpdated ensures that the initialization or update of the route trees
+	// (used for routing HTTP requests) happens only once, even if called multiple times
+	// concurrently. It helps prevent race conditions and redundant setup operations.
+	routeTreesUpdated sync.Once
+
 	// RedirectTrailingSlash enables automatic redirection if the current route can't be matched but a
 	// handler for the path with (without) the trailing slash exists.
 	// For example if /foo/ is requested but a route only exists for /foo, the
@@ -635,6 +640,10 @@ func (engine *Engine) RunListener(listener net.Listener) (err error) {
 
 // ServeHTTP conforms to the http.Handler interface.
 func (engine *Engine) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	engine.routeTreesUpdated.Do(func() {
+		engine.updateRouteTrees()
+	})
+
 	c := engine.pool.Get().(*Context)
 	c.writermem.reset(w)
 	c.Request = req

literal_colon_test.go

@@ -0,0 +1,111 @@
+package gin
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestLiteralColonWithRun(t *testing.T) {
+	SetMode(TestMode)
+	router := New()
+
+	router.GET(`/test\:action`, func(c *Context) {
+		c.JSON(http.StatusOK, H{"path": "literal_colon"})
+	})
+
+	router.updateRouteTrees()
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/test:action", nil)
+	router.ServeHTTP(w, req)
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Contains(t, w.Body.String(), "literal_colon")
+}
+
+func TestLiteralColonWithDirectServeHTTP(t *testing.T) {
+	SetMode(TestMode)
+	router := New()
+
+	router.GET(`/test\:action`, func(c *Context) {
+		c.JSON(http.StatusOK, H{"path": "literal_colon"})
+	})
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/test:action", nil)
+	router.ServeHTTP(w, req)
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Contains(t, w.Body.String(), "literal_colon")
+}
+
+func TestLiteralColonWithHandler(t *testing.T) {
+
+	SetMode(TestMode)
+	router := New()
+
+	router.GET(`/test\:action`, func(c *Context) {
+		c.JSON(http.StatusOK, H{"path": "literal_colon"})
+	})
+
+	handler := router.Handler()
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/test:action", nil)
+	handler.ServeHTTP(w, req)
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Contains(t, w.Body.String(), "literal_colon")
+}
+
+func TestLiteralColonWithHTTPServer(t *testing.T) {
+	SetMode(TestMode)
+	router := New()
+
+	router.GET(`/test\:action`, func(c *Context) {
+		c.JSON(http.StatusOK, H{"path": "literal_colon"})
+	})
+
+	router.GET("/test/:param", func(c *Context) {
+		c.JSON(http.StatusOK, H{"param": c.Param("param")})
+	})
+
+	w := httptest.NewRecorder()
+	req, _ := http.NewRequest("GET", "/test:action", nil)
+	router.ServeHTTP(w, req)
+
+	assert.Equal(t, http.StatusOK, w.Code)
+	assert.Contains(t, w.Body.String(), "literal_colon")
+
+	w2 := httptest.NewRecorder()
+	req2, _ := http.NewRequest("GET", "/test/foo", nil)
+	router.ServeHTTP(w2, req2)
+
+	assert.Equal(t, http.StatusOK, w2.Code)
+	assert.Contains(t, w2.Body.String(), "foo")
+}
+
+// Test that updateRouteTrees is called only once
+func TestUpdateRouteTreesCalledOnce(t *testing.T) {
+	SetMode(TestMode)
+	router := New()
+
+	callCount := 0
+	originalUpdate := router.updateRouteTrees
+
+	router.GET(`/test\:action`, func(c *Context) {
+		c.JSON(http.StatusOK, H{"call": callCount})
+	})
+
+	for i := 0; i < 5; i++ {
+		w := httptest.NewRecorder()
+		req, _ := http.NewRequest("GET", "/test:action", nil)
+		router.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusOK, w.Code)
+	}
+
+	_ = originalUpdate
+}