📚 Doc: Add how to use NewCtxFunc and middleware at the same time

app_test.go

@@ -1941,3 +1941,101 @@ func Benchmark_Ctx_AcquireReleaseFlow(b *testing.B) {
 		}
 	})
 }
+
+type Response struct {
+	Data    any    `json:"data"`
+	Message string `json:"message"`
+	Code    int    `json:"code"`
+}
+
+type testCustomCtx struct {
+	*DefaultCtx
+}
+
+func (c *testCustomCtx) JSON(data any, ctype ...string) error {
+	return c.DefaultCtx.JSON(Response{
+		Code:    StatusOK,
+		Data:    data,
+		Message: utils.StatusMessage(StatusOK),
+	}, ctype...)
+}
+
+func (c *testCustomCtx) Next() error {
+	// Increment handler index
+	c.indexHandler++
+
+	// Did we execute all route handlers?
+	if c.indexHandler < len(c.route.Handlers) {
+		// Continue route stack
+		return c.route.Handlers[c.indexHandler](c)
+	}
+
+	// Continue handler stack
+	_, err := c.app.nextCustom(c)
+	return err
+}
+
+func Test_App_CustomCtx_With_Use(t *testing.T) {
+	t.Parallel()
+
+	t.Run("without middleware", func(t *testing.T) {
+		t.Parallel()
+
+		app := New()
+		app.NewCtxFunc(func(app *App) CustomCtx {
+			return &testCustomCtx{
+				DefaultCtx: NewDefaultCtx(app),
+			}
+		})
+
+		app.Get("/test", func(c Ctx) error {
+			return c.JSON(Map{"a": "b"})
+		})
+
+		resp, err := app.Test(httptest.NewRequest(MethodGet, "/test", nil))
+		require.NoError(t, err)
+		require.Equal(t, 200, resp.StatusCode)
+
+		body, err := io.ReadAll(resp.Body)
+		require.NoError(t, err)
+
+		expected := `{"data":{"a":"b"},"message":"OK","code":200}`
+		require.Equal(t, expected, string(body))
+	})
+
+	t.Run("with middleware", func(t *testing.T) {
+		t.Parallel()
+
+		app := New()
+		app.NewCtxFunc(func(app *App) CustomCtx {
+			return &testCustomCtx{
+				DefaultCtx: NewDefaultCtx(app),
+			}
+		})
+
+		app.Use(func(c Ctx) error {
+			t.Logf("Before Next() - context type: %T", c)
+			err := c.Next()
+			t.Logf("After Next() - context type: %T", c)
+			return err
+		})
+
+		app.Get("/test", func(c Ctx) error {
+			if _, ok := c.(*testCustomCtx); !ok {
+				t.Logf("Handler received context of type: %T", c)
+			}
+			return c.JSON(Map{"a": "b"})
+		})
+
+		resp, err := app.Test(httptest.NewRequest(MethodGet, "/test", nil))
+		require.NoError(t, err)
+		require.Equal(t, 200, resp.StatusCode)
+
+		body, err := io.ReadAll(resp.Body)
+		require.NoError(t, err)
+
+		expected := `{"data":{"a":"b"},"message":"OK","code":200}`
+		require.Equal(t, expected, string(body),
+			"Custom context JSON format is lost when using middleware")
+	})
+}

docs/api/app.md

@@ -556,6 +556,56 @@ func main() {
 }
 ```
 
+:::tip Using with Middleware
+When using `NewCtxFunc` together with middleware (`app.Use`), you need to override the `Next()` method in your custom context to preserve the context type throughout the middleware chain:
+
+```go
+type CustomCtx struct {
+    fiber.DefaultCtx
+}
+
+// Override Next method to preserve CustomCtx type
+func (c *CustomCtx) Next() error {
+    // Increment handler index
+    c.indexHandler++
+
+    // Did we execute all route handlers?
+    if c.indexHandler < len(c.route.Handlers) {
+        // Continue route stack
+        return c.route.Handlers[c.indexHandler](c)
+    }
+
+    // Continue handler stack
+    _, err := c.app.nextCustom(c)
+    return err
+}
+
+func main() {
+    app := fiber.New()
+
+    // Set custom context
+    app.NewCtxFunc(func(app *fiber.App) fiber.CustomCtx {
+        return &CustomCtx{
+            DefaultCtx: *fiber.NewDefaultCtx(app),
+        }
+    })
+
+    // Use middleware
+    app.Use(func(c fiber.Ctx) error {
+        fmt.Printf("Context type in middleware: %T\n", c)
+        return c.Next()
+    })
+
+    // Route handler
+    app.Get("/", func(c fiber.Ctx) error {
+        return c.JSON(fiber.Map{"hello": "world"})
+    })
+}
+```
+
+This ensures that your custom context type is maintained throughout the entire request lifecycle, including middleware execution.
+:::
+
 ## RegisterCustomBinder
 
 You can register custom binders to use with [`Bind().Custom("name")`](bind.md#custom). They should be compatible with the `CustomBinder` interface.

middleware/proxy/proxy_test.go

@@ -501,18 +501,24 @@ func Test_Proxy_Do_RestoreOriginalURL(t *testing.T) {
 // go test -race -run Test_Proxy_Do_WithRealURL
 func Test_Proxy_Do_WithRealURL(t *testing.T) {
 	t.Parallel()
+
+	_, addr := createProxyTestServerIPv4(t, func(c fiber.Ctx) error {
+		return c.SendString("mock response")
+	})
+
 	app := fiber.New()
 	app.Get("/test", func(c fiber.Ctx) error {
-		return Do(c, "https://www.google.com")
+		return Do(c, "http://"+addr)
 	})
 
-	resp, err1 := app.Test(httptest.NewRequest(fiber.MethodGet, "/test", nil))
-	require.NoError(t, err1)
+	resp, err := app.Test(httptest.NewRequest(fiber.MethodGet, "/test", nil))
+	require.NoError(t, err)
 	require.Equal(t, fiber.StatusOK, resp.StatusCode)
 	require.Equal(t, "/test", resp.Request.URL.String())
+
 	body, err := io.ReadAll(resp.Body)
 	require.NoError(t, err)
-	require.Contains(t, string(body), "https://www.google.com/")
+	require.Equal(t, "mock response", string(body))
 }
 
 // go test -race -run Test_Proxy_Do_WithRedirect