🐛 [Bug]: There is a conflict between app.NewCtxFunc and app.Use

[attains-cloud]

Bug Description

CustomCtx no effect when app.newCtxFunc and app.use simultaneously existing

How to Reproduce

Steps to reproduce the behavior:

1. create custom ctx

      type Ctx struct {
      	fiber.DefaultCtx
      }
      
      func (c *Ctx) JSON(data any, ctype ...string) error {
      	return c.DefaultCtx.JSON(Response{
      		Code:    http.StatusOK,
      		Data:    data,
      		Message: http.StatusText(http.StatusOK),
      	}, ctype...)
      }

      type Response struct {
      	Code    int    `json:"code,omitempty" xml:"code,omitempty" yaml:"code,omitempty"`
      	Data    any    `json:"data,omitempty" xml:"data,omitempty" yaml:"data,omitempty"`
      	Message string `json:"message,omitempty" xml:"message,omitempty" yaml:"message,omitempty"`
      }

2. create app with newCtxFunc:

              app := fiber.New(fiber.Config{
			JSONEncoder: sonic.Marshal,
			JSONDecoder: sonic.Unmarshal,
		})

		app.NewCtxFunc(func(app *fiber.App) fiber.CustomCtx {
			return &Ctx{
				DefaultCtx: *fiber.NewDefaultCtx(app),
			}
		})

                app.Get("/vvv", func(ctx fiber.Ctx) error {
			return ctx.JSON(fiber.Map{"a": "b"})
		})
                _ = app.Listen(":8080")

3. request:

curl localhost:8080/vvv   
{"code":200,"data":{"a":"b"},"message":"OK"}%

4. create app with newCtxFunc and app.use:

          app := fiber.New(fiber.Config{
			JSONEncoder: sonic.Marshal,
			JSONDecoder: sonic.Unmarshal,
		})

		app.NewCtxFunc(func(app *fiber.App) fiber.CustomCtx {
			return &Ctx{
				DefaultCtx: *fiber.NewDefaultCtx(app),
			}
		})

                app.Use(func(c fiber.Ctx) error {
			return c.Next()
		})

                app.Get("/vvv", func(ctx fiber.Ctx) error {
			return ctx.JSON(fiber.Map{"a": "b"})
		})
                _ = app.Listen(":8080")

5. request:

curl localhost:8080/vvv
{"a":"b"}

Expected Behavior

app.NewCtxFunc and app.Use can coexist

Fiber Version

v3.0.0-beta.4

Code Snippet (optional)

package main

import "github.com/gofiber/fiber/v3"
import "log"

func main() {
  app := fiber.New()

  // Steps to reproduce

  log.Fatal(app.Listen(":3000"))
}

Checklist:

• I agree to follow Fiber's Code of Conduct.
• I have checked for existing issues that describe my problem prior to opening this one.
• I understand that improperly formatted bug reports may be closed without explanation.

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[JIeJaitt]

This is because when not using app.Use, HTTP -> customRequestHandler -> nextCustom (which executes the route handler directly);

If you use middleware, testCustomCtx doesn't implement the c.Next() method, so it will call *DefaultCtx's c.Next() method by default, and the c.Next() method will call nextCustom again internally and then go to call the route handler.

But here is the problem, because *DefaultCtx's Next method receiver is *DefaultCtx , he can't handle the JSON method implemented by CustomCtx, so your custom middleware fails. @ReneWerner87 @gaby @efectn Am I right?

// Next executes the next method in the stack that matches the current route.
func (c *DefaultCtx) 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
	if c.app.newCtxFunc != nil {
		_, err := c.app.nextCustom(c)
		return err
	}

	_, err := c.app.next(c)
	return err
}

If you want to achieve the effect you want, maybe you need to customize a Next method belonging to testCustomCtx. I didn't do any specific experiments, you can try it or I will when I have time. @attains-cloud

[JIeJaitt]

If u want to access the full CustomCtx in inherited methods, we have to override those methods like Next(). The following unit test verified my suspicions:

type Response struct {
	Code    int    `json:"code"`
	Data    any    `json:"data"`
	Message string `json:"message"`
}

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) {
		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 := `{"code":200,"data":{"a":"b"},"message":"OK"}`
		require.Equal(t, expected, string(body))
	})

	t.Run("with middleware", func(t *testing.T) {
		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 := `{"code":200,"data":{"a":"b"},"message":"OK"}`
		require.Equal(t, expected, string(body),
			"Custom context JSON format is lost when using middleware")
	})
}

When we customize the Next method of testCustomCtx, the unit test called with middleware will pass, otherwise it will report an error

[JIeJaitt]

@ReneWerner87 @gaby @efectn As mentioned above, this issue may not be considered a bug, and perhaps we should add a hint to the documentation telling users how to use both app.NewCtxFunc and app.Use.

[ReneWerner87]

just as a hint
in this pull request which is still being implemented
https://github.com/gofiber/fiber/pull/3296/files
we try to do without these extra processes for the custom ctx