Suggest: How to Use Custom Binder

[iktakahiro]

I'd like to suggest that adding a practice to the document.

• CustomBinder - Json Binding with validation

type ValidateBinder struct{}

func (ValidateBinder) Bind(i interface{}, c echo.Context) (err error) {
    rq := c.Request()
    ct := rq.Header().Get(echo.ContentType)
    err = echo.ErrUnsupportedMediaType
    if strings.HasPrefix(ct, echo.ApplicationJSON) {
        if err = json.NewDecoder(rq.Body()).Decode(i); err != nil {
            return
        }
        if tagName := c.Get("ValidateTagName"); tagName == nil {
            c.Set("ValidateTagName", "validate")
        }
        config := &validator.Config{TagName: c.Get("ValidateTagName").(string)}
        validate := validator.New(config)
        if err = validate.Struct(i); err != nil {
            return
        }
    }
    return
}

• Set CustomBinder

e := echo.New()
e.SetBinder(&ValidateBinder{})

• How to Use

type User struct {
    ID    int64     `json:"id" validate:"required"`
    Email string    `json:"email" validate:"required,email"`
}

func MyFunc() echo.HandlerFunc {
    return func(c echo.Context) (err error) {

            user := new(model.User)
            c.Set("ValidateTagName", "validate")

            if err = c.Bind(user); err != nil {
               return echo.NewHTTPError(fasthttp.StatusBadRequest, "Request parameters are invalid.")
            }
    }
}

[LuisUrrutia]

+1

[chrislewispac]

i get the following err with this

e.SetBinder undefined (type *echo.Echo has no field or method SetBinder)

[vishr]

@chrislewispac In Echo v3, the property is directly exposed. So you do e.Binder =

[shyandsy]

how to use customerBind in v4? any documents?

[Gaadek]

Hello, In case of, the custom binder in Echo v4 can be implemented this way:

package main

import (
	"fmt"
	"net/http"

	"github.com/labstack/echo/v4"
)

type CustomBinder struct{}

func (cb *CustomBinder) Bind(i interface{}, c echo.Context) (err error) {
	// You may use default binder
	db := &echo.DefaultBinder{}
	if err = db.Bind(i, c); err != echo.ErrUnsupportedMediaType {
		return
	}

	// Then define your custom implementation
	println("And now for some logic")

	return
}

func handler(c echo.Context) error {
	req := new(Request)
	if err := c.Bind(req); err != nil {
		return err
	}
	return c.String(http.StatusOK, fmt.Sprint("all good, req = ", req))
}

func main() {
	e := echo.New()
	e.Binder := &CustomBinder{}
	e.POST("/", handler)
	e.Start(":3000")
}

[mrccnt]

Besides that that it should be req := new(http.Request) and e.Binder = &CustomBinder{} this snippet does not work. The println("And now for some logic") never gets printed. The default binder is still used.

Any ideas whats wrong?

[mrccnt]

Ok guess I got it. The err != echo.ErrUnsupportedMediaType comparison prevents execution. Here a full example using custom binder and custom validator more or less straight from the examples:

package main

import (
	"github.com/go-playground/validator/v10"
	"github.com/labstack/echo/v4"
	"net/http"
)

type CustomBinder struct {}

type CustomValidator struct {
	validator *validator.Validate
}

type User struct {
	Name  string `json:"name"  validate:"required"`
	Email string `json:"email" validate:"required,email"`
}

func main() {

	e := echo.New()
	e.Binder = new(CustomBinder)
	e.Validator = &CustomValidator{validator: validator.New()}

	e.POST("/users", func(c echo.Context) error {
		u := new(User)
		if err := c.Bind(u); err != nil {
		    return err
		}
		if err := c.Validate(u); err != nil {
		    return err
		}
		return c.JSON(http.StatusOK, u)
	})

	e.Logger.Fatal(e.Start(":1323"))

}

func (cb *CustomBinder) Bind(i interface{}, c echo.Context) error {
	db := new(echo.DefaultBinder)
	if err := db.Bind(i, c); err != nil {
	    return err
	}
	println("CustomBinder", "Bind")
	return nil
}

func (cv *CustomValidator) Validate(i interface{}) error {
	println("CustomValidator", "Validate")
	return cv.validator.Struct(i)
}