HTTP Request Validation Middleware In Go

I am trying to create a common HTTP request validator middleware function that accepts type (maybe reflect.Type) as an argument and then using the package github.com/go-playground/validator/v10 to be able to unmarshall JSON into struct of mentioned type and validate the struct. I've tried to explain with the following example code...

EXAMPLE

type LoginRequestBody struct {
   Username string `json:"username",validate:"required"`
   Password string `json:"password",validate:"required"`
}

type SignupReqBody struct {
   Username string `json:"username",validate:"required"`
   Password string `json:"password",validate:"required"`
   Age      int    `json:"age",validate:"required"`
}

// sample routers with a common middleware validator function
router.POST("/login", ReqValidate("LoginRequestBody"), LoginController)
router.POST("/signup", ReqValidate("SignupReqBody"), SignupController)

func ReqValidate(<something>) gin.HandlerFunc {
   return func (c *gin.Context) {
      // unmarshalling JSON into a struct
      // common validation logic...
      c.Next()
   }
}

Overall, i wanna achieve the same validator flexibility as there in Node.js using Joi package.

I don't know if it is necessary to use middleware but I was recently trying to do something and I found an excellent tutorial that you can see here.

With Gin You can use binding:

Example:

package main
import (
  "github.com/gin-gonic/gin"
  "net/http"
)
type AnyStruct struct {
   Price uint `json:"price" binding:"required,gte=10,lte=1000"`
}
func main() {
  engine:=gin.New()
  engine.POST("/test", func(context *gin.Context) {
     body:=AnyStruct{}
     if err:=context.ShouldBindJSON(&body);err!=nil{
        context.AbortWithStatusJSON(http.StatusBadRequest,
        gin.H{
            "error": "VALIDATEERR-1",
            "message": "Invalid inputs. Please check your inputs"})
        return
     }
     context.JSON(http.StatusAccepted,&body)
  })
  engine.Run(":3000")
}

Don't use commas to separate struct tag key-value pairs, use space.

You can use generics (type parameters) to replace <something> but your controllers need to have the concrete type as their argument.

For example:

func ReqValidate[T any](next func(*gin.Context, *T)) gin.HandlerFunc {
	return func(c *gin.Context) {
		params := new(T)
		if err := c.ShouldBindJSON(params); err != nil {
			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
			return
		}
		next(c, params)
	}
}

And then the controllers:

type LoginRequestBody struct {
	Username string `json:"username" validate:"required"`
	Password string `json:"password" validate:"required"`
}

func LoginController(c *gin.Context, params *LoginRequestBody) {
	// ...
}

type SignupReqBody struct {
	Username string `json:"username" validate:"required"`
	Password string `json:"password" validate:"required"`
	Age      int    `json:"age" validate:"required"`
}

func SignupController(c *gin.Context, params *SignupReqBody) {
	// ...
}

And then the routing:

router := gin.Default()
router.POST("/login", ReqValidate(LoginController))
router.POST("/signup", ReqValidate(SignupController))