HTTP Request Validation Middleware In Go - go

Question

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.

Answer 1

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")
}

Answer 2

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))