Unable to access json data from request in request handler after calling BindJSON in middleware

Question

I have created a basic CRUD API using Go-Gin. Calling BindJSON in request handler gives me a blank object after calling BindJSON in middleware but works fine if I remove BindJSON in middleware.

This is the user model:

type User struct {
    ID      uint   `json:"id" gorm:"primary_key"`
    Rollnum string `json:"rollnum" gorm:"primary_key;unique"`
    Name    string `json:"name"`
    Email   string `json:"email"`
    Phone   uint   `json:"phone"`
    Address string `json:"address"`
}

This is my middleware:

func NameMiddleware() gin.HandlerFunc {
    return func(c *gin.Context) {
        var user Models.User
        c.BindJSON(&user)
        fmt.Println(user.Rollnum)
        if user.Name == "" {
            c.JSON(http.StatusNotFound, gin.H{"No Key": "Name"})
            c.AbortWithStatus(http.StatusNotFound)
        }
    }
}

This is my route:

r := gin.Default()
grp1 := r.Group("/user-api")
grp1.POST("user", Middleware.NameMiddleware(), Controllers.CreateUser)

And this is my handler for the POST request:

func CreateUser(c *gin.Context) {
    var user Models.User
    c.BindJSON(&user)

    fmt.Println(user)

    err := Models.CreateUser(&user)
    return
}

Works fine if the BindJSON in middleware is removed. Is it possible that you can only BindJSON once? What should I do to get that object again in my request handler?

Answer 1

The c.bindJSON() is intended to be used in the initial request handler and not in the middleware. If you want, you can pass data to your middleware using context https://www.nicolasmerouze.com/share-values-between-middlewares-context-golang but I think this can get ugly quik.

If you just want to perform validation on the JSON, I'd recommend performing this logic in your handler and not the middleware.