Request body validation

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I'm using gin to handle requests, but I'm having trouble validating data in a request body, e.g.

type User struct {
    Username  string  `json:"username" binding:"required,min=1,max=16"`
    Name  string  `json:"name" binding:"required,min=1,max=16"`
    Password string `json:"password" binding:"required,min=1,max=16"`
}

func loginHandler(ctx *gin.Context) {
    var user User
    if err := ctx.ShouldBindJSON(&user); err != nil {
        ctx.JSON(http.StatusBadRequest, gin.H{
            "error": err.Error(),
        })
}

How can I handle values with whitespaces like " username " or " John Doe "? As far as I know it's not possible to use regex in gin's validator. What are the best practices or patterns for request body validation in Golang?

go http-post request validation json
1 Answers

Reg validator package: https://godoc.org/gopkg.in/validator.v2

// main.go
package main

import (
    "net/http"

    "github.com/gin-gonic/gin"
    "gopkg.in/validator.v2"
)

type User struct {
    Username string `json:"username" validate:"min=1,max=16,regexp=^[a-zA-Z]*$"`
    Name     string `json:"name" validate:"min=1,max=16"`
    Password string `json:"password" validate:"min=1,max=16"`
}

func loginHandler(ctx *gin.Context) {
    var user User
    if err := ctx.ShouldBindJSON(&user); err != nil {
        ctx.JSON(http.StatusBadRequest, gin.H{
            "error": err.Error(),
        })
    }

    if err := validator.Validate(user); err != nil {
        ctx.JSON(http.StatusBadRequest, gin.H{
            "error": err.Error(),
        })
    }
}

func main() {
    r := gin.Default()
    r.POST("/login", loginHandler)
    r.Run()
}

Request: POST: localhost:8080/login

{
    "username":"123123",
    "name":"golang",
    "password":"gin"
}

Response: 

{
    "error": "Username: regular expression mismatch "
}
user_19824180
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