Gin Shouldn't ShouldBindJson return an error when the request body doesn't match the structure?

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Description

I'm currently trying to validate the request body with ShouldBindJSON and I'm sending a random JSON body (ex. {"a":"a"} -which is the one I'm using btw-) and it returns no error

How to reproduce

My struct:

type UserSignUp struct {
    Username string `json:"username"`
    Password string `json:"password"`
    Email    string `json:"email"`
}

The code that implements the validation

var dto register.UserSignUp

    if err := c.ShouldBindJSON(&dto); err != nil {
        // do something
    }

Expectations

An error

Actual result

No error

Environment

• go version:go version go1.13.6 windows/amd64
• gin version (or commit ref):github.com/gin-gonic/gin v1.5.0
• operating system:Windows 10

Comment From: linvis

hi, ShouldBindJSON is based on encoding/json, and encoding/jsondoesn't support to check if a field is existed see this issus for why not support: https://github.com/golang/go/issues/17163

so if you really need it, you could do it by yourself

Comment From: whatvn

if you want to return error on invalid input, use validator

type UserSignUp struct {
    Username string `json:"username" binding:"required"`
    Password string `json:"password"`
    Email    string `json:"email"`
}

Comment From: appleboy

See https://github.com/gin-gonic/gin#model-binding-and-validation or https://gin-gonic.com/docs/examples/custom-validators/

Comment From: umermansoor

type UserSignUp struct {
    Username string `json:"username" binding:"required"`
    Password string `json:"password"`
    Email    string `json:"email"`
}

Is there any easy way to error when extraneous fields are present i.e. in this case the request body is: {"username": "123", "a":"a"}?