How can I validate a single value?

[AngangGuo]

I want to validate the id parameter get from api/customers/:id.
I can validate it by using validate.Var(i, "gt=1,lt=10")

I can validate a struct according to this fix.
How can I validate a parameter from within Echo?

Thanks

[aldas]

What you want to do is to:

1. bind path parameter to struct
2. validate that field

Path parameter can be bind to struct with param="id" tag
Validation can be added with field tag validate:"gt=1,lt=10"

so you need to add similar field to your bindable struct
ID int64 `param:"id" validate:"required,gt=1,lt=10"`

If you do not want to use struct then you need to first convert path param to int and then use validator.Var on it.

		var id int64
		if err = echo.PathParamsBinder(c).Int64("id", &id).BindError(); err != nil {
			return echo.NewHTTPError(http.StatusBadRequest, err.Error())
		}

		if err = validator.New().Var(id, "gt=1,lt=10"); err != nil {
			return echo.NewHTTPError(http.StatusBadRequest, err.Error())
		}

Working example for validating single variable:

var validate = validator.New()

func main() {
	e := echo.New()
	
	e.POST("/users/:id", func(c echo.Context) error {
		var id int64
		if err := echo.PathParamsBinder(c).Int64("id", &id).BindError(); err != nil {
			return echo.NewHTTPError(http.StatusBadRequest, err.Error())
		}

		if err := validate.Var(id, "gt=1,lt=10"); err != nil {
			return echo.NewHTTPError(http.StatusBadRequest, err.Error())
		}

		return c.JSON(http.StatusOK, map[string]string{"status": "ok"})
	})
	e.Logger.Fatal(e.Start(":1323"))
}

Working example for struct:

type (
	User struct {
		ID int64 `param:"id" validate:"required,gt=1,lt=10"`
		Name  string `json:"name" validate:"required"`
		Email string `json:"email" validate:"required,email"`
	}

	CustomValidator struct {
		validator *validator.Validate
	}
)

func (cv *CustomValidator) Validate(i interface{}) error {
	if err := cv.validator.Struct(i); err != nil {
		return echo.NewHTTPError(http.StatusInternalServerError, err.Error())
	}
	return nil
}

func main() {
	e := echo.New()
	e.Validator = &CustomValidator{validator: validator.New()}
	e.POST("/users/:id", func(c echo.Context) (err error) {
		u := new(User)
		if err = c.Bind(u); err != nil {
			return echo.NewHTTPError(http.StatusBadRequest, err.Error())
		}
		if err = c.Validate(u); err != nil {
			return echo.NewHTTPError(http.StatusBadRequest, err.Error())
		}
		return c.JSON(http.StatusOK, u)
	})
	e.Logger.Fatal(e.Start(":1323"))
}

Example request:

x@x~/code$ curl -v -X POST http://localhost:1323/users/2   -H 'Content-Type: application/json'   -d '{"name":"Joe","email":"joe@test.com"}'
Note: Unnecessary use of -X or --request, POST is already inferred.
*   Trying 127.0.0.1:1323...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 1323 (#0)
> POST /users/2 HTTP/1.1
> Host: localhost:1323
> User-Agent: curl/7.68.0
> Accept: */*
> Content-Type: application/json
> Content-Length: 37
> 
* upload completely sent off: 37 out of 37 bytes
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Content-Type: application/json; charset=UTF-8
< Date: Thu, 25 Mar 2021 20:38:19 GMT
< Content-Length: 45
< 
{"ID":2,"name":"Joe","email":"joe@test.com"}
* Connection #0 to host localhost left intact

and example of validation error:

x@x:~/code$ curl -v -X POST http://localhost:1323/users/11   -H 'Content-Type: application/json'   -d '{"name":"Joe","email":"joe@test.com"}'
Note: Unnecessary use of -X or --request, POST is already inferred.
*   Trying 127.0.0.1:1323...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 1323 (#0)
> POST /users/11 HTTP/1.1
> Host: localhost:1323
> User-Agent: curl/7.68.0
> Accept: */*
> Content-Type: application/json
> Content-Length: 37
> 
* upload completely sent off: 37 out of 37 bytes
* Mark bundle as not supporting multiuse
< HTTP/1.1 400 Bad Request
< Content-Type: application/json; charset=UTF-8
< Date: Thu, 25 Mar 2021 20:46:08 GMT
< Content-Length: 102
< 
{"message":"code=500, message=Key: 'User.ID' Error:Field validation for 'ID' failed on the 'lt' tag"}
* Connection #0 to host localhost left intact

[AngangGuo]

Great thanks for your answer.
It seems more flexible if we use the validator library directly as in your first example.
If we register the validator to Echo, it can only validate struct as in your second example. I still need to create a validator instance to validate a variable or we must wrap it into a struct.