Using validator to check if value is boolean - validation

Question

I'm new to Go, so this might be very easy, but I can't find it. I have an entity Page with these two properties:
type Page struct {
Title string `form:"title" binding:"required"`
Active bool
}
Now, if you don't send a title we get a (not very pretty, but acceptable*):
Key: 'Page.Title' Error:Field validation for 'Title' failed on the 'required' tag.
Now, if I send this to the endpoint:
{
"title": "I'm a valid title",
"active": "I'm not a boolean at all!"
}
We get this:
json: cannot unmarshal string into Go struct field Page.Active of type bool
Which, IMO, is giving way too much info. What is the standard practice in Go to validate user input?
I was first making a page-validor.go with some checks, then I found this, but I'm not sure what is good practice in Go.
How do I validate this properly? Should I find check what is provided and then try to move it into the struct and validate the actual contents?
I am using GinGonic
* I've found a way to unwrap the errors and make it nicer

Answer 1

Write custom JSON Unmarshaller method for the type Page and inside UnmarshalJSON(bytes []byte) method, you can unmarshal the JSON bytes to map[string]interface{} and then validate the types you need with the JSON field keys.
An example of the JSON Unmarshaller looks like below.
type Page struct {
Title string `form:"title" binding:"required"`
Active bool
}
func (p *Page) UnmarshalJSON(bytes []byte) error {
var data map[string]interface{}
err := json.Unmarshal(bytes, &data)
if err != nil {
return err
}
actv, _ := data["active"]
if reflect.TypeOf(actv).Kind() != reflect.Bool {
return errors.New("active field should be a boolean")
}
p.Active = actv.(bool)
return nil
}
See the full example here in Playground.

Answer 2

After some more research, I've implemented Go-map-schema.
var page Page
src := make(map[string]interface{})
json.Unmarshal(jsonData, &src)
results, _ := schema.CompareMapToStruct(page, src, nil)
fmt.Println(results.MissingFields)
fmt.Println(results.MismatchedFields)
This works simple with the standard notations for an struct:
type Page struct {
Title string `json:"title" validator:"required"`
Active bool `json:"metaRobotsFollow" validate:"required,bool"`
}

Answer 3

You should use validator v10 available with Go
validator documentation go
For your use case you can use boolean validator
https://pkg.go.dev/github.com/go-playground/validator/v10#hdr-Boolean
type Page struct {
Title string `json:"title" binding:"required"`
Active bool `json:"active" binding:"required,boolean"`
}
Below is sample Test case with one positive and negative
func TestPage(t *testing.T) {
tests := []struct {
testName string
input string
wantErr bool
}{
{
testName: "positive test",
input: `{
"title": "first book title",
"active": false
}`,
wantErr: false,
}, {
testName: "wrong boolean",
input: `{
"title": "second book title",
"active": falsee
}`,
wantErr: false,
},
}
for _, tt := range tests {
t.Run(tt.input, func(t *testing.T) {
var p Page
b := []byte(tt.input)
err := json.Unmarshal(b, &p)
assert.Nil(t, err, "got error %v", err)
})
}