Determine if POST data value matches struct field type - go

Question

Using the gin framework I am trying to determine if POST'ed data does not match the struct field type and inform API user of their error.
type CreateApp struct {
LearnMoreImage string `db:"learn_more_image" json:"learn_more_image,omitempty" valid:"string,omitempty"`
ApiVersion int64 `db:"api_version" json:"api_version" valid:"int,omitempty"`
}
...
func CreateApps(c *gin.Context) {
var json models.CreateApp
c.Bind(&json)
So when I POST
curl -H "Content-Type: application/json" -d '{"learn_more_image":"someimage.jpg","api_version":"somestring"}' "http://127.0.0.1:8080/v1.0/apps"
I would like to determine whether the POST'ed data for field 'api_version' (passed as string) does not match the struct field it is being binded to (int). If the data doesnt match I'd like to send a message back to the user. Its for this reason I was hoping I could loop through the gin contexts data and check it.
The gin function 'c.Bind()' seems to omit invalid data and all subsequent data fields with it.

Answer 1

Gin has a built-in validation engine: https://github.com/bluesuncorp/validator/blob/v5/baked_in.go
but you can use your own or disable it completely.
The validator does not validate the wire data (json string), instead it validates the binded struct:
LearnMoreImage string `db:"learn_more_image" json:"learn_more_image,omitempty" binding:"required"`
ApiVersion int64 `db:"api_version" json:"api_version" binding:"required,min=1"`
Notice this: binding:"required,min=1"
Then:
err := c.Bind(&json)
or use a middleware and read c.Errors.
UPDATED:
Three workarounds:
Validate the json string your own (it can not be done with enconding/json)
Validate if integer is > 0 binding:"min=1"
Use a map[string]interface{} instead of a Struct, then validate the type.
func endpoint(c *gin.Context) {
var json map[string]interface{}
c.Bind(&json)
struct, ok := validateCreateApp(json)
if ok { /** DO SOMETHING */ }
}
func validateCreateApp(json map[string]interface{}) (CreateApp, bool) {
learn_more_image, ok := json["learn_more_image"].(string)
if !ok {
return CreateApp{}, false
}
api_version, ok = json["api_version"].(int)
if !ok {
return CreateApp{}, false
}
return CreateApp{
learn_more_image, api_version,
}
}