How to check string is in json format

Question

I want to create a function to receive an input string which can be string in json format or just a string. For example, something easy like following function.

Answer 1

Standard encoding/json library contains json.Valid function starting from go 1.9 - see https://github.com/golang/go/issues/18086 . This function may be used for checking whether the provided string is a valid json:

if json.Valid(input) {
    // input contains valid json
}

But json.Valid may be quite slow comparing to third-party solutions such as fastjson.Validate, which is up to 5x faster than the standard json.Valid - see json validation section in benchmarks.