$ go get github.com/pgollangi/go-portfinder

package main

import (
    "github.com/pgollangi/go-portfinder"
)

func main(){
     // scans and returns first open port on all network interfaces of current machine.
     openPort, err := portfinder.GetPort(&PortFinderOptions {
         StartPort: 9090,
         StopPort: 9099
     })
}