TCP Check

package main

import (
        "log"
        "net"
)

func main() {
        var status string
        conn, err := net.Dial("tcp", "127.0.0.1:80")
        if err != nil {
                log.Println("Connection error:", err)
                status = "Unreachable"
        } else {
                status = "Online"
                defer conn.Close()
        }
        log.Println(status)
}

This check will only work if someone is accepting connections on that port. If the port is taken but the holder does not accept connections the port is certainly unreachable, but not available for use.

You might want to use net.ListenTCP and try to bind to the address. This will fail when the port is already taken. This naturally only works for local checks.

like

https://github.com/akutz/gotil/blob/master/gotil.go#L284