gogjango/gjango

package testhelper

import (
    "fmt"
    "net"
)

// GetFreePort asks the kernel for a free open port that is ready to use.
func GetFreePort(host string, preferredPort uint32) (int, error) {
    address := host + ":" + fmt.Sprint(preferredPort)
    addr, err := net.ResolveTCPAddr("tcp", address)
    if err != nil {
        return 0, err
    }

    l, err := net.ListenTCP("tcp", addr)
    if err != nil {
        return 0, err
    }
    defer l.Close()
    return l.Addr().(*net.TCPAddr).Port, nil
}

// AllocatePort returns a port that is available, given host and a preferred port
// if none of the preferred ports are available, it will keep searching by adding 1 to the port number
func AllocatePort(host string, preferredPort uint32) uint32 {
    preferredPortStr := fmt.Sprint(preferredPort)
    allocatedPort, err := GetFreePort(host, preferredPort)
    for err != nil {
        preferredPort = preferredPort + 1
        allocatedPort, err = GetFreePort(host, preferredPort)
        if err != nil {
            fmt.Println("Failed to connect to", preferredPortStr)
        }
    }
    fmt.Println("Allocated port", allocatedPort)
    return uint32(allocatedPort)
}