freeport.go

package freeport

import (
	"errors"
	"fmt"
	"net"
)

// GetFreePortOnInterface by name and protocol
func GetFreePortOnInterface(interfaceName string, protocol Protocol) (*Port, error) {
	itf, err := net.InterfaceByName(interfaceName)
	if err != nil {
		return nil, err
	}
	addresses, err := itf.Addrs()
	if err != nil {
		return nil, err
	}
	for _, address := range addresses {
		switch protocol {
		case UDP:
			if port, err := GetFreeUDPPort(address.String()); err == nil {
				return port, nil
			}
		default:
			if port, err := GetFreeTCPPort(address.String()); err == nil {
				return port, nil
			}
		}
	}
	return nil, fmt.Errorf("couldn't find any free port on interface %s", interfaceName)
}

// GetFreePort from ip address and protocol
func GetFreePort(address string, protocol Protocol) (*Port, error) {
	switch protocol {
	case UDP:
		return GetFreeUDPPort(address)
	default:
		return GetFreeTCPPort(address)
	}
}

// GetFreePorts collects "count" free ports of specific protocol
func GetFreePorts(address string, protocol Protocol, count int) ([]*Port, error) {
	ports := make([]*Port, count)
	for i := 0; i < count; i++ {
		port, err := GetFreePort(address, protocol)
		if err != nil {
			return nil, err
		}
		ports[i] = port
	}
	return ports, nil
}

// GetFreePortInRange for protocol within a port range
func GetFreePortInRange(address string, protocol Protocol, minPort, maxPort int) (*Port, error) {
	if minPort > maxPort {
		return nil, errors.New("invalid interval")
	}
	for port := minPort; port <= maxPort; port++ {
		if port, err := GetPort(protocol, address, port); err == nil {
			return port, nil
		}
	}
	return nil, fmt.Errorf("couldn't find free ports between %d and %d", minPort, maxPort)
}

// GetFreeTCPPort gets a free tcp port on address
func GetFreeTCPPort(address string) (*Port, error) {
	addr, err := net.ResolveTCPAddr("tcp", address+":0")
	if err != nil {
		return nil, err
	}

	l, err := net.ListenTCP("tcp", addr)
	if err != nil {
		return nil, err
	}
	if err := l.Close(); err != nil {
		return nil, err
	}
	var port int
	if tcpAddr, ok := l.Addr().(*net.TCPAddr); ok {
		port = tcpAddr.Port
	}

	// We could just use address as for GetPort, but this change
	// honors spirit of original code in allowing the listen IP
	// to change in some way
	return &Port{Address: address, Port: port, Protocol: TCP, NetListenAddress: l.Addr().String()}, nil
}

// GetPort for protocol is the specific port is free
func GetPort(protocol Protocol, address string, port int) (*Port, error) {
	hostport := net.JoinHostPort(address, fmt.Sprint(port))
	switch protocol {
	case UDP:
		addr, err := net.ResolveUDPAddr("udp", hostport)
		if err != nil {
			return nil, err
		}
		l, err := net.ListenUDP("udp", addr)
		if err != nil {
			return nil, err
		}
		if err := l.Close(); err != nil {
			return nil, err
		}
		return &Port{Address: address, Port: port, Protocol: UDP, NetListenAddress: l.LocalAddr().String()}, nil
	default:
		l, err := net.Listen("tcp", hostport)
		if err != nil {
			return nil, err
		}
		if err := l.Close(); err != nil {
			return nil, err
		}
		return &Port{Address: address, Port: port, Protocol: TCP, NetListenAddress: l.Addr().String()}, nil

	}
}

// GetFreeUDPPort gets a free udp port on address
func GetFreeUDPPort(address string) (*Port, error) {
	addr, err := net.ResolveUDPAddr("udp", address+":0")
	if err != nil {
		return nil, err
	}

	l, err := net.ListenUDP("udp", addr)
	if err != nil {
		return nil, err
	}
	if err := l.Close(); err != nil {
		return nil, err
	}
	var port int
	if udpAddr, ok := l.LocalAddr().(*net.UDPAddr); ok {
		port = udpAddr.Port
	}

	// This should always be equal to address, but if for some reason the OS remaps
	// this honors the returned address
	return &Port{Address: address, Port: port, Protocol: UDP, NetListenAddress: l.LocalAddr().String()}, nil
}

// MustGetFreeTCPPort get a free tcp port for address or panic
func MustGetFreeTCPPort(address string) *Port {
	port, err := GetFreeTCPPort(address)
	if err != nil {
		panic(err)
	}
	return port
}

// MustGetFreeUDPPort get a free udp port for address or panic
func MustGetFreeUDPPort(address string) *Port {
	port, err := GetFreeUDPPort(address)
	if err != nil {
		panic(err)
	}
	return port
}