micro/util/net/net.go

package net

import (
	"errors"
	"fmt"
	"net"
	"strconv"
	"strings"
)

// HostPort format addr and port suitable for dial
func HostPort(addr string, port interface{}) string {
	host := addr
	if strings.Count(addr, ":") > 0 {
		host = fmt.Sprintf("[%s]", addr)
	}
	return fmt.Sprintf("%s:%v", host, port)
}

// Listen takes addr:portmin-portmax and binds to the first available port
// Example: Listen("localhost:5000-6000", fn)
func Listen(addr string, fn func(string) (net.Listener, error)) (net.Listener, error) {

	if strings.Count(addr, ":") == 1 && strings.Count(addr, "-") == 0 {
		return fn(addr)
	}

	// host:port || host:min-max
	host, ports, err := net.SplitHostPort(addr)
	if err != nil {
		return nil, err
	}

	// try to extract port range
	prange := strings.Split(ports, "-")

	// single port
	if len(prange) < 2 {
		return fn(addr)
	}

	// we have a port range

	// extract min port
	min, err := strconv.Atoi(prange[0])
	if err != nil {
		return nil, errors.New("unable to extract port range")
	}

	// extract max port
	max, err := strconv.Atoi(prange[1])
	if err != nil {
		return nil, errors.New("unable to extract port range")
	}

	// range the ports
	for port := min; port <= max; port++ {
		// try bind to host:port
		ln, err := fn(HostPort(host, port))
		if err == nil {
			return ln, nil
		}

		// hit max port
		if port == max {
			return nil, err
		}
	}

	// why are we here?
	return nil, fmt.Errorf("unable to bind to %s", addr)
}