Add ability to detect free port

Signed-off-by: Syrone Wong <[email protected]>

Makefile

@@ -1,5 +1,8 @@
 BUILDDIR=$(shell pwd)/build
-SOURCES=github.com/trojan-gfw/igniter-go-libs/clash github.com/trojan-gfw/igniter-go-libs/tun2socks
+SOURCES= \
+	github.com/trojan-gfw/igniter-go-libs/clash \
+	github.com/trojan-gfw/igniter-go-libs/tun2socks \
+	github.com/trojan-gfw/igniter-go-libs/freeport
 
 all: ios android
 

freeport/freeport.go

@@ -0,0 +1,40 @@
+// Taken from https://github.com/phayes/freeport
+package freeport
+
+import (
+	"net"
+)
+
+// GetFreePort asks the kernel for a free open port that is ready to use.
+func GetFreePort() (int, error) {
+	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
+	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
+}
+
+// GetFreePort asks the kernel for free open ports that are ready to use.
+func GetFreePorts(count int) ([]int, error) {
+	var ports []int
+	for i := 0; i < count; i++ {
+		addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
+		if err != nil {
+			return nil, err
+		}
+
+		l, err := net.ListenTCP("tcp", addr)
+		if err != nil {
+			return nil, err
+		}
+		defer l.Close()
+		ports = append(ports, l.Addr().(*net.TCPAddr).Port)
+	}
+	return ports, nil
+}