Add functions to find freeport UDP/TCP ports

go/reuse_port/freeport.go

@@ -0,0 +1,45 @@
+package reuseport
+
+import (
+	"context"
+	"errors"
+	"net"
+)
+
+func FreeTcpPort() (*net.TCPListener, int, error) {
+	l, err := ReusePortListenConfig.Listen(context.Background(), "tcp", "localhost:0")
+	if err != nil {
+		return nil, 0, err
+	}
+
+	tl, ok := l.(*net.TCPListener)
+	if !ok {
+		return nil, 0, errors.New("Bad Cast")
+	}
+
+	addr, ok := l.Addr().(*net.TCPAddr)
+	if !ok {
+		return nil, 0, errors.New("Bad Cast")
+	}
+
+	return tl, addr.Port, nil
+}
+
+func FreeUdpPort() (*net.UDPConn, int, error) {
+	l, err := ReusePortListenConfig.ListenPacket(context.Background(), "udp", "localhost:0")
+	if err != nil {
+		return nil, 0, err
+	}
+
+	uc, ok := l.(*net.UDPConn)
+	if !ok {
+		return nil, 0, errors.New("Bad Cast")
+	}
+
+	addr, ok := l.LocalAddr().(*net.UDPAddr)
+	if !ok {
+		return nil, 0, errors.New("Bad Cast")
+	}
+
+	return uc, addr.Port, nil
+}

go/reuse_port/freeport_test.go

@@ -0,0 +1,40 @@
+package reuseport
+
+import (
+	"context"
+	"testing"
+)
+
+func TestFreeTcpPort(t *testing.T) {
+	l1, _, err := FreeTcpPort()
+	if err != nil {
+		t.Fatalf("%s", err.Error())
+	}
+
+	defer l1.Close()
+	l2, err := ReusePortListenConfig.Listen(context.Background(), "tcp", l1.Addr().String())
+	if err != nil {
+		t.Fatalf("%s", err.Error())
+	}
+
+	if l2.Addr().String() != l1.Addr().String() {
+		t.Fatalf("Not the same address")
+	}
+}
+
+func TestFreeUdpPort(t *testing.T) {
+	l1, _, err := FreeUdpPort()
+	if err != nil {
+		t.Fatalf("%s", err.Error())
+	}
+
+	defer l1.Close()
+	l2, err := ReusePortListenConfig.ListenPacket(context.Background(), "udp", l1.LocalAddr().String())
+	if err != nil {
+		t.Fatalf("%s", err.Error())
+	}
+
+	if l2.LocalAddr().String() != l1.LocalAddr().String() {
+		t.Fatalf("Not the same address")
+	}
+}

go/reuse_port/reuse_port.go

@@ -0,0 +1,24 @@
+package reuseport
+
+import (
+	"net"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func reusePort(network, address string, conn syscall.RawConn) error {
+	var opErr error
+	err := conn.Control(func(fd uintptr) {
+		opErr = syscall.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
+	})
+	if err != nil {
+		return err
+	}
+
+	return opErr
+}
+
+var ReusePortListenConfig = net.ListenConfig{
+	Control: reusePort,
+}