Fix: set SO_REUSEADDR for UDP listeners on linux (#630)

common/sockopt/reuseaddr_linux.go

@@ -0,0 +1,19 @@
+package sockopt
+
+import (
+	"net"
+	"syscall"
+)
+
+func UDPReuseaddr(c *net.UDPConn) (err error) {
+	rc, err := c.SyscallConn()
+	if err != nil {
+		return
+	}
+
+	rc.Control(func(fd uintptr) {
+		err = syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+	})
+
+	return
+}

common/sockopt/reuseaddr_other.go

@@ -0,0 +1,11 @@
+// +build !linux
+
+package sockopt
+
+import (
+	"net"
+)
+
+func UDPReuseaddr(c *net.UDPConn) (err error) {
+	return
+}

dns/server.go

@@ -3,6 +3,8 @@ package dns
 import (
 	"net"
 
+	"github.com/Dreamacro/clash/common/sockopt"
+
 	D "github.com/miekg/dns"
 )
 
@@ -58,6 +60,11 @@ func ReCreateServer(addr string, resolver *Resolver) error {
 		return err
 	}
 
+	err = sockopt.UDPReuseaddr(p)
+	if err != nil {
+		return err
+	}
+
 	address = addr
 	handler := newHandler(resolver)
 	server = &Server{handler: handler}

proxy/redir/udp_linux.go

@@ -31,7 +31,11 @@ func setsockopt(c *net.UDPConn, addr string) error {
 	}
 
 	rc.Control(func(fd uintptr) {
-		err = syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_TRANSPARENT, 1)
+		err = syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+
+		if err == nil {
+			err = syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_TRANSPARENT, 1)
+		}
 		if err == nil && isIPv6 {
 			err = syscall.SetsockoptInt(int(fd), syscall.SOL_IPV6, IPV6_TRANSPARENT, 1)
 		}

proxy/socks/udp.go

@@ -5,6 +5,7 @@ import (
 
 	adapters "github.com/Dreamacro/clash/adapters/inbound"
 	"github.com/Dreamacro/clash/common/pool"
+	"github.com/Dreamacro/clash/common/sockopt"
 	"github.com/Dreamacro/clash/component/socks5"
 	C "github.com/Dreamacro/clash/constant"
 	"github.com/Dreamacro/clash/tunnel"
@@ -22,6 +23,11 @@ func NewSocksUDPProxy(addr string) (*SockUDPListener, error) {
 		return nil, err
 	}
 
+	err = sockopt.UDPReuseaddr(l.(*net.UDPConn))
+	if err != nil {
+		return nil, err
+	}
+
 	sl := &SockUDPListener{l, addr, false}
 	go func() {
 		for {