[mdns] Simplify SO_REUSEPORT usage for UDP sockets.
This CL simplifies the function used to create a UDP socket
with both SO_REUSEADDR and SO_REUSEPORT before binding it.
Using the net.ListenConfig type introduced in Go 1.11 allows
one to specify a control function to set socket options before
it is actually bound to an interface/address.
BUG: DX-1664
Change-Id: I6c520342652f1eb763f87383c745eca89cbb94f3
diff --git a/mdns/mdns.go b/mdns/mdns.go
index 807635c..d33c15e 100644
--- a/mdns/mdns.go
+++ b/mdns/mdns.go
@@ -11,12 +11,12 @@
"fmt"
"io"
"net"
- "os"
"strings"
"syscall"
"unicode/utf8"
"golang.org/x/net/ipv4"
+ "golang.org/x/sys/unix"
)
// DefaultPort is the mDNS port required of the spec, though this library is port-agnostic.
@@ -438,7 +438,7 @@
Send(buf bytes.Buffer) error
Listen(port int) error
JoinGroup(iface net.Interface) error
- ConnectTo(port int, ip net.IP) error
+ ConnectTo(port int, ip net.IP, iface *net.Interface) error
ReadFrom(buf []byte) (size int, iface *net.Interface, src net.Addr, err error)
}
@@ -515,11 +515,12 @@
return nil
}
-func (c *mDNSConn4) ConnectTo(port int, ip net.IP) error {
- if len(ip) != 4 {
+func (c *mDNSConn4) ConnectTo(port int, ip net.IP, iface *net.Interface) error {
+ ip4 := ip.To4()
+ if ip4 == nil {
return fmt.Errorf("Not a valid IPv4 address: %v", ip)
}
- conn, err := makeUnixIpv4Socket(port, ip.To4())
+ conn, err := makeUdpSocketWithReusePort(port, ip4, iface)
if err != nil {
return err
}
@@ -608,36 +609,37 @@
return m.conn4.Send(buf)
}
-func makeUnixIpv4Socket(port int, ip net.IP) (net.PacketConn, error) {
- fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, syscall.IPPROTO_UDP)
- if err != nil {
- return nil, fmt.Errorf("creating socket: %v", err)
+func makeUdpSocketWithReusePort(port int, ip net.IP, iface *net.Interface) (net.PacketConn, error) {
+ is_ipv6 := ip.To4() == nil
+ network := "udp4"
+ var zone string
+ if is_ipv6 {
+ network = "udp6"
+ zone = iface.Name
}
- // SO_REUSEADDR and SO_REUSEPORT allows binding to the same port multiple
- // times which is necessary in the case when there are multiple instances.
- if err := syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, 0x2 /*SO_REUSEADDR*/, 1); err != nil {
- syscall.Close(fd)
- return nil, fmt.Errorf("setting reuse addr: %v", err)
+ address := (&net.UDPAddr{IP: ip, Port: port, Zone: zone}).String()
+
+ // A net.ListenConfig control function to set both SO_REUSEADDR and SO_REUSEPORT
+ // on a given socket fd. Only works on Unix-based systems, not Windows. For portability
+ // an alternative might be to use something like the go-reuseport library.
+ control := func(network, address string, c syscall.RawConn) error {
+ var err error
+ c.Control(func(fd uintptr) {
+ err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEADDR, 1)
+ if err != nil {
+ return
+ }
+
+ err = unix.SetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1)
+ if err != nil {
+ return
+ }
+ })
+ return err
}
- if err := syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, 0xf /*SO_REUSEPORT*/, 1); err != nil {
- syscall.Close(fd)
- return nil, fmt.Errorf("setting reuse port: %v", err)
- }
- // Bind the socket to the specified port.
- var ipArray [4]byte
- copy(ipArray[:], []byte(ip))
- if err := syscall.Bind(fd, &syscall.SockaddrInet4{Addr: ipArray, Port: port}); err != nil {
- syscall.Close(fd)
- return nil, fmt.Errorf("binding to %v: %v", ip, err)
- }
- // Now make a socket.
- f := os.NewFile(uintptr(fd), "")
- conn, err := net.FilePacketConn(f)
- f.Close()
- if err != nil {
- return nil, fmt.Errorf("creating packet conn: %v", err)
- }
- return conn, nil
+
+ listenConfig := net.ListenConfig{Control: control}
+ return listenConfig.ListenPacket(context.Background(), network, address)
}
// Start causes m to start listening for MDNS packets on all interfaces on
@@ -677,7 +679,7 @@
if ip == nil || ip.To4() == nil {
continue
}
- err := m.conn4.ConnectTo(port, ip.To4())
+ err := m.conn4.ConnectTo(port, ip.To4(), &iface)
if err != nil {
return fmt.Errorf("creating socket for %v via %v: %v", iface, ip, err)
}
