fix addressing and deadlines

- setting a now deadline unblocks a blocked read
- setting a specific deadline over a previous deadline honors
  the new one
- WriteTo will accept a net.Addr, not just a PingAddr

Signed-off-by: Thomas Ptacek <thomas@sockpuppet.org>

tun/netstack/tun.go

@@ -17,6 +17,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"golang.zx2c4.com/go118/netip"
@@ -285,11 +286,13 @@ func (net *Net) DialUDP(laddr, raddr *net.UDPAddr) (*gonet.UDPConn, error) {
 }
 
 type PingConn struct {
-	laddr    PingAddr
-	raddr    PingAddr
-	wq       waiter.Queue
-	ep       tcpip.Endpoint
-	deadline time.Time
+	laddr           PingAddr
+	raddr           PingAddr
+	wq              waiter.Queue
+	ep              tcpip.Endpoint
+	mu              sync.RWMutex
+	deadline        time.Time
+	deadlineBreaker chan struct{}
 }
 
 type PingAddr struct{ addr netip.Addr }
@@ -307,6 +310,20 @@ func (ia PingAddr) Network() string {
 	return "ping"
 }
 
+func PingAddrFromAddr(addr net.Addr) (PingAddr, error) {
+	switch v := addr.(type) {
+	case PingAddr:
+		return v, nil
+
+	case *net.IPAddr:
+		nip := netip.AddrFromSlice(v.IP)
+		return PingAddr{nip}, nil
+
+	default:
+		return PingAddr{}, errors.New("wrong address format")
+	}
+}
+
 func (net *Net) DialPingAddr(laddr, raddr netip.Addr) (*PingConn, error) {
 	v6 := laddr.Is6() || raddr.Is6()
 	bind := laddr.IsValid()
@@ -325,7 +342,10 @@ func (net *Net) DialPingAddr(laddr, raddr netip.Addr) (*PingConn, error) {
 		pn = ipv6.ProtocolNumber
 	}
 
-	pc := &PingConn{laddr: PingAddr{laddr}}
+	pc := &PingConn{
+		laddr:           PingAddr{laddr},
+		deadlineBreaker: make(chan struct{}, 1),
+	}
 
 	ep, tcpipErr := net.stack.NewEndpoint(tn, pn, &pc.wq)
 	if tcpipErr != nil {
@@ -360,6 +380,7 @@ func (pc *PingConn) RemoteAddr() net.Addr {
 }
 
 func (pc *PingConn) Close() error {
+	close(pc.deadlineBreaker)
 	pc.ep.Close()
 	return nil
 }
@@ -369,8 +390,11 @@ func (pc *PingConn) SetWriteDeadline(t time.Time) error {
 }
 
 func (pc *PingConn) WriteTo(p []byte, addr net.Addr) (n int, err error) {
-	ia, ok := addr.(PingAddr)
-	if !ok || !((ia.addr.Is4() && pc.laddr.addr.Is4()) || (ia.addr.Is6() && pc.laddr.addr.Is6())) {
+	ia, err := PingAddrFromAddr(addr)
+	if err != nil {
+		return 0, fmt.Errorf("ping write: %w", err)
+	}
+	if !((ia.addr.Is4() && pc.laddr.addr.Is4()) || (ia.addr.Is6() && pc.laddr.addr.Is6())) {
 		return 0, fmt.Errorf("ping write: mismatched protocols")
 	}
 
@@ -409,15 +433,32 @@ func (pc *PingConn) ReadFrom(p []byte) (n int, addr net.Addr, err error) {
 	pc.wq.EventRegister(&e, waiter.EventIn)
 	defer pc.wq.EventUnregister(&e)
 
-	deadline := pc.deadline
+	ready := false
 
-	if deadline.IsZero() {
-		<-notifyCh
-	} else {
-		select {
-		case <-time.NewTimer(deadline.Sub(time.Now())).C:
-			return 0, nil, os.ErrDeadlineExceeded
-		case <-notifyCh:
+	for !ready {
+		pc.mu.RLock()
+		deadlineBreaker := pc.deadlineBreaker
+		deadline := pc.deadline
+		pc.mu.RUnlock()
+
+		if deadline.IsZero() {
+			select {
+			case <-deadlineBreaker:
+			case <-notifyCh:
+				ready = true
+			}
+		} else {
+			t := time.NewTimer(deadline.Sub(time.Now()))
+			defer t.Stop()
+
+			select {
+			case <-t.C:
+				return 0, nil, os.ErrDeadlineExceeded
+
+			case <-deadlineBreaker:
+			case <-notifyCh:
+				ready = true
+			}
 		}
 	}
 
@@ -452,6 +493,10 @@ func (pc *PingConn) SetDeadline(t time.Time) error {
 }
 
 func (pc *PingConn) SetReadDeadline(t time.Time) error {
+	pc.mu.Lock()
+	defer pc.mu.Unlock()
+	close(pc.deadlineBreaker)
+	pc.deadlineBreaker = make(chan struct{}, 1)
 	pc.deadline = t
 	return nil
 }