server: ping

pool.go

@@ -5,10 +5,12 @@
 package tunnel
 
 import (
+	"context"
 	"fmt"
 	"net"
 	"net/http"
 	"sync"
+	"time"
 
 	"golang.org/x/net/http2"
 
@@ -37,6 +39,10 @@ func newConnPool(t *http2.Transport, l onDisconnectListener) *connPool {
 	}
 }
 
+func (p *connPool) URL(identifier id.ID) string {
+	return fmt.Sprint("https://", identifier)
+}
+
 func (p *connPool) GetClientConn(req *http.Request, addr string) (*http2.ClientConn, error) {
 	p.mu.RLock()
 	defer p.mu.RUnlock()
@@ -54,11 +60,7 @@ func (p *connPool) MarkDead(c *http2.ClientConn) {
 
 	for addr, cp := range p.conns {
 		if cp.clientConn == c {
-			cp.conn.Close()
+			p.close(cp, addr)
-			delete(p.conns, addr)
-			if p.listener != nil {
-				p.listener(p.addrToIdentifier(addr))
-			}
 			return
 		}
 	}
@@ -70,9 +72,13 @@ func (p *connPool) AddConn(conn net.Conn, identifier id.ID) error {
 
 	addr := p.addr(identifier)
 
-	if _, ok := p.conns[addr]; ok {
+	if cp, ok := p.conns[addr]; ok {
+		if err := p.ping(cp); err != nil {
+			p.close(cp, addr)
+		} else {
 			return errClientAlreadyConnected
 		}
+	}
 
 	c, err := p.t.NewClientConn(conn)
 	if err != nil {
@@ -93,24 +99,46 @@ func (p *connPool) DeleteConn(identifier id.ID) {
 	addr := p.addr(identifier)
 
 	if cp, ok := p.conns[addr]; ok {
-		cp.conn.Close()
+		p.close(cp, addr)
-		delete(p.conns, addr)
-		if p.listener != nil {
-			p.listener(identifier)
-		}
 	}
 }
 
-func (p *connPool) URL(identifier id.ID) string {
+func (p *connPool) Ping(identifier id.ID) (time.Duration, error) {
-	return fmt.Sprint("https://", identifier)
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	addr := p.addr(identifier)
+
+	if cp, ok := p.conns[addr]; ok {
+		start := time.Now()
+		err := p.ping(cp)
+		return time.Since(start), err
+	}
+
+	return 0, errClientNotConnected
+}
+
+func (p *connPool) ping(cp connPair) error {
+	ctx, cancel := context.WithTimeout(context.Background(), DefaultPingTimeout)
+	defer cancel()
+
+	return cp.clientConn.Ping(ctx)
+}
+
+func (p *connPool) close(cp connPair, addr string) {
+	cp.conn.Close()
+	delete(p.conns, addr)
+	if p.listener != nil {
+		p.listener(p.identifier(addr))
+	}
 }
 
 func (p *connPool) addr(identifier id.ID) string {
 	return fmt.Sprint(identifier.String(), ":443")
 }
 
-func (p *connPool) addrToIdentifier(addr string) id.ID {
+func (p *connPool) identifier(addr string) id.ID {
-	identifier := id.ID{}
+	var identifier id.ID
 	identifier.UnmarshalText([]byte(addr[:len(addr)-4]))
 	return identifier
 }

server.go

@@ -150,7 +150,7 @@ func (s *Server) Start() {
 		if err := keepAlive(conn); err != nil {
 			s.logger.Log(
 				"level", 1,
-				"msg", "connection keepAlive failed",
+				"msg", "could not enable TCP keepalive for control connection",
 				"addr", addr,
 				"err", err,
 			)
@@ -408,6 +408,11 @@ func (s *Server) Unsubscribe(identifier id.ID) *RegistryItem {
 	return s.registry.Unsubscribe(identifier)
 }
 
+// Ping measures the RTT response time.
+func (s *Server) Ping(identifier id.ID) (time.Duration, error) {
+	return s.connPool.Ping(identifier)
+}
+
 func (s *Server) listen(l net.Listener, identifier id.ID) {
 	addr := l.Addr().String()