Try all addresses when connecting to a DNS name

Fixes #980

src/core/link_tcp.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"net"
 	"net/url"
+	"strconv"
 	"strings"
 	"time"
 
@@ -31,25 +32,40 @@ func (l *links) newLinkTCP() *linkTCP {
 }
 
 func (l *linkTCP) dial(url *url.URL, options linkOptions, sintf string) error {
-	addr, err := net.ResolveTCPAddr("tcp", url.Host)
+	info := linkInfoFor("tcp", sintf, url.Host)
-	if err != nil {
-		return err
-	}
-	dialer, err := l.dialerFor(addr, sintf)
-	if err != nil {
-		return err
-	}
-	info := linkInfoFor("tcp", sintf, tcpIDFor(dialer.LocalAddr, addr))
 	if l.links.isConnectedTo(info) {
 		return nil
 	}
-	conn, err := dialer.DialContext(l.core.ctx, "tcp", addr.String())
+	host, p, err := net.SplitHostPort(url.Host)
 	if err != nil {
 		return err
 	}
+	port, err := strconv.Atoi(p)
+	if err != nil {
+		return err
+	}
+	ips, err := net.LookupIP(host)
+	if err != nil {
+		return err
+	}
+	for _, ip := range ips {
+		addr := &net.TCPAddr{
+			IP:   ip,
+			Port: port,
+		}
+		dialer, err := l.dialerFor(addr, sintf)
+		if err != nil {
+			continue
+		}
+		conn, err := dialer.DialContext(l.core.ctx, "tcp", addr.String())
+		if err != nil {
+			continue
+		}
 		uri := strings.TrimRight(strings.SplitN(url.String(), "?", 2)[0], "/")
 		return l.handler(uri, info, conn, options, false, false)
 	}
+	return fmt.Errorf("failed to connect via %d addresses", len(ips))
+}
 
 func (l *linkTCP) listen(url *url.URL, sintf string) (*Listener, error) {
 	ctx, cancel := context.WithCancel(l.core.ctx)
@@ -82,10 +98,9 @@ func (l *linkTCP) listen(url *url.URL, sintf string) (*Listener, error) {
 				cancel()
 				break
 			}
-			laddr := conn.LocalAddr().(*net.TCPAddr)
 			raddr := conn.RemoteAddr().(*net.TCPAddr)
 			name := fmt.Sprintf("tcp://%s", raddr)
-			info := linkInfoFor("tcp", sintf, tcpIDFor(laddr, raddr))
+			info := linkInfoFor("tcp", sintf, raddr.String())
 			if err = l.handler(name, info, conn, linkOptionsForListener(url), true, raddr.IP.IsLinkLocalUnicast()); err != nil {
 				l.core.log.Errorln("Failed to create inbound link:", err)
 			}
@@ -180,16 +195,3 @@ func (l *linkTCP) dialerFor(dst *net.TCPAddr, sintf string) (*net.Dialer, error)
 	}
 	return dialer, nil
 }
-
-func tcpIDFor(local net.Addr, remoteAddr *net.TCPAddr) string {
-	if localAddr, ok := local.(*net.TCPAddr); ok && localAddr.IP.Equal(remoteAddr.IP) {
-		// Nodes running on the same host — include both the IP and port.
-		return remoteAddr.String()
-	}
-	if remoteAddr.IP.IsLinkLocalUnicast() {
-		// Nodes discovered via multicast — include the IP only.
-		return remoteAddr.IP.String()
-	}
-	// Nodes connected remotely — include both the IP and port.
-	return remoteAddr.String()
-}

src/core/link_tls.go

@@ -13,6 +13,7 @@ import (
 	"math/big"
 	"net"
 	"net/url"
+	"strconv"
 	"strings"
 	"time"
 
@@ -47,17 +48,30 @@ func (l *links) newLinkTLS(tcp *linkTCP) *linkTLS {
 }
 
 func (l *linkTLS) dial(url *url.URL, options linkOptions, sintf, sni string) error {
-	addr, err := net.ResolveTCPAddr("tcp", url.Host)
+	info := linkInfoFor("tls", sintf, url.Host)
+	if l.links.isConnectedTo(info) {
+		return nil
+	}
+	host, p, err := net.SplitHostPort(url.Host)
 	if err != nil {
 		return err
 	}
+	port, err := strconv.Atoi(p)
+	if err != nil {
+		return err
+	}
+	ips, err := net.LookupIP(host)
+	if err != nil {
+		return err
+	}
+	for _, ip := range ips {
+		addr := &net.TCPAddr{
+			IP:   ip,
+			Port: port,
+		}
 		dialer, err := l.tcp.dialerFor(addr, sintf)
 		if err != nil {
-		return err
+			continue
-	}
-	info := linkInfoFor("tls", sintf, tcpIDFor(dialer.LocalAddr, addr))
-	if l.links.isConnectedTo(info) {
-		return nil
 		}
 		tlsconfig := l.config.Clone()
 		tlsconfig.ServerName = sni
@@ -67,11 +81,13 @@ func (l *linkTLS) dial(url *url.URL, options linkOptions, sintf, sni string) err
 		}
 		conn, err := tlsdialer.DialContext(l.core.ctx, "tcp", addr.String())
 		if err != nil {
-		return err
+			continue
 		}
 		uri := strings.TrimRight(strings.SplitN(url.String(), "?", 2)[0], "/")
 		return l.handler(uri, info, conn, options, false, false)
 	}
+	return fmt.Errorf("failed to connect via %d addresses", len(ips))
+}
 
 func (l *linkTLS) listen(url *url.URL, sintf string) (*Listener, error) {
 	ctx, cancel := context.WithCancel(l.core.ctx)
@@ -105,10 +121,9 @@ func (l *linkTLS) listen(url *url.URL, sintf string) (*Listener, error) {
 				cancel()
 				break
 			}
-			laddr := conn.LocalAddr().(*net.TCPAddr)
 			raddr := conn.RemoteAddr().(*net.TCPAddr)
 			name := fmt.Sprintf("tls://%s", raddr)
-			info := linkInfoFor("tls", sintf, tcpIDFor(laddr, raddr))
+			info := linkInfoFor("tls", sintf, raddr.String())
 			if err = l.handler(name, info, conn, linkOptionsForListener(url), true, raddr.IP.IsLinkLocalUnicast()); err != nil {
 				l.core.log.Errorln("Failed to create inbound link:", err)
 			}