lib/connections: Refactor

1. Removes separate relay lists and relay clients/services, just makes it a listen address
2. Easier plugging-in of other transports
3. Allows "hot" disabling and enabling NAT services
4. Allows "hot" listen address changes
5. Changes listen address list with a preferable "default" value just like for discovery
6. Debounces global discovery announcements as external addresses change (which it might alot upon starting)
7. Stops this whole "pick other peers relay by latency". This information is no longer available,
   but I don't think it matters as most of the time other peer only has one relay.
8. Rename ListenAddress to ListenAddresses, as well as in javascript land.
9. Stop serializing deprecated values to JSON

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/2982

lib/relay/client/static.go

@@ -32,6 +32,7 @@ type staticClient struct {
 	conn *tls.Conn
 
 	mut       sync.RWMutex
+	err       error
 	connected bool
 	latency   time.Duration
 }
@@ -57,8 +58,7 @@ func newStaticClient(uri *url.URL, certs []tls.Certificate, invitations chan pro
 		stop:    make(chan struct{}),
 		stopped: make(chan struct{}),
 
-		mut:       sync.NewRWMutex(),
-		connected: false,
+		mut: sync.NewRWMutex(),
 	}
 }
 
@@ -69,6 +69,7 @@ func (c *staticClient) Serve() {
 
 	if err := c.connect(); err != nil {
 		l.Infof("Could not connect to relay %s: %s", c.uri, err)
+		c.setError(err)
 		return
 	}
 
@@ -77,12 +78,14 @@ func (c *staticClient) Serve() {
 	if err := c.join(); err != nil {
 		c.conn.Close()
 		l.Infof("Could not join relay %s: %s", c.uri, err)
+		c.setError(err)
 		return
 	}
 
 	if err := c.conn.SetDeadline(time.Time{}); err != nil {
 		c.conn.Close()
 		l.Infoln("Relay set deadline:", err)
+		c.setError(err)
 		return
 	}
 
@@ -109,6 +112,7 @@ func (c *staticClient) Serve() {
 			case protocol.Ping:
 				if err := protocol.WriteMessage(c.conn, protocol.Pong{}); err != nil {
 					l.Infoln("Relay write:", err)
+					c.setError(err)
 					c.disconnect()
 				} else {
 					l.Debugln(c, "sent pong")
@@ -123,15 +127,18 @@ func (c *staticClient) Serve() {
 
 			case protocol.RelayFull:
 				l.Infof("Disconnected from relay %s due to it becoming full.", c.uri)
+				c.setError(fmt.Errorf("Relay full"))
 				c.disconnect()
 
 			default:
 				l.Infoln("Relay: protocol error: unexpected message %v", msg)
+				c.setError(fmt.Errorf("protocol error: unexpected message %v", msg))
 				c.disconnect()
 			}
 
 		case <-c.stop:
 			l.Debugln(c, "stopping")
+			c.setError(nil)
 			c.disconnect()
 
 		// We always exit via this branch of the select, to make sure the
@@ -144,6 +151,9 @@ func (c *staticClient) Serve() {
 				c.conn.Close()
 				c.connected = false
 				l.Infof("Disconnecting from relay %s due to error: %s", c.uri, err)
+				c.err = err
+			} else {
+				c.err = nil
 			}
 			if c.closeInvitationsOnFinish {
 				close(c.invitations)
@@ -155,6 +165,7 @@ func (c *staticClient) Serve() {
 		case <-timeout.C:
 			l.Debugln(c, "timed out")
 			c.disconnect()
+			c.setError(fmt.Errorf("timed out"))
 		}
 	}
 }
@@ -237,6 +248,19 @@ func (c *staticClient) disconnect() {
 	c.conn.Close()
 }
 
+func (c *staticClient) setError(err error) {
+	c.mut.Lock()
+	c.err = err
+	c.mut.Unlock()
+}
+
+func (c *staticClient) Error() error {
+	c.mut.RLock()
+	err := c.err
+	c.mut.RUnlock()
+	return err
+}
+
 func (c *staticClient) join() error {
 	if err := protocol.WriteMessage(c.conn, protocol.JoinRelayRequest{}); err != nil {
 		return err