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/dynamic.go

@@ -25,6 +25,7 @@ type dynamicClient struct {
 	timeout                  time.Duration
 
 	mut    sync.RWMutex
+	err    error
 	client RelayClient
 	stop   chan struct{}
 }
@@ -61,6 +62,7 @@ func (c *dynamicClient) Serve() {
 	data, err := http.Get(uri.String())
 	if err != nil {
 		l.Debugln(c, "failed to lookup dynamic relays", err)
+		c.setError(err)
 		return
 	}
 
@@ -69,6 +71,7 @@ func (c *dynamicClient) Serve() {
 	data.Body.Close()
 	if err != nil {
 		l.Debugln(c, "failed to lookup dynamic relays", err)
+		c.setError(err)
 		return
 	}
 
@@ -89,6 +92,7 @@ func (c *dynamicClient) Serve() {
 		select {
 		case <-c.stop:
 			l.Debugln(c, "stopping")
+			c.setError(nil)
 			return
 		default:
 			ruri, err := url.Parse(addr)
@@ -112,6 +116,7 @@ func (c *dynamicClient) Serve() {
 		}
 	}
 	l.Debugln(c, "could not find a connectable relay")
+	c.setError(fmt.Errorf("could not find a connectable relay"))
 }
 
 func (c *dynamicClient) Stop() {
@@ -124,13 +129,13 @@ func (c *dynamicClient) Stop() {
 	c.client.Stop()
 }
 
-func (c *dynamicClient) StatusOK() bool {
+func (c *dynamicClient) Error() error {
 	c.mut.RLock()
 	defer c.mut.RUnlock()
 	if c.client == nil {
-		return false
+		return c.err
 	}
-	return c.client.StatusOK()
+	return c.client.Error()
 }
 
 func (c *dynamicClient) Latency() time.Duration {
@@ -150,7 +155,7 @@ func (c *dynamicClient) URI() *url.URL {
 	c.mut.RLock()
 	defer c.mut.RUnlock()
 	if c.client == nil {
-		return c.pooladdr
+		return nil
 	}
 	return c.client.URI()
 }
@@ -171,6 +176,12 @@ func (c *dynamicClient) cleanup() {
 	c.mut.Unlock()
 }
 
+func (c *dynamicClient) setError(err error) {
+	c.mut.Lock()
+	c.err = err
+	c.mut.Unlock()
+}
+
 // This is the announcement recieved from the relay server;
 // {"relays": [{"url": "relay://10.20.30.40:5060"}, ...]}
 type dynamicAnnouncement struct {