network: use and improve discovery mechanism for reconnections

This makes our node reconnect to other nodes if connection drops for some
reason. Fixes #390.

pkg/network/discovery.go

@@ -107,8 +107,21 @@ func (d *DefaultDiscovery) work(addrCh chan string) {
 	}
 }
 
-func (d *DefaultDiscovery) next() string {
-	return <-d.pool
+func (d *DefaultDiscovery) requestToWork(workCh chan string) {
+	var requested int
+
+	for {
+		for requested = <-d.requestCh; requested > 0; requested-- {
+			select {
+			case r := <-d.requestCh:
+				if requested < r {
+					requested = r
+				}
+			case addr := <-d.pool:
+				workCh <- addr
+			}
+		}
+	}
 }
 
 func (d *DefaultDiscovery) run() {
@@ -121,6 +134,7 @@ func (d *DefaultDiscovery) run() {
 		go d.work(workCh)
 	}
 
+	go d.requestToWork(workCh)
 	for {
 		select {
 		case addr := <-d.backFill:
@@ -132,18 +146,10 @@ func (d *DefaultDiscovery) run() {
 				d.unconnectedAddrs[addr] = true
 				d.pool <- addr
 			}
-		case n := <-d.requestCh:
-			go func() {
-				for i := 0; i < n; i++ {
-					workCh <- d.next()
-				}
-			}()
 		case addr := <-d.badAddrCh:
 			d.badAddrs[addr] = true
 			delete(d.unconnectedAddrs, addr)
-			go func() {
-				workCh <- d.next()
-			}()
+			d.RequestRemote(1)
 
 		case addr := <-d.connectedCh:
 			delete(d.unconnectedAddrs, addr)

pkg/network/server.go

@@ -15,7 +15,9 @@ import (
 )
 
 const (
+	// peer numbers are arbitrary at the moment
 	minPeers      = 5
+	maxPeers      = 20
 	maxBlockBatch = 200
 	minPoolCount  = 30
 )
@@ -90,12 +92,7 @@ func (s *Server) Start(errChan chan error) {
 		"headerHeight": s.chain.HeaderHeight(),
 	}).Info("node started")
 
-	for _, addr := range s.Seeds {
-		if err := s.transport.Dial(addr, s.DialTimeout); err != nil {
-			log.Warnf("failed to connect to remote node %s", addr)
-			continue
-		}
-	}
+	s.discovery.BackFill(s.Seeds...)
 
 	go s.transport.Accept()
 	s.run()
@@ -122,6 +119,10 @@ func (s *Server) BadPeers() []string {
 
 func (s *Server) run() {
 	for {
+		c := s.PeerCount()
+		if c < minPeers {
+			s.discovery.RequestRemote(maxPeers - c)
+		}
 		select {
 		case <-s.quit:
 			s.transport.Close()
@@ -147,6 +148,7 @@ func (s *Server) run() {
 				"reason":    drop.reason,
 				"peerCount": s.PeerCount(),
 			}).Warn("peer disconnected")
+			s.discovery.BackFill(drop.peer.NetAddr().String())
 		}
 	}
 }