server: Retry seeder connections

If all seeders are unreachable (e.g. the network is not up yet, or DNS lookups
are failing) and the address manager is flagged as needing more addresses,
continue to try and reach the seeders in additional background goroutines with
an increasing backoff timeout.

server.go

@@ -3096,36 +3096,59 @@ func (s *server) rebroadcastHandler(ctx context.Context) {
 func (s *server) querySeeders(ctx context.Context) {
 	// Add peers discovered through DNS to the address manager.
 	seeders := s.chainParams.Seeders()
-	for _, seeder := range seeders {
-		go func(seeder string) {
-			ctx, cancel := context.WithTimeout(ctx, time.Minute)
-			defer cancel()
+	errs := make(chan error, len(seeders))
+	seed := func(seeder string) {
+		ctx, cancel := context.WithTimeout(ctx, time.Minute)
+		defer cancel()
 
-			addrs, err := connmgr.SeedAddrs(ctx, seeder, dcrdDial,
-				connmgr.SeedFilterServices(defaultRequiredServices))
-			if err != nil {
-				srvrLog.Infof("seeder '%s' error: %v", seeder, err)
-				return
-			}
+		addrs, err := connmgr.SeedAddrs(ctx, seeder, dcrdDial,
+			connmgr.SeedFilterServices(defaultRequiredServices))
+		if err != nil {
+			srvrLog.Infof("seeder '%s' error: %v", seeder, err)
+			errs <- err
+			return
+		}
 
-			// Nothing to do if the seeder didn't return any addresses.
-			if len(addrs) == 0 {
-				return
-			}
+		// Nothing to do if the seeder didn't return any addresses.
+		if len(addrs) == 0 {
+			errs <- nil
+			return
+		}
 
-			// Lookup the IP of the https seeder to use as the source of the
-			// seeded addresses.  In the incredibly rare event that the lookup
-			// fails after it just succeeded, fall back to using the first
-			// returned address as the source.
-			srcAddr := wireToAddrmgrNetAddress(addrs[0])
-			srcIPs, err := dcrdLookup(seeder)
-			if err == nil && len(srcIPs) > 0 {
-				const httpsPort = 443
-				srcAddr = addrmgr.NewNetAddressIPPort(srcIPs[0], httpsPort, 0)
+		// Lookup the IP of the https seeder to use as the source of the
+		// seeded addresses.  In the incredibly rare event that the lookup
+		// fails after it just succeeded, fall back to using the first
+		// returned address as the source.
+		srcAddr := wireToAddrmgrNetAddress(addrs[0])
+		srcIPs, err := dcrdLookup(seeder)
+		if err == nil && len(srcIPs) > 0 {
+			const httpsPort = 443
+			srcAddr = addrmgr.NewNetAddressIPPort(srcIPs[0], httpsPort, 0)
+		}
+		addresses := wireToAddrmgrNetAddresses(addrs)
+		s.addrManager.AddAddresses(addresses, srcAddr)
+		errs <- nil
+	}
+
+	backoff := time.Second
+	for {
+		for _, seeder := range seeders {
+			go seed(seeder)
+		}
+		var errCount int
+		for range seeders {
+			if err := <-errs; err != nil {
+				errCount++
 			}
-			addresses := wireToAddrmgrNetAddresses(addrs)
-			s.addrManager.AddAddresses(addresses, srcAddr)
-		}(seeder)
+		}
+		if errCount < len(seeders) || !s.addrManager.NeedMoreAddresses() {
+			return
+		}
+
+		time.Sleep(backoff)
+		if backoff < 10*time.Second {
+			backoff += time.Second
+		}
 	}
 }
 
@@ -3153,7 +3176,7 @@ func (s *server) Run(ctx context.Context) {
 	wg.Add(1)
 	go func() {
 		if !cfg.DisableSeeders {
-			s.querySeeders(ctx)
+			go s.querySeeders(ctx)
 		}
 		s.connManager.Run(ctx)
 		wg.Done()