p2p: dial addrs which came from seed instead of calling ensurePeers (#3762)

Calling ensurePeers outside of ensurePeersRoutine can lead to nodes
disconnecting from us due to "sent next PEX request too soon" error.

Solution is to just dial addrs we got from src instead of calling
ensurePeers.

Refs #2093

Fixes #3338

CHANGELOG_PENDING.md

@@ -20,3 +20,5 @@
 - [abci] \#3809 Recover from application panics in `server/socket_server.go` to allow socket cleanup (@ruseinov)
 
 ### BUG FIXES:
+- [p2p] \#3338 Prevent "sent next PEX request too soon" errors by not calling
+  ensurePeers outside of ensurePeersRoutine

p2p/pex/pex_reactor.go

@@ -340,6 +340,15 @@ func (r *PEXReactor) ReceiveAddrs(addrs []*p2p.NetAddress, src Peer) error {
 	if err != nil {
 		return err
 	}
+
+	srcIsSeed := false
+	for _, seedAddr := range r.seedAddrs {
+		if seedAddr.Equals(srcAddr) {
+			srcIsSeed = true
+			break
+		}
+	}
+
 	for _, netAddr := range addrs {
 		// Validate netAddr. Disconnect from a peer if it sends us invalid data.
 		if netAddr == nil {
@@ -365,13 +374,23 @@ func (r *PEXReactor) ReceiveAddrs(addrs []*p2p.NetAddress, src Peer) error {
 		}
 
 		// If this address came from a seed node, try to connect to it without
-		// waiting.
-		for _, seedAddr := range r.seedAddrs {
-			if seedAddr.Equals(srcAddr) {
-				r.ensurePeers()
-			}
+		// waiting (#2093)
+		if srcIsSeed {
+			r.Logger.Info("Will dial address, which came from seed", "addr", netAddr, "seed", srcAddr)
+			go func(addr *p2p.NetAddress) {
+				err := r.dialPeer(addr)
+				if err != nil {
+					switch err.(type) {
+					case errMaxAttemptsToDial, errTooEarlyToDial:
+						r.Logger.Debug(err.Error(), "addr", addr)
+					default:
+						r.Logger.Error(err.Error(), "addr", addr)
+					}
+				}
+			}(netAddr)
 		}
 	}
+
 	return nil
 }