From 6078aa08ebf165e523cc00b67d89f0f946ba4fb5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Mon, 25 May 2015 15:04:40 +0300
Subject: [PATCH] p2p/discover: watch find failures, evacuate on too many,
 rebond if failed

---
 p2p/discover/table.go | 55 ++++++++++++++++++++++++++++++++++++-------
 1 file changed, 47 insertions(+), 8 deletions(-)

diff --git a/p2p/discover/table.go b/p2p/discover/table.go
index b523a0684..c45143307 100644
--- a/p2p/discover/table.go
+++ b/p2p/discover/table.go
@@ -27,6 +27,7 @@ const (
 	nBuckets   = hashBits + 1 // Number of buckets
 
 	maxBondingPingPongs = 16
+	maxFindnodeFailures = 5
 )
 
 type Table struct {
@@ -198,7 +199,19 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
 				asked[n.ID] = true
 				pendingQueries++
 				go func() {
-					r, _ := tab.net.findnode(n.ID, n.addr(), targetID)
+					// Find potential neighbors to bond with
+					r, err := tab.net.findnode(n.ID, n.addr(), targetID)
+					if err != nil {
+						// Bump the failure counter to detect and evacuate non-bonded entries
+						fails := tab.db.findFails(n.ID) + 1
+						tab.db.updateFindFails(n.ID, fails)
+						glog.V(logger.Detail).Infof("Bumping failures for %x: %d", n.ID[:8], fails)
+
+						if fails > maxFindnodeFailures {
+							glog.V(logger.Detail).Infof("Evacuating node %x: %d findnode failures", n.ID[:8], fails)
+							tab.del(n)
+						}
+					}
 					reply <- tab.bondall(r)
 				}()
 			}
@@ -305,8 +318,15 @@ func (tab *Table) bondall(nodes []*Node) (result []*Node) {
 // If pinged is true, the remote node has just pinged us and one half
 // of the process can be skipped.
 func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) (*Node, error) {
-	var n *Node
-	if n = tab.db.node(id); n == nil {
+	// Retrieve a previously known node and any recent findnode failures
+	node, fails := tab.db.node(id), 0
+	if node != nil {
+		fails = tab.db.findFails(id)
+	}
+	// If the node is unknown (non-bonded) or failed (remotely unknown), bond from scratch
+	if node == nil || fails > 0 {
+		glog.V(logger.Detail).Infof("Bonding %x: known=%v, fails=%v", id[:8], node != nil, fails)
+
 		tab.bondmu.Lock()
 		w := tab.bonding[id]
 		if w != nil {
@@ -325,18 +345,22 @@ func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16
 			delete(tab.bonding, id)
 			tab.bondmu.Unlock()
 		}
-		n = w.n
+		node = w.n
 		if w.err != nil {
 			return nil, w.err
 		}
 	}
+	// Bonding succeeded, add to the table and reset previous findnode failures
 	tab.mutex.Lock()
 	defer tab.mutex.Unlock()
-	b := tab.buckets[logdist(tab.self.sha, n.sha)]
-	if !b.bump(n) {
-		tab.pingreplace(n, b)
+
+	b := tab.buckets[logdist(tab.self.sha, node.sha)]
+	if !b.bump(node) {
+		tab.pingreplace(node, b)
 	}
-	return n, nil
+	tab.db.updateFindFails(id, 0)
+
+	return node, nil
 }
 
 func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16) {
@@ -414,6 +438,21 @@ outer:
 	}
 }
 
+// del removes an entry from the node table (used to evacuate failed/non-bonded
+// discovery peers).
+func (tab *Table) del(node *Node) {
+	tab.mutex.Lock()
+	defer tab.mutex.Unlock()
+
+	bucket := tab.buckets[logdist(tab.self.sha, node.sha)]
+	for i := range bucket.entries {
+		if bucket.entries[i].ID == node.ID {
+			bucket.entries = append(bucket.entries[:i], bucket.entries[i+1:]...)
+			return
+		}
+	}
+}
+
 func (b *bucket) bump(n *Node) bool {
 	for i := range b.entries {
 		if b.entries[i].ID == n.ID {