From cae0e85ed75cb6fde220a1452156bd7b1fde0e08 Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Fri, 6 Mar 2015 11:12:54 -0700
Subject: [PATCH] Update higher term on leader during stream request.

This commit adds a check for newer terms in the streaming endpoint.
---
 raft/log.go | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/raft/log.go b/raft/log.go
index 026869d628..9c16025804 100644
--- a/raft/log.go
+++ b/raft/log.go
@@ -82,6 +82,7 @@ type Log struct {
 
 	state      State          // current node state
 	heartbeats chan heartbeat // incoming heartbeat channel
+	terms      chan uint64    // incoming channel of newer terms
 
 	lastLogTerm  uint64 // highest term in the log
 	lastLogIndex uint64 // highest index in the log
@@ -143,6 +144,7 @@ func NewLog() *Log {
 		Transport:  &HTTPTransport{},
 		Rand:       rand.NewSource(time.Now().UnixNano()).Int63,
 		heartbeats: make(chan heartbeat, 1),
+		terms:      make(chan uint64, 1),
 	}
 	l.SetLogOutput(os.Stderr)
 	return l
@@ -880,9 +882,20 @@ func (l *Log) leaderLoop(closing <-chan struct{}) State {
 		case <-closing: // wait for state change.
 			return Stopped
 
+		case newTerm := <-l.terms: // step down on higher term
+			if newTerm > term {
+				l.mu.Lock()
+				l.term = newTerm
+				l.truncate()
+				l.mu.Unlock()
+				return Follower
+			}
+			continue
+
 		case hb := <-l.heartbeats: // step down on higher term
 			if hb.term > term {
 				l.mu.Lock()
+				l.term = hb.term
 				l.truncate()
 				l.mu.Unlock()
 				return Follower
@@ -1461,12 +1474,16 @@ func (l *Log) initWriter(w io.Writer, id, term, index uint64) (*logWriter, error
 
 	// Do not begin streaming if:
 	//   1. Node is not the leader.
-	//   2. Term is earlier than current term.
+	//   2. Term is after current term.
 	//   3. Index is after the commit index.
 	if l.state != Leader {
 		return nil, ErrNotLeader
 	} else if term > l.term {
-		return nil, ErrStaleTerm
+		select {
+		case l.terms <- term:
+		default:
+		}
+		return nil, ErrNotLeader
 	} else if index > l.lastLogIndex {
 		return nil, ErrUncommittedIndex
 	}