Vendor main dependencies.

vendor/github.com/docker/leadership/follower.go

@@ -0,0 +1,74 @@
+package leadership
+
+import (
+	"errors"
+
+	"github.com/docker/libkv/store"
+)
+
+// Follower can follow an election in real-time and push notifications whenever
+// there is a change in leadership.
+type Follower struct {
+	client store.Store
+	key    string
+
+	leader   string
+	leaderCh chan string
+	stopCh   chan struct{}
+	errCh    chan error
+}
+
+// NewFollower creates a new follower.
+func NewFollower(client store.Store, key string) *Follower {
+	return &Follower{
+		client: client,
+		key:    key,
+		stopCh: make(chan struct{}),
+	}
+}
+
+// Leader returns the current leader.
+func (f *Follower) Leader() string {
+	return f.leader
+}
+
+// FollowElection starts monitoring the election.
+func (f *Follower) FollowElection() (<-chan string, <-chan error) {
+	f.leaderCh = make(chan string)
+	f.errCh = make(chan error)
+
+	go f.follow()
+
+	return f.leaderCh, f.errCh
+}
+
+// Stop stops monitoring an election.
+func (f *Follower) Stop() {
+	close(f.stopCh)
+}
+
+func (f *Follower) follow() {
+	defer close(f.leaderCh)
+	defer close(f.errCh)
+
+	ch, err := f.client.Watch(f.key, f.stopCh)
+	if err != nil {
+		f.errCh <- err
+	}
+
+	f.leader = ""
+	for kv := range ch {
+		if kv == nil {
+			continue
+		}
+		curr := string(kv.Value)
+		if curr == f.leader {
+			continue
+		}
+		f.leader = curr
+		f.leaderCh <- f.leader
+	}
+
+	// Channel closed, we return an error
+	f.errCh <- errors.New("Leader Election: watch leader channel closed, the store may be unavailable...")
+}