From 4b48876f0e9362016bab966bd3cca5aaeb9ba2fe Mon Sep 17 00:00:00 2001
From: "Jason E. Aten" <j.e.aten@gmail.com>
Date: Sun, 28 Aug 2016 00:58:57 -0500
Subject: [PATCH] clientv3/concurrency: allow election on prefixes of keys.

After winning an election or obtaining a lock, we
auto-append a slash after the provided key prefix.
This avoids the previous deadlock due to waiting
on the wrong key.

Fixes #6278

Conflicts:
	clientv3/concurrency/election.go
	clientv3/concurrency/mutex.go
---
 clientv3/concurrency/election.go |  3 +--
 clientv3/concurrency/mutex.go    |  4 ++--
 integration/v3_election_test.go  | 28 ++++++++++++++++++++++++++++
 3 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/clientv3/concurrency/election.go b/clientv3/concurrency/election.go
index 89b52089a..b6800053a 100644
--- a/clientv3/concurrency/election.go
+++ b/clientv3/concurrency/election.go
@@ -40,7 +40,7 @@ type Election struct {
 
 // NewElection returns a new election on a given key prefix.
 func NewElection(client *v3.Client, pfx string) *Election {
-	return &Election{client: client, keyPrefix: pfx}
+	return &Election{client: client, keyPrefix: pfx + "/"}
 }
 
 // Campaign puts a value as eligible for the election. It blocks until
@@ -59,7 +59,6 @@ func (e *Election) Campaign(ctx context.Context, val string) error {
 	if err != nil {
 		return err
 	}
-
 	e.leaderKey, e.leaderRev, e.leaderSession = k, resp.Header.Revision, s
 	if !resp.Succeeded {
 		kv := resp.Responses[0].GetResponseRange().Kvs[0]
diff --git a/clientv3/concurrency/mutex.go b/clientv3/concurrency/mutex.go
index 803a8470a..e588b33bc 100644
--- a/clientv3/concurrency/mutex.go
+++ b/clientv3/concurrency/mutex.go
@@ -32,7 +32,7 @@ type Mutex struct {
 }
 
 func NewMutex(client *v3.Client, pfx string) *Mutex {
-	return &Mutex{client, pfx, "", -1}
+	return &Mutex{client, pfx + "/", "", -1}
 }
 
 // Lock locks the mutex with a cancellable context. If the context is cancelled
@@ -43,7 +43,7 @@ func (m *Mutex) Lock(ctx context.Context) error {
 		return serr
 	}
 
-	m.myKey = fmt.Sprintf("%s/%x", m.pfx, s.Lease())
+	m.myKey = fmt.Sprintf("%s%x", m.pfx, s.Lease())
 	cmp := v3.Compare(v3.CreateRevision(m.myKey), "=", 0)
 	// put self in lock waiters via myKey; oldest waiter holds lock
 	put := v3.OpPut(m.myKey, "", v3.WithLease(s.Lease()))
diff --git a/integration/v3_election_test.go b/integration/v3_election_test.go
index 9f4cea6be..8ca3298ed 100644
--- a/integration/v3_election_test.go
+++ b/integration/v3_election_test.go
@@ -174,3 +174,31 @@ func TestElectionSessionRecampaign(t *testing.T) {
 		t.Fatalf("expected value=%q, got response %v", "def", resp)
 	}
 }
+
+// TestElectionOnPrefixOfExistingKey checks that a single
+// candidate can be elected on a new key that is a prefix
+// of an existing key. To wit, check for regression
+// of bug #6278. https://github.com/coreos/etcd/issues/6278
+//
+func TestElectionOnPrefixOfExistingKey(t *testing.T) {
+	clus := NewClusterV3(t, &ClusterConfig{Size: 1})
+	defer clus.Terminate(t)
+
+	cli := clus.RandClient()
+	if _, err := cli.Put(context.TODO(), "testa", "value"); err != nil {
+		t.Fatal(err)
+	}
+	s, serr := concurrency.NewSession(cli)
+	if serr != nil {
+		t.Fatal(serr)
+	}
+	e := concurrency.NewElection(s, "test")
+	ctx, cancel := context.WithTimeout(context.TODO(), 5*time.Second)
+	err := e.Campaign(ctx, "abc")
+	cancel()
+	if err != nil {
+		// after 5 seconds, deadlock results in
+		// 'context deadline exceeded' here.
+		t.Fatal(err)
+	}
+}