From af5531cbf62fbc179f74141feac765ec290c8a45 Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Thu, 28 May 2015 18:12:30 +0100
Subject: [PATCH 1/2] Fix incorrect calculation of free space when granting a
 range that spans a token and inserting a new token, the free space on the
 last token that we are handing over has to change. Add unit test for this
 too.

---
 ipam/address/address.go |  7 +++++++
 ipam/ring/ring.go       |  2 +-
 ipam/ring/ring_test.go  | 11 +++++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/ipam/address/address.go b/ipam/address/address.go
index b9f47ac3..97e162d0 100644
--- a/ipam/address/address.go
+++ b/ipam/address/address.go
@@ -52,3 +52,10 @@ func Subtract(a, b Address) Offset {
 	common.Assert(a >= b)
 	return Offset(a - b)
 }
+
+func Min(a, b Offset) Offset {
+	if a > b {
+		return b
+	}
+	return a
+}
diff --git a/ipam/ring/ring.go b/ipam/ring/ring.go
index 7590a3ce..16ae1451 100644
--- a/ipam/ring/ring.go
+++ b/ipam/ring/ring.go
@@ -167,7 +167,7 @@ func (r *Ring) GrantRangeToHost(start, end address.Address, peer router.PeerName
 	pos := preceedingPos + 1
 	for ; pos < len(r.Entries) && r.Entries.entry(pos).Token < end; pos++ {
 		entry := r.Entries.entry(pos)
-		entry.update(peer, entry.Free)
+		entry.update(peer, address.Min(entry.Free, r.distance(entry.Token, end)))
 	}
 
 	// There is never an entry with a token of r.End, as the end of
diff --git a/ipam/ring/ring_test.go b/ipam/ring/ring_test.go
index 1c12c777..f3ec1e0f 100644
--- a/ipam/ring/ring_test.go
+++ b/ipam/ring/ring_test.go
@@ -158,6 +158,17 @@ func TestGrantSplit(t *testing.T) {
 	wt.AssertEquals(t, ring1.Entries, entries{{Token: start, Peer: peer1name, Free: 10, Version: 1},
 		{Token: dot10, Peer: peer2name, Free: 235},
 		{Token: dot245, Peer: peer1name, Free: 10}})
+	ring1.assertInvariants()
+
+	// Grant range spanning a live token, and inserting a new token
+	ring1.Entries = []*entry{{Token: start, Peer: peer1name, Free: 10, Version: 2},
+		{Token: dot10, Peer: peer1name, Free: 118}, {Token: middle, Peer: peer1name, Free: 127}}
+	ring1.GrantRangeToHost(dot10, dot245, peer2name)
+	wt.AssertEquals(t, ring1.Entries, entries{{Token: start, Peer: peer1name, Free: 10, Version: 2},
+		{Token: dot10, Peer: peer2name, Free: 118, Version: 1},
+		{Token: middle, Peer: peer2name, Free: 117, Version: 1},
+		{Token: dot245, Peer: peer1name, Free: 10, Version: 0}})
+	ring1.assertInvariants()
 }
 
 func TestMergeSimple(t *testing.T) {

From 915bf392e9aa772bc59d4ff1c7407b6c5394ff72 Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Thu, 28 May 2015 16:22:22 +0100
Subject: [PATCH 2/2] Improve error reporting of too much free space

---
 ipam/ring/ring.go | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/ipam/ring/ring.go b/ipam/ring/ring.go
index 16ae1451..1bb891f4 100644
--- a/ipam/ring/ring.go
+++ b/ipam/ring/ring.go
@@ -40,7 +40,6 @@ var (
 	ErrInvalidEntry     = errors.New("Received invalid state update!")
 	ErrEntryInMyRange   = errors.New("Received new entry in my range!")
 	ErrNoFreeSpace      = errors.New("No free space found!")
-	ErrTooMuchFreeSpace = errors.New("Entry reporting too much free space!")
 	ErrInvalidTimeout   = errors.New("dt must be greater than 0")
 	ErrNotFound         = errors.New("No entries for peer found")
 )
@@ -76,7 +75,7 @@ func (r *Ring) checkInvariants() error {
 		distance := r.distance(entry.Token, next.Token)
 
 		if entry.Free > distance {
-			return ErrTooMuchFreeSpace
+			return fmt.Errorf("Entry %s-%s reporting too much free space: %d > %d", entry.Token, next.Token, entry.Free, distance)
 		}
 	}