From 6bc199a8bc369567bbde20af9083d95cd3fcbd30 Mon Sep 17 00:00:00 2001
From: Bryan Boreham <bjboreham@gmail.com>
Date: Tue, 22 Mar 2016 14:35:00 +0000
Subject: [PATCH] Change invariant fail on Merge() from panic to error

---
 ipam/ring/ring.go | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/ipam/ring/ring.go b/ipam/ring/ring.go
index 2e384eca16..7d0e9cfa58 100644
--- a/ipam/ring/ring.go
+++ b/ipam/ring/ring.go
@@ -46,33 +46,37 @@ var (
 )
 
 func (r *Ring) checkInvariants() error {
-	if !sort.IsSorted(r.Entries) {
+	return r.checkEntries(r.Entries)
+}
+
+func (r *Ring) checkEntries(entries entries) error {
+	if !sort.IsSorted(entries) {
 		return ErrNotSorted
 	}
 
 	// Check no token appears twice
 	// We know it's sorted...
-	for i := 1; i < len(r.Entries); i++ {
-		if r.Entries[i-1].Token == r.Entries[i].Token {
+	for i := 1; i < len(entries); i++ {
+		if entries[i-1].Token == entries[i].Token {
 			return ErrTokenRepeated
 		}
 	}
 
-	if len(r.Entries) == 0 {
+	if len(entries) == 0 {
 		return nil
 	}
 
 	// Check tokens are in range
-	if r.Entries.entry(0).Token < r.Start {
+	if entries.entry(0).Token < r.Start {
 		return ErrTokenOutOfRange
 	}
-	if r.Entries.entry(-1).Token >= r.End {
+	if entries.entry(-1).Token >= r.End {
 		return ErrTokenOutOfRange
 	}
 
 	// Check all the freespaces are in range
-	for i, entry := range r.Entries {
-		next := r.Entries.entry(i + 1)
+	for i, entry := range entries {
+		next := entries.entry(i + 1)
 		distance := r.distance(entry.Token, next.Token)
 
 		if entry.Free > distance {
@@ -181,7 +185,6 @@ func (r *Ring) GrantRangeToHost(start, end address.Address, peer mesh.PeerName)
 // Merge the given ring into this ring and return any new ranges added
 func (r *Ring) Merge(gossip Ring) error {
 	r.assertInvariants()
-	defer r.assertInvariants()
 	defer r.updateExportedVariables()
 
 	// Don't panic when checking the gossiped in ring.
@@ -267,6 +270,10 @@ func (r *Ring) Merge(gossip Ring) error {
 		previousOwner = nil
 	}
 
+	if err := r.checkEntries(result); err != nil {
+		return fmt.Errorf("Merge of incoming data causes: %s", err)
+	}
+
 	if len(r.Seeds) == 0 {
 		r.Seeds = gossip.Seeds
 	}