make rmpeer report on size of transferred space, and not fail

Closes #2058.

ipam/allocator.go

@@ -376,29 +376,40 @@ func (alloc *Allocator) Shutdown() {
 	<-doneChan
 }
 
-// AdminTakeoverRanges (Sync) - take over the ranges owned by a given peer.
+// AdminTakeoverRanges (Sync) - take over the ranges owned by a given
+// peer, and return how much space was transferred in the process.
 // Only done on adminstrator command.
-func (alloc *Allocator) AdminTakeoverRanges(peerNameOrNickname string) error {
-	resultChan := make(chan error)
+func (alloc *Allocator) AdminTakeoverRanges(peerNameOrNickname string) address.Count {
+	resultChan := make(chan address.Count)
 	alloc.actionChan <- func() {
 		peername, err := alloc.lookupPeername(peerNameOrNickname)
 		if err != nil {
-			resultChan <- fmt.Errorf("Cannot find peer '%s'", peerNameOrNickname)
+			alloc.warnf("attempt to take over range from unknown peer '%s'", peerNameOrNickname)
+			resultChan <- address.Count(0)
 			return
 		}
 
 		alloc.debugln("AdminTakeoverRanges:", peername)
 		if peername == alloc.ourName {
-			resultChan <- fmt.Errorf("Cannot take over ranges from yourself!")
+			alloc.warnf("attempt to take over range from ourself")
+			resultChan <- address.Count(0)
 			return
 		}
 
-		newRanges, err := alloc.ring.Transfer(peername, alloc.ourName)
-		if err == nil && len(newRanges) > 0 {
-			alloc.space.AddRanges(newRanges)
-			alloc.gossip.GossipBroadcast(alloc.Gossip())
+		newRanges := alloc.ring.Transfer(peername, alloc.ourName)
+
+		if len(newRanges) == 0 {
+			resultChan <- address.Count(0)
+			return
 		}
-		resultChan <- err
+
+		before := alloc.space.NumFreeAddressesInRange(alloc.universe)
+		alloc.space.AddRanges(newRanges)
+		after := alloc.space.NumFreeAddressesInRange(alloc.universe)
+
+		alloc.gossip.GossipBroadcast(alloc.Gossip())
+
+		resultChan <- after - before
 	}
 	return <-resultChan
 }

ipam/allocator_test.go

@@ -336,13 +336,18 @@ func TestTransfer(t *testing.T) {
 	router.Flush()
 	alloc2.gossip.GossipBroadcast(alloc3.Gossip())
 	router.Flush()
+
+	free2 := alloc2.NumFreeAddresses(subnet.Range())
+	free3 := alloc3.NumFreeAddresses(subnet.Range())
+
 	router.RemovePeer(alloc2.ourName)
 	router.RemovePeer(alloc3.ourName)
 	alloc2.Stop()
 	alloc3.Stop()
 	router.Flush()
-	require.NoError(t, alloc1.AdminTakeoverRanges(alloc2.ourName.String()))
-	require.NoError(t, alloc1.AdminTakeoverRanges(alloc3.ourName.String()))
+
+	require.Equal(t, free2+1, alloc1.AdminTakeoverRanges(alloc2.ourName.String()))
+	require.Equal(t, free3+1, alloc1.AdminTakeoverRanges(alloc3.ourName.String()))
 	router.Flush()
 
 	require.Equal(t, address.Count(1024), alloc1.NumFreeAddresses(subnet.Range()))

ipam/http.go

@@ -151,11 +151,7 @@ func (alloc *Allocator) HandleHTTP(router *mux.Router, defaultSubnet address.CID
 
 	router.Methods("DELETE").Path("/peer/{id}").HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		ident := mux.Vars(r)["id"]
-		if err := alloc.AdminTakeoverRanges(ident); err != nil {
-			badRequest(w, err)
-			return
-		}
-
-		w.WriteHeader(204)
+		transferred := alloc.AdminTakeoverRanges(ident)
+		fmt.Fprintf(w, "%d IPs taken over from %s\n", transferred, ident)
 	})
 }

ipam/ring/ring.go

@@ -498,28 +498,22 @@ func (r *Ring) PickPeerForTransfer(isValid func(mesh.PeerName) bool) mesh.PeerNa
 
 // Transfer will mark all entries associated with 'from' peer as owned by 'to' peer
 // and return ranges indicating the new space we picked up
-func (r *Ring) Transfer(from, to mesh.PeerName) ([]address.Range, error) {
+func (r *Ring) Transfer(from, to mesh.PeerName) []address.Range {
 	r.assertInvariants()
 	defer r.assertInvariants()
 	defer r.updateExportedVariables()
 
 	var newRanges []address.Range
-	found := false
 
 	for i, entry := range r.Entries {
 		if entry.Peer == from {
-			found = true
 			entry.Peer = to
 			entry.Version++
 			newRanges = append(newRanges, address.Range{Start: entry.Token, End: r.Entries.entry(i + 1).Token})
 		}
 	}
 
-	if !found {
-		return nil, ErrNotFound
-	}
-
-	return r.splitRangesOverZero(newRanges), nil
+	return r.splitRangesOverZero(newRanges)
 }
 
 // Contains returns true if addr is in this ring

site/ipam/stop-remove-peers-ipam.md

@@ -24,6 +24,7 @@ Assume you had started the three peers in the example earlier, and
 then host3 caught fire, you can go to one of the other hosts and run:
 
     host1$ weave rmpeer host3
+    524288 IPs taken over from host3
 
 Weave Net takes all the IP address ranges owned by host3 and transfers
 them to be owned by host1. The name "host3" is resolved via the
@@ -36,4 +37,4 @@ status`.
  * [Address Allocation with IP Address Management (IPAM)](/site/ipam/overview-init-ipam.md)
  * [Automatic Allocation Across Multiple Subnets](/site/ipam/allocation-multi-ipam.md)
  * [Isolating Applications on a Weave Network](/site/using-weave/isolating-applications.md)
- 
+