From a21c1b6b6229e8fc01defca2f57141194d38aa1a Mon Sep 17 00:00:00 2001
From: Juan Batiz-Benet <juan@benet.ai>
Date: Wed, 17 Sep 2014 02:58:10 -0700
Subject: [PATCH] PeerQueue (based on XOR distance metric)

---
 peer/queue/distance.go   | 84 ++++++++++++++++++++++++++++++++++++++++
 peer/queue/interface.go  | 15 +++++++
 peer/queue/queue_test.go | 62 +++++++++++++++++++++++++++++
 3 files changed, 161 insertions(+)
 create mode 100644 peer/queue/distance.go
 create mode 100644 peer/queue/interface.go
 create mode 100644 peer/queue/queue_test.go

diff --git a/peer/queue/distance.go b/peer/queue/distance.go
new file mode 100644
index 000000000..0a53adb04
--- /dev/null
+++ b/peer/queue/distance.go
@@ -0,0 +1,84 @@
+package queue
+
+import (
+	"container/heap"
+	"math/big"
+
+	peer "github.com/jbenet/go-ipfs/peer"
+	ks "github.com/jbenet/go-ipfs/routing/keyspace"
+	u "github.com/jbenet/go-ipfs/util"
+)
+
+// peerDistance tracks a peer and its distance to something else.
+type peerDistance struct {
+	// the peer
+	peer *peer.Peer
+
+	// big.Int for XOR metric
+	distance *big.Int
+}
+
+// distancePQ implements heap.Interface and PeerQueue
+type distancePQ struct {
+	// from is the Key this PQ measures against
+	from ks.Key
+
+	// peers is a heap of peerDistance items
+	peers []*peerDistance
+}
+
+func (pq distancePQ) Len() int {
+	return len(pq.peers)
+}
+
+func (pq distancePQ) Less(i, j int) bool {
+	return -1 == pq.peers[i].distance.Cmp(pq.peers[j].distance)
+}
+
+func (pq distancePQ) Swap(i, j int) {
+	p := pq.peers
+	p[i], p[j] = p[j], p[i]
+}
+
+func (pq *distancePQ) Push(x interface{}) {
+	item := x.(*peerDistance)
+	pq.peers = append(pq.peers, item)
+}
+
+func (pq *distancePQ) Pop() interface{} {
+	old := pq.peers
+	n := len(old)
+	item := old[n-1]
+	pq.peers = old[0 : n-1]
+	return item
+}
+
+func (pq *distancePQ) Enqueue(p *peer.Peer) {
+	distance := ks.XORKeySpace.Key(p.ID).Distance(pq.from)
+
+	heap.Push(pq, &peerDistance{
+		peer:     p,
+		distance: distance,
+	})
+}
+
+func (pq *distancePQ) Dequeue() *peer.Peer {
+	if len(pq.peers) < 1 {
+		panic("called Dequeue on an empty PeerQueue")
+		// will panic internally anyway, but we can help debug here
+	}
+
+	o := heap.Pop(pq)
+	p := o.(*peerDistance)
+	return p.peer
+}
+
+// NewXORDistancePQ returns a PeerQueue which maintains its peers sorted
+// in terms of their distances to each other in an XORKeySpace (i.e. using
+// XOR as a metric of distance).
+func NewXORDistancePQ(fromKey u.Key) PeerQueue {
+	return &distancePQ{
+		from:  ks.XORKeySpace.Key([]byte(fromKey)),
+		peers: []*peerDistance{},
+	}
+}
diff --git a/peer/queue/interface.go b/peer/queue/interface.go
new file mode 100644
index 000000000..180cc9ce9
--- /dev/null
+++ b/peer/queue/interface.go
@@ -0,0 +1,15 @@
+package queue
+
+import peer "github.com/jbenet/go-ipfs/peer"
+
+// PeerQueue maintains a set of peers ordered according to a metric.
+// Implementations of PeerQueue could order peers based on distances along
+// a KeySpace, latency measurements, trustworthiness, reputation, etc.
+type PeerQueue interface {
+
+	// Enqueue adds this node to the queue.
+	Enqueue(*peer.Peer)
+
+	// Dequeue retrieves the highest (smallest int) priority node
+	Dequeue() *peer.Peer
+}
diff --git a/peer/queue/queue_test.go b/peer/queue/queue_test.go
new file mode 100644
index 000000000..f9a843396
--- /dev/null
+++ b/peer/queue/queue_test.go
@@ -0,0 +1,62 @@
+package queue
+
+import (
+	"testing"
+
+	peer "github.com/jbenet/go-ipfs/peer"
+	u "github.com/jbenet/go-ipfs/util"
+)
+
+func newPeer(id string) *peer.Peer {
+	return &peer.Peer{ID: peer.ID(id)}
+}
+
+func TestPeerstore(t *testing.T) {
+
+	p1 := newPeer("11140beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a31")
+	p2 := newPeer("11140beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a32")
+	p3 := newPeer("11140beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33")
+	p4 := newPeer("11140beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a34")
+	p5 := newPeer("11140beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a31")
+
+	// these are the peer.IDs' XORKeySpace Key values:
+	// [228 47 151 130 156 102 222 232 218 31 132 94 170 208 80 253 120 103 55 35 91 237 48 157 81 245 57 247 66 150 9 40]
+	// [26 249 85 75 54 49 25 30 21 86 117 62 85 145 48 175 155 194 210 216 58 14 241 143 28 209 129 144 122 28 163 6]
+	// [78 135 26 216 178 181 224 181 234 117 2 248 152 115 255 103 244 34 4 152 193 88 9 225 8 127 216 158 226 8 236 246]
+	// [125 135 124 6 226 160 101 94 192 57 39 12 18 79 121 140 190 154 147 55 44 83 101 151 63 255 94 179 51 203 241 51]
+
+	pq := NewXORDistancePQ(u.Key("11140beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a31"))
+	pq.Enqueue(p3)
+	pq.Enqueue(p1)
+	pq.Enqueue(p2)
+	pq.Enqueue(p4)
+	pq.Enqueue(p5)
+	pq.Enqueue(p1)
+
+	// should come out as: p1, p4, p3, p2
+
+	if d := pq.Dequeue(); d != p1 && d != p5 {
+		t.Error("ordering failed")
+	}
+
+	if d := pq.Dequeue(); d != p1 && d != p5 {
+		t.Error("ordering failed")
+	}
+
+	if d := pq.Dequeue(); d != p1 && d != p5 {
+		t.Error("ordering failed")
+	}
+
+	if pq.Dequeue() != p4 {
+		t.Error("ordering failed")
+	}
+
+	if pq.Dequeue() != p3 {
+		t.Error("ordering failed")
+	}
+
+	if pq.Dequeue() != p2 {
+		t.Error("ordering failed")
+	}
+
+}