From dbc22690e5e16617342bb4679fc4bc72acb215d2 Mon Sep 17 00:00:00 2001
From: zelig <viktor.tron@gmail.com>
Date: Sun, 21 Dec 2014 19:09:47 +0000
Subject: [PATCH] initial commit of p2p peer selection/cademlia

---
 p2p/TODO             |   3 +
 p2p/peer_selector.go | 163 +++++++++++++++++++++++++++++++++++++++++++
 p2p/server.go        |  21 +++++-
 3 files changed, 184 insertions(+), 3 deletions(-)
 create mode 100644 p2p/TODO
 create mode 100644 p2p/peer_selector.go

diff --git a/p2p/TODO b/p2p/TODO
new file mode 100644
index 0000000000..ad8ce170be
--- /dev/null
+++ b/p2p/TODO
@@ -0,0 +1,3 @@
+Define peer address' time field and lastSeen function.
+Overwrite time field when connect and disconnect.
+Change protocol getPeers message response conditional on target. peerList if noTarget else server.getPeers
diff --git a/p2p/peer_selector.go b/p2p/peer_selector.go
new file mode 100644
index 0000000000..e60b19eee8
--- /dev/null
+++ b/p2p/peer_selector.go
@@ -0,0 +1,163 @@
+package p2p
+
+import (
+	"time"
+)
+
+type PeerSelector interface {
+	SuggestPeer(addr *peerAddr) (ok bool)
+	// AddPeer(addr *peerAddr) (ok bool)
+	GetPeers(target []byte) []*peerAddr
+	Start()
+	Stop()
+}
+
+type BaseSelector struct {
+	DirPath string
+}
+
+func (self *BaseSelector) SuggestPeer(addr *peerAddr) bool {
+	return true
+}
+
+const (
+	hashBits  = 160
+	rowLength = 10
+	maxAge    = 1
+)
+
+type Cademlia struct {
+	rows      [hashBits]*row
+	hashBits  int
+	rowLength int
+	maxAge    time.Duration
+	index     map[string]*peerData
+}
+
+type row struct {
+	length int
+	row    []*peerData
+	lock   sync.RWMutex
+}
+
+func (self *row) addresses() (addrs []*peerAddr) {
+	self.lock.RLock()
+	defer self.lock.RUnlock()
+	for _, p := range self.row {
+		addrs = append(addrs, p.addr)
+	}
+	return
+}
+
+func (self *row) insert(addr *peerAddr) (ok bool) {
+	self.lock.Lock()
+	defer self.lock.Unlock()
+	peerData := &peerData{addr: addr}
+	if len(self.row) >= self.length {
+		self.row[self.worst()] = peerData
+	} else {
+		self.row = append(self.row, peerData)
+		ok = true
+	}
+	return
+}
+
+func (self *row) worst() (index int) {
+	var oldest time.Time
+	for i, p := range self.row {
+		if oldest == nil || p.addr.LastSeen().Before(oldest) {
+			oldest = p.addr.LastSeen
+			index = i
+		}
+	}
+	return
+}
+
+func (self *row) purge(maxAge time.Time) {
+	var newRow []*peerData
+	for _, p := range self.row {
+		if !p.addr.LastSeen().Before(maxAge) {
+			newRow = append(newRow, p)
+		}
+	}
+}
+
+type peerData struct {
+	addr *peerAddr
+	hash []byte
+}
+
+func Hash([]byte) []byte {
+
+}
+
+func (self *Cademlia) prefixLength(other []byte) {
+
+}
+
+func newCademlia() *Cademlia {
+	return &Cademlia{
+		hashBits:  hashBits,
+		rowLength: rowLength,
+		maxAge:    maxAge * time.Second,
+		rows:      make([hashBits]*row),
+		index:     make(map[string]*peerData),
+	}
+}
+
+func (self *Cademlia) Start() {
+	go self.purgeLoop()
+}
+
+func (self *Cademlia) purgeLoop() {
+	ticker := time.Tick(self.purgeInterval)
+	for {
+		select {
+		case <-ticker:
+			for _, r := range self.rows {
+				r.purge(time.Since(self.maxAge))
+			}
+		}
+	}
+}
+
+func (self *Cademlia) SuggestPeer(addr *peerAddr) bool {
+	index := self.commonPrefixLength(Hash(addr.Pubkey))
+	row := self.rows[index]
+	longer := row.insert(addr)
+	if index >= self.depth && longer {
+		self.updateDepth()
+	}
+	return longer
+}
+
+func (self *Cademlia) GetPeers(target []byte) (peers []*peerAddr) {
+	index := self.prefixLength(target)
+	if index >= self.depth {
+		for i := self.depth; i < hashBits; i++ {
+			peers = append(peers, self.rows[i].addresses())
+		}
+	} else {
+		peers = self.rows[index].addresses()
+	}
+	return
+}
+
+func Xor(one, other []byte) (xor []byte) {
+	for i := 0; i < len(one); i++ {
+		xor[i] = one[i] ^ other[i]
+	}
+	return
+}
+
+func (self *Cademlia) commonPrefixLength(other []byte) (ret int) {
+	xor := Xor(self.hash, other)
+	for i := 0; i < len(self.hash); i++ {
+		for j := 0; j < 8; j++ {
+			if (xor[i]>>uint8(7-j))&0x1 != 0 {
+				return i*8 + j
+			}
+		}
+	}
+	return len(self.hash)*8 - 1
+}
diff --git a/p2p/server.go b/p2p/server.go
index 3267812343..e91a83061c 100644
--- a/p2p/server.go
+++ b/p2p/server.go
@@ -62,6 +62,9 @@ type Server struct {
 	// If NoDial is true, the server will not dial any peers.
 	NoDial bool
 
+	// peer selector
+	PeerSelector PeerSelector
+
 	// Hook for testing. This is useful because we can inhibit
 	// the whole protocol stack.
 	newPeerFunc peerFunc
@@ -104,6 +107,10 @@ func (srv *Server) Peers() (peers []*Peer) {
 	return
 }
 
+func (srv *Server) GetPeers(target []byte) (peers []*Peer) {
+	// delegate to selector
+}
+
 // PeerCount returns the number of connected peers.
 func (srv *Server) PeerCount() int {
 	srv.lock.RLock()
@@ -113,9 +120,13 @@ func (srv *Server) PeerCount() int {
 
 // SuggestPeer injects an address into the outbound address pool.
 func (srv *Server) SuggestPeer(ip net.IP, port int, nodeID []byte) {
-	select {
-	case srv.peerConnect <- &peerAddr{ip, uint64(port), nodeID}:
-	default: // don't block
+	addr := &peerAddr{ip, uint64(port), nodeID, time.Now()}
+	ok := srv.PeerSelector.SuggestPeer(addr)
+	if ok {
+		select {
+		case srv.peerConnect <- addr:
+		default: // don't block
+		}
 	}
 }
 
@@ -185,6 +196,10 @@ func (srv *Server) Start() (err error) {
 		srvlog.Warnln("I will be kind-of useless, neither dialing nor listening.")
 	}
 
+	if srv.PeerSelector == nil {
+		srv.PeerSelector = &BaseSelector{}
+	}
+
 	// make all slots available
 	for i := range srv.peers {
 		srv.peerSlots <- i