From 707b929acda6d7a10f19443e6673d79d6dda6ed7 Mon Sep 17 00:00:00 2001
From: zelig <viktor.tron@gmail.com>
Date: Tue, 6 Jan 2015 18:15:26 +0000
Subject: [PATCH] extract cademlia (implements the peer selector interface) to
 a separate file - maybe should be in a different package...

---
 p2p/cademlia.go | 177 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 177 insertions(+)
 create mode 100644 p2p/cademlia.go

diff --git a/p2p/cademlia.go b/p2p/cademlia.go
new file mode 100644
index 0000000000..d1567b74b0
--- /dev/null
+++ b/p2p/cademlia.go
@@ -0,0 +1,177 @@
+package p2p
+
+import (
+	"sync"
+	"time"
+
+	ethlogger "github.com/ethereum/go-ethereum/logger"
+)
+
+var cadlogger = ethlogger.NewLogger("CAD")
+
+const (
+	hashBits  = 160
+	rowLength = 10
+	maxAge    = 1
+)
+
+type Cademlia struct {
+	hash      []byte
+	hashBits  int
+	rowLength int
+	rows      [hashBits]*row
+
+	depth int
+
+	maxAge        time.Duration
+	purgeInterval time.Duration
+
+	lock  sync.RWMutex
+	quitC chan bool
+}
+
+func newCademlia(hash []byte) *Cademlia {
+	return &Cademlia{
+		hash:      hash,
+		hashBits:  hashBits,
+		rowLength: rowLength,
+		maxAge:    maxAge * time.Second,
+		rows:      [hashBits]*row{},
+	}
+}
+
+func (self *Cademlia) Start() error {
+	self.lock.Lock()
+	defer self.lock.Unlock()
+	if self.quitC != nil {
+		return nil
+	}
+	self.quitC = make(chan bool)
+	go self.purgeLoop()
+	return nil
+}
+
+func (self *Cademlia) Stop() {
+	self.lock.Lock()
+	defer self.lock.Unlock()
+	if self.quitC == nil {
+		return
+	}
+	close(self.quitC)
+	self.quitC = nil
+}
+
+func (self *Cademlia) AddPeer(peer peerInfo) (needed bool) {
+	index := self.commonPrefixLength(peer.Hash())
+	row := self.rows[index]
+	needed = row.insert(&entry{peer: peer})
+	if needed {
+		if index >= self.depth {
+			go self.updateDepth()
+		}
+		cadlogger.Infof("accept peer %x...", peer.Hash()[:8])
+	} else {
+		cadlogger.Infof("reject peer %x... no worse peer found", peer.Hash()[:8])
+	}
+	return
+}
+
+func (self *Cademlia) GetPeers(target []byte) (peers []peerInfo) {
+	index := self.commonPrefixLength(target)
+	var entries []*entry
+	if index >= self.depth {
+		for i := self.depth; i < self.hashBits; i++ {
+			entries = append(entries, self.rows[i].row...)
+		}
+	} else {
+		entries = self.rows[index].row
+	}
+	return
+}
+
+type entry struct {
+	peer peerInfo
+	// metadata
+}
+
+type row struct {
+	length int
+	row    []*entry
+	lock   sync.RWMutex
+}
+
+func (self *row) insert(entry *entry) (ok bool) {
+	self.lock.Lock()
+	defer self.lock.Unlock()
+	if len(self.row) >= self.length {
+		worst := self.worst()
+		// err = diconnectF(self.row[worst])
+		self.row[worst] = entry
+	} else {
+		self.row = append(self.row, entry)
+		ok = true
+	}
+	return
+}
+
+func (self *row) worst() (index int) {
+	var oldest time.Time
+	for i, entry := range self.row {
+		if (oldest == time.Time{}) || entry.peer.LastActive().Before(oldest) {
+			oldest = entry.peer.LastActive()
+			index = i
+		}
+	}
+	return
+}
+
+func (self *row) purge(recently time.Time) {
+	var newRow []*entry
+	for _, entry := range self.row {
+		if !entry.peer.LastActive().Before(recently) {
+			newRow = append(newRow, entry)
+		} else {
+			// self.DisconnectF(entry.peer)
+		}
+	}
+}
+
+func Hash(key []byte) []byte {
+	return key
+}
+
+func (self *Cademlia) updateDepth() {
+}
+
+func (self *Cademlia) purgeLoop() {
+	ticker := time.Tick(self.purgeInterval)
+	for {
+		select {
+		case <-self.quitC:
+			return
+		case <-ticker:
+			for _, r := range self.rows {
+				r.purge(time.Now().Add(-self.maxAge))
+			}
+		}
+	}
+}
+
+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 < self.hashBits; i++ {
+		for j := 0; j < 8; j++ {
+			if (xor[i]>>uint8(7-j))&0x1 != 0 {
+				return i*8 + j
+			}
+		}
+	}
+	return self.hashBits*8 - 1
+}