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-rw-r--r--p2p/discover/table.go447
1 files changed, 447 insertions, 0 deletions
diff --git a/p2p/discover/table.go b/p2p/discover/table.go
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+// Package discover implements the Node Discovery Protocol.
+//
+// The Node Discovery protocol provides a way to find RLPx nodes that
+// can be connected to. It uses a Kademlia-like protocol to maintain a
+// distributed database of the IDs and endpoints of all listening
+// nodes.
+package discover
+
+import (
+ "crypto/ecdsa"
+ "crypto/elliptic"
+ "encoding/hex"
+ "fmt"
+ "io"
+ "math/rand"
+ "net"
+ "sort"
+ "strings"
+ "sync"
+ "time"
+
+ "github.com/ethereum/go-ethereum/crypto/secp256k1"
+ "github.com/ethereum/go-ethereum/rlp"
+)
+
+const (
+ alpha = 3 // Kademlia concurrency factor
+ bucketSize = 16 // Kademlia bucket size
+ nBuckets = len(NodeID{})*8 + 1 // Number of buckets
+)
+
+type Table struct {
+ mutex sync.Mutex // protects buckets, their content, and nursery
+ buckets [nBuckets]*bucket // index of known nodes by distance
+ nursery []*Node // bootstrap nodes
+
+ net transport
+ self *Node // metadata of the local node
+}
+
+// transport is implemented by the UDP transport.
+// it is an interface so we can test without opening lots of UDP
+// sockets and without generating a private key.
+type transport interface {
+ ping(*Node) error
+ findnode(e *Node, target NodeID) ([]*Node, error)
+ close()
+}
+
+// bucket contains nodes, ordered by their last activity.
+type bucket struct {
+ lastLookup time.Time
+ entries []*Node
+}
+
+// Node represents node metadata that is stored in the table.
+type Node struct {
+ Addr *net.UDPAddr
+ ID NodeID
+
+ active time.Time
+}
+
+type rpcNode struct {
+ IP string
+ Port uint16
+ ID NodeID
+}
+
+func (n Node) EncodeRLP(w io.Writer) error {
+ return rlp.Encode(w, rpcNode{IP: n.Addr.IP.String(), Port: uint16(n.Addr.Port), ID: n.ID})
+}
+func (n *Node) DecodeRLP(s *rlp.Stream) (err error) {
+ var ext rpcNode
+ if err = s.Decode(&ext); err == nil {
+ n.Addr = &net.UDPAddr{IP: net.ParseIP(ext.IP), Port: int(ext.Port)}
+ n.ID = ext.ID
+ }
+ return err
+}
+
+func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr) *Table {
+ tab := &Table{net: t, self: &Node{ID: ourID, Addr: ourAddr}}
+ for i := range tab.buckets {
+ tab.buckets[i] = &bucket{}
+ }
+ return tab
+}
+
+// Bootstrap sets the bootstrap nodes. These nodes are used to connect
+// to the network if the table is empty. Bootstrap will also attempt to
+// fill the table by performing random lookup operations on the
+// network.
+func (tab *Table) Bootstrap(nodes []Node) {
+ tab.mutex.Lock()
+ // TODO: maybe filter nodes with bad fields (nil, etc.) to avoid strange crashes
+ tab.nursery = make([]*Node, 0, len(nodes))
+ for _, n := range nodes {
+ cpy := n
+ tab.nursery = append(tab.nursery, &cpy)
+ }
+ tab.mutex.Unlock()
+ tab.refresh()
+}
+
+// Lookup performs a network search for nodes close
+// to the given target. It approaches the target by querying
+// nodes that are closer to it on each iteration.
+func (tab *Table) Lookup(target NodeID) []*Node {
+ var (
+ asked = make(map[NodeID]bool)
+ seen = make(map[NodeID]bool)
+ reply = make(chan []*Node, alpha)
+ pendingQueries = 0
+ )
+ // don't query further if we hit the target.
+ // unlikely to happen often in practice.
+ asked[target] = true
+
+ tab.mutex.Lock()
+ // update last lookup stamp (for refresh logic)
+ tab.buckets[logdist(tab.self.ID, target)].lastLookup = time.Now()
+ // generate initial result set
+ result := tab.closest(target, bucketSize)
+ tab.mutex.Unlock()
+
+ for {
+ // ask the closest nodes that we haven't asked yet
+ for i := 0; i < len(result.entries) && pendingQueries < alpha; i++ {
+ n := result.entries[i]
+ if !asked[n.ID] {
+ asked[n.ID] = true
+ pendingQueries++
+ go func() {
+ result, _ := tab.net.findnode(n, target)
+ reply <- result
+ }()
+ }
+ }
+ if pendingQueries == 0 {
+ // we have asked all closest nodes, stop the search
+ break
+ }
+
+ // wait for the next reply
+ for _, n := range <-reply {
+ cn := n
+ if !seen[n.ID] {
+ seen[n.ID] = true
+ result.push(cn, bucketSize)
+ }
+ }
+ pendingQueries--
+ }
+ return result.entries
+}
+
+// refresh performs a lookup for a random target to keep buckets full.
+func (tab *Table) refresh() {
+ ld := -1 // logdist of chosen bucket
+ tab.mutex.Lock()
+ for i, b := range tab.buckets {
+ if i > 0 && b.lastLookup.Before(time.Now().Add(-1*time.Hour)) {
+ ld = i
+ break
+ }
+ }
+ tab.mutex.Unlock()
+
+ result := tab.Lookup(randomID(tab.self.ID, ld))
+ if len(result) == 0 {
+ // bootstrap the table with a self lookup
+ tab.mutex.Lock()
+ tab.add(tab.nursery)
+ tab.mutex.Unlock()
+ tab.Lookup(tab.self.ID)
+ // TODO: the Kademlia paper says that we're supposed to perform
+ // random lookups in all buckets further away than our closest neighbor.
+ }
+}
+
+// closest returns the n nodes in the table that are closest to the
+// given id. The caller must hold tab.mutex.
+func (tab *Table) closest(target NodeID, nresults int) *nodesByDistance {
+ // This is a very wasteful way to find the closest nodes but
+ // obviously correct. I believe that tree-based buckets would make
+ // this easier to implement efficiently.
+ close := &nodesByDistance{target: target}
+ for _, b := range tab.buckets {
+ for _, n := range b.entries {
+ close.push(n, nresults)
+ }
+ }
+ return close
+}
+
+func (tab *Table) len() (n int) {
+ for _, b := range tab.buckets {
+ n += len(b.entries)
+ }
+ return n
+}
+
+// bumpOrAdd updates the activity timestamp for the given node and
+// attempts to insert the node into a bucket. The returned Node might
+// not be part of the table. The caller must hold tab.mutex.
+func (tab *Table) bumpOrAdd(node NodeID, from *net.UDPAddr) (n *Node) {
+ b := tab.buckets[logdist(tab.self.ID, node)]
+ if n = b.bump(node); n == nil {
+ n = &Node{ID: node, Addr: from, active: time.Now()}
+ if len(b.entries) == bucketSize {
+ tab.pingReplace(n, b)
+ } else {
+ b.entries = append(b.entries, n)
+ }
+ }
+ return n
+}
+
+func (tab *Table) pingReplace(n *Node, b *bucket) {
+ old := b.entries[bucketSize-1]
+ go func() {
+ if err := tab.net.ping(old); err == nil {
+ // it responded, we don't need to replace it.
+ return
+ }
+ // it didn't respond, replace the node if it is still the oldest node.
+ tab.mutex.Lock()
+ if len(b.entries) > 0 && b.entries[len(b.entries)-1] == old {
+ // slide down other entries and put the new one in front.
+ copy(b.entries[1:], b.entries)
+ b.entries[0] = n
+ }
+ tab.mutex.Unlock()
+ }()
+}
+
+// bump updates the activity timestamp for the given node.
+// The caller must hold tab.mutex.
+func (tab *Table) bump(node NodeID) {
+ tab.buckets[logdist(tab.self.ID, node)].bump(node)
+}
+
+// add puts the entries into the table if their corresponding
+// bucket is not full. The caller must hold tab.mutex.
+func (tab *Table) add(entries []*Node) {
+outer:
+ for _, n := range entries {
+ if n == nil || n.ID == tab.self.ID {
+ // skip bad entries. The RLP decoder returns nil for empty
+ // input lists.
+ continue
+ }
+ bucket := tab.buckets[logdist(tab.self.ID, n.ID)]
+ for i := range bucket.entries {
+ if bucket.entries[i].ID == n.ID {
+ // already in bucket
+ continue outer
+ }
+ }
+ if len(bucket.entries) < bucketSize {
+ bucket.entries = append(bucket.entries, n)
+ }
+ }
+}
+
+func (b *bucket) bump(id NodeID) *Node {
+ for i, n := range b.entries {
+ if n.ID == id {
+ n.active = time.Now()
+ // move it to the front
+ copy(b.entries[1:], b.entries[:i+1])
+ b.entries[0] = n
+ return n
+ }
+ }
+ return nil
+}
+
+// nodesByDistance is a list of nodes, ordered by
+// distance to target.
+type nodesByDistance struct {
+ entries []*Node
+ target NodeID
+}
+
+// push adds the given node to the list, keeping the total size below maxElems.
+func (h *nodesByDistance) push(n *Node, maxElems int) {
+ ix := sort.Search(len(h.entries), func(i int) bool {
+ return distcmp(h.target, h.entries[i].ID, n.ID) > 0
+ })
+ if len(h.entries) < maxElems {
+ h.entries = append(h.entries, n)
+ }
+ if ix == len(h.entries) {
+ // farther away than all nodes we already have.
+ // if there was room for it, the node is now the last element.
+ } else {
+ // slide existing entries down to make room
+ // this will overwrite the entry we just appended.
+ copy(h.entries[ix+1:], h.entries[ix:])
+ h.entries[ix] = n
+ }
+}
+
+// NodeID is a unique identifier for each node.
+// The node identifier is a marshaled elliptic curve public key.
+type NodeID [512 / 8]byte
+
+// NodeID prints as a long hexadecimal number.
+func (n NodeID) String() string {
+ return fmt.Sprintf("%#x", n[:])
+}
+
+// The Go syntax representation of a NodeID is a call to HexID.
+func (n NodeID) GoString() string {
+ return fmt.Sprintf("HexID(\"%#x\")", n[:])
+}
+
+// HexID converts a hex string to a NodeID.
+// The string may be prefixed with 0x.
+func HexID(in string) NodeID {
+ if strings.HasPrefix(in, "0x") {
+ in = in[2:]
+ }
+ var id NodeID
+ b, err := hex.DecodeString(in)
+ if err != nil {
+ panic(err)
+ } else if len(b) != len(id) {
+ panic("wrong length")
+ }
+ copy(id[:], b)
+ return id
+}
+
+func newNodeID(priv *ecdsa.PrivateKey) (id NodeID) {
+ pubkey := elliptic.Marshal(priv.Curve, priv.X, priv.Y)
+ if len(pubkey)-1 != len(id) {
+ panic(fmt.Errorf("invalid key: need %d bit pubkey, got %d bits", (len(id)+1)*8, len(pubkey)))
+ }
+ copy(id[:], pubkey[1:])
+ return id
+}
+
+// recoverNodeID computes the public key used to sign the
+// given hash from the signature.
+func recoverNodeID(hash, sig []byte) (id NodeID, err error) {
+ pubkey, err := secp256k1.RecoverPubkey(hash, sig)
+ if err != nil {
+ return id, err
+ }
+ if len(pubkey)-1 != len(id) {
+ return id, fmt.Errorf("recovered pubkey has %d bits, want %d bits", len(pubkey)*8, (len(id)+1)*8)
+ }
+ for i := range id {
+ id[i] = pubkey[i+1]
+ }
+ return id, nil
+}
+
+// distcmp compares the distances a->target and b->target.
+// Returns -1 if a is closer to target, 1 if b is closer to target
+// and 0 if they are equal.
+func distcmp(target, a, b NodeID) int {
+ for i := range target {
+ da := a[i] ^ target[i]
+ db := b[i] ^ target[i]
+ if da > db {
+ return 1
+ } else if da < db {
+ return -1
+ }
+ }
+ return 0
+}
+
+// table of leading zero counts for bytes [0..255]
+var lzcount = [256]int{
+ 8, 7, 6, 6, 5, 5, 5, 5,
+ 4, 4, 4, 4, 4, 4, 4, 4,
+ 3, 3, 3, 3, 3, 3, 3, 3,
+ 3, 3, 3, 3, 3, 3, 3, 3,
+ 2, 2, 2, 2, 2, 2, 2, 2,
+ 2, 2, 2, 2, 2, 2, 2, 2,
+ 2, 2, 2, 2, 2, 2, 2, 2,
+ 2, 2, 2, 2, 2, 2, 2, 2,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+}
+
+// logdist returns the logarithmic distance between a and b, log2(a ^ b).
+func logdist(a, b NodeID) int {
+ lz := 0
+ for i := range a {
+ x := a[i] ^ b[i]
+ if x == 0 {
+ lz += 8
+ } else {
+ lz += lzcount[x]
+ break
+ }
+ }
+ return len(a)*8 - lz
+}
+
+// randomID returns a random NodeID such that logdist(a, b) == n
+func randomID(a NodeID, n int) (b NodeID) {
+ if n == 0 {
+ return a
+ }
+ // flip bit at position n, fill the rest with random bits
+ b = a
+ pos := len(a) - n/8 - 1
+ bit := byte(0x01) << (byte(n%8) - 1)
+ if bit == 0 {
+ pos++
+ bit = 0x80
+ }
+ b[pos] = a[pos]&^bit | ^a[pos]&bit // TODO: randomize end bits
+ for i := pos + 1; i < len(a); i++ {
+ b[i] = byte(rand.Intn(255))
+ }
+ return b
+}
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