package discover
import (
"bytes"
"crypto/ecdsa"
"errors"
"fmt"
"net"
"time"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/logger"
"github.com/ethereum/go-ethereum/logger/glog"
"github.com/ethereum/go-ethereum/p2p/nat"
"github.com/ethereum/go-ethereum/rlp"
)
const Version = 3
// Errors
var (
errPacketTooSmall = errors.New("too small")
errBadHash = errors.New("bad hash")
errExpired = errors.New("expired")
errBadVersion = errors.New("version mismatch")
errUnsolicitedReply = errors.New("unsolicited reply")
errUnknownNode = errors.New("unknown node")
errTimeout = errors.New("RPC timeout")
errClosed = errors.New("socket closed")
)
// Timeouts
const (
respTimeout = 300 * time.Millisecond
sendTimeout = 300 * time.Millisecond
expiration = 20 * time.Second
refreshInterval = 1 * time.Hour
)
// RPC packet types
const (
pingPacket = iota + 1 // zero is 'reserved'
pongPacket
findnodePacket
neighborsPacket
)
// RPC request structures
type (
ping struct {
Version uint // must match Version
IP string // our IP
Port uint16 // our port
Expiration uint64
}
// reply to Ping
pong struct {
ReplyTok []byte
Expiration uint64
}
findnode struct {
// Id to look up. The responding node will send back nodes
// closest to the target.
Target NodeID
Expiration uint64
}
// reply to findnode
neighbors struct {
Nodes []*Node
Expiration uint64
}
)
type rpcNode struct {
IP string
Port uint16
ID NodeID
}
type packet interface {
handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error
}
type conn interface {
ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error)
WriteToUDP(b []byte, addr *net.UDPAddr) (n int, err error)
Close() error
LocalAddr() net.Addr
}
// udp implements the RPC protocol.
type udp struct {
conn conn
priv *ecdsa.PrivateKey
addpending chan *pending
gotreply chan reply
closing chan struct{}
nat nat.Interface
*Table
}
// pending represents a pending reply.
//
// some implementations of the protocol wish to send more than one
// reply packet to findnode. in general, any neighbors packet cannot
// be matched up with a specific findnode packet.
//
// our implementation handles this by storing a callback function for
// each pending reply. incoming packets from a node are dispatched
// to all the callback functions for that node.
type pending struct {
// these fields must match in the reply.
from NodeID
ptype byte
// time when the request must complete
deadline time.Time
// callback is called when a matching reply arrives. if it returns
// true, the callback is removed from the pending reply queue.
// if it returns false, the reply is considered incomplete and
// the callback will be invoked again for the next matching reply.
callback func(resp interface{}) (done bool)
// errc receives nil when the callback indicates completion or an
// error if no further reply is received within the timeout.
errc chan<- error
}
type reply struct {
from NodeID
ptype byte
data interface{}
// loop indicates whether there was
// a matching request by sending on this channel.
matched chan<- bool
}
// ListenUDP returns a new table that listens for UDP packets on laddr.
func ListenUDP(priv *ecdsa.PrivateKey, laddr string, natm nat.Interface, nodeDBPath string) (*Table, error) {
addr, err := net.ResolveUDPAddr("udp", laddr)
if err != nil {
return nil, err
}
conn, err := net.ListenUDP("udp", addr)
if err != nil {
return nil, err
}
tab, _ := newUDP(priv, conn, natm, nodeDBPath)
glog.V(logger.Info).Infoln("Listening,", tab.self)
return tab, nil
}
func newUDP(priv *ecdsa.PrivateKey, c conn, natm nat.Interface, nodeDBPath string) (*Table, *udp) {
udp := &udp{
conn: c,
priv: priv,
closing: make(chan struct{}),
gotreply: make(chan reply),
addpending: make(chan *pending),
}
realaddr := c.LocalAddr().(*net.UDPAddr)
if natm != nil {
if !realaddr.IP.IsLoopback() {
go nat.Map(natm, udp.closing, "udp", realaddr.Port, realaddr.Port, "ethereum discovery")
}
// TODO: react to external IP changes over time.
if ext, err := natm.ExternalIP(); err == nil {
realaddr = &net.UDPAddr{IP: ext, Port: realaddr.Port}
}
}
udp.Table = newTable(udp, PubkeyID(&priv.PublicKey), realaddr, nodeDBPath)
go udp.loop()
go udp.readLoop()
return udp.Table, udp
}
func (t *udp) close() {
close(t.closing)
t.conn.Close()
// TODO: wait for the loops to end.
}
// ping sends a ping message to the given node and waits for a reply.
func (t *udp) ping(toid NodeID, toaddr *net.UDPAddr) error {
// TODO: maybe check for ReplyTo field in callback to measure RTT
errc := t.pending(toid, pongPacket, func(interface{}) bool { return true })
t.send(toaddr, pingPacket, ping{
Version: Version,
IP: t.self.IP.String(),
Port: uint16(t.self.TCPPort),
Expiration: uint64(time.Now().Add(expiration).Unix()),
})
return <-errc
}
func (t *udp) waitping(from NodeID) error {
return <-t.pending(from, pingPacket, func(interface{}) bool { return true })
}
// findnode sends a findnode request to the given node and waits until
// the node has sent up to k neighbors.
func (t *udp) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID) ([]*Node, error) {
nodes := make([]*Node, 0, bucketSize)
nreceived := 0
errc := t.pending(toid, neighborsPacket, func(r interface{}) bool {
reply := r.(*neighbors)
for _, n := range reply.Nodes {
nreceived++
if n.isValid() {
nodes = append(nodes, n)
}
}
return nreceived >= bucketSize
})
t.send(toaddr, findnodePacket, findnode{
Target: target,
Expiration: uint64(time.Now().Add(expiration).Unix()),
})
err := <-errc
return nodes, err
}
// pending adds a reply callback to the pending reply queue.
// see the documentation of type pending for a detailed explanation.
func (t *udp) pending(id NodeID, ptype byte, callback func(interface{}) bool) <-chan error {
ch := make(chan error, 1)
p := &pending{from: id, ptype: ptype, callback: callback, errc: ch}
select {
case t.addpending <- p:
// loop will handle it
case <-t.closing:
ch <- errClosed
}
return ch
}
func (t *udp) handleReply(from NodeID, ptype byte, req packet) bool {
matched := make(chan bool)
select {
case t.gotreply <- reply{from, ptype, req, matched}:
// loop will handle it
return <-matched
case <-t.closing:
return false
}
}
// loop runs in its own goroutin. it keeps track of
// the refresh timer and the pending reply queue.
func (t *udp) loop() {
var (
pending []*pending
nextDeadline time.Time
timeout = time.NewTimer(0)
refresh = time.NewTicker(refreshInterval)
)
<-timeout.C // ignore first timeout
defer refresh.Stop()
defer timeout.Stop()
rearmTimeout := func() {
now := time.Now()
if len(pending) == 0 || now.Before(nextDeadline) {
return
}
nextDeadline = pending[0].deadline
timeout.Reset(nextDeadline.Sub(now))
}
for {
select {
case <-refresh.C:
go t.refresh()
case <-t.closing:
for _, p := range pending {
p.errc <- errClosed
}
pending = nil
return
case p := <-t.addpending:
p.deadline = time.Now().Add(respTimeout)
pending = append(pending, p)
rearmTimeout()
case r := <-t.gotreply:
var matched bool
for i := 0; i < len(pending); i++ {
if p := pending[i]; p.from == r.from && p.ptype == r.ptype {
matched = true
if p.callback(r.data) {
// callback indicates the request is done, remove it.
p.errc <- nil
copy(pending[i:], pending[i+1:])
pending = pending[:len(pending)-1]
i--
}
}
}
r.matched <- matched
case now := <-timeout.C:
// notify and remove callbacks whose deadline is in the past.
i := 0
for ; i < len(pending) && now.After(pending[i].deadline); i++ {
pending[i].errc <- errTimeout
}
if i > 0 {
copy(pending, pending[i:])
pending = pending[:len(pending)-i]
}
rearmTimeout()
}
}
}
const (
macSize = 256 / 8
sigSize = 520 / 8
headSize = macSize + sigSize // space of packet frame data
)
var headSpace = make([]byte, headSize)
func (t *udp) send(toaddr *net.UDPAddr, ptype byte, req interface{}) error {
packet, err := encodePacket(t.priv, ptype, req)
if err != nil {
return err
}
glog.V(logger.Detail).Infof(">>> %v %T\n", toaddr, req)
if _, err = t.conn.WriteToUDP(packet, toaddr); err != nil {
glog.V(logger.Detail).Infoln("UDP send failed:", err)
}
return err
}
func encodePacket(priv *ecdsa.PrivateKey, ptype byte, req interface{}) ([]byte, error) {
b := new(bytes.Buffer)
b.Write(headSpace)
b.WriteByte(ptype)
if err := rlp.Encode(b, req); err != nil {
glog.V(logger.Error).Infoln("error encoding packet:", err)
return nil, err
}
packet := b.Bytes()
sig, err := crypto.Sign(crypto.Sha3(packet[headSize:]), priv)
if err != nil {
glog.V(logger.Error).Infoln("could not sign packet:", err)
return nil, err
}
copy(packet[macSize:], sig)
// add the hash to the front. Note: this doesn't protect the
// packet in any way. Our public key will be part of this hash in
// The future.
copy(packet, crypto.Sha3(packet[macSize:]))
return packet, nil
}
// readLoop runs in its own goroutine. it handles incoming UDP packets.
func (t *udp) readLoop() {
defer t.conn.Close()
buf := make([]byte, 4096) // TODO: good buffer size
for {
nbytes, from, err := t.conn.ReadFromUDP(buf)
if err != nil {
return
}
packet, fromID, hash, err := decodePacket(buf[:nbytes])
if err != nil {
glog.V(logger.Debug).Infof("Bad packet from %v: %v\n", from, err)
continue
}
status := "ok"
if err := packet.handle(t, from, fromID, hash); err != nil {
status = err.Error()
}
glog.V(logger.Detail).Infof("<<< %v %T: %s\n", from, packet, status)
}
}
func decodePacket(buf []byte) (packet, NodeID, []byte, error) {
if len(buf) < headSize+1 {
return nil, NodeID{}, nil, errPacketTooSmall
}
hash, sig, sigdata := buf[:macSize], buf[macSize:headSize], buf[headSize:]
shouldhash := crypto.Sha3(buf[macSize:])
if !bytes.Equal(hash, shouldhash) {
return nil, NodeID{}, nil, errBadHash
}
fromID, err := recoverNodeID(crypto.Sha3(buf[headSize:]), sig)
if err != nil {
return nil, NodeID{}, hash, err
}
var req packet
switch ptype := sigdata[0]; ptype {
case pingPacket:
req = new(ping)
case pongPacket:
req = new(pong)
case findnodePacket:
req = new(findnode)
case neighborsPacket:
req = new(neighbors)
default:
return nil, fromID, hash, fmt.Errorf("unknown type: %d", ptype)
}
err = rlp.DecodeBytes(sigdata[1:], req)
return req, fromID, hash, err
}
func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
if expired(req.Expiration) {
return errExpired
}
if req.Version != Version {
return errBadVersion
}
t.send(from, pongPacket, pong{
ReplyTok: mac,
Expiration: uint64(time.Now().Add(expiration).Unix()),
})
if !t.handleReply(fromID, pingPacket, req) {
// Note: we're ignoring the provided IP address right now
go t.bond(true, fromID, from, req.Port)
}
return nil
}
func (req *pong) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
if expired(req.Expiration) {
return errExpired
}
if !t.handleReply(fromID, pongPacket, req) {
return errUnsolicitedReply
}
return nil
}
func (req *findnode) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
if expired(req.Expiration) {
return errExpired
}
if t.db.node(fromID) == nil {
// No bond exists, we don't process the packet. This prevents
// an attack vector where the discovery protocol could be used
// to amplify traffic in a DDOS attack. A malicious actor
// would send a findnode request with the IP address and UDP
// port of the target as the source address. The recipient of
// the findnode packet would then send a neighbors packet
// (which is a much bigger packet than findnode) to the victim.
return errUnknownNode
}
t.mutex.Lock()
closest := t.closest(req.Target, bucketSize).entries
t.mutex.Unlock()
t.send(from, neighborsPacket, neighbors{
Nodes: closest,
Expiration: uint64(time.Now().Add(expiration).Unix()),
})
return nil
}
func (req *neighbors) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
if expired(req.Expiration) {
return errExpired
}
if !t.handleReply(fromID, neighborsPacket, req) {
return errUnsolicitedReply
}
return nil
}
func expired(ts uint64) bool {
return time.Unix(int64(ts), 0).Before(time.Now())
}
