mirror of
https://gitlab.com/pulsechaincom/erigon-pulse.git
synced 2024-12-25 13:07:17 +00:00
de7af720d6
This a fix for 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 16x the size of findnode) to the victim. Our solution is to require a 'bond' with the sender of findnode. If no bond exists, the findnode packet is not processed. A bond between nodes α and β is created when α replies to a ping from β. This (initial) version of the bonding implementation might still be vulnerable against replay attacks during the expiration time window. We will add stricter source address validation later.
487 lines
12 KiB
Go
487 lines
12 KiB
Go
package discover
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import (
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"bytes"
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"crypto/ecdsa"
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"errors"
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"fmt"
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"net"
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"time"
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"github.com/ethereum/go-ethereum/crypto"
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"github.com/ethereum/go-ethereum/logger"
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"github.com/ethereum/go-ethereum/p2p/nat"
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"github.com/ethereum/go-ethereum/rlp"
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)
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var log = logger.NewLogger("P2P Discovery")
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const Version = 3
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// Errors
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var (
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errPacketTooSmall = errors.New("too small")
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errBadHash = errors.New("bad hash")
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errExpired = errors.New("expired")
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errBadVersion = errors.New("version mismatch")
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errUnsolicitedReply = errors.New("unsolicited reply")
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errUnknownNode = errors.New("unknown node")
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errTimeout = errors.New("RPC timeout")
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errClosed = errors.New("socket closed")
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)
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// Timeouts
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const (
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respTimeout = 300 * time.Millisecond
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sendTimeout = 300 * time.Millisecond
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expiration = 20 * time.Second
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refreshInterval = 1 * time.Hour
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)
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// RPC packet types
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const (
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pingPacket = iota + 1 // zero is 'reserved'
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pongPacket
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findnodePacket
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neighborsPacket
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)
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// RPC request structures
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type (
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ping struct {
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Version uint // must match Version
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IP string // our IP
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Port uint16 // our port
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Expiration uint64
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}
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// reply to Ping
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pong struct {
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ReplyTok []byte
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Expiration uint64
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}
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findnode struct {
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// Id to look up. The responding node will send back nodes
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// closest to the target.
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Target NodeID
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Expiration uint64
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}
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// reply to findnode
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neighbors struct {
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Nodes []*Node
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Expiration uint64
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}
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)
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type rpcNode struct {
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IP string
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Port uint16
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ID NodeID
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}
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type packet interface {
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handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error
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}
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type conn interface {
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ReadFromUDP(b []byte) (n int, addr *net.UDPAddr, err error)
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WriteToUDP(b []byte, addr *net.UDPAddr) (n int, err error)
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Close() error
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LocalAddr() net.Addr
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}
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// udp implements the RPC protocol.
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type udp struct {
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conn conn
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priv *ecdsa.PrivateKey
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addpending chan *pending
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gotreply chan reply
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closing chan struct{}
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nat nat.Interface
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*Table
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}
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// pending represents a pending reply.
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//
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// some implementations of the protocol wish to send more than one
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// reply packet to findnode. in general, any neighbors packet cannot
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// be matched up with a specific findnode packet.
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//
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// our implementation handles this by storing a callback function for
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// each pending reply. incoming packets from a node are dispatched
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// to all the callback functions for that node.
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type pending struct {
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// these fields must match in the reply.
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from NodeID
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ptype byte
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// time when the request must complete
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deadline time.Time
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// callback is called when a matching reply arrives. if it returns
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// true, the callback is removed from the pending reply queue.
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// if it returns false, the reply is considered incomplete and
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// the callback will be invoked again for the next matching reply.
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callback func(resp interface{}) (done bool)
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// errc receives nil when the callback indicates completion or an
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// error if no further reply is received within the timeout.
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errc chan<- error
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}
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type reply struct {
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from NodeID
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ptype byte
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data interface{}
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// loop indicates whether there was
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// a matching request by sending on this channel.
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matched chan<- bool
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}
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// ListenUDP returns a new table that listens for UDP packets on laddr.
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func ListenUDP(priv *ecdsa.PrivateKey, laddr string, natm nat.Interface) (*Table, error) {
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addr, err := net.ResolveUDPAddr("udp", laddr)
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if err != nil {
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return nil, err
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}
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conn, err := net.ListenUDP("udp", addr)
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if err != nil {
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return nil, err
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}
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tab, _ := newUDP(priv, conn, natm)
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log.Infoln("Listening,", tab.self)
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return tab, nil
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}
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func newUDP(priv *ecdsa.PrivateKey, c conn, natm nat.Interface) (*Table, *udp) {
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udp := &udp{
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conn: c,
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priv: priv,
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closing: make(chan struct{}),
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gotreply: make(chan reply),
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addpending: make(chan *pending),
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}
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realaddr := c.LocalAddr().(*net.UDPAddr)
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if natm != nil {
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if !realaddr.IP.IsLoopback() {
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go nat.Map(natm, udp.closing, "udp", realaddr.Port, realaddr.Port, "ethereum discovery")
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}
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// TODO: react to external IP changes over time.
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if ext, err := natm.ExternalIP(); err == nil {
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realaddr = &net.UDPAddr{IP: ext, Port: realaddr.Port}
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}
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}
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udp.Table = newTable(udp, PubkeyID(&priv.PublicKey), realaddr)
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go udp.loop()
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go udp.readLoop()
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return udp.Table, udp
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}
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func (t *udp) close() {
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close(t.closing)
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t.conn.Close()
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// TODO: wait for the loops to end.
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}
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// ping sends a ping message to the given node and waits for a reply.
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func (t *udp) ping(toid NodeID, toaddr *net.UDPAddr) error {
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// TODO: maybe check for ReplyTo field in callback to measure RTT
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errc := t.pending(toid, pongPacket, func(interface{}) bool { return true })
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t.send(toaddr, pingPacket, ping{
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Version: Version,
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IP: t.self.IP.String(),
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Port: uint16(t.self.TCPPort),
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Expiration: uint64(time.Now().Add(expiration).Unix()),
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})
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return <-errc
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}
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func (t *udp) waitping(from NodeID) error {
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return <-t.pending(from, pingPacket, func(interface{}) bool { return true })
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}
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// findnode sends a findnode request to the given node and waits until
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// the node has sent up to k neighbors.
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func (t *udp) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID) ([]*Node, error) {
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nodes := make([]*Node, 0, bucketSize)
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nreceived := 0
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errc := t.pending(toid, neighborsPacket, func(r interface{}) bool {
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reply := r.(*neighbors)
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for _, n := range reply.Nodes {
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nreceived++
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if n.isValid() {
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nodes = append(nodes, n)
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}
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}
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return nreceived >= bucketSize
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})
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t.send(toaddr, findnodePacket, findnode{
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Target: target,
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Expiration: uint64(time.Now().Add(expiration).Unix()),
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})
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err := <-errc
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return nodes, err
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}
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// pending adds a reply callback to the pending reply queue.
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// see the documentation of type pending for a detailed explanation.
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func (t *udp) pending(id NodeID, ptype byte, callback func(interface{}) bool) <-chan error {
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ch := make(chan error, 1)
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p := &pending{from: id, ptype: ptype, callback: callback, errc: ch}
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select {
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case t.addpending <- p:
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// loop will handle it
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case <-t.closing:
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ch <- errClosed
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}
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return ch
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}
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func (t *udp) handleReply(from NodeID, ptype byte, req packet) bool {
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matched := make(chan bool)
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select {
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case t.gotreply <- reply{from, ptype, req, matched}:
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// loop will handle it
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return <-matched
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case <-t.closing:
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return false
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}
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}
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// loop runs in its own goroutin. it keeps track of
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// the refresh timer and the pending reply queue.
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func (t *udp) loop() {
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var (
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pending []*pending
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nextDeadline time.Time
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timeout = time.NewTimer(0)
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refresh = time.NewTicker(refreshInterval)
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)
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<-timeout.C // ignore first timeout
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defer refresh.Stop()
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defer timeout.Stop()
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rearmTimeout := func() {
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if len(pending) == 0 || nextDeadline == pending[0].deadline {
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return
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}
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nextDeadline = pending[0].deadline
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timeout.Reset(nextDeadline.Sub(time.Now()))
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}
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for {
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select {
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case <-refresh.C:
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go t.refresh()
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case <-t.closing:
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for _, p := range pending {
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p.errc <- errClosed
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}
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pending = nil
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return
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case p := <-t.addpending:
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p.deadline = time.Now().Add(respTimeout)
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pending = append(pending, p)
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rearmTimeout()
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case r := <-t.gotreply:
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var matched bool
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for i := 0; i < len(pending); i++ {
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if p := pending[i]; p.from == r.from && p.ptype == r.ptype {
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matched = true
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if p.callback(r.data) {
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// callback indicates the request is done, remove it.
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p.errc <- nil
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copy(pending[i:], pending[i+1:])
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pending = pending[:len(pending)-1]
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i--
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}
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}
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}
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r.matched <- matched
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case now := <-timeout.C:
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// notify and remove callbacks whose deadline is in the past.
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i := 0
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for ; i < len(pending) && now.After(pending[i].deadline); i++ {
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pending[i].errc <- errTimeout
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}
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if i > 0 {
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copy(pending, pending[i:])
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pending = pending[:len(pending)-i]
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}
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rearmTimeout()
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}
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}
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}
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const (
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macSize = 256 / 8
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sigSize = 520 / 8
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headSize = macSize + sigSize // space of packet frame data
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)
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var headSpace = make([]byte, headSize)
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func (t *udp) send(toaddr *net.UDPAddr, ptype byte, req interface{}) error {
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packet, err := encodePacket(t.priv, ptype, req)
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if err != nil {
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return err
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}
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log.DebugDetailf(">>> %v %T %v\n", toaddr, req, req)
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if _, err = t.conn.WriteToUDP(packet, toaddr); err != nil {
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log.DebugDetailln("UDP send failed:", err)
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}
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return err
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}
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func encodePacket(priv *ecdsa.PrivateKey, ptype byte, req interface{}) ([]byte, error) {
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b := new(bytes.Buffer)
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b.Write(headSpace)
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b.WriteByte(ptype)
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if err := rlp.Encode(b, req); err != nil {
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log.Errorln("error encoding packet:", err)
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return nil, err
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}
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packet := b.Bytes()
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sig, err := crypto.Sign(crypto.Sha3(packet[headSize:]), priv)
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if err != nil {
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log.Errorln("could not sign packet:", err)
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return nil, err
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}
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copy(packet[macSize:], sig)
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// add the hash to the front. Note: this doesn't protect the
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// packet in any way. Our public key will be part of this hash in
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// The future.
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copy(packet, crypto.Sha3(packet[macSize:]))
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return packet, nil
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}
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// readLoop runs in its own goroutine. it handles incoming UDP packets.
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func (t *udp) readLoop() {
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defer t.conn.Close()
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buf := make([]byte, 4096) // TODO: good buffer size
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for {
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nbytes, from, err := t.conn.ReadFromUDP(buf)
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if err != nil {
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return
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}
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packet, fromID, hash, err := decodePacket(buf[:nbytes])
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if err != nil {
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log.Debugf("Bad packet from %v: %v\n", from, err)
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continue
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}
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log.DebugDetailf("<<< %v %T %v\n", from, packet, packet)
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go func() {
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if err := packet.handle(t, from, fromID, hash); err != nil {
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log.Debugf("error handling %T from %v: %v", packet, from, err)
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}
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}()
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}
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}
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func decodePacket(buf []byte) (packet, NodeID, []byte, error) {
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if len(buf) < headSize+1 {
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return nil, NodeID{}, nil, errPacketTooSmall
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}
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hash, sig, sigdata := buf[:macSize], buf[macSize:headSize], buf[headSize:]
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shouldhash := crypto.Sha3(buf[macSize:])
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if !bytes.Equal(hash, shouldhash) {
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return nil, NodeID{}, nil, errBadHash
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}
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fromID, err := recoverNodeID(crypto.Sha3(buf[headSize:]), sig)
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if err != nil {
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return nil, NodeID{}, hash, err
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}
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var req packet
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switch ptype := sigdata[0]; ptype {
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case pingPacket:
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req = new(ping)
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case pongPacket:
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req = new(pong)
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case findnodePacket:
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req = new(findnode)
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case neighborsPacket:
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req = new(neighbors)
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default:
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return nil, fromID, hash, fmt.Errorf("unknown type: %d", ptype)
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}
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err = rlp.Decode(bytes.NewReader(sigdata[1:]), req)
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return req, fromID, hash, err
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}
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func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
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if expired(req.Expiration) {
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return errExpired
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}
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if req.Version != Version {
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return errBadVersion
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}
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t.send(from, pongPacket, pong{
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ReplyTok: mac,
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Expiration: uint64(time.Now().Add(expiration).Unix()),
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})
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if !t.handleReply(fromID, pingPacket, req) {
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// Note: we're ignoring the provided IP address right now
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t.bond(true, fromID, from, req.Port)
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}
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return nil
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}
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func (req *pong) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
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if expired(req.Expiration) {
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return errExpired
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}
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if !t.handleReply(fromID, pongPacket, req) {
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return errUnsolicitedReply
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}
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return nil
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}
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func (req *findnode) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
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if expired(req.Expiration) {
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return errExpired
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}
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if t.db.get(fromID) == nil {
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// No bond exists, we don't process the packet. This prevents
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// an attack vector where the discovery protocol could be used
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// to amplify traffic in a DDOS attack. A malicious actor
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// would send a findnode request with the IP address and UDP
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// port of the target as the source address. The recipient of
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// the findnode packet would then send a neighbors packet
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// (which is a much bigger packet than findnode) to the victim.
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return errUnknownNode
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}
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t.mutex.Lock()
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closest := t.closest(req.Target, bucketSize).entries
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t.mutex.Unlock()
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t.send(from, neighborsPacket, neighbors{
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Nodes: closest,
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Expiration: uint64(time.Now().Add(expiration).Unix()),
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})
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return nil
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}
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func (req *neighbors) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) error {
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if expired(req.Expiration) {
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return errExpired
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}
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if !t.handleReply(fromID, neighborsPacket, req) {
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return errUnsolicitedReply
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}
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return nil
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}
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func expired(ts uint64) bool {
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return time.Unix(int64(ts), 0).Before(time.Now())
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}
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