lnd.xprv/discovery/bootstrapper.go
2018-08-02 18:20:49 -07:00

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package discovery
import (
"bytes"
"crypto/rand"
"crypto/sha256"
"errors"
"fmt"
prand "math/rand"
"net"
"strconv"
"strings"
"time"
"github.com/btcsuite/btcd/btcec"
"github.com/btcsuite/btcutil/bech32"
"github.com/davecgh/go-spew/spew"
"github.com/lightningnetwork/lnd/autopilot"
"github.com/lightningnetwork/lnd/lnwire"
"github.com/lightningnetwork/lnd/tor"
"github.com/miekg/dns"
)
func init() {
prand.Seed(time.Now().Unix())
}
// NetworkPeerBootstrapper is an interface that represents an initial peer
// bootstrap mechanism. This interface is to be used to bootstrap a new peer to
// the connection by providing it with the pubkey+address of a set of existing
// peers on the network. Several bootstrap mechanisms can be implemented such
// as DNS, in channel graph, DHT's, etc.
type NetworkPeerBootstrapper interface {
// SampleNodeAddrs uniformly samples a set of specified address from
// the network peer bootstrapper source. The num addrs field passed in
// denotes how many valid peer addresses to return. The passed set of
// node nodes allows the caller to ignore a set of nodes perhaps
// because they already have connections established.
SampleNodeAddrs(numAddrs uint32,
ignore map[autopilot.NodeID]struct{}) ([]*lnwire.NetAddress, error)
// Name returns a human readable string which names the concrete
// implementation of the NetworkPeerBootstrapper.
Name() string
}
// MultiSourceBootstrap attempts to utilize a set of NetworkPeerBootstrapper
// passed in to return the target (numAddrs) number of peer addresses that can
// be used to bootstrap a peer just joining the Lightning Network. Each
// bootstrapper will be queried successively until the target amount is met. If
// the ignore map is populated, then the bootstrappers will be instructed to
// skip those nodes.
func MultiSourceBootstrap(ignore map[autopilot.NodeID]struct{}, numAddrs uint32,
bootstrappers ...NetworkPeerBootstrapper) ([]*lnwire.NetAddress, error) {
// We'll randomly shuffle our bootstrappers before querying them in
// order to avoid from querying the same bootstrapper method over and
// over, as some of these might tend to provide better/worse results
// than others.
bootstrappers = shuffleBootstrappers(bootstrappers)
var addrs []*lnwire.NetAddress
for _, bootstrapper := range bootstrappers {
// If we already have enough addresses, then we can exit early
// w/o querying the additional bootstrappers.
if uint32(len(addrs)) >= numAddrs {
break
}
log.Infof("Attempting to bootstrap with: %v", bootstrapper.Name())
// If we still need additional addresses, then we'll compute
// the number of address remaining that we need to fetch.
numAddrsLeft := numAddrs - uint32(len(addrs))
log.Tracef("Querying for %v addresses", numAddrsLeft)
netAddrs, err := bootstrapper.SampleNodeAddrs(numAddrsLeft, ignore)
if err != nil {
// If we encounter an error with a bootstrapper, then
// we'll continue on to the next available
// bootstrapper.
log.Errorf("Unable to query bootstrapper %v: %v",
bootstrapper.Name(), err)
continue
}
addrs = append(addrs, netAddrs...)
}
if len(addrs) == 0 {
return nil, errors.New("no addresses found")
}
log.Infof("Obtained %v addrs to bootstrap network with", len(addrs))
return addrs, nil
}
// shuffleBootstrappers shuffles the set of bootstrappers in order to avoid
// querying the same bootstrapper over and over. To shuffle the set of
// candidates, we use a version of the FisherYates shuffle algorithm.
func shuffleBootstrappers(candidates []NetworkPeerBootstrapper) []NetworkPeerBootstrapper {
shuffled := make([]NetworkPeerBootstrapper, len(candidates))
perm := prand.Perm(len(candidates))
for i, v := range perm {
shuffled[v] = candidates[i]
}
return shuffled
}
// ChannelGraphBootstrapper is an implementation of the NetworkPeerBootstrapper
// which attempts to retrieve advertised peers directly from the active channel
// graph. This instance requires a backing autopilot.ChannelGraph instance in
// order to operate properly.
type ChannelGraphBootstrapper struct {
chanGraph autopilot.ChannelGraph
// hashAccumulator is a set of 32 random bytes that are read upon the
// creation of the channel graph bootstrapper. We use this value to
// randomly select nodes within the known graph to connect to. After
// each selection, we rotate the accumulator by hashing it with itself.
hashAccumulator [32]byte
tried map[autopilot.NodeID]struct{}
}
// A compile time assertion to ensure that ChannelGraphBootstrapper meets the
// NetworkPeerBootstrapper interface.
var _ NetworkPeerBootstrapper = (*ChannelGraphBootstrapper)(nil)
// NewGraphBootstrapper returns a new instance of a ChannelGraphBootstrapper
// backed by an active autopilot.ChannelGraph instance. This type of network
// peer bootstrapper will use the authenticated nodes within the known channel
// graph to bootstrap connections.
func NewGraphBootstrapper(cg autopilot.ChannelGraph) (NetworkPeerBootstrapper, error) {
c := &ChannelGraphBootstrapper{
chanGraph: cg,
tried: make(map[autopilot.NodeID]struct{}),
}
if _, err := rand.Read(c.hashAccumulator[:]); err != nil {
return nil, err
}
return c, nil
}
// SampleNodeAddrs uniformly samples a set of specified address from the
// network peer bootstrapper source. The num addrs field passed in denotes how
// many valid peer addresses to return.
//
// NOTE: Part of the NetworkPeerBootstrapper interface.
func (c *ChannelGraphBootstrapper) SampleNodeAddrs(numAddrs uint32,
ignore map[autopilot.NodeID]struct{}) ([]*lnwire.NetAddress, error) {
// We'll merge the ignore map with our currently selected map in order
// to ensure we don't return any duplicate nodes.
for n := range ignore {
c.tried[n] = struct{}{}
}
// In order to bootstrap, we'll iterate all the nodes in the channel
// graph, accumulating nodes until either we go through all active
// nodes, or we reach our limit. We ensure that we meet the randomly
// sample constraint as we maintain an xor accumulator to ensure we
// randomly sample nodes independent of the iteration of the channel
// graph.
sampleAddrs := func() ([]*lnwire.NetAddress, error) {
var (
a []*lnwire.NetAddress
// We'll create a special error so we can return early
// and abort the transaction once we find a match.
errFound = fmt.Errorf("found node")
)
err := c.chanGraph.ForEachNode(func(node autopilot.Node) error {
nID := autopilot.NewNodeID(node.PubKey())
if _, ok := c.tried[nID]; ok {
return nil
}
// We'll select the first node we come across who's
// public key is less than our current accumulator
// value. When comparing, we skip the first byte as
// it's 50/50. If it isn't less, than then we'll
// continue forward.
nodePub := node.PubKey().SerializeCompressed()[1:]
if bytes.Compare(c.hashAccumulator[:], nodePub) > 0 {
return nil
}
for _, nodeAddr := range node.Addrs() {
// If we haven't yet reached our limit, then
// we'll copy over the details of this node
// into the set of addresses to be returned.
switch nodeAddr.(type) {
case *net.TCPAddr, *tor.OnionAddr:
default:
// If this isn't a valid address
// supported by the protocol, then we'll
// skip this node.
return nil
}
// At this point, we've found an eligible node,
// so we'll return early with our shibboleth
// error.
a = append(a, &lnwire.NetAddress{
IdentityKey: node.PubKey(),
Address: nodeAddr,
})
}
c.tried[nID] = struct{}{}
return errFound
})
if err != nil && err != errFound {
return nil, err
}
return a, nil
}
// We'll loop and sample new addresses from the graph source until
// we've reached our target number of outbound connections or we hit 50
// attempts, which ever comes first.
var (
addrs []*lnwire.NetAddress
tries uint32
)
for tries < 30 && uint32(len(addrs)) < numAddrs {
sampleAddrs, err := sampleAddrs()
if err != nil {
return nil, err
}
tries++
// We'll now rotate our hash accumulator one value forwards.
c.hashAccumulator = sha256.Sum256(c.hashAccumulator[:])
// If this attempt didn't yield any addresses, then we'll exit
// early.
if len(sampleAddrs) == 0 {
continue
}
addrs = append(addrs, sampleAddrs...)
}
log.Tracef("Ending hash accumulator state: %x", c.hashAccumulator)
return addrs, nil
}
// Name returns a human readable string which names the concrete implementation
// of the NetworkPeerBootstrapper.
//
// NOTE: Part of the NetworkPeerBootstrapper interface.
func (c *ChannelGraphBootstrapper) Name() string {
return "Authenticated Channel Graph"
}
// DNSSeedBootstrapper as an implementation of the NetworkPeerBootstrapper
// interface which implements peer bootstrapping via a special DNS seed as
// defined in BOLT-0010. For further details concerning Lightning's current DNS
// boot strapping protocol, see this link:
// * https://github.com/lightningnetwork/lightning-rfc/blob/master/10-dns-bootstrap.md
type DNSSeedBootstrapper struct {
// dnsSeeds is an array of two tuples we'll use for bootstrapping. The
// first item in the tuple is the primary host we'll use to attempt the
// SRV lookup we require. If we're unable to receive a response over
// UDP, then we'll fall back to manual TCP resolution. The second item
// in the tuple is a special A record that we'll query in order to
// receive the IP address of the current authoritative DNS server for
// the network seed.
dnsSeeds [][2]string
net tor.Net
}
// A compile time assertion to ensure that DNSSeedBootstrapper meets the
// NetworkPeerjBootstrapper interface.
var _ NetworkPeerBootstrapper = (*ChannelGraphBootstrapper)(nil)
// NewDNSSeedBootstrapper returns a new instance of the DNSSeedBootstrapper.
// The set of passed seeds should point to DNS servers that properly implement
// Lightning's DNS peer bootstrapping protocol as defined in BOLT-0010. The set
// of passed DNS seeds should come in pairs, with the second host name to be
// used as a fallback for manual TCP resolution in the case of an error
// receiving the UDP response. The second host should return a single A record
// with the IP address of the authoritative name server.
func NewDNSSeedBootstrapper(seeds [][2]string, net tor.Net) NetworkPeerBootstrapper {
return &DNSSeedBootstrapper{dnsSeeds: seeds, net: net}
}
// fallBackSRVLookup attempts to manually query for SRV records we need to
// properly bootstrap. We do this by querying the special record at the "soa."
// sub-domain of supporting DNS servers. The retuned IP address will be the IP
// address of the authoritative DNS server. Once we have this IP address, we'll
// connect manually over TCP to request the SRV record. This is necessary as
// the records we return are currently too large for a class of resolvers,
// causing them to be filtered out. The targetEndPoint is the original end
// point that was meant to be hit.
func (d *DNSSeedBootstrapper) fallBackSRVLookup(soaShim string,
targetEndPoint string) ([]*net.SRV, error) {
log.Tracef("Attempting to query fallback DNS seed")
// First, we'll lookup the IP address of the server that will act as
// our shim.
addrs, err := d.net.LookupHost(soaShim)
if err != nil {
return nil, err
}
// Once we have the IP address, we'll establish a TCP connection using
// port 53.
dnsServer := net.JoinHostPort(addrs[0], "53")
conn, err := d.net.Dial("tcp", dnsServer)
if err != nil {
return nil, err
}
dnsHost := fmt.Sprintf("_nodes._tcp.%v.", targetEndPoint)
dnsConn := &dns.Conn{Conn: conn}
defer dnsConn.Close()
// With the connection established, we'll craft our SRV query, write
// toe request, then wait for the server to give our response.
msg := new(dns.Msg)
msg.SetQuestion(dnsHost, dns.TypeSRV)
if err := dnsConn.WriteMsg(msg); err != nil {
return nil, err
}
resp, err := dnsConn.ReadMsg()
if err != nil {
return nil, err
}
// If the message response code was not the success code, fail.
if resp.Rcode != dns.RcodeSuccess {
return nil, fmt.Errorf("Unsuccessful SRV request, "+
"received: %v", resp.Rcode)
}
// Retrieve the RR(s) of the Answer section, and covert to the format
// that net.LookupSRV would normally return.
var rrs []*net.SRV
for _, rr := range resp.Answer {
srv := rr.(*dns.SRV)
rrs = append(rrs, &net.SRV{
Target: srv.Target,
Port: srv.Port,
Priority: srv.Priority,
Weight: srv.Weight,
})
}
return rrs, nil
}
// SampleNodeAddrs uniformly samples a set of specified address from the
// network peer bootstrapper source. The num addrs field passed in denotes how
// many valid peer addresses to return. The set of DNS seeds are used
// successively to retrieve eligible target nodes.
func (d *DNSSeedBootstrapper) SampleNodeAddrs(numAddrs uint32,
ignore map[autopilot.NodeID]struct{}) ([]*lnwire.NetAddress, error) {
var netAddrs []*lnwire.NetAddress
// We'll continue this loop until we reach our target address limit.
// Each SRV query to the seed will return 25 random nodes, so we can
// continue to query until we reach our target.
search:
for uint32(len(netAddrs)) < numAddrs {
for _, dnsSeedTuple := range d.dnsSeeds {
// We'll first query the seed with an SRV record so we
// can obtain a random sample of the encoded public
// keys of nodes. We use the lndLookupSRV function for
// this task.
primarySeed := dnsSeedTuple[0]
_, addrs, err := d.net.LookupSRV("nodes", "tcp", primarySeed)
if err != nil {
log.Tracef("Unable to lookup SRV records via "+
"primary seed: %v", err)
log.Trace("Falling back to secondary")
// If the host of the secondary seed is blank,
// then we'll bail here as we can't proceed.
if dnsSeedTuple[1] == "" {
return nil, fmt.Errorf("Secondary seed is blank")
}
// If we get an error when trying to query via
// the primary seed, we'll fallback to the
// secondary seed before concluding failure.
soaShim := dnsSeedTuple[1]
addrs, err = d.fallBackSRVLookup(
soaShim, primarySeed,
)
if err != nil {
return nil, err
}
log.Tracef("Successfully queried fallback DNS seed")
}
log.Tracef("Retrieved SRV records from dns seed: %v",
spew.Sdump(addrs))
// Next, we'll need to issue an A record request for
// each of the nodes, skipping it if nothing comes
// back.
for _, nodeSrv := range addrs {
if uint32(len(netAddrs)) >= numAddrs {
break search
}
// With the SRV target obtained, we'll now
// perform another query to obtain the IP
// address for the matching bech32 encoded node
// key. We use the lndLookup function for this
// task.
bechNodeHost := nodeSrv.Target
addrs, err := d.net.LookupHost(bechNodeHost)
if err != nil {
return nil, err
}
if len(addrs) == 0 {
log.Tracef("No addresses for %v, skipping",
bechNodeHost)
continue
}
log.Tracef("Attempting to convert: %v", bechNodeHost)
// If we have a set of valid addresses, then
// we'll need to parse the public key from the
// original bech32 encoded string.
bechNode := strings.Split(bechNodeHost, ".")
_, nodeBytes5Bits, err := bech32.Decode(bechNode[0])
if err != nil {
return nil, err
}
// Once we have the bech32 decoded pubkey,
// we'll need to convert the 5-bit word
// grouping into our regular 8-bit word
// grouping so we can convert it into a public
// key.
nodeBytes, err := bech32.ConvertBits(
nodeBytes5Bits, 5, 8, false,
)
if err != nil {
return nil, err
}
nodeKey, err := btcec.ParsePubKey(
nodeBytes, btcec.S256(),
)
if err != nil {
return nil, err
}
// If we have an ignore list, and this node is
// in the ignore list, then we'll go to the
// next candidate.
if ignore != nil {
nID := autopilot.NewNodeID(nodeKey)
if _, ok := ignore[nID]; ok {
continue
}
}
// Finally we'll convert the host:port peer to
// a proper TCP address to use within the
// lnwire.NetAddress. We don't need to use
// the lndResolveTCP function here because we
// already have the host:port peer.
addr := net.JoinHostPort(addrs[0],
strconv.FormatUint(uint64(nodeSrv.Port), 10))
tcpAddr, err := net.ResolveTCPAddr("tcp", addr)
if err != nil {
return nil, err
}
// Finally, with all the information parsed,
// we'll return this fully valid address as a
// connection attempt.
lnAddr := &lnwire.NetAddress{
IdentityKey: nodeKey,
Address: tcpAddr,
}
log.Tracef("Obtained %v as valid reachable "+
"node", lnAddr)
netAddrs = append(netAddrs, lnAddr)
}
}
}
return netAddrs, nil
}
// Name returns a human readable string which names the concrete
// implementation of the NetworkPeerBootstrapper.
func (d *DNSSeedBootstrapper) Name() string {
return fmt.Sprintf("BOLT-0010 DNS Seed: %v", d.dnsSeeds)
}