chain: implement GetNodeAddresses fallback for PrunedBlockDispatcher

It's possible for bitcoind instances to only have connections to pruned
nodes after its initial block download, which are incompatible with the
PrunedBlockDispatcher. This would result in GetBlock requests for pruned
blocks to never resolve. Since bitcoind also exposes a GetNodeAddresses
RPC, which returns random reachable addresses from its address manager,
we can leverage it to obtain a new candidate set of peers that we
otherwise wouldn't obtain through GetPeers.

chain/bitcoind_conn.go

@@ -196,10 +196,9 @@ func NewBitcoindConn(cfg *BitcoindConfig) (*BitcoindConn, error) {
 				NumTargetPeers:     cfg.PrunedModeMaxPeers,
 				Dial:               cfg.Dialer,
 				GetPeers:           client.GetPeerInfo,
+				GetNodeAddresses:   client.GetNodeAddresses,
 				PeerReadyTimeout:   defaultPeerReadyTimeout,
-				RefreshPeersTicker: ticker.New(
+				RefreshPeersTicker: ticker.New(defaultRefreshPeersInterval),
-					defaultRefreshPeersInterval,
-				),
 				MaxRequestInvs:     wire.MaxInvPerMsg,
 			},
 		)

chain/pruned_block_dispatcher.go

@@ -99,6 +99,11 @@ type PrunedBlockDispatcherConfig struct {
 	// GetPeers retrieves the active set of peers known to the backend node.
 	GetPeers func() ([]btcjson.GetPeerInfoResult, error)
 
+	// GetNodeAddresses returns random reachable addresses known to the
+	// backend node. An optional number of addresses to return can be
+	// provided, otherwise 8 are returned by default.
+	GetNodeAddresses func(*int32) ([]btcjson.GetNodeAddressesResult, error)
+
 	// PeerReadyTimeout is the amount of time we'll wait for a query peer to
 	// be ready to receive incoming block requests. Peers cannot respond to
 	// requests until the version exchange is completed upon connection
@@ -256,7 +261,7 @@ func (d *PrunedBlockDispatcher) pollPeers() {
 			// If we do, attempt to establish connections until
 			// we've reached our target number.
 			if err := d.connectToPeers(); err != nil {
-				log.Warnf("Unable to establish peer "+
+				log.Warnf("Failed to establish peer "+
 					"connections: %v", err)
 				continue
 			}
@@ -277,90 +282,150 @@ func (d *PrunedBlockDispatcher) connectToPeers() error {
 	if err != nil {
 		return err
 	}
-	peers, err = filterPeers(peers)
+	addrs, err := filterPeers(peers)
 	if err != nil {
 		return err
 	}
-	rand.Shuffle(len(peers), func(i, j int) {
+	rand.Shuffle(len(addrs), func(i, j int) {
-		peers[i], peers[j] = peers[j], peers[i]
+		addrs[i], addrs[j] = addrs[j], addrs[i]
 	})
 
-	// For each unbanned peer we don't already have a connection to, try to
+	for _, addr := range addrs {
-	// establish one, and if successful, notify the peer.
+		needMore, err := d.connectToPeer(addr)
-	for _, peer := range peers {
-		d.peerMtx.Lock()
-		_, isBanned := d.bannedPeers[peer.Addr]
-		_, isConnected := d.currentPeers[peer.Addr]
-		d.peerMtx.Unlock()
-		if isBanned || isConnected {
-			continue
-		}
-
-		queryPeer, err := d.newQueryPeer(peer)
 		if err != nil {
-			return fmt.Errorf("unable to configure query peer %v: "+
+			log.Debugf("Failed connecting to peer %v: %v", addr, err)
-				"%v", peer.Addr, err)
-		}
-		if err := d.connectToPeer(queryPeer); err != nil {
-			log.Debugf("Failed connecting to peer %v: %v",
-				peer.Addr, err)
 			continue
 		}
-
+		if !needMore {
-		select {
+			return nil
-		case d.peersConnected <- queryPeer:
+		}
-		case <-d.quit:
-			return errors.New("shutting down")
 	}
 
-		// If the new peer helped us reach our target number, we're done
+	// We still need more addresses so we'll also invoke the
-		// and can exit.
+	// `getnodeaddresses` RPC to receive random reachable addresses. We'll
-		d.peerMtx.Lock()
+	// also filter out any that do not meet our requirements. The nil
-		d.currentPeers[queryPeer.Addr()] = queryPeer.Peer
+	// argument will return a default number of addresses, which is
-		numPeers := len(d.currentPeers)
+	// currently 8. We don't care how many addresses are returned as long as
-		d.peerMtx.Unlock()
+	// 1 is returned, since this will be polled regularly if needed.
-		if numPeers == d.cfg.NumTargetPeers {
+	nodeAddrs, err := d.cfg.GetNodeAddresses(nil)
-			break
+	if err != nil {
+		return err
+	}
+	addrs = filterNodeAddrs(nodeAddrs)
+	for _, addr := range addrs {
+		if _, err := d.connectToPeer(addr); err != nil {
+			log.Debugf("Failed connecting to peer %v: %v", addr, err)
 		}
 	}
 
 	return nil
 }
 
+// connectToPeer attempts to establish a connection to the given peer and waits
+// up to PeerReadyTimeout for the version exchange to complete so that we can
+// begin sending it our queries.
+func (d *PrunedBlockDispatcher) connectToPeer(addr string) (bool, error) {
+	// Prevent connections to peers we've already connected to or we've
+	// banned.
+	d.peerMtx.Lock()
+	_, isBanned := d.bannedPeers[addr]
+	_, isConnected := d.currentPeers[addr]
+	d.peerMtx.Unlock()
+	if isBanned || isConnected {
+		return true, nil
+	}
+
+	peer, err := d.newQueryPeer(addr)
+	if err != nil {
+		return true, fmt.Errorf("unable to configure query peer %v: "+
+			"%v", addr, err)
+	}
+
+	// Establish the connection and wait for the protocol negotiation to
+	// complete.
+	conn, err := d.cfg.Dial(addr)
+	if err != nil {
+		return true, err
+	}
+	peer.AssociateConnection(conn)
+
+	select {
+	case <-peer.ready:
+	case <-time.After(d.cfg.PeerReadyTimeout):
+		peer.Disconnect()
+		return true, errors.New("timed out waiting for protocol negotiation")
+	case <-d.quit:
+		return false, errors.New("shutting down")
+	}
+
+	// Remove the peer once it has disconnected.
+	peer.signalUponDisconnect(func() {
+		d.peerMtx.Lock()
+		delete(d.currentPeers, peer.Addr())
+		d.peerMtx.Unlock()
+	})
+
+	d.peerMtx.Lock()
+	d.currentPeers[addr] = peer.Peer
+	numPeers := len(d.currentPeers)
+	d.peerMtx.Unlock()
+
+	// Notify the new peer connection to our workManager.
+	select {
+	case d.peersConnected <- peer:
+	case <-d.quit:
+		return false, errors.New("shutting down")
+	}
+
+	// Request more peer connections if we haven't reached our target number
+	// with the new peer.
+	return numPeers < d.cfg.NumTargetPeers, nil
+}
+
 // filterPeers filters out any peers which cannot handle arbitrary witness block
 // requests, i.e., any peer which is not considered a segwit-enabled
 // "full-node".
-func filterPeers(peers []btcjson.GetPeerInfoResult) (
+func filterPeers(peers []btcjson.GetPeerInfoResult) ([]string, error) {
-	[]btcjson.GetPeerInfoResult, error) {
+	var eligible []string
-
-	var eligible []btcjson.GetPeerInfoResult
 	for _, peer := range peers {
 		rawServices, err := hex.DecodeString(peer.Services)
 		if err != nil {
 			return nil, err
 		}
 		services := wire.ServiceFlag(binary.BigEndian.Uint64(rawServices))
-
+		if !satisfiesRequiredServices(services) {
-		// Skip nodes that cannot serve full block witness data.
-		if services&requiredServices != requiredServices {
 			continue
 		}
-		// Skip pruned nodes.
+		eligible = append(eligible, peer.Addr)
-		if services&prunedNodeService == prunedNodeService {
-			continue
 	}
-
-		eligible = append(eligible, peer)
-	}
-
 	return eligible, nil
 }
 
+// filterNodeAddrs filters out any peers which cannot handle arbitrary witness
+// block requests, i.e., any peer which is not considered a segwit-enabled
+// "full-node".
+func filterNodeAddrs(nodeAddrs []btcjson.GetNodeAddressesResult) []string {
+	var eligible []string
+	for _, nodeAddr := range nodeAddrs {
+		services := wire.ServiceFlag(nodeAddr.Services)
+		if !satisfiesRequiredServices(services) {
+			continue
+		}
+		eligible = append(eligible, nodeAddr.Address)
+	}
+	return eligible
+}
+
+// satisfiesRequiredServices determines whether the services signaled by a peer
+// satisfy our requirements for retrieving pruned blocks from them.
+func satisfiesRequiredServices(services wire.ServiceFlag) bool {
+	return services&requiredServices == requiredServices &&
+		services&prunedNodeService != prunedNodeService
+}
+
 // newQueryPeer creates a new peer instance configured to relay any received
 // messages to the internal workManager.
-func (d *PrunedBlockDispatcher) newQueryPeer(
+func (d *PrunedBlockDispatcher) newQueryPeer(addr string) (*queryPeer, error) {
-	peerInfo btcjson.GetPeerInfoResult) (*queryPeer, error) {
-
 	ready := make(chan struct{})
 	msgsRecvd := make(chan wire.Message)
 
@@ -409,7 +474,7 @@ func (d *PrunedBlockDispatcher) newQueryPeer(
 		},
 		AllowSelfConns: true,
 	}
-	p, err := peer.NewOutboundPeer(cfg, peerInfo.Addr)
+	p, err := peer.NewOutboundPeer(cfg, addr)
 	if err != nil {
 		return nil, err
 	}
@@ -422,35 +487,6 @@ func (d *PrunedBlockDispatcher) newQueryPeer(
 	}, nil
 }
 
-// connectToPeer attempts to establish a connection to the given peer and waits
-// up to PeerReadyTimeout for the version exchange to complete so that we can
-// begin sending it our queries.
-func (d *PrunedBlockDispatcher) connectToPeer(peer *queryPeer) error {
-	conn, err := d.cfg.Dial(peer.Addr())
-	if err != nil {
-		return err
-	}
-	peer.AssociateConnection(conn)
-
-	select {
-	case <-peer.ready:
-	case <-time.After(d.cfg.PeerReadyTimeout):
-		peer.Disconnect()
-		return errors.New("timed out waiting for protocol negotiation")
-	case <-d.quit:
-		return errors.New("shutting down")
-	}
-
-	// Remove the peer once it has disconnected.
-	peer.signalUponDisconnect(func() {
-		d.peerMtx.Lock()
-		delete(d.currentPeers, peer.Addr())
-		d.peerMtx.Unlock()
-	})
-
-	return nil
-}
-
 // banPeer bans a peer by disconnecting them and ensuring we don't reconnect.
 func (d *PrunedBlockDispatcher) banPeer(peer string) {
 	d.peerMtx.Lock()

chain/pruned_block_dispatcher_test.go

@@ -5,7 +5,6 @@ import (
 	"encoding/hex"
 	"fmt"
 	"net"
-	"os"
 	"sync"
 	"sync/atomic"
 	"testing"
@@ -16,18 +15,10 @@ import (
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/peer"
 	"github.com/btcsuite/btcd/wire"
-	"github.com/btcsuite/btclog"
 	"github.com/lightningnetwork/lnd/ticker"
 	"github.com/stretchr/testify/require"
 )
 
-func init() {
-	b := btclog.NewBackend(os.Stdout)
-	l := b.Logger("")
-	l.SetLevel(btclog.LevelTrace)
-	UseLogger(l)
-}
-
 var (
 	addrCounter int32 // Increased atomically.
 
@@ -51,10 +42,11 @@ type prunedBlockDispatcherHarness struct {
 
 	peerMtx       sync.Mutex
 	peers         map[string]*peer.Peer
+	fallbackAddrs map[string]*peer.Peer
 	localConns    map[string]net.Conn // Connections to peers.
 	remoteConns   map[string]net.Conn // Connections from peers.
 
-	dialedPeer    chan struct{}
+	dialedPeer    chan string
 	queriedPeer   chan struct{}
 	blocksQueried map[chainhash.Hash]int
 
@@ -68,22 +60,25 @@ func newNetworkBlockTestHarness(t *testing.T, numBlocks,
 
 	h := &prunedBlockDispatcherHarness{
 		t:             t,
+		dispatcher:    &PrunedBlockDispatcher{},
 		peers:         make(map[string]*peer.Peer, numPeers),
+		fallbackAddrs: make(map[string]*peer.Peer, numPeers),
 		localConns:    make(map[string]net.Conn, numPeers),
 		remoteConns:   make(map[string]net.Conn, numPeers),
-		dialedPeer:    make(chan struct{}),
+		dialedPeer:    make(chan string),
 		queriedPeer:   make(chan struct{}),
 		blocksQueried: make(map[chainhash.Hash]int),
+		shouldReply:   0,
 	}
 
 	h.hashes, h.blocks = genBlockChain(numBlocks)
 	for i := uint32(0); i < numPeers; i++ {
-		h.addPeer()
+		h.addPeer(false)
 	}
 
 	dial := func(addr string) (net.Conn, error) {
 		go func() {
-			h.dialedPeer <- struct{}{}
+			h.dialedPeer <- addr
 		}()
 
 		h.peerMtx.Lock()
@@ -98,7 +93,12 @@ func newNetworkBlockTestHarness(t *testing.T, numBlocks,
 			return nil, fmt.Errorf("remote conn %v not found", addr)
 		}
 
-		h.peers[addr].AssociateConnection(remoteConn)
+		if p, ok := h.peers[addr]; ok {
+			p.AssociateConnection(remoteConn)
+		}
+		if p, ok := h.fallbackAddrs[addr]; ok {
+			p.AssociateConnection(remoteConn)
+		}
 		return localConn, nil
 	}
 
@@ -126,6 +126,22 @@ func newNetworkBlockTestHarness(t *testing.T, numBlocks,
 
 			return res, nil
 		},
+		GetNodeAddresses: func(*int32) ([]btcjson.GetNodeAddressesResult, error) {
+			h.peerMtx.Lock()
+			defer h.peerMtx.Unlock()
+
+			res := make(
+				[]btcjson.GetNodeAddressesResult, 0,
+				len(h.fallbackAddrs),
+			)
+			for addr, peer := range h.fallbackAddrs {
+				res = append(res, btcjson.GetNodeAddressesResult{
+					Services: uint64(peer.Services()),
+					Address:  addr,
+				})
+			}
+			return res, nil
+		},
 		PeerReadyTimeout:   time.Hour,
 		RefreshPeersTicker: ticker.NewForce(time.Hour),
 		AllowSelfPeerConns: true,
@@ -175,20 +191,24 @@ func (h *prunedBlockDispatcherHarness) stop() {
 
 // addPeer adds a new random peer available for use by the
 // PrunedBlockDispatcher.
-func (h *prunedBlockDispatcherHarness) addPeer() string {
+func (h *prunedBlockDispatcherHarness) addPeer(fallback bool) string {
 	addr := nextAddr()
 
 	h.peerMtx.Lock()
 	defer h.peerMtx.Unlock()
 
-	h.resetPeer(addr)
+	h.resetPeer(addr, fallback)
 	return addr
 }
 
 // resetPeer resets the internal peer connection state allowing the
 // PrunedBlockDispatcher to establish a mock connection to it.
-func (h *prunedBlockDispatcherHarness) resetPeer(addr string) {
+func (h *prunedBlockDispatcherHarness) resetPeer(addr string, fallback bool) {
+	if fallback {
+		h.fallbackAddrs[addr] = h.newPeer()
+	} else {
 		h.peers[addr] = h.newPeer()
+	}
 
 	// Establish a mock connection between us and each peer.
 	inConn, outConn := pipe(
@@ -280,7 +300,7 @@ func (h *prunedBlockDispatcherHarness) refreshPeers() {
 }
 
 // disconnectPeer simulates a peer disconnecting from the PrunedBlockDispatcher.
-func (h *prunedBlockDispatcherHarness) disconnectPeer(addr string) {
+func (h *prunedBlockDispatcherHarness) disconnectPeer(addr string, fallback bool) {
 	h.t.Helper()
 
 	h.peerMtx.Lock()
@@ -303,7 +323,7 @@ func (h *prunedBlockDispatcherHarness) disconnectPeer(addr string) {
 	}, time.Second, 200*time.Millisecond)
 
 	// Reset the peer connection state to allow connections to them again.
-	h.resetPeer(addr)
+	h.resetPeer(addr, fallback)
 }
 
 // assertPeerDialed asserts that a connection was made to the given peer.
@@ -317,6 +337,18 @@ func (h *prunedBlockDispatcherHarness) assertPeerDialed() {
 	}
 }
 
+// assertPeerDialedWithAddr asserts that a connection was made to the given peer.
+func (h *prunedBlockDispatcherHarness) assertPeerDialedWithAddr(addr string) {
+	h.t.Helper()
+
+	select {
+	case dialedAddr := <-h.dialedPeer:
+		require.Equal(h.t, addr, dialedAddr)
+	case <-time.After(5 * time.Second):
+		h.t.Fatalf("expected peer to be dialed")
+	}
+}
+
 // assertPeerQueried asserts that query was sent to the given peer.
 func (h *prunedBlockDispatcherHarness) assertPeerQueried() {
 	h.t.Helper()
@@ -494,7 +526,7 @@ func TestPrunedBlockDispatcherMultipleQueryPeers(t *testing.T) {
 	// We should see one query per block.
 	for i := 0; i < numBlocks; i++ {
 		h.assertPeerQueried()
-		h.assertPeerReplied(blockChans[i], errChans[i], i == numBlocks-1)
+		h.assertPeerReplied(blockChans[i], errChans[i], true)
 	}
 }
 
@@ -523,13 +555,13 @@ func TestPrunedBlockDispatcherPeerPoller(t *testing.T) {
 	// We'll disable replies for now, as we'll want to test the disconnect
 	// case.
 	h.disablePeerReplies()
-	peer := h.addPeer()
+	peer := h.addPeer(false)
 	h.refreshPeers()
-	h.assertPeerDialed()
+	h.assertPeerDialedWithAddr(peer)
 	h.assertPeerQueried()
 
 	// Disconnect our peer and re-enable replies.
-	h.disconnectPeer(peer)
+	h.disconnectPeer(peer, false)
 	h.enablePeerReplies()
 	h.assertNoReply(blockChan, errChan)
 
@@ -539,11 +571,11 @@ func TestPrunedBlockDispatcherPeerPoller(t *testing.T) {
 	h.assertPeerDialed()
 	h.assertPeerQueried()
 
-	// Refresh our peers again. We can afford to have one more query peer,
+	// Add a fallback addresses and force refresh our peers again. We can
-	// but there isn't another one available. We also shouldn't dial the one
+	// afford to have one more query peer, so a connection should be made.
-	// we're currently connected to again.
+	fallbackPeer := h.addPeer(true)
 	h.refreshPeers()
-	h.assertNoPeerDialed()
+	h.assertPeerDialedWithAddr(fallbackPeer)
 
 	// Now that we know we've connected to the peer, we should be able to
 	// receive their response.
@@ -578,7 +610,7 @@ func TestPrunedBlockDispatcherInvalidBlock(t *testing.T) {
 
 	// Signal to our peers to send valid replies and add a new peer.
 	h.enablePeerReplies()
-	_ = h.addPeer()
+	_ = h.addPeer(false)
 
 	// Force a refresh, which should cause our new peer to be dialed and
 	// queried. We expect them to send a valid block and fulfill our