lnd.xprv/watchtower/wtdb/client_db.go

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package wtdb
import (
"bytes"
"errors"
"fmt"
"math"
"net"
"github.com/coreos/bbolt"
"github.com/lightningnetwork/lnd/lnwire"
)
const (
// clientDBName is the filename of client database.
clientDBName = "wtclient.db"
)
var (
// cSessionKeyIndexBkt is a top-level bucket storing:
// tower-id -> reserved-session-key-index (uint32).
cSessionKeyIndexBkt = []byte("client-session-key-index-bucket")
// cChanSummaryBkt is a top-level bucket storing:
// channel-id -> encoded ClientChanSummary.
cChanSummaryBkt = []byte("client-channel-summary-bucket")
// cSessionBkt is a top-level bucket storing:
// session-id => cSessionBody -> encoded ClientSessionBody
// => cSessionCommits => seqnum -> encoded CommittedUpdate
// => cSessionAcks => seqnum -> encoded BackupID
cSessionBkt = []byte("client-session-bucket")
// cSessionBody is a sub-bucket of cSessionBkt storing only the body of
// the ClientSession.
cSessionBody = []byte("client-session-body")
// cSessionBody is a sub-bucket of cSessionBkt storing:
// seqnum -> encoded CommittedUpdate.
cSessionCommits = []byte("client-session-commits")
// cSessionAcks is a sub-bucket of cSessionBkt storing:
// seqnum -> encoded BackupID.
cSessionAcks = []byte("client-session-acks")
// cTowerBkt is a top-level bucket storing:
// tower-id -> encoded Tower.
cTowerBkt = []byte("client-tower-bucket")
// cTowerIndexBkt is a top-level bucket storing:
// tower-pubkey -> tower-id.
cTowerIndexBkt = []byte("client-tower-index-bucket")
// ErrTowerNotFound signals that the target tower was not found in the
// database.
ErrTowerNotFound = errors.New("tower not found")
// ErrCorruptClientSession signals that the client session's on-disk
// structure deviates from what is expected.
ErrCorruptClientSession = errors.New("client session corrupted")
// ErrClientSessionAlreadyExists signals an attempt to reinsert a client
// session that has already been created.
ErrClientSessionAlreadyExists = errors.New(
"client session already exists",
)
// ErrChannelAlreadyRegistered signals a duplicate attempt to register a
// channel with the client database.
ErrChannelAlreadyRegistered = errors.New("channel already registered")
// ErrChannelNotRegistered signals a channel has not yet been registered
// in the client database.
ErrChannelNotRegistered = errors.New("channel not registered")
// ErrClientSessionNotFound signals that the requested client session
// was not found in the database.
ErrClientSessionNotFound = errors.New("client session not found")
// ErrUpdateAlreadyCommitted signals that the chosen sequence number has
// already been committed to an update with a different breach hint.
ErrUpdateAlreadyCommitted = errors.New("update already committed")
// ErrCommitUnorderedUpdate signals the client tried to commit a
// sequence number other than the next unallocated sequence number.
ErrCommitUnorderedUpdate = errors.New("update seqnum not monotonic")
// ErrCommittedUpdateNotFound signals that the tower tried to ACK a
// sequence number that has not yet been allocated by the client.
ErrCommittedUpdateNotFound = errors.New("committed update not found")
// ErrUnallocatedLastApplied signals that the tower tried to provide a
// LastApplied value greater than any allocated sequence number.
ErrUnallocatedLastApplied = errors.New("tower echoed last appiled " +
"greater than allocated seqnum")
// ErrNoReservedKeyIndex signals that a client session could not be
// created because no session key index was reserved.
ErrNoReservedKeyIndex = errors.New("key index not reserved")
// ErrIncorrectKeyIndex signals that the client session could not be
// created because session key index differs from the reserved key
// index.
ErrIncorrectKeyIndex = errors.New("incorrect key index")
)
// ClientDB is single database providing a persistent storage engine for the
// wtclient.
type ClientDB struct {
db *bbolt.DB
dbPath string
}
// OpenClientDB opens the client database given the path to the database's
// directory. If no such database exists, this method will initialize a fresh
// one using the latest version number and bucket structure. If a database
// exists but has a lower version number than the current version, any necessary
// migrations will be applied before returning. Any attempt to open a database
// with a version number higher that the latest version will fail to prevent
// accidental reversion.
func OpenClientDB(dbPath string) (*ClientDB, error) {
bdb, firstInit, err := createDBIfNotExist(dbPath, clientDBName)
if err != nil {
return nil, err
}
clientDB := &ClientDB{
db: bdb,
dbPath: dbPath,
}
err = initOrSyncVersions(clientDB, firstInit, clientDBVersions)
if err != nil {
bdb.Close()
return nil, err
}
// Now that the database version fully consistent with our latest known
// version, ensure that all top-level buckets known to this version are
// initialized. This allows us to assume their presence throughout all
// operations. If an known top-level bucket is expected to exist but is
// missing, this will trigger a ErrUninitializedDB error.
err = clientDB.db.Update(initClientDBBuckets)
if err != nil {
bdb.Close()
return nil, err
}
return clientDB, nil
}
// initClientDBBuckets creates all top-level buckets required to handle database
// operations required by the latest version.
func initClientDBBuckets(tx *bbolt.Tx) error {
buckets := [][]byte{
cSessionKeyIndexBkt,
cChanSummaryBkt,
cSessionBkt,
cTowerBkt,
cTowerIndexBkt,
}
for _, bucket := range buckets {
_, err := tx.CreateBucketIfNotExists(bucket)
if err != nil {
return err
}
}
return nil
}
// bdb returns the backing bbolt.DB instance.
//
// NOTE: Part of the versionedDB interface.
func (c *ClientDB) bdb() *bbolt.DB {
return c.db
}
// Version returns the database's current version number.
//
// NOTE: Part of the versionedDB interface.
func (c *ClientDB) Version() (uint32, error) {
var version uint32
err := c.db.View(func(tx *bbolt.Tx) error {
var err error
version, err = getDBVersion(tx)
return err
})
if err != nil {
return 0, err
}
return version, nil
}
// Close closes the underlying database.
func (c *ClientDB) Close() error {
return c.db.Close()
}
// CreateTower initializes a database entry with the given lightning address. If
// the tower exists, the address is append to the list of all addresses used to
// that tower previously.
func (c *ClientDB) CreateTower(lnAddr *lnwire.NetAddress) (*Tower, error) {
var towerPubKey [33]byte
copy(towerPubKey[:], lnAddr.IdentityKey.SerializeCompressed())
var tower *Tower
err := c.db.Update(func(tx *bbolt.Tx) error {
towerIndex := tx.Bucket(cTowerIndexBkt)
if towerIndex == nil {
return ErrUninitializedDB
}
towers := tx.Bucket(cTowerBkt)
if towers == nil {
return ErrUninitializedDB
}
// Check if the tower index already knows of this pubkey.
towerIDBytes := towerIndex.Get(towerPubKey[:])
if len(towerIDBytes) == 8 {
// The tower already exists, deserialize the existing
// record.
var err error
tower, err = getTower(towers, towerIDBytes)
if err != nil {
return err
}
// Add the new address to the existing tower. If the
// address is a duplicate, this will result in no
// change.
tower.AddAddress(lnAddr.Address)
} else {
// No such tower exists, create a new tower id for our
// new tower. The error is unhandled since NextSequence
// never fails in an Update.
towerID, _ := towerIndex.NextSequence()
tower = &Tower{
ID: TowerID(towerID),
IdentityKey: lnAddr.IdentityKey,
Addresses: []net.Addr{lnAddr.Address},
}
towerIDBytes = tower.ID.Bytes()
// Since this tower is new, record the mapping from
// tower pubkey to tower id in the tower index.
err := towerIndex.Put(towerPubKey[:], towerIDBytes)
if err != nil {
return err
}
}
// Store the new or updated tower under its tower id.
return putTower(towers, tower)
})
if err != nil {
return nil, err
}
return tower, nil
}
// LoadTower retrieves a tower by its tower ID.
func (c *ClientDB) LoadTower(towerID TowerID) (*Tower, error) {
var tower *Tower
err := c.db.View(func(tx *bbolt.Tx) error {
towers := tx.Bucket(cTowerBkt)
if towers == nil {
return ErrUninitializedDB
}
var err error
tower, err = getTower(towers, towerID.Bytes())
return err
})
if err != nil {
return nil, err
}
return tower, nil
}
// NextSessionKeyIndex reserves a new session key derivation index for a
// particular tower id. The index is reserved for that tower until
// CreateClientSession is invoked for that tower and index, at which point a new
// index for that tower can be reserved. Multiple calls to this method before
// CreateClientSession is invoked should return the same index.
func (c *ClientDB) NextSessionKeyIndex(towerID TowerID) (uint32, error) {
var index uint32
err := c.db.Update(func(tx *bbolt.Tx) error {
keyIndex := tx.Bucket(cSessionKeyIndexBkt)
if keyIndex == nil {
return ErrUninitializedDB
}
// Check the session key index to see if a key has already been
// reserved for this tower. If so, we'll deserialize and return
// the index directly.
towerIDBytes := towerID.Bytes()
indexBytes := keyIndex.Get(towerIDBytes)
if len(indexBytes) == 4 {
index = byteOrder.Uint32(indexBytes)
return nil
}
// Otherwise, generate a new session key index since the node
// doesn't already have reserved index. The error is ignored
// since NextSequence can't fail inside Update.
index64, _ := keyIndex.NextSequence()
// As a sanity check, assert that the index is still in the
// valid range of unhardened pubkeys. In the future, we should
// move to only using hardened keys, and this will prevent any
// overlap from occurring until then. This also prevents us from
// overflowing uint32s.
if index64 > math.MaxInt32 {
return fmt.Errorf("exhausted session key indexes")
}
index = uint32(index64)
var indexBuf [4]byte
byteOrder.PutUint32(indexBuf[:], index)
// Record the reserved session key index under this tower's id.
return keyIndex.Put(towerIDBytes, indexBuf[:])
})
if err != nil {
return 0, err
}
return index, nil
}
// CreateClientSession records a newly negotiated client session in the set of
// active sessions. The session can be identified by its SessionID.
func (c *ClientDB) CreateClientSession(session *ClientSession) error {
return c.db.Update(func(tx *bbolt.Tx) error {
keyIndexes := tx.Bucket(cSessionKeyIndexBkt)
if keyIndexes == nil {
return ErrUninitializedDB
}
sessions := tx.Bucket(cSessionBkt)
if sessions == nil {
return ErrUninitializedDB
}
// Check that client session with this session id doesn't
// already exist.
existingSessionBytes := sessions.Bucket(session.ID[:])
if existingSessionBytes != nil {
return ErrClientSessionAlreadyExists
}
// Check that this tower has a reserved key index.
towerIDBytes := session.TowerID.Bytes()
keyIndexBytes := keyIndexes.Get(towerIDBytes)
if len(keyIndexBytes) != 4 {
return ErrNoReservedKeyIndex
}
// Assert that the key index of the inserted session matches the
// reserved session key index.
index := byteOrder.Uint32(keyIndexBytes)
if index != session.KeyIndex {
return ErrIncorrectKeyIndex
}
// Remove the key index reservation.
err := keyIndexes.Delete(towerIDBytes)
if err != nil {
return err
}
// Finally, write the client session's body in the sessions
// bucket.
return putClientSessionBody(sessions, session)
})
}
// ListClientSessions returns the set of all client sessions known to the db.
func (c *ClientDB) ListClientSessions() (map[SessionID]*ClientSession, error) {
clientSessions := make(map[SessionID]*ClientSession)
err := c.db.View(func(tx *bbolt.Tx) error {
sessions := tx.Bucket(cSessionBkt)
if sessions == nil {
return ErrUninitializedDB
}
return sessions.ForEach(func(k, _ []byte) error {
// We'll load the full client session since the client
// will need the CommittedUpdates and AckedUpdates on
// startup to resume committed updates and compute the
// highest known commit height for each channel.
session, err := getClientSession(sessions, k)
if err != nil {
return err
}
clientSessions[session.ID] = session
return nil
})
})
if err != nil {
return nil, err
}
return clientSessions, nil
}
// FetchChanSummaries loads a mapping from all registered channels to their
// channel summaries.
func (c *ClientDB) FetchChanSummaries() (ChannelSummaries, error) {
summaries := make(map[lnwire.ChannelID]ClientChanSummary)
err := c.db.View(func(tx *bbolt.Tx) error {
chanSummaries := tx.Bucket(cChanSummaryBkt)
if chanSummaries == nil {
return ErrUninitializedDB
}
return chanSummaries.ForEach(func(k, v []byte) error {
var chanID lnwire.ChannelID
copy(chanID[:], k)
var summary ClientChanSummary
err := summary.Decode(bytes.NewReader(v))
if err != nil {
return err
}
summaries[chanID] = summary
return nil
})
})
if err != nil {
return nil, err
}
return summaries, nil
}
// RegisterChannel registers a channel for use within the client database. For
// now, all that is stored in the channel summary is the sweep pkscript that
// we'd like any tower sweeps to pay into. In the future, this will be extended
// to contain more info to allow the client efficiently request historical
// states to be backed up under the client's active policy.
func (c *ClientDB) RegisterChannel(chanID lnwire.ChannelID,
sweepPkScript []byte) error {
return c.db.Update(func(tx *bbolt.Tx) error {
chanSummaries := tx.Bucket(cChanSummaryBkt)
if chanSummaries == nil {
return ErrUninitializedDB
}
_, err := getChanSummary(chanSummaries, chanID)
switch {
// Summary already exists.
case err == nil:
return ErrChannelAlreadyRegistered
// Channel is not registered, proceed with registration.
case err == ErrChannelNotRegistered:
// Unexpected error.
case err != nil:
return err
}
summary := ClientChanSummary{
SweepPkScript: sweepPkScript,
}
return putChanSummary(chanSummaries, chanID, &summary)
})
}
// MarkBackupIneligible records that the state identified by the (channel id,
// commit height) tuple was ineligible for being backed up under the current
// policy. This state can be retried later under a different policy.
func (c *ClientDB) MarkBackupIneligible(chanID lnwire.ChannelID,
commitHeight uint64) error {
return nil
}
// CommitUpdate persists the CommittedUpdate provided in the slot for (session,
// seqNum). This allows the client to retransmit this update on startup.
func (c *ClientDB) CommitUpdate(id *SessionID,
update *CommittedUpdate) (uint16, error) {
var lastApplied uint16
err := c.db.Update(func(tx *bbolt.Tx) error {
sessions := tx.Bucket(cSessionBkt)
if sessions == nil {
return ErrUninitializedDB
}
// We'll only load the ClientSession body for performance, since
// we primarily need to inspect its SeqNum and TowerLastApplied
// fields. The CommittedUpdates will be modified on disk
// directly.
session, err := getClientSessionBody(sessions, id[:])
if err != nil {
return err
}
// Can't fail if the above didn't fail.
sessionBkt := sessions.Bucket(id[:])
// Ensure the session commits sub-bucket is initialized.
sessionCommits, err := sessionBkt.CreateBucketIfNotExists(
cSessionCommits,
)
if err != nil {
return err
}
var seqNumBuf [2]byte
byteOrder.PutUint16(seqNumBuf[:], update.SeqNum)
// Check to see if a committed update already exists for this
// sequence number.
committedUpdateBytes := sessionCommits.Get(seqNumBuf[:])
if committedUpdateBytes != nil {
var dbUpdate CommittedUpdate
err := dbUpdate.Decode(
bytes.NewReader(committedUpdateBytes),
)
if err != nil {
return err
}
// If an existing committed update has a different hint,
// we'll reject this newer update.
if dbUpdate.Hint != update.Hint {
return ErrUpdateAlreadyCommitted
}
// Otherwise, capture the last applied value and
// succeed.
lastApplied = session.TowerLastApplied
return nil
}
// There's no committed update for this sequence number, ensure
// that we are committing the next unallocated one.
if update.SeqNum != session.SeqNum+1 {
return ErrCommitUnorderedUpdate
}
// Increment the session's sequence number and store the updated
// client session.
//
// TODO(conner): split out seqnum and last applied own bucket to
// eliminate serialization of full struct during CommitUpdate?
// Can also read/write directly to byes [:2] without migration.
session.SeqNum++
err = putClientSessionBody(sessions, session)
if err != nil {
return err
}
// Encode and store the committed update in the sessionCommits
// sub-bucket under the requested sequence number.
var b bytes.Buffer
err = update.Encode(&b)
if err != nil {
return err
}
err = sessionCommits.Put(seqNumBuf[:], b.Bytes())
if err != nil {
return err
}
// Finally, capture the session's last applied value so it can
// be sent in the next state update to the tower.
lastApplied = session.TowerLastApplied
return nil
})
if err != nil {
return 0, err
}
return lastApplied, nil
}
// AckUpdate persists an acknowledgment for a given (session, seqnum) pair. This
// removes the update from the set of committed updates, and validates the
// lastApplied value returned from the tower.
func (c *ClientDB) AckUpdate(id *SessionID, seqNum uint16,
lastApplied uint16) error {
return c.db.Update(func(tx *bbolt.Tx) error {
sessions := tx.Bucket(cSessionBkt)
if sessions == nil {
return ErrUninitializedDB
}
// We'll only load the ClientSession body for performance, since
// we primarily need to inspect its SeqNum and TowerLastApplied
// fields. The CommittedUpdates and AckedUpdates will be
// modified on disk directly.
session, err := getClientSessionBody(sessions, id[:])
if err != nil {
return err
}
// If the tower has acked a sequence number beyond our highest
// sequence number, fail.
if lastApplied > session.SeqNum {
return ErrUnallocatedLastApplied
}
// If the tower acked with a lower sequence number than it gave
// us prior, fail.
if lastApplied < session.TowerLastApplied {
return ErrLastAppliedReversion
}
// TODO(conner): split out seqnum and last applied own bucket to
// eliminate serialization of full struct during AckUpdate? Can
// also read/write directly to byes [2:4] without migration.
session.TowerLastApplied = lastApplied
// Write the client session with the updated last applied value.
err = putClientSessionBody(sessions, session)
if err != nil {
return err
}
// Can't fail because of getClientSession succeeded.
sessionBkt := sessions.Bucket(id[:])
// If the commits sub-bucket doesn't exist, there can't possibly
// be a corresponding committed update to remove.
sessionCommits := sessionBkt.Bucket(cSessionCommits)
if sessionCommits == nil {
return ErrCommittedUpdateNotFound
}
var seqNumBuf [2]byte
byteOrder.PutUint16(seqNumBuf[:], seqNum)
// Assert that a committed update exists for this sequence
// number.
committedUpdateBytes := sessionCommits.Get(seqNumBuf[:])
if committedUpdateBytes == nil {
return ErrCommittedUpdateNotFound
}
var committedUpdate CommittedUpdate
err = committedUpdate.Decode(
bytes.NewReader(committedUpdateBytes),
)
if err != nil {
return err
}
// Remove the corresponding committed update.
err = sessionCommits.Delete(seqNumBuf[:])
if err != nil {
return err
}
// Ensure that the session acks sub-bucket is initialized so we
// can insert an entry.
sessionAcks, err := sessionBkt.CreateBucketIfNotExists(
cSessionAcks,
)
if err != nil {
return err
}
// The session acks only need to track the backup id of the
// update, so we can discard the blob and hint.
var b bytes.Buffer
err = committedUpdate.BackupID.Encode(&b)
if err != nil {
return err
}
// Finally, insert the ack into the sessionAcks sub-bucket.
return sessionAcks.Put(seqNumBuf[:], b.Bytes())
})
}
// getClientSessionBody loads the body of a ClientSession from the sessions
// bucket corresponding to the serialized session id. This does not deserialize
// the CommittedUpdates or AckUpdates associated with the session. If the caller
// requires this info, use getClientSession.
func getClientSessionBody(sessions *bbolt.Bucket,
idBytes []byte) (*ClientSession, error) {
sessionBkt := sessions.Bucket(idBytes)
if sessionBkt == nil {
return nil, ErrClientSessionNotFound
}
// Should never have a sessionBkt without also having its body.
sessionBody := sessionBkt.Get(cSessionBody)
if sessionBody == nil {
return nil, ErrCorruptClientSession
}
var session ClientSession
copy(session.ID[:], idBytes)
err := session.Decode(bytes.NewReader(sessionBody))
if err != nil {
return nil, err
}
return &session, nil
}
// getClientSession loads the full ClientSession associated with the serialized
// session id. This method populates the CommittedUpdates and AckUpdates in
// addition to the ClientSession's body.
func getClientSession(sessions *bbolt.Bucket,
idBytes []byte) (*ClientSession, error) {
session, err := getClientSessionBody(sessions, idBytes)
if err != nil {
return nil, err
}
// Fetch the committed updates for this session.
commitedUpdates, err := getClientSessionCommits(sessions, idBytes)
if err != nil {
return nil, err
}
// Fetch the acked updates for this session.
ackedUpdates, err := getClientSessionAcks(sessions, idBytes)
if err != nil {
return nil, err
}
session.CommittedUpdates = commitedUpdates
session.AckedUpdates = ackedUpdates
return session, nil
}
// getClientSessionCommits retrieves all committed updates for the session
// identified by the serialized session id.
func getClientSessionCommits(sessions *bbolt.Bucket,
idBytes []byte) ([]CommittedUpdate, error) {
// Can't fail because client session body has already been read.
sessionBkt := sessions.Bucket(idBytes)
// Initialize commitedUpdates so that we can return an initialized map
// if no committed updates exist.
committedUpdates := make([]CommittedUpdate, 0)
sessionCommits := sessionBkt.Bucket(cSessionCommits)
if sessionCommits == nil {
return committedUpdates, nil
}
err := sessionCommits.ForEach(func(k, v []byte) error {
var committedUpdate CommittedUpdate
err := committedUpdate.Decode(bytes.NewReader(v))
if err != nil {
return err
}
committedUpdate.SeqNum = byteOrder.Uint16(k)
committedUpdates = append(committedUpdates, committedUpdate)
return nil
})
if err != nil {
return nil, err
}
return committedUpdates, nil
}
// getClientSessionAcks retrieves all acked updates for the session identified
// by the serialized session id.
func getClientSessionAcks(sessions *bbolt.Bucket,
idBytes []byte) (map[uint16]BackupID, error) {
// Can't fail because client session body has already been read.
sessionBkt := sessions.Bucket(idBytes)
// Initialize ackedUpdates so that we can return an initialized map if
// no acked updates exist.
ackedUpdates := make(map[uint16]BackupID)
sessionAcks := sessionBkt.Bucket(cSessionAcks)
if sessionAcks == nil {
return ackedUpdates, nil
}
err := sessionAcks.ForEach(func(k, v []byte) error {
seqNum := byteOrder.Uint16(k)
var backupID BackupID
err := backupID.Decode(bytes.NewReader(v))
if err != nil {
return err
}
ackedUpdates[seqNum] = backupID
return nil
})
if err != nil {
return nil, err
}
return ackedUpdates, nil
}
// putClientSessionBody stores the body of the ClientSession (everything but the
// CommittedUpdates and AckedUpdates).
func putClientSessionBody(sessions *bbolt.Bucket,
session *ClientSession) error {
sessionBkt, err := sessions.CreateBucketIfNotExists(session.ID[:])
if err != nil {
return err
}
var b bytes.Buffer
err = session.Encode(&b)
if err != nil {
return err
}
return sessionBkt.Put(cSessionBody, b.Bytes())
}
// getChanSummary loads a ClientChanSummary for the passed chanID.
func getChanSummary(chanSummaries *bbolt.Bucket,
chanID lnwire.ChannelID) (*ClientChanSummary, error) {
chanSummaryBytes := chanSummaries.Get(chanID[:])
if chanSummaryBytes == nil {
return nil, ErrChannelNotRegistered
}
var summary ClientChanSummary
err := summary.Decode(bytes.NewReader(chanSummaryBytes))
if err != nil {
return nil, err
}
return &summary, nil
}
// putChanSummary stores a ClientChanSummary for the passed chanID.
func putChanSummary(chanSummaries *bbolt.Bucket, chanID lnwire.ChannelID,
summary *ClientChanSummary) error {
var b bytes.Buffer
err := summary.Encode(&b)
if err != nil {
return err
}
return chanSummaries.Put(chanID[:], b.Bytes())
}
// getTower loads a Tower identified by its serialized tower id.
func getTower(towers *bbolt.Bucket, id []byte) (*Tower, error) {
towerBytes := towers.Get(id)
if towerBytes == nil {
return nil, ErrTowerNotFound
}
var tower Tower
err := tower.Decode(bytes.NewReader(towerBytes))
if err != nil {
return nil, err
}
tower.ID = TowerIDFromBytes(id)
return &tower, nil
}
// putTower stores a Tower identified by its serialized tower id.
func putTower(towers *bbolt.Bucket, tower *Tower) error {
var b bytes.Buffer
err := tower.Encode(&b)
if err != nil {
return err
}
return towers.Put(tower.ID.Bytes(), b.Bytes())
}