lnd.xprv/channeldb/witness_cache.go

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package channeldb
import (
"fmt"
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"github.com/lightningnetwork/lnd/kvdb"
"github.com/lightningnetwork/lnd/lntypes"
)
var (
// ErrNoWitnesses is an error that's returned when no new witnesses have
// been added to the WitnessCache.
ErrNoWitnesses = fmt.Errorf("no witnesses")
// ErrUnknownWitnessType is returned if a caller attempts to
ErrUnknownWitnessType = fmt.Errorf("unknown witness type")
)
// WitnessType is enum that denotes what "type" of witness is being
// stored/retrieved. As the WitnessCache itself is agnostic and doesn't enforce
// any structure on added witnesses, we use this type to partition the
// witnesses on disk, and also to know how to map a witness to its look up key.
type WitnessType uint8
var (
// Sha256HashWitness is a witness that is simply the pre image to a
// hash image. In order to map to its key, we'll use sha256.
Sha256HashWitness WitnessType = 1
)
// toDBKey is a helper method that maps a witness type to the key that we'll
// use to store it within the database.
func (w WitnessType) toDBKey() ([]byte, error) {
switch w {
case Sha256HashWitness:
return []byte{byte(w)}, nil
default:
return nil, ErrUnknownWitnessType
}
}
var (
// witnessBucketKey is the name of the bucket that we use to store all
// witnesses encountered. Within this bucket, we'll create a sub-bucket for
// each witness type.
witnessBucketKey = []byte("byte")
)
// WitnessCache is a persistent cache of all witnesses we've encountered on the
// network. In the case of multi-hop, multi-step contracts, a cache of all
// witnesses can be useful in the case of partial contract resolution. If
// negotiations break down, we may be forced to locate the witness for a
// portion of the contract on-chain. In this case, we'll then add that witness
// to the cache so the incoming contract can fully resolve witness.
// Additionally, as one MUST always use a unique witness on the network, we may
// use this cache to detect duplicate witnesses.
//
// TODO(roasbeef): need expiry policy?
// * encrypt?
type WitnessCache struct {
db *DB
}
// NewWitnessCache returns a new instance of the witness cache.
func (d *DB) NewWitnessCache() *WitnessCache {
return &WitnessCache{
db: d,
}
}
// witnessEntry is a key-value struct that holds each key -> witness pair, used
// when inserting records into the cache.
type witnessEntry struct {
key []byte
witness []byte
}
// AddSha256Witnesses adds a batch of new sha256 preimages into the witness
// cache. This is an alias for AddWitnesses that uses Sha256HashWitness as the
// preimages' witness type.
func (w *WitnessCache) AddSha256Witnesses(preimages ...lntypes.Preimage) error {
// Optimistically compute the preimages' hashes before attempting to
// start the db transaction.
entries := make([]witnessEntry, 0, len(preimages))
for i := range preimages {
hash := preimages[i].Hash()
entries = append(entries, witnessEntry{
key: hash[:],
witness: preimages[i][:],
})
}
return w.addWitnessEntries(Sha256HashWitness, entries)
}
// addWitnessEntries inserts the witnessEntry key-value pairs into the cache,
// using the appropriate witness type to segment the namespace of possible
// witness types.
func (w *WitnessCache) addWitnessEntries(wType WitnessType,
entries []witnessEntry) error {
// Exit early if there are no witnesses to add.
if len(entries) == 0 {
return nil
}
return kvdb.Batch(w.db.Backend, func(tx kvdb.RwTx) error {
witnessBucket, err := tx.CreateTopLevelBucket(witnessBucketKey)
if err != nil {
return err
}
witnessTypeBucketKey, err := wType.toDBKey()
if err != nil {
return err
}
witnessTypeBucket, err := witnessBucket.CreateBucketIfNotExists(
witnessTypeBucketKey,
)
if err != nil {
return err
}
for _, entry := range entries {
err = witnessTypeBucket.Put(entry.key, entry.witness)
if err != nil {
return err
}
}
return nil
})
}
// LookupSha256Witness attempts to lookup the preimage for a sha256 hash. If
// the witness isn't found, ErrNoWitnesses will be returned.
func (w *WitnessCache) LookupSha256Witness(hash lntypes.Hash) (lntypes.Preimage, error) {
witness, err := w.lookupWitness(Sha256HashWitness, hash[:])
if err != nil {
return lntypes.Preimage{}, err
}
return lntypes.MakePreimage(witness)
}
// lookupWitness attempts to lookup a witness according to its type and also
// its witness key. In the case that the witness isn't found, ErrNoWitnesses
// will be returned.
func (w *WitnessCache) lookupWitness(wType WitnessType, witnessKey []byte) ([]byte, error) {
var witness []byte
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err := kvdb.View(w.db, func(tx kvdb.RTx) error {
witnessBucket := tx.ReadBucket(witnessBucketKey)
if witnessBucket == nil {
return ErrNoWitnesses
}
witnessTypeBucketKey, err := wType.toDBKey()
if err != nil {
return err
}
witnessTypeBucket := witnessBucket.NestedReadBucket(witnessTypeBucketKey)
if witnessTypeBucket == nil {
return ErrNoWitnesses
}
dbWitness := witnessTypeBucket.Get(witnessKey)
if dbWitness == nil {
return ErrNoWitnesses
}
witness = make([]byte, len(dbWitness))
copy(witness[:], dbWitness)
return nil
}, func() {
witness = nil
})
if err != nil {
return nil, err
}
return witness, nil
}
// DeleteSha256Witness attempts to delete a sha256 preimage identified by hash.
func (w *WitnessCache) DeleteSha256Witness(hash lntypes.Hash) error {
return w.deleteWitness(Sha256HashWitness, hash[:])
}
// deleteWitness attempts to delete a particular witness from the database.
func (w *WitnessCache) deleteWitness(wType WitnessType, witnessKey []byte) error {
return kvdb.Batch(w.db.Backend, func(tx kvdb.RwTx) error {
witnessBucket, err := tx.CreateTopLevelBucket(witnessBucketKey)
if err != nil {
return err
}
witnessTypeBucketKey, err := wType.toDBKey()
if err != nil {
return err
}
witnessTypeBucket, err := witnessBucket.CreateBucketIfNotExists(
witnessTypeBucketKey,
)
if err != nil {
return err
}
return witnessTypeBucket.Delete(witnessKey)
})
}
// DeleteWitnessClass attempts to delete an *entire* class of witnesses. After
// this function return with a non-nil error,
func (w *WitnessCache) DeleteWitnessClass(wType WitnessType) error {
return kvdb.Batch(w.db.Backend, func(tx kvdb.RwTx) error {
witnessBucket, err := tx.CreateTopLevelBucket(witnessBucketKey)
if err != nil {
return err
}
witnessTypeBucketKey, err := wType.toDBKey()
if err != nil {
return err
}
return witnessBucket.DeleteNestedBucket(witnessTypeBucketKey)
})
}