package htlcswitch import ( "bytes" "encoding/binary" "errors" "io" "sync" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/channeldb/kvdb" "github.com/lightningnetwork/lnd/lnwire" "github.com/lightningnetwork/lnd/multimutex" ) var ( // networkResultStoreBucketKey is used for the root level bucket that // stores the network result for each payment ID. networkResultStoreBucketKey = []byte("network-result-store-bucket") // ErrPaymentIDNotFound is an error returned if the given paymentID is // not found. ErrPaymentIDNotFound = errors.New("paymentID not found") // ErrPaymentIDAlreadyExists is returned if we try to write a pending // payment whose paymentID already exists. ErrPaymentIDAlreadyExists = errors.New("paymentID already exists") ) // PaymentResult wraps a decoded result received from the network after a // payment attempt was made. This is what is eventually handed to the router // for processing. type PaymentResult struct { // Preimage is set by the switch in case a sent HTLC was settled. Preimage [32]byte // Error is non-nil in case a HTLC send failed, and the HTLC is now // irrevocably canceled. If the payment failed during forwarding, this // error will be a *ForwardingError. Error error } // networkResult is the raw result received from the network after a payment // attempt has been made. Since the switch doesn't always have the necessary // data to decode the raw message, we store it together with some meta data, // and decode it when the router query for the final result. type networkResult struct { // msg is the received result. This should be of type UpdateFulfillHTLC // or UpdateFailHTLC. msg lnwire.Message // unencrypted indicates whether the failure encoded in the message is // unencrypted, and hence doesn't need to be decrypted. unencrypted bool // isResolution indicates whether this is a resolution message, in // which the failure reason might not be included. isResolution bool } // serializeNetworkResult serializes the networkResult. func serializeNetworkResult(w io.Writer, n *networkResult) error { if _, err := lnwire.WriteMessage(w, n.msg, 0); err != nil { return err } return channeldb.WriteElements(w, n.unencrypted, n.isResolution) } // deserializeNetworkResult deserializes the networkResult. func deserializeNetworkResult(r io.Reader) (*networkResult, error) { var ( err error ) n := &networkResult{} n.msg, err = lnwire.ReadMessage(r, 0) if err != nil { return nil, err } if err := channeldb.ReadElements(r, &n.unencrypted, &n.isResolution, ); err != nil { return nil, err } return n, nil } // networkResultStore is a persistent store that stores any results of HTLCs in // flight on the network. Since payment results are inherently asynchronous, it // is used as a common access point for senders of HTLCs, to know when a result // is back. The Switch will checkpoint any received result to the store, and // the store will keep results and notify the callers about them. type networkResultStore struct { db *channeldb.DB // results is a map from paymentIDs to channels where subscribers to // payment results will be notified. results map[uint64][]chan *networkResult resultsMtx sync.Mutex // paymentIDMtx is a multimutex used to make sure the database and // result subscribers map is consistent for each payment ID in case of // concurrent callers. paymentIDMtx *multimutex.Mutex } func newNetworkResultStore(db *channeldb.DB) *networkResultStore { return &networkResultStore{ db: db, results: make(map[uint64][]chan *networkResult), paymentIDMtx: multimutex.NewMutex(), } } // storeResult stores the networkResult for the given paymentID, and // notifies any subscribers. func (store *networkResultStore) storeResult(paymentID uint64, result *networkResult) error { // We get a mutex for this payment ID. This is needed to ensure // consistency between the database state and the subscribers in case // of concurrent calls. store.paymentIDMtx.Lock(paymentID) defer store.paymentIDMtx.Unlock(paymentID) // Serialize the payment result. var b bytes.Buffer if err := serializeNetworkResult(&b, result); err != nil { return err } var paymentIDBytes [8]byte binary.BigEndian.PutUint64(paymentIDBytes[:], paymentID) err := kvdb.Batch(store.db.Backend, func(tx kvdb.RwTx) error { networkResults, err := tx.CreateTopLevelBucket( networkResultStoreBucketKey, ) if err != nil { return err } return networkResults.Put(paymentIDBytes[:], b.Bytes()) }) if err != nil { return err } // Now that the result is stored in the database, we can notify any // active subscribers. store.resultsMtx.Lock() for _, res := range store.results[paymentID] { res <- result } delete(store.results, paymentID) store.resultsMtx.Unlock() return nil } // subscribeResult is used to get the payment result for the given // payment ID. It returns a channel on which the result will be delivered when // ready. func (store *networkResultStore) subscribeResult(paymentID uint64) ( <-chan *networkResult, error) { // We get a mutex for this payment ID. This is needed to ensure // consistency between the database state and the subscribers in case // of concurrent calls. store.paymentIDMtx.Lock(paymentID) defer store.paymentIDMtx.Unlock(paymentID) var ( result *networkResult resultChan = make(chan *networkResult, 1) ) err := kvdb.View(store.db, func(tx kvdb.RTx) error { var err error result, err = fetchResult(tx, paymentID) switch { // Result not yet available, we will notify once a result is // available. case err == ErrPaymentIDNotFound: return nil case err != nil: return err // The result was found, and will be returned immediately. default: return nil } }) if err != nil { return nil, err } // If the result was found, we can send it on the result channel // imemdiately. if result != nil { resultChan <- result return resultChan, nil } // Otherwise we store the result channel for when the result is // available. store.resultsMtx.Lock() store.results[paymentID] = append( store.results[paymentID], resultChan, ) store.resultsMtx.Unlock() return resultChan, nil } // getResult attempts to immediately fetch the result for the given pid from // the store. If no result is available, ErrPaymentIDNotFound is returned. func (store *networkResultStore) getResult(pid uint64) ( *networkResult, error) { var result *networkResult err := kvdb.View(store.db, func(tx kvdb.RTx) error { var err error result, err = fetchResult(tx, pid) return err }) if err != nil { return nil, err } return result, nil } func fetchResult(tx kvdb.RTx, pid uint64) (*networkResult, error) { var paymentIDBytes [8]byte binary.BigEndian.PutUint64(paymentIDBytes[:], pid) networkResults := tx.ReadBucket(networkResultStoreBucketKey) if networkResults == nil { return nil, ErrPaymentIDNotFound } // Check whether a result is already available. resultBytes := networkResults.Get(paymentIDBytes[:]) if resultBytes == nil { return nil, ErrPaymentIDNotFound } // Decode the result we found. r := bytes.NewReader(resultBytes) return deserializeNetworkResult(r) }