package chainview import ( "bytes" "encoding/hex" "fmt" "sync" "sync/atomic" "github.com/btcsuite/btcd/btcjson" "github.com/btcsuite/btcd/chaincfg/chainhash" "github.com/btcsuite/btcd/rpcclient" "github.com/btcsuite/btcd/wire" "github.com/btcsuite/btcutil" "github.com/lightningnetwork/lnd/channeldb" ) // BtcdFilteredChainView is an implementation of the FilteredChainView // interface which is backed by an active websockets connection to btcd. type BtcdFilteredChainView struct { started int32 // To be used atomically. stopped int32 // To be used atomically. // bestHeight is the height of the latest block added to the // blockQueue from the onFilteredConnectedMethod. It is used to // determine up to what height we would need to rescan in case // of a filter update. bestHeightMtx sync.Mutex bestHeight uint32 btcdConn *rpcclient.Client // blockEventQueue is the ordered queue used to keep the order // of connected and disconnected blocks sent to the reader of the // chainView. blockQueue *blockEventQueue // filterUpdates is a channel in which updates to the utxo filter // attached to this instance are sent over. filterUpdates chan filterUpdate // chainFilter is the set of utox's that we're currently watching // spends for within the chain. filterMtx sync.RWMutex chainFilter map[wire.OutPoint]struct{} // filterBlockReqs is a channel in which requests to filter select // blocks will be sent over. filterBlockReqs chan *filterBlockReq quit chan struct{} wg sync.WaitGroup } // A compile time check to ensure BtcdFilteredChainView implements the // chainview.FilteredChainView. var _ FilteredChainView = (*BtcdFilteredChainView)(nil) // NewBtcdFilteredChainView creates a new instance of a FilteredChainView from // RPC credentials for an active btcd instance. func NewBtcdFilteredChainView(config rpcclient.ConnConfig) (*BtcdFilteredChainView, error) { chainView := &BtcdFilteredChainView{ chainFilter: make(map[wire.OutPoint]struct{}), filterUpdates: make(chan filterUpdate), filterBlockReqs: make(chan *filterBlockReq), quit: make(chan struct{}), } ntfnCallbacks := &rpcclient.NotificationHandlers{ OnFilteredBlockConnected: chainView.onFilteredBlockConnected, OnFilteredBlockDisconnected: chainView.onFilteredBlockDisconnected, } // Disable connecting to btcd within the rpcclient.New method. We // defer establishing the connection to our .Start() method. config.DisableConnectOnNew = true config.DisableAutoReconnect = false chainConn, err := rpcclient.New(&config, ntfnCallbacks) if err != nil { return nil, err } chainView.btcdConn = chainConn chainView.blockQueue = newBlockEventQueue() return chainView, nil } // Start starts all goroutines necessary for normal operation. // // NOTE: This is part of the FilteredChainView interface. func (b *BtcdFilteredChainView) Start() error { // Already started? if atomic.AddInt32(&b.started, 1) != 1 { return nil } log.Infof("FilteredChainView starting") // Connect to btcd, and register for notifications on connected, and // disconnected blocks. if err := b.btcdConn.Connect(20); err != nil { return err } if err := b.btcdConn.NotifyBlocks(); err != nil { return err } _, bestHeight, err := b.btcdConn.GetBestBlock() if err != nil { return err } b.bestHeightMtx.Lock() b.bestHeight = uint32(bestHeight) b.bestHeightMtx.Unlock() b.blockQueue.Start() b.wg.Add(1) go b.chainFilterer() return nil } // Stop stops all goroutines which we launched by the prior call to the Start // method. // // NOTE: This is part of the FilteredChainView interface. func (b *BtcdFilteredChainView) Stop() error { // Already shutting down? if atomic.AddInt32(&b.stopped, 1) != 1 { return nil } // Shutdown the rpc client, this gracefully disconnects from btcd, and // cleans up all related resources. b.btcdConn.Shutdown() b.blockQueue.Stop() log.Infof("FilteredChainView stopping") close(b.quit) b.wg.Wait() return nil } // onFilteredBlockConnected is called for each block that's connected to the // end of the main chain. Based on our current chain filter, the block may or // may not include any relevant transactions. func (b *BtcdFilteredChainView) onFilteredBlockConnected(height int32, header *wire.BlockHeader, txns []*btcutil.Tx) { mtxs := make([]*wire.MsgTx, len(txns)) b.filterMtx.Lock() for i, tx := range txns { mtx := tx.MsgTx() mtxs[i] = mtx for _, txIn := range mtx.TxIn { // We can delete this outpoint from the chainFilter, as // we just received a block where it was spent. In case // of a reorg, this outpoint might get "un-spent", but // that's okay since it would never be wise to consider // the channel open again (since a spending transaction // exists on the network). delete(b.chainFilter, txIn.PreviousOutPoint) } } b.filterMtx.Unlock() // We record the height of the last connected block added to the // blockQueue such that we can scan up to this height in case of // a rescan. It must be protected by a mutex since a filter update // might be trying to read it concurrently. b.bestHeightMtx.Lock() b.bestHeight = uint32(height) b.bestHeightMtx.Unlock() block := &FilteredBlock{ Hash: header.BlockHash(), Height: uint32(height), Transactions: mtxs, } b.blockQueue.Add(&blockEvent{ eventType: connected, block: block, }) } // onFilteredBlockDisconnected is a callback which is executed once a block is // disconnected from the end of the main chain. func (b *BtcdFilteredChainView) onFilteredBlockDisconnected(height int32, header *wire.BlockHeader) { log.Debugf("got disconnected block at height %d: %v", height, header.BlockHash()) filteredBlock := &FilteredBlock{ Hash: header.BlockHash(), Height: uint32(height), } b.blockQueue.Add(&blockEvent{ eventType: disconnected, block: filteredBlock, }) } // filterBlockReq houses a request to manually filter a block specified by // block hash. type filterBlockReq struct { blockHash *chainhash.Hash resp chan *FilteredBlock err chan error } // FilterBlock takes a block hash, and returns a FilteredBlocks which is the // result of applying the current registered UTXO sub-set on the block // corresponding to that block hash. If any watched UTOX's are spent by the // selected lock, then the internal chainFilter will also be updated. // // NOTE: This is part of the FilteredChainView interface. func (b *BtcdFilteredChainView) FilterBlock(blockHash *chainhash.Hash) (*FilteredBlock, error) { req := &filterBlockReq{ blockHash: blockHash, resp: make(chan *FilteredBlock, 1), err: make(chan error, 1), } select { case b.filterBlockReqs <- req: case <-b.quit: return nil, fmt.Errorf("FilteredChainView shutting down") } return <-req.resp, <-req.err } // chainFilterer is the primary goroutine which: listens for new blocks coming // and dispatches the relevant FilteredBlock notifications, updates the filter // due to requests by callers, and finally is able to preform targeted block // filtration. // // TODO(roasbeef): change to use loadfilter RPC's func (b *BtcdFilteredChainView) chainFilterer() { defer b.wg.Done() // filterBlock is a helper function that scans the given block, and // notes which transactions spend outputs which are currently being // watched. Additionally, the chain filter will also be updated by // removing any spent outputs. filterBlock := func(blk *wire.MsgBlock) []*wire.MsgTx { b.filterMtx.Lock() defer b.filterMtx.Unlock() var filteredTxns []*wire.MsgTx for _, tx := range blk.Transactions { var txAlreadyFiltered bool for _, txIn := range tx.TxIn { prevOp := txIn.PreviousOutPoint if _, ok := b.chainFilter[prevOp]; !ok { continue } delete(b.chainFilter, prevOp) // Only add this txn to our list of filtered // txns if it is the first previous outpoint to // cause a match. if txAlreadyFiltered { continue } filteredTxns = append(filteredTxns, tx) txAlreadyFiltered = true } } return filteredTxns } decodeJSONBlock := func(block *btcjson.RescannedBlock, height uint32) (*FilteredBlock, error) { hash, err := chainhash.NewHashFromStr(block.Hash) if err != nil { return nil, err } txs := make([]*wire.MsgTx, 0, len(block.Transactions)) for _, str := range block.Transactions { b, err := hex.DecodeString(str) if err != nil { return nil, err } tx := &wire.MsgTx{} err = tx.Deserialize(bytes.NewReader(b)) if err != nil { return nil, err } txs = append(txs, tx) } return &FilteredBlock{ Hash: *hash, Height: height, Transactions: txs, }, nil } for { select { // The caller has just sent an update to the current chain // filter, so we'll apply the update, possibly rewinding our // state partially. case update := <-b.filterUpdates: // First, we'll add all the new UTXO's to the set of // watched UTXO's, eliminating any duplicates in the // process. log.Debugf("Updating chain filter with new UTXO's: %v", update.newUtxos) b.filterMtx.Lock() for _, newOp := range update.newUtxos { b.chainFilter[newOp] = struct{}{} } b.filterMtx.Unlock() // Apply the new TX filter to btcd, which will cause // all following notifications from and calls to it // return blocks filtered with the new filter. b.btcdConn.LoadTxFilter(false, []btcutil.Address{}, update.newUtxos) // All blocks gotten after we loaded the filter will // have the filter applied, but we will need to rescan // the blocks up to the height of the block we last // added to the blockQueue. b.bestHeightMtx.Lock() bestHeight := b.bestHeight b.bestHeightMtx.Unlock() // If the update height matches our best known height, // then we don't need to do any rewinding. if update.updateHeight == bestHeight { continue } // Otherwise, we'll rewind the state to ensure the // caller doesn't miss any relevant notifications. // Starting from the height _after_ the update height, // we'll walk forwards, rescanning one block at a time // with btcd applying the newly loaded filter to each // block. for i := update.updateHeight + 1; i < bestHeight+1; i++ { blockHash, err := b.btcdConn.GetBlockHash(int64(i)) if err != nil { log.Warnf("Unable to get block hash "+ "for block at height %d: %v", i, err) continue } // To avoid dealing with the case where a reorg // is happening while we rescan, we scan one // block at a time, skipping blocks that might // have gone missing. rescanned, err := b.btcdConn.RescanBlocks( []chainhash.Hash{*blockHash}) if err != nil { log.Warnf("Unable to rescan block "+ "with hash %v at height %d: %v", blockHash, i, err) continue } // If no block was returned from the rescan, it // means no matching transactions were found. if len(rescanned) != 1 { log.Tracef("rescan of block %v at "+ "height=%d yielded no "+ "transactions", blockHash, i) continue } decoded, err := decodeJSONBlock( &rescanned[0], uint32(i)) if err != nil { log.Errorf("Unable to decode block: %v", err) continue } b.blockQueue.Add(&blockEvent{ eventType: connected, block: decoded, }) } // We've received a new request to manually filter a block. case req := <-b.filterBlockReqs: // First we'll fetch the block itself as well as some // additional information including its height. block, err := b.btcdConn.GetBlock(req.blockHash) if err != nil { req.err <- err req.resp <- nil continue } header, err := b.btcdConn.GetBlockHeaderVerbose(req.blockHash) if err != nil { req.err <- err req.resp <- nil continue } // Once we have this info, we can directly filter the // block and dispatch the proper notification. req.resp <- &FilteredBlock{ Hash: *req.blockHash, Height: uint32(header.Height), Transactions: filterBlock(block), } req.err <- err case <-b.quit: return } } } // filterUpdate is a message sent to the chainFilterer to update the current // chainFilter state. type filterUpdate struct { newUtxos []wire.OutPoint updateHeight uint32 done chan struct{} } // UpdateFilter updates the UTXO filter which is to be consulted when creating // FilteredBlocks to be sent to subscribed clients. This method is cumulative // meaning repeated calls to this method should _expand_ the size of the UTXO // sub-set currently being watched. If the set updateHeight is _lower_ than // the best known height of the implementation, then the state should be // rewound to ensure all relevant notifications are dispatched. // // NOTE: This is part of the FilteredChainView interface. func (b *BtcdFilteredChainView) UpdateFilter(ops []channeldb.EdgePoint, updateHeight uint32) error { newUtxos := make([]wire.OutPoint, len(ops)) for i, op := range ops { newUtxos[i] = op.OutPoint } select { case b.filterUpdates <- filterUpdate{ newUtxos: newUtxos, updateHeight: updateHeight, }: return nil case <-b.quit: return fmt.Errorf("chain filter shutting down") } } // FilteredBlocks returns the channel that filtered blocks are to be sent over. // Each time a block is connected to the end of a main chain, and appropriate // FilteredBlock which contains the transactions which mutate our watched UTXO // set is to be returned. // // NOTE: This is part of the FilteredChainView interface. func (b *BtcdFilteredChainView) FilteredBlocks() <-chan *FilteredBlock { return b.blockQueue.newBlocks } // DisconnectedBlocks returns a receive only channel which will be sent upon // with the empty filtered blocks of blocks which are disconnected from the // main chain in the case of a re-org. // // NOTE: This is part of the FilteredChainView interface. func (b *BtcdFilteredChainView) DisconnectedBlocks() <-chan *FilteredBlock { return b.blockQueue.staleBlocks }