lnd.xprv/chainntnfs/interface.go

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package chainntnfs
import (
"fmt"
"sync"
"github.com/btcsuite/btcd/btcjson"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/wire"
)
// ChainNotifier represents a trusted source to receive notifications concerning
// targeted events on the Bitcoin blockchain. The interface specification is
// intentionally general in order to support a wide array of chain notification
// implementations such as: btcd's websockets notifications, Bitcoin Core's
// ZeroMQ notifications, various Bitcoin API services, Electrum servers, etc.
//
// Concrete implementations of ChainNotifier should be able to support multiple
// concurrent client requests, as well as multiple concurrent notification events.
// TODO(roasbeef): all events should have a Cancel() method to free up the
// resource
type ChainNotifier interface {
// RegisterConfirmationsNtfn registers an intent to be notified once
// txid reaches numConfs confirmations. We also pass in the pkScript as
// the default light client instead needs to match on scripts created
// in the block. The returned ConfirmationEvent should properly notify
// the client once the specified number of confirmations has been
// reached for the txid, as well as if the original tx gets re-org'd
// out of the mainchain. The heightHint parameter is provided as a
// convenience to light clients. The heightHint denotes the earliest
// height in the blockchain in which the target txid _could_ have been
// included in the chain. This can be used to bound the search space
// when checking to see if a notification can immediately be dispatched
// due to historical data.
//
// NOTE: Dispatching notifications to multiple clients subscribed to
// the same (txid, numConfs) tuple MUST be supported.
RegisterConfirmationsNtfn(txid *chainhash.Hash, pkScript []byte, numConfs,
heightHint uint32) (*ConfirmationEvent, error)
// RegisterSpendNtfn registers an intent to be notified once the target
// outpoint is successfully spent within a transaction. The script that
// the outpoint creates must also be specified. This allows this
// interface to be implemented by BIP 158-like filtering. The returned
// SpendEvent will receive a send on the 'Spend' transaction once a
// transaction spending the input is detected on the blockchain. The
// heightHint parameter is provided as a convenience to light clients.
// The heightHint denotes the earliest height in the blockchain in
// which the target output could have been created.
//
// NOTE: The notification should only be triggered when the spending
// transaction receives a single confirmation.
//
// NOTE: Dispatching notifications to multiple clients subscribed to a
// spend of the same outpoint MUST be supported.
RegisterSpendNtfn(outpoint *wire.OutPoint, pkScript []byte,
heightHint uint32) (*SpendEvent, error)
// RegisterBlockEpochNtfn registers an intent to be notified of each
// new block connected to the tip of the main chain. The returned
// BlockEpochEvent struct contains a channel which will be sent upon
// for each new block discovered.
//
// Clients have the option of passing in their best known block.
// If they specify a block, the ChainNotifier checks whether the client
// is behind on blocks. If they are, the ChainNotifier sends a backlog
// of block notifications for the missed blocks.
RegisterBlockEpochNtfn(*BlockEpoch) (*BlockEpochEvent, error)
// Start the ChainNotifier. Once started, the implementation should be
// ready, and able to receive notification registrations from clients.
Start() error
// Stops the concrete ChainNotifier. Once stopped, the ChainNotifier
// should disallow any future requests from potential clients.
// Additionally, all pending client notifications will be cancelled
// by closing the related channels on the *Event's.
Stop() error
}
// TxConfirmation carries some additional block-level details of the exact
// block that specified transactions was confirmed within.
type TxConfirmation struct {
// BlockHash is the hash of the block that confirmed the original
// transition.
BlockHash *chainhash.Hash
// BlockHeight is the height of the block in which the transaction was
// confirmed within.
BlockHeight uint32
// TxIndex is the index within the block of the ultimate confirmed
// transaction.
TxIndex uint32
}
// ConfirmationEvent encapsulates a confirmation notification. With this struct,
// callers can be notified of: the instance the target txid reaches the targeted
// number of confirmations, how many confirmations are left for the target txid
// to be fully confirmed at every new block height, and also in the event that
// the original txid becomes disconnected from the blockchain as a result of a
// re-org.
//
// Once the txid reaches the specified number of confirmations, the 'Confirmed'
// channel will be sent upon fulfilling the notification.
//
// If the event that the original transaction becomes re-org'd out of the main
// chain, the 'NegativeConf' will be sent upon with a value representing the
// depth of the re-org.
type ConfirmationEvent struct {
// Confirmed is a channel that will be sent upon once the transaction
// has been fully confirmed. The struct sent will contain all the
// details of the channel's confirmation.
Confirmed chan *TxConfirmation // MUST be buffered.
// Updates is a channel that will sent upon, at every incremental
// confirmation, how many confirmations are left to declare the
// transaction as fully confirmed.
Updates chan uint32 // MUST be buffered.
// TODO(roasbeef): all goroutines on ln channel updates should also
// have a struct chan that's closed if funding gets re-org out. Need
// to sync, to request another confirmation event ntfn, then re-open
// channel after confs.
NegativeConf chan int32 // MUST be buffered.
}
// SpendDetail contains details pertaining to a spent output. This struct itself
// is the spentness notification. It includes the original outpoint which triggered
// the notification, the hash of the transaction spending the output, the
// spending transaction itself, and finally the input index which spent the
// target output.
type SpendDetail struct {
SpentOutPoint *wire.OutPoint
SpenderTxHash *chainhash.Hash
SpendingTx *wire.MsgTx
SpenderInputIndex uint32
SpendingHeight int32
}
// SpendEvent encapsulates a spentness notification. Its only field 'Spend' will
// be sent upon once the target output passed into RegisterSpendNtfn has been
// spent on the blockchain.
//
// NOTE: If the caller wishes to cancel their registered spend notification,
// the Cancel closure MUST be called.
type SpendEvent struct {
// Spend is a receive only channel which will be sent upon once the
// target outpoint has been spent.
Spend <-chan *SpendDetail // MUST be buffered.
// Cancel is a closure that should be executed by the caller in the
// case that they wish to prematurely abandon their registered spend
// notification.
Cancel func()
}
// BlockEpoch represents metadata concerning each new block connected to the
// main chain.
type BlockEpoch struct {
// Hash is the block hash of the latest block to be added to the tip of
// the main chain.
Hash *chainhash.Hash
// Height is the height of the latest block to be added to the tip of
// the main chain.
Height int32
}
// BlockEpochEvent encapsulates an on-going stream of block epoch
// notifications. Its only field 'Epochs' will be sent upon for each new block
// connected to the main-chain.
//
// NOTE: If the caller wishes to cancel their registered block epoch
// notification, the Cancel closure MUST be called.
type BlockEpochEvent struct {
// Epochs is a receive only channel that will be sent upon each time a
// new block is connected to the end of the main chain.
Epochs <-chan *BlockEpoch // MUST be buffered.
// Cancel is a closure that should be executed by the caller in the
// case that they wish to abandon their registered spend notification.
Cancel func()
}
// NotifierDriver represents a "driver" for a particular interface. A driver is
// identified by a globally unique string identifier along with a 'New()'
// method which is responsible for initializing a particular ChainNotifier
// concrete implementation.
type NotifierDriver struct {
// NotifierType is a string which uniquely identifies the ChainNotifier
// that this driver, drives.
NotifierType string
// New creates a new instance of a concrete ChainNotifier
// implementation given a variadic set up arguments. The function takes
// a variadic number of interface parameters in order to provide
// initialization flexibility, thereby accommodating several potential
// ChainNotifier implementations.
New func(args ...interface{}) (ChainNotifier, error)
}
var (
notifiers = make(map[string]*NotifierDriver)
registerMtx sync.Mutex
)
// RegisteredNotifiers returns a slice of all currently registered notifiers.
//
// NOTE: This function is safe for concurrent access.
func RegisteredNotifiers() []*NotifierDriver {
registerMtx.Lock()
defer registerMtx.Unlock()
drivers := make([]*NotifierDriver, 0, len(notifiers))
for _, driver := range notifiers {
drivers = append(drivers, driver)
}
return drivers
}
// RegisterNotifier registers a NotifierDriver which is capable of driving a
// concrete ChainNotifier interface. In the case that this driver has already
// been registered, an error is returned.
//
// NOTE: This function is safe for concurrent access.
func RegisterNotifier(driver *NotifierDriver) error {
registerMtx.Lock()
defer registerMtx.Unlock()
if _, ok := notifiers[driver.NotifierType]; ok {
return fmt.Errorf("notifier already registered")
}
notifiers[driver.NotifierType] = driver
return nil
}
// SupportedNotifiers returns a slice of strings that represent the database
// drivers that have been registered and are therefore supported.
//
// NOTE: This function is safe for concurrent access.
func SupportedNotifiers() []string {
registerMtx.Lock()
defer registerMtx.Unlock()
supportedNotifiers := make([]string, 0, len(notifiers))
for driverName := range notifiers {
supportedNotifiers = append(supportedNotifiers, driverName)
}
return supportedNotifiers
}
// ChainConn enables notifiers to pass in their chain backend to interface
// functions that require it.
type ChainConn interface {
// GetBlockHeader returns the block header for a hash.
GetBlockHeader(blockHash *chainhash.Hash) (*wire.BlockHeader, error)
// GetBlockHeaderVerbose returns the verbose block header for a hash.
GetBlockHeaderVerbose(blockHash *chainhash.Hash) (
*btcjson.GetBlockHeaderVerboseResult, error)
// GetBlockHash returns the hash from a block height.
GetBlockHash(blockHeight int64) (*chainhash.Hash, error)
}
// GetCommonBlockAncestorHeight takes in:
// (1) the hash of a block that has been reorged out of the main chain
// (2) the hash of the block of the same height from the main chain
// It returns the height of the nearest common ancestor between the two hashes,
// or an error
func GetCommonBlockAncestorHeight(chainConn ChainConn, reorgHash,
chainHash chainhash.Hash) (int32, error) {
for reorgHash != chainHash {
reorgHeader, err := chainConn.GetBlockHeader(&reorgHash)
if err != nil {
return 0, fmt.Errorf("unable to get header for hash=%v: %v",
reorgHash, err)
}
chainHeader, err := chainConn.GetBlockHeader(&chainHash)
if err != nil {
return 0, fmt.Errorf("unable to get header for hash=%v: %v",
chainHash, err)
}
reorgHash = reorgHeader.PrevBlock
chainHash = chainHeader.PrevBlock
}
verboseHeader, err := chainConn.GetBlockHeaderVerbose(&chainHash)
if err != nil {
return 0, fmt.Errorf("unable to get verbose header for hash=%v: %v",
chainHash, err)
}
return verboseHeader.Height, nil
}
// GetClientMissedBlocks uses a client's best block to determine what blocks
// it missed being notified about, and returns them in a slice. Its
// backendStoresReorgs parameter tells it whether or not the notifier's
// chainConn stores information about blocks that have been reorged out of the
// chain, which allows GetClientMissedBlocks to find out whether the client's
// best block has been reorged out of the chain, rewind to the common ancestor
// and return blocks starting right after the common ancestor.
func GetClientMissedBlocks(chainConn ChainConn, clientBestBlock *BlockEpoch,
notifierBestHeight int32, backendStoresReorgs bool) ([]BlockEpoch, error) {
startingHeight := clientBestBlock.Height
if backendStoresReorgs {
// If a reorg causes the client's best hash to be incorrect,
// retrieve the closest common ancestor and dispatch
// notifications from there.
hashAtBestHeight, err := chainConn.GetBlockHash(
int64(clientBestBlock.Height))
if err != nil {
return nil, fmt.Errorf("unable to find blockhash for "+
"height=%d: %v", clientBestBlock.Height, err)
}
startingHeight, err = GetCommonBlockAncestorHeight(
chainConn, *clientBestBlock.Hash, *hashAtBestHeight,
)
if err != nil {
return nil, fmt.Errorf("unable to find common ancestor: "+
"%v", err)
}
}
// We want to start dispatching historical notifications from the block
// right after the client's best block, to avoid a redundant notification.
missedBlocks, err := getMissedBlocks(
chainConn, startingHeight+1, notifierBestHeight+1,
)
if err != nil {
return nil, fmt.Errorf("unable to get missed blocks: %v", err)
}
return missedBlocks, nil
}
// RewindChain handles internal state updates for the notifier's TxConfNotifier
// It has no effect if given a height greater than or equal to our current best
// known height. It returns the new best block for the notifier.
func RewindChain(chainConn ChainConn, txConfNotifier *TxConfNotifier,
currBestBlock BlockEpoch, targetHeight int32) (BlockEpoch, error) {
newBestBlock := BlockEpoch{
Height: currBestBlock.Height,
Hash: currBestBlock.Hash,
}
for height := currBestBlock.Height; height > targetHeight; height-- {
hash, err := chainConn.GetBlockHash(int64(height - 1))
if err != nil {
return newBestBlock, fmt.Errorf("unable to "+
"find blockhash for disconnected height=%d: %v",
height, err)
}
Log.Infof("Block disconnected from main chain: "+
"height=%v, sha=%v", height, newBestBlock.Hash)
err = txConfNotifier.DisconnectTip(uint32(height))
if err != nil {
return newBestBlock, fmt.Errorf("unable to "+
" disconnect tip for height=%d: %v",
height, err)
}
newBestBlock.Height = height - 1
newBestBlock.Hash = hash
}
return newBestBlock, nil
}
// HandleMissedBlocks is called when the chain backend for a notifier misses a
// series of blocks, handling a reorg if necessary. Its backendStoresReorgs
// parameter tells it whether or not the notifier's chainConn stores
// information about blocks that have been reorged out of the chain, which allows
// HandleMissedBlocks to check whether the notifier's best block has been
// reorged out, and rewind the chain accordingly. It returns the best block for
// the notifier and a slice of the missed blocks. The new best block needs to be
// returned in case a chain rewind occurs and partially completes before
// erroring. In the case where there is no rewind, the notifier's
// current best block is returned.
func HandleMissedBlocks(chainConn ChainConn, txConfNotifier *TxConfNotifier,
currBestBlock BlockEpoch, newHeight int32,
backendStoresReorgs bool) (BlockEpoch, []BlockEpoch, error) {
startingHeight := currBestBlock.Height
if backendStoresReorgs {
// If a reorg causes our best hash to be incorrect, rewind the
// chain so our best block is set to the closest common
// ancestor, then dispatch notifications from there.
hashAtBestHeight, err :=
chainConn.GetBlockHash(int64(currBestBlock.Height))
if err != nil {
return currBestBlock, nil, fmt.Errorf("unable to find "+
"blockhash for height=%d: %v",
currBestBlock.Height, err)
}
startingHeight, err = GetCommonBlockAncestorHeight(
chainConn, *currBestBlock.Hash, *hashAtBestHeight,
)
if err != nil {
return currBestBlock, nil, fmt.Errorf("unable to find "+
"common ancestor: %v", err)
}
currBestBlock, err = RewindChain(chainConn, txConfNotifier,
currBestBlock, startingHeight)
if err != nil {
return currBestBlock, nil, fmt.Errorf("unable to "+
"rewind chain: %v", err)
}
}
// We want to start dispatching historical notifications from the block
// right after our best block, to avoid a redundant notification.
missedBlocks, err := getMissedBlocks(chainConn, startingHeight+1, newHeight)
if err != nil {
return currBestBlock, nil, fmt.Errorf("unable to get missed "+
"blocks: %v", err)
}
return currBestBlock, missedBlocks, nil
}
// getMissedBlocks returns a slice of blocks: [startingHeight, endingHeight)
// fetched from the chain.
func getMissedBlocks(chainConn ChainConn, startingHeight,
endingHeight int32) ([]BlockEpoch, error) {
numMissedBlocks := endingHeight - startingHeight
if numMissedBlocks < 0 {
return nil, fmt.Errorf("starting height %d is greater than "+
"ending height %d", startingHeight, endingHeight)
}
missedBlocks := make([]BlockEpoch, 0, numMissedBlocks)
for height := startingHeight; height < endingHeight; height++ {
hash, err := chainConn.GetBlockHash(int64(height))
if err != nil {
return nil, fmt.Errorf("unable to find blockhash for "+
"height=%d: %v", height, err)
}
missedBlocks = append(missedBlocks,
BlockEpoch{Hash: hash, Height: height})
}
return missedBlocks, nil
}