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btc spv: give wallet precedence for block notifications
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When a wallet is able to provide block notifications, allow wallet notifications
to take precedence. Queue polled new tips for 10 seconds, canceling
their broadcast and sending the notification earlier if the wallet
notification comes during this window. If the wallet note doesn't
come by 10 seconds, send the queued notification and log a warning.

SPV tip updates are provided by the FilteredBlockConnected
notification, which can come after neutrino stores the block header(s).
Care is taken not to spam the caller with notifications, since they
are not limited by the polling frequency. The same mechanism for
limiting spam is used to solve the non-existent wallet error messages
for *Core though, so you get two for the price of one with that solution.
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@buck54321
buck54321 committed Oct 30, 2021
1 parent 0124247 commit 2d18cc8
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Showing 9 changed files with 331 additions and 88 deletions.
172 changes: 121 additions & 51 deletions client/asset/btc/btc.go
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Expand Up @@ -77,6 +77,7 @@ const (
var (
// blockTicker is the delay between calls to check for new blocks.
blockTicker = time.Second
walletBlockAllowance = time.Second * 10
conventionalConversionFactor = float64(dexbtc.UnitInfo.Conventional.ConversionFactor)
rpcOpts = []*asset.ConfigOption{
{
Expand Down Expand Up @@ -521,7 +522,7 @@ type ExchangeWallet struct {

type block struct {
height int64
hash string
hash chainhash.Hash
}

// findRedemptionReq represents a request to find a contract's redemption,
Expand Down Expand Up @@ -754,7 +755,7 @@ func (btc *ExchangeWallet) Connect(ctx context.Context) (*sync.WaitGroup, error)
return nil, err
}
// Initialize the best block.
h, err := btc.node.getBestBlockHash()
bestBlockHash, err := btc.node.getBestBlockHash()
if err != nil {
return nil, fmt.Errorf("error initializing best block for %s: %w", btc.symbol, err)
}
Expand All @@ -765,7 +766,7 @@ func (btc *ExchangeWallet) Connect(ctx context.Context) (*sync.WaitGroup, error)
}

btc.tipMtx.Lock()
btc.currentTip, err = btc.blockFromHash(h.String())
btc.currentTip, err = btc.blockFromHash(bestBlockHash)
btc.tipMtx.Unlock()
if err != nil {
return nil, fmt.Errorf("error parsing best block for %s: %w", btc.symbol, err)
Expand All @@ -774,7 +775,7 @@ func (btc *ExchangeWallet) Connect(ctx context.Context) (*sync.WaitGroup, error)
wg.Add(1)
go func() {
defer wg.Done()
btc.run(ctx)
btc.watchBlocks(ctx)
btc.shutdown()
}()
return &wg, nil
Expand Down Expand Up @@ -1930,7 +1931,7 @@ func (btc *ExchangeWallet) LocktimeExpired(contract dex.Bytes) (bool, time.Time,
if err != nil {
return false, time.Time{}, fmt.Errorf("get best block hash error: %w", err)
}
bestBlockHeader, err := btc.node.getBlockHeader(bestBlockHash.String())
bestBlockHeader, err := btc.node.getBlockHeader(bestBlockHash)
if err != nil {
return false, time.Time{}, fmt.Errorf("get best block header error: %w", err)
}
Expand Down Expand Up @@ -2390,15 +2391,98 @@ func (btc *ExchangeWallet) RegFeeConfirmations(_ context.Context, id dex.Bytes)
return uint32(tx.Confirmations), nil
}

// run pings for new blocks and runs the tipChange callback function when the
// block changes.
func (btc *ExchangeWallet) run(ctx context.Context) {
// watchBlocks pings for new blocks and runs the tipChange callback function
// when the block changes.
func (btc *ExchangeWallet) watchBlocks(ctx context.Context) {
ticker := time.NewTicker(blockTicker)
defer ticker.Stop()

var walletBlock <-chan *block
if notifier, isNotifier := btc.node.(tipNotifier); isNotifier {
walletBlock = notifier.tipFeed()
}

// A polledBlock is a block found during polling, but whose broadcast has
// been queued in anticipation of a wallet notification.
type polledBlock struct {
*block
queue *time.Timer
}

// queuedBlock is the currently queued, polling-discovered block that will
// be broadcast after a timeout if the wallet doesn't send the matching
// notification.
var queuedBlock *polledBlock

for {
select {

// Poll for the block. If the wallet offers tip reports, delay reporting
// the tip to give the wallet a moment to request and scan block data.
case <-ticker.C:
btc.checkForNewBlocks(ctx)
newTipHash, err := btc.node.getBestBlockHash()
if err != nil {
go btc.tipChange(fmt.Errorf("failed to get best block hash from %s node", btc.symbol))
return
}

if queuedBlock != nil && *newTipHash == queuedBlock.block.hash {
continue
}

btc.tipMtx.RLock()
sameTip := btc.currentTip.hash == *newTipHash
btc.tipMtx.RUnlock()
if sameTip {
continue
}

newTip, err := btc.blockFromHash(newTipHash)
if err != nil {
go btc.tipChange(fmt.Errorf("error setting new tip: %w", err))
}

// If the wallet is not offering tip reports, send this one right
// away.
if walletBlock == nil {
btc.reportNewTip(ctx, newTip)
} else {
// Queue it for reporting, but don't send it right away. Give the
// wallet a chance to provide their block update. SPV wallet may
// need more time after storing the block header to fetch and
// scan filters and issue the FilteredBlockConnected report.
if queuedBlock != nil {
queuedBlock.queue.Stop()
}
blockAllowance := walletBlockAllowance
syncStatus, err := btc.node.syncStatus()
if err != nil {
btc.log.Errorf("Error retreiving sync status before queuing polled block: %v", err)
} else if syncStatus.Syncing {
blockAllowance *= 10
}
queuedBlock = &polledBlock{
block: newTip,
queue: time.AfterFunc(blockAllowance, func() {
btc.log.Warnf("Reporting a block found in polling that the wallet apparently "+
"never reported: %d %s. If you see this message repeatedly, it may indicate "+
"an issue with the wallet.", newTip.height, newTip.hash)
btc.reportNewTip(ctx, newTip)
}),
}
}

// Tip reports from the wallet are always sent, and we'll clear any
// queued polled block that would appear to be superceded by this one.
case walletTip := <-walletBlock:
if queuedBlock != nil && walletTip.height >= queuedBlock.height {
if !queuedBlock.queue.Stop() && walletTip.hash == queuedBlock.hash {
continue
}
queuedBlock = nil
}
btc.reportNewTip(ctx, walletTip)

case <-ctx.Done():
return
}
Expand All @@ -2424,10 +2508,18 @@ func (btc *ExchangeWallet) prepareRedemptionRequestsForBlockCheck() []*findRedem
return reqs
}

// checkForNewBlocks checks for new blocks. When a tip change is detected, the
// tipChange callback function is invoked and a goroutine is started to check
// if any contracts in the findRedemptionQueue are redeemed in the new blocks.
func (btc *ExchangeWallet) checkForNewBlocks(ctx context.Context) {
// reportNewTip sets the currentTip. The tipChange callback function is invoked
// and a goroutine is started to check if any contracts in the
// findRedemptionQueue are redeemed in the new blocks.
func (btc *ExchangeWallet) reportNewTip(ctx context.Context, newTip *block) {
btc.tipMtx.Lock()
defer btc.tipMtx.Unlock()

prevTip := btc.currentTip
btc.currentTip = newTip
btc.log.Debugf("tip change: %d (%s) => %d (%s)", prevTip.height, prevTip.hash, newTip.height, newTip.hash)
go btc.tipChange(nil)

reqs := btc.prepareRedemptionRequestsForBlockCheck()
// Redemption search would be compromised if the starting point cannot
// be determined, as searching just the new tip might result in blocks
Expand All @@ -2439,41 +2531,12 @@ func (btc *ExchangeWallet) checkForNewBlocks(ctx context.Context) {
}
}

newTipHash, err := btc.node.getBestBlockHash()
if err != nil {
go btc.tipChange(fmt.Errorf("failed to get best block hash from %s node", btc.symbol))
return
}

// This method is called frequently. Don't hold write lock
// unless tip has changed.
btc.tipMtx.RLock()
sameTip := btc.currentTip.hash == newTipHash.String()
btc.tipMtx.RUnlock()
if sameTip {
return
}

btc.tipMtx.Lock()
defer btc.tipMtx.Unlock()

newTip, err := btc.blockFromHash(newTipHash.String())
if err != nil {
go btc.tipChange(fmt.Errorf("error setting new tip: %w", err))
return
}

prevTip := btc.currentTip
btc.currentTip = newTip
btc.log.Debugf("tip change: %d (%s) => %d (%s)", prevTip.height, prevTip.hash, newTip.height, newTip.hash)
go btc.tipChange(nil)

var startPoint *block
// Check if the previous tip is still part of the mainchain (prevTip confs >= 0).
// Redemption search would typically resume from prevTipHeight + 1 unless the
// previous tip was re-orged out of the mainchain, in which case redemption
// search will resume from the mainchain ancestor of the previous tip.
prevTipHeader, err := btc.node.getBlockHeader(prevTip.hash)
prevTipHeader, err := btc.node.getBlockHeader(&prevTip.hash)
switch {
case err != nil:
// Redemption search cannot continue reliably without knowing if there
Expand All @@ -2486,7 +2549,11 @@ func (btc *ExchangeWallet) checkForNewBlocks(ctx context.Context) {
// The previous tip is no longer part of the mainchain. Crawl blocks
// backwards until finding a mainchain block. Start with the block
// that is the immediate ancestor to the previous tip.
ancestorBlockHash := prevTipHeader.PreviousBlockHash
ancestorBlockHash, err := chainhash.NewHashFromStr(prevTipHeader.PreviousBlockHash)
if err != nil {
notifyFatalFindRedemptionError("hash decode error for block %s: %w", prevTipHeader.PreviousBlockHash, err)
return
}
for {
aBlock, err := btc.node.getBlockHeader(ancestorBlockHash)
if err != nil {
Expand All @@ -2495,7 +2562,7 @@ func (btc *ExchangeWallet) checkForNewBlocks(ctx context.Context) {
}
if aBlock.Confirmations > -1 {
// Found the mainchain ancestor of previous tip.
startPoint = &block{height: aBlock.Height, hash: aBlock.Hash}
startPoint = &block{height: aBlock.Height, hash: *ancestorBlockHash}
btc.log.Debugf("reorg detected from height %d to %d", aBlock.Height, newTip.height)
break
}
Expand All @@ -2505,7 +2572,11 @@ func (btc *ExchangeWallet) checkForNewBlocks(ctx context.Context) {
notifyFatalFindRedemptionError("no mainchain ancestor for orphaned block %s", prevTipHeader.Hash)
return
}
ancestorBlockHash = aBlock.PreviousBlockHash
ancestorBlockHash, err = chainhash.NewHashFromStr(aBlock.PreviousBlockHash)
if err != nil {
notifyFatalFindRedemptionError("hash decode error for block %s: %w", prevTipHeader.PreviousBlockHash, err)
return
}
}

case newTip.height-prevTipHeader.Height > 1:
Expand All @@ -2516,16 +2587,15 @@ func (btc *ExchangeWallet) checkForNewBlocks(ctx context.Context) {
notifyFatalFindRedemptionError("getBlockHash error for height %d: %w", afterPrivTip, err)
return
}
startPoint = &block{hash: hashAfterPrevTip.String(), height: afterPrivTip}
startPoint = &block{hash: *hashAfterPrevTip, height: afterPrivTip}

default:
// Just 1 new block since last tip report, search the lone block.
startPoint = newTip
}

if len(reqs) > 0 {
startHash, _ := chainhash.NewHashFromStr(startPoint.hash)
go btc.tryRedemptionRequests(ctx, startHash, reqs)
go btc.tryRedemptionRequests(ctx, &startPoint.hash, reqs)
}
}

Expand Down Expand Up @@ -2598,12 +2668,12 @@ out:
return blockHeight, nil
}

func (btc *ExchangeWallet) blockFromHash(hash string) (*block, error) {
func (btc *ExchangeWallet) blockFromHash(hash *chainhash.Hash) (*block, error) {
blk, err := btc.node.getBlockHeader(hash)
if err != nil {
return nil, fmt.Errorf("getBlockHeader error for hash %s: %w", hash, err)
}
return &block{hash: hash, height: blk.Height}, nil
return &block{hash: *hash, height: blk.Height}, nil
}

// convertCoin converts the asset.Coin to an output.
Expand Down

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