lnd.xprv/witness_beacon.go

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package main
import (
"sync"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/contractcourt"
"github.com/lightningnetwork/lnd/lnwallet"
"github.com/btcsuite/btcd/chaincfg/chainhash"
)
// preimageSubscriber reprints an active subscription to be notified once the
// daemon discovers new preimages, either on chain or off-chain.
type preimageSubscriber struct {
updateChan chan []byte
quit chan struct{}
}
// preimageBeacon is an implementation of the contractcourt.WitnessBeacon
// interface, and the lnwallet.PreimageCache interface. This implementation is
// concerned with a single witness type: sha256 hahsh preimages.
type preimageBeacon struct {
sync.RWMutex
invoices *invoiceRegistry
wCache *channeldb.WitnessCache
clientCounter uint64
subscribers map[uint64]*preimageSubscriber
}
// SubscribeUpdates returns a channel that will be sent upon *each* time a new
// preimage is discovered.
func (p *preimageBeacon) SubscribeUpdates() *contractcourt.WitnessSubscription {
p.Lock()
defer p.Unlock()
clientID := p.clientCounter
client := &preimageSubscriber{
updateChan: make(chan []byte, 10),
quit: make(chan struct{}),
}
p.subscribers[p.clientCounter] = client
p.clientCounter++
srvrLog.Debugf("Creating new witness beacon subscriber, id=%v",
p.clientCounter)
return &contractcourt.WitnessSubscription{
WitnessUpdates: client.updateChan,
CancelSubscription: func() {
p.Lock()
defer p.Unlock()
delete(p.subscribers, clientID)
close(client.quit)
},
}
}
// LookupPreImage attempts to lookup a preimage in the global cache. True is
// returned for the second argument if the preimage is found.
func (p *preimageBeacon) LookupPreimage(payHash []byte) ([]byte, bool) {
p.RLock()
defer p.RUnlock()
// First, we'll check the invoice registry to see if we already know of
// the preimage as it's on that we created ourselves.
var invoiceKey chainhash.Hash
copy(invoiceKey[:], payHash)
invoice, _, err := p.invoices.LookupInvoice(invoiceKey)
switch {
case err == channeldb.ErrInvoiceNotFound:
// If we get this error, then it simply means that this invoice
// wasn't found, so we don't treat it as a critical error.
case err != nil:
return nil, false
}
// If we've found the invoice, then we can return the preimage
// directly.
if err != channeldb.ErrInvoiceNotFound {
return invoice.Terms.PaymentPreimage[:], true
}
// Otherwise, we'll perform a final check using the witness cache.
preimage, err := p.wCache.LookupWitness(
channeldb.Sha256HashWitness, payHash,
)
if err != nil {
ltndLog.Errorf("unable to lookup witness: %v", err)
return nil, false
}
return preimage, true
}
// AddPreImage adds a newly discovered preimage to the global cache, and also
// signals any subscribers of the newly discovered witness.
func (p *preimageBeacon) AddPreimage(pre []byte) error {
p.Lock()
defer p.Unlock()
srvrLog.Infof("Adding preimage=%x to witness cache", pre[:])
// First, we'll add the witness to the decaying witness cache.
err := p.wCache.AddWitness(channeldb.Sha256HashWitness, pre)
if err != nil {
return err
}
// With the preimage added to our state, we'll now send a new
// notification to all subscribers.
for _, client := range p.subscribers {
go func(c *preimageSubscriber) {
select {
case c.updateChan <- pre:
case <-c.quit:
return
}
}(client)
}
return nil
}
var _ contractcourt.WitnessBeacon = (*preimageBeacon)(nil)
var _ lnwallet.PreimageCache = (*preimageBeacon)(nil)