lnwallet/btcwallet: remove internal utxoCache

The cache wasn't really serving a purpose as FetchInputInfo isn't known
to be a hot path. Also, with a planned addition of returning the
confirmation status of an output within FetchInputInfo in a later
commit, caching won't be useful as we'll have to go to disk anyway to
determine the confirmation status.

lnwallet/btcwallet/btcwallet.go

@@ -59,11 +59,6 @@ type BtcWallet struct {
 	netParams *chaincfg.Params
 
 	chainKeyScope waddrmgr.KeyScope
-
-	// utxoCache is a cache used to speed up repeated calls to
-	// FetchInputInfo.
-	utxoCache map[wire.OutPoint]*wire.TxOut
-	cacheMtx  sync.RWMutex
 }
 
 // A compile time check to ensure that BtcWallet implements the
@@ -130,7 +125,6 @@ func New(cfg Config) (*BtcWallet, error) {
 		chain:         cfg.ChainSource,
 		netParams:     cfg.NetParams,
 		chainKeyScope: chainKeyScope,
-		utxoCache:     make(map[wire.OutPoint]*wire.TxOut),
 	}, nil
 }
 

lnwallet/btcwallet/signer.go

@@ -26,17 +26,7 @@ func (b *BtcWallet) FetchInputInfo(prevOut *wire.OutPoint) (*wire.TxOut, error)
 		err    error
 		output *wire.TxOut
 	)
-
-	// First check to see if the output is already within the utxo cache.
-	// If so we can return directly saving a disk access.
-	b.cacheMtx.RLock()
-	if output, ok := b.utxoCache[*prevOut]; ok {
-		b.cacheMtx.RUnlock()
-		return output, nil
-	}
-	b.cacheMtx.RUnlock()
-
-	// Otherwise, we manually look up the output within the tx store.
+	// We manually look up the output within the tx store.
 	txid := &prevOut.Hash
 	txDetail, err := base.UnstableAPI(b.wallet).TxDetails(txid)
 	if err != nil {
@@ -54,9 +44,6 @@ func (b *BtcWallet) FetchInputInfo(prevOut *wire.OutPoint) (*wire.TxOut, error)
 		return nil, err
 	}
 
-	b.cacheMtx.Lock()
-	b.utxoCache[*prevOut] = output
-	b.cacheMtx.Unlock()
 
 	return output, nil
 }