decred.org/dcrdex@v1.0.3/client/asset/btc/electrum_client.go

// This code is available on the terms of the project LICENSE.md file,
// also available online at https://blueoakcouncil.org/license/1.0.0.

package btc

import (
	"bytes"
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"math/rand"
	"net"
	"sort"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"decred.org/dcrdex/client/asset"
	"decred.org/dcrdex/client/asset/btc/electrum"
	"decred.org/dcrdex/dex"
	"decred.org/dcrdex/dex/config"
	dexbtc "decred.org/dcrdex/dex/networks/btc"
	"github.com/btcsuite/btcd/btcec/v2"
	"github.com/btcsuite/btcd/btcutil"
	"github.com/btcsuite/btcd/btcutil/psbt"
	"github.com/btcsuite/btcd/chaincfg"
	"github.com/btcsuite/btcd/chaincfg/chainhash"
	"github.com/btcsuite/btcd/txscript"
	"github.com/btcsuite/btcd/wire"
)

type electrumWalletClient interface {
	FeeRate(ctx context.Context, confTarget int64) (int64, error)
	Broadcast(ctx context.Context, tx []byte) (string, error)
	AddLocalTx(ctx context.Context, tx []byte) (string, error)
	RemoveLocalTx(ctx context.Context, txid string) error
	Commands(ctx context.Context) ([]string, error)
	GetInfo(ctx context.Context) (*electrum.GetInfoResult, error)
	GetServers(ctx context.Context) ([]*electrum.GetServersResult, error)
	GetBalance(ctx context.Context) (*electrum.Balance, error)
	ListUnspent(ctx context.Context) ([]*electrum.ListUnspentResult, error)
	FreezeUTXO(ctx context.Context, txid string, out uint32) error
	UnfreezeUTXO(ctx context.Context, txid string, out uint32) error
	CreateNewAddress(ctx context.Context) (string, error)
	GetUnusedAddress(ctx context.Context) (string, error)
	CheckAddress(ctx context.Context, addr string) (valid, mine bool, err error)
	SignTx(ctx context.Context, walletPass string, psbtB64 string) ([]byte, error)
	GetPrivateKeys(ctx context.Context, walletPass, addr string) (string, error)
	GetWalletTxConfs(ctx context.Context, txid string) (int, error)     // shortcut if owned
	GetRawTransaction(ctx context.Context, txid string) ([]byte, error) // wallet method
	GetAddressHistory(ctx context.Context, addr string) ([]*electrum.GetAddressHistoryResult, error)
	GetAddressUnspent(ctx context.Context, addr string) ([]*electrum.GetAddressUnspentResult, error)
	OnchainHistory(ctx context.Context, from, to int64) ([]electrum.TransactionResult, error)
	Version(ctx context.Context) (string, error)
	SetIncludeIgnoreWarnings(include bool)
}

type electrumNetworkClient interface {
	Done() <-chan struct{}
	Shutdown()
	Features(ctx context.Context) (*electrum.ServerFeatures, error)
	GetTransaction(ctx context.Context, txid string) (*electrum.GetTransactionResult, error)
	BlockHeader(ctx context.Context, height uint32) (string, error)
	BlockHeaders(ctx context.Context, startHeight, count uint32) (*electrum.GetBlockHeadersResult, error)
}

type electrumWallet struct {
	log         dex.Logger
	chainParams *chaincfg.Params
	decodeAddr  dexbtc.AddressDecoder
	stringAddr  dexbtc.AddressStringer
	rpcCfg      *RPCConfig // supports live reconfigure check
	wallet      electrumWalletClient
	chainV      atomic.Value // electrumNetworkClient
	segwit      bool

	// ctx is set on connect, and used in asset.Wallet and btc.Wallet interface
	// method implementations that have no ctx arg yet (refactoring TODO).
	ctx context.Context

	lockedOutpointsMtx sync.RWMutex
	lockedOutpoints    map[OutPoint]struct{}

	pwMtx    sync.RWMutex
	pw       string
	unlocked bool
}

func (ew *electrumWallet) chain() electrumNetworkClient {
	cl, _ := ew.chainV.Load().(electrumNetworkClient)
	return cl
}

func (ew *electrumWallet) resetChain(cl electrumNetworkClient) {
	ew.chainV.Store(cl)
}

type electrumWalletConfig struct {
	params       *chaincfg.Params
	log          dex.Logger
	addrDecoder  dexbtc.AddressDecoder
	addrStringer dexbtc.AddressStringer
	segwit       bool // indicates if segwit addresses are expected from requests
	rpcCfg       *RPCConfig
}

func newElectrumWallet(ew electrumWalletClient, cfg *electrumWalletConfig) *electrumWallet {
	addrDecoder := cfg.addrDecoder
	if addrDecoder == nil {
		addrDecoder = btcutil.DecodeAddress
	}

	addrStringer := cfg.addrStringer
	if addrStringer == nil {
		addrStringer = func(addr btcutil.Address, _ *chaincfg.Params) (string, error) {
			return addr.String(), nil
		}
	}

	return &electrumWallet{
		log:         cfg.log,
		chainParams: cfg.params,
		decodeAddr:  addrDecoder,
		stringAddr:  addrStringer,
		wallet:      ew,
		segwit:      cfg.segwit,
		// TODO: remove this when all interface methods are given a Context. In
		// the meantime, init with a valid sentry context until connect().
		ctx: context.TODO(),
		// chain is constructed after wallet connects to a server
		lockedOutpoints: make(map[OutPoint]struct{}),
		rpcCfg:          cfg.rpcCfg,
	}
}

// BEGIN unimplemented asset.Wallet methods

func (ew *electrumWallet) RawRequest(context.Context, string, []json.RawMessage) (json.RawMessage, error) {
	return nil, errors.New("not available") // and not used
}

// END unimplemented methods

// Prefer the SSL port if set, but allow TCP if that's all it has.
func bestAddr(host string, gsr *electrum.GetServersResult) (string, *tls.Config) {
	if gsr.SSL != 0 {
		rootCAs, _ := x509.SystemCertPool()
		tlsConfig := &tls.Config{
			InsecureSkipVerify: true,
			RootCAs:            rootCAs,
			// MinVersion:         tls.VersionTLS12,
			ServerName: host,
		}
		port := strconv.FormatUint(uint64(gsr.SSL), 10)
		return net.JoinHostPort(host, port), tlsConfig
	} else if gsr.TCP != 0 {
		port := strconv.FormatUint(uint64(gsr.TCP), 10)
		return net.JoinHostPort(host, port), nil
	}
	return "", nil
}

// Look up the port of the active server via getservers and return a "host:port"
// formatted address. A non-nil tls.Config is returned if an SSL port. A empty
// host input will pick a random SSL host.
func (ew *electrumWallet) connInfo(ctx context.Context, host string) (addr string, tlsConfig *tls.Config, err error) {
	servers, err := ew.wallet.GetServers(ctx)
	if err != nil {
		return "", nil, err
	}
	var wsrv *electrum.GetServersResult
	if host == "" { // pick a random SSL host
		var sslServers []*electrum.GetServersResult
		for _, srv := range servers {
			if srv.SSL != 0 {
				sslServers = append(sslServers, srv)
			}
		}
		// TODO: allow non-tcp onion hosts
		if len(sslServers) == 0 {
			return "", nil, errors.New("no SSL servers")
		}
		wsrv = sslServers[rand.Intn(len(sslServers))]
	} else {
		for _, srv := range servers {
			if srv.Host == host {
				wsrv = srv
				break
			}
		}
		if wsrv == nil {
			return "", nil, fmt.Errorf("Electrum wallet server %q not found in getservers result", host)
		}
	}
	addr, tlsConfig = bestAddr(host, wsrv)
	if addr == "" {
		return "", nil, fmt.Errorf("no suitable address for host %v", host)
	}
	return addr, tlsConfig, nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) connect(ctx context.Context, wg *sync.WaitGroup) error {
	// Helper to get a host:port string and connection options for a host name.
	connInfo := func(host string) (addr string, srvOpts *electrum.ConnectOpts, err error) {
		addr, tlsConfig, err := ew.connInfo(ctx, host)
		if err != nil {
			return "", nil, fmt.Errorf("no suitable address for host %q: %w", host, err)
		}
		srvOpts = &electrum.ConnectOpts{
			// TorProxy: TODO
			TLSConfig:   tlsConfig, // may be nil if not ssl host
			DebugLogger: ew.log.Debugf,
		}
		return addr, srvOpts, nil
	}

	info, err := ew.wallet.GetInfo(ctx) // also initial connectivity test with the external wallet
	if err != nil {
		return err
	}
	if !info.Connected || info.Server == "" {
		return errors.New("Electrum wallet has no server connections")
	}

	// Determine if segwit expectation is met. Request and decode an address,
	// then compare with the segwit config field.
	addr, err := ew.wallet.GetUnusedAddress(ctx)
	if err != nil {
		return err
	}
	address, err := ew.decodeAddr(addr, ew.chainParams)
	if err != nil {
		return err
	}
	_, segwit := address.(interface {
		WitnessVersion() byte
	})
	if segwit != ew.segwit {
		return fmt.Errorf("segwit expectation not met: wanted segwit = %v (old wallet seed?)", ew.segwit)
	}

	addr, srvOpts, err := connInfo(info.Server)
	if err != nil {
		return fmt.Errorf("no suitable address for host %v: %w", info.Server, err)
	}
	chain, err := electrum.ConnectServer(ctx, addr, srvOpts)
	if err != nil {
		return err // maybe just try a different one if it doesn't allow multiple conns
	}
	ew.log.Infof("Now connected to electrum server %v.", addr)
	ew.resetChain(chain)
	ew.ctx = ctx // for requests via methods that lack a context arg

	// This wallet may not be "protected", in which case we omit the password
	// from the requests. Detect this now and flag the wallet as unlocked.
	_ = ew.walletUnlock([]byte{})

	// Start a goroutine to keep the chain client alive and on the same
	// ElectrumX server as the external Electrum wallet if possible.
	wg.Add(1)
	go func() {
		defer wg.Done()
		defer ew.chain().Shutdown()
		lastWalletServer := info.Server

		failing := make(map[string]int)
		const maxFails = 8

		ticker := time.NewTicker(6 * time.Second) // to keep wallet and chain client on same server
		defer ticker.Stop()

		for {
			var walletCheck bool
			select {
			case <-ew.chain().Done():
				ew.log.Warnf("Electrum server connection lost. Reconnecting in 5 seconds...")
				select {
				case <-time.After(5 * time.Second):
				case <-ctx.Done():
					return
				}

			case <-ticker.C: // just checking with wallet for changes
				walletCheck = true

			case <-ctx.Done():
				return
			}

			info, err := ew.wallet.GetInfo(ctx)
			if err != nil {
				ew.log.Errorf("Electrum wallet getinfo failed: %v", err)
				continue
			}
			if walletCheck { // just checking if wallet's server changed
				if lastWalletServer == info.Server {
					continue // no change
				}
				delete(failing, info.Server) // clean slate now that wallet has just gotten on it
				ew.log.Infof("Electrum wallet changed server to %v", info.Server)
			}
			lastWalletServer = info.Server

			tryAddr := info.Server
			if fails := failing[tryAddr]; fails > maxFails {
				ew.log.Warnf("Server %q has failed to connect %d times. Trying a random one...", tryAddr, fails)
				tryAddr = "" // try a random one instead
			}

			addr, srvOpts, err := connInfo(tryAddr)
			if err != nil {
				failing[tryAddr]++
				ew.log.Errorf("No suitable address for host %q: %v", tryAddr, err)
				continue
			}

			if walletCheck {
				ew.chain().Shutdown()
			}
			ew.log.Infof("Connecting to new server %v...", addr)
			chain, err := electrum.ConnectServer(ctx, addr, srvOpts)
			if err != nil {
				ew.log.Errorf("Failed to connect to %v: %v", addr, err)
				failing[tryAddr]++
				continue
			}
			ew.log.Infof("Chain service now connected to electrum server %v", addr)
			ew.resetChain(chain)

			if ctx.Err() != nil { // in case shutdown while waiting on ConnectServer
				return
			}
		}
	}()

	return err
}

func (ew *electrumWallet) reconfigure(cfg *asset.WalletConfig, currentAddress string) (restartRequired bool, err error) {
	// electrumWallet only handles walletTypeElectrum.
	if cfg.Type != walletTypeElectrum {
		restartRequired = true
		return
	}

	// Check the RPC configuration.
	var parsedCfg RPCWalletConfig // {RPCConfig, WalletConfig} - former may not change
	err = config.Unmapify(cfg.Settings, &parsedCfg)
	if err != nil {
		return false, fmt.Errorf("error parsing rpc wallet config: %w", err)
	}
	dexbtc.StandardizeRPCConf(&parsedCfg.RPCConfig.RPCConfig, "")

	// Changing RPC settings is not supported without restart.
	return parsedCfg.RPCConfig != *ew.rpcCfg, nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) sendRawTransaction(tx *wire.MsgTx) (*chainhash.Hash, error) {
	b, err := serializeMsgTx(tx)
	if err != nil {
		return nil, err
	}
	// Add the transaction to the wallet DB before broadcasting it on the
	// network, otherwise it is not immediately recorded. This is expected to
	// error on non-wallet transactions such as counterparty transactions.
	_, err = ew.wallet.AddLocalTx(ew.ctx, b)
	if err != nil && !strings.Contains(err.Error(), "unrelated to this wallet") {
		ew.log.Warnf("Failed to add tx to the wallet DB: %v", err)
	}
	txid, err := ew.wallet.Broadcast(ew.ctx, b)
	if err != nil {
		ew.tryRemoveLocalTx(ew.ctx, tx.TxHash().String())
		return nil, err
	}
	hash, err := chainhash.NewHashFromStr(txid)
	if err != nil {
		return nil, err // well that sucks, it's already sent
	}
	ops := make([]*Output, len(tx.TxIn))
	for i, txIn := range tx.TxIn {
		prevOut := txIn.PreviousOutPoint
		ops[i] = &Output{Pt: NewOutPoint(&prevOut.Hash, prevOut.Index)}
	}
	if err = ew.lockUnspent(true, ops); err != nil {
		ew.log.Errorf("Failed to unlock spent UTXOs: %v", err)
	}
	return hash, nil
}

func (ew *electrumWallet) outputIsSpent(ctx context.Context, txHash *chainhash.Hash, vout uint32, pkScript []byte) (bool, error) {
	_, addrs, _, err := txscript.ExtractPkScriptAddrs(pkScript, ew.chainParams)
	if err != nil {
		return false, fmt.Errorf("failed to decode pkScript: %w", err)
	}
	if len(addrs) != 1 {
		return false, fmt.Errorf("pkScript encodes %d addresses, not 1", len(addrs))
	}
	addr, err := ew.stringAddr(addrs[0], ew.chainParams)
	if err != nil {
		return false, fmt.Errorf("invalid address encoding: %w", err)
	}
	// Now see if the unspent outputs for this address include this outpoint.
	addrUnspents, err := ew.wallet.GetAddressUnspent(ctx, addr)
	if err != nil {
		return false, fmt.Errorf("getaddressunspent: %w", err)
	}
	txid := txHash.String()
	for _, utxo := range addrUnspents {
		if utxo.TxHash == txid && uint32(utxo.TxPos) == vout {
			return false, nil // still unspent
		}
	}
	ew.log.Infof("Output %s:%d not found in unspent output list. Searching for spending txn...",
		txid, vout)
	// getaddressunspent can sometimes exclude an unspent output if it is new,
	// so now search for an actual spending txn, which is a more expensive
	// operation so we only fall back on this.
	spendTx, _, err := ew.findOutputSpender(ctx, txHash, vout)
	if err != nil {
		return false, fmt.Errorf("failure while checking for spending txn: %v", err)
	}
	return spendTx != nil, nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) getTxOut(txHash *chainhash.Hash, vout uint32, _ []byte, _ time.Time) (*wire.TxOut, uint32, error) {
	return ew.getTxOutput(ew.ctx, txHash, vout)
}

func (ew *electrumWallet) getTxOutput(ctx context.Context, txHash *chainhash.Hash, vout uint32) (*wire.TxOut, uint32, error) {
	// In case this is a wallet transaction, try the wallet DB methods first,
	// then fall back to the more expensive server request.
	txid := txHash.String()
	txRaw, confs, err := ew.checkWalletTx(txid)
	if err != nil {
		txRes, err := ew.chain().GetTransaction(ctx, txid)
		if err != nil {
			return nil, 0, err
		}
		confs = uint32(txRes.Confirmations)
		txRaw, err = hex.DecodeString(txRes.Hex)
		if err != nil {
			return nil, 0, err
		}
	}

	msgTx, err := msgTxFromBytes(txRaw)
	if err != nil {
		return nil, 0, err
	}
	if vout >= uint32(len(msgTx.TxOut)) {
		return nil, 0, fmt.Errorf("output %d of tx %v does not exists", vout, txid)
	}
	pkScript := msgTx.TxOut[vout].PkScript
	amt := msgTx.TxOut[vout].Value

	// Given the pkScript, we can query for unspent outputs to see if this one
	// is unspent.
	spent, err := ew.outputIsSpent(ctx, txHash, vout, pkScript)
	if err != nil {
		return nil, 0, err
	}
	if spent {
		return nil, 0, nil
	}

	return wire.NewTxOut(amt, pkScript), confs, nil
}

func (ew *electrumWallet) getBlockHeaderByHeight(ctx context.Context, height int64) (*wire.BlockHeader, error) {
	hdrStr, err := ew.chain().BlockHeader(ctx, uint32(height))
	if err != nil {
		return nil, err
	}
	hdr := &wire.BlockHeader{}
	err = hdr.Deserialize(hex.NewDecoder(strings.NewReader(hdrStr)))
	if err != nil {
		return nil, err
	}
	return hdr, nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) medianTime() (time.Time, error) {
	chainHeight, err := ew.getBestBlockHeight()
	if err != nil {
		return time.Time{}, err
	}
	return ew.calcMedianTime(ew.ctx, int64(chainHeight))
}

func (ew *electrumWallet) calcMedianTime(ctx context.Context, height int64) (time.Time, error) {
	startHeight := height - medianTimeBlocks + 1
	if startHeight < 0 {
		startHeight = 0
	}

	// TODO: check a block hash => median time cache

	hdrsRes, err := ew.chain().BlockHeaders(ctx, uint32(startHeight),
		uint32(height-startHeight+1))
	if err != nil {
		return time.Time{}, err
	}

	if hdrsRes.Count != medianTimeBlocks {
		ew.log.Warnf("Failed to retrieve headers for %d blocks since block %v, got %d",
			medianTimeBlocks, height, hdrsRes.Count)
	}
	if hdrsRes.Count == 0 {
		return time.Time{}, errors.New("no headers retrieved")
	}

	hdrReader := hex.NewDecoder(strings.NewReader(hdrsRes.HexConcat))

	timestamps := make([]int64, 0, hdrsRes.Count)
	for i := int64(0); i < int64(hdrsRes.Count); i++ {
		hdr := &wire.BlockHeader{}
		err = hdr.Deserialize(hdrReader)
		if err != nil {
			if i > 0 {
				ew.log.Errorf("Failed to deserialize header for block %d: %v",
					startHeight+i, err)
				break // we have at least one time stamp, work with it
			}
			return time.Time{}, err
		}
		timestamps = append(timestamps, hdr.Timestamp.Unix())
	}
	// Naive way fetching each header separately, if we needed to use
	// btc.calcMedianTime as a chainStamper:
	// for i := height; i > height-medianTimeBlocks && i > 0; i-- {
	// 	hdr, err := ew.getBlockHeaderByHeight(ctx, height)
	// 	if err != nil {
	// 		return time.Time{}, err
	// 	}
	// 	timestamps = append(timestamps, hdr.Timestamp.Unix())
	// }

	sort.Slice(timestamps, func(i, j int) bool {
		return timestamps[i] < timestamps[j]
	})

	medianTimestamp := timestamps[len(timestamps)/2]
	return time.Unix(medianTimestamp, 0), nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) getBlockHash(height int64) (*chainhash.Hash, error) {
	hdr, err := ew.getBlockHeaderByHeight(ew.ctx, height)
	if err != nil {
		return nil, err
	}
	hash := hdr.BlockHash()
	return &hash, nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) getBestBlockHash() (*chainhash.Hash, error) {
	inf, err := ew.wallet.GetInfo(ew.ctx)
	if err != nil {
		return nil, err
	}
	return ew.getBlockHash(inf.SyncHeight)
}

// part of btc.Wallet interface
func (ew *electrumWallet) getBestBlockHeight() (int32, error) {
	inf, err := ew.wallet.GetInfo(ew.ctx)
	if err != nil {
		return 0, err
	}
	return int32(inf.SyncHeight), nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) getBestBlockHeader() (*BlockHeader, error) {
	inf, err := ew.wallet.GetInfo(ew.ctx)
	if err != nil {
		return nil, err
	}

	hdr, err := ew.getBlockHeaderByHeight(ew.ctx, inf.SyncHeight)
	if err != nil {
		return nil, err
	}

	header := &BlockHeader{
		Hash:              hdr.BlockHash().String(),
		Height:            inf.SyncHeight,
		Confirmations:     1, // it's the head
		Time:              hdr.Timestamp.Unix(),
		PreviousBlockHash: hdr.PrevBlock.String(),
	}
	return header, nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) balances() (*GetBalancesResult, error) {
	eBal, err := ew.wallet.GetBalance(ew.ctx)
	if err != nil {
		return nil, err
	}
	// NOTE: Nothing from the Electrum wallet's response indicates trusted vs.
	// untrusted. To allow unconfirmed coins to be spent, we treat both
	// confirmed and unconfirmed as trusted. This is like dogecoind's handling
	// of balance. TODO: listunspent -> checkWalletTx(txid) -> for each
	// input, checkWalletTx(prevout) and ismine(addr)
	return &GetBalancesResult{
		Mine: Balances{
			Trusted:  eBal.Confirmed + eBal.Unconfirmed,
			Immature: eBal.Immature,
		},
	}, nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) listUnspent() ([]*ListUnspentResult, error) {
	eUnspent, err := ew.wallet.ListUnspent(ew.ctx)
	if err != nil {
		return nil, err
	}
	chainHeight, err := ew.getBestBlockHeight()
	if err != nil {
		return nil, err
	}

	// Filter out locked outpoints since listUnspent includes them.
	lockedOPs := ew.listLockedOutpoints()
	lockedOPMap := make(map[RPCOutpoint]bool, len(lockedOPs))
	for _, pt := range lockedOPs {
		lockedOPMap[*pt] = true
	}

	unspents := make([]*ListUnspentResult, 0, len(eUnspent))
	for _, utxo := range eUnspent {
		if lockedOPMap[RPCOutpoint{utxo.PrevOutHash, utxo.PrevOutIdx}] {
			continue
		}
		addr, err := ew.decodeAddr(utxo.Address, ew.chainParams)
		if err != nil {
			ew.log.Warnf("Output (%v:%d) with bad address %v found: %v",
				utxo.PrevOutHash, utxo.PrevOutIdx, utxo.Address, err)
			continue
		}
		pkScript, err := txscript.PayToAddrScript(addr)
		if err != nil {
			ew.log.Warnf("Output (%v:%d) with bad address %v found: %v",
				utxo.PrevOutHash, utxo.PrevOutIdx, utxo.Address, err)
			continue
		}
		val, err := strconv.ParseFloat(utxo.Value, 64)
		if err != nil {
			ew.log.Warnf("Output (%v:%d) with bad value %v found: %v",
				utxo.PrevOutHash, utxo.PrevOutIdx, val, err)
			continue
		}
		var confs uint32
		if height := int32(utxo.Height); height > 0 {
			// height is non-zero, so confirmed, but if the RPCs are
			// inconsistent with respect to height, avoid an underflow or
			// appearing unconfirmed.
			if height > chainHeight {
				confs = 1
			} else {
				confs = uint32(chainHeight - height + 1)
			}
		}
		redeemScript, err := hex.DecodeString(utxo.RedeemScript)
		if err != nil {
			ew.log.Warnf("Output (%v:%d) with bad redeemscript %v found: %v",
				utxo.PrevOutHash, utxo.PrevOutIdx, utxo.RedeemScript, err)
			continue
		}

		unspents = append(unspents, &ListUnspentResult{
			TxID:          utxo.PrevOutHash,
			Vout:          utxo.PrevOutIdx,
			Address:       utxo.Address,
			ScriptPubKey:  pkScript,
			Amount:        val,
			Confirmations: confs,
			RedeemScript:  redeemScript,
			Spendable:     true, // can electrum have unspendable?
			Solvable:      true,
			// Safe is unknown, leave ptr nil
		})
	}
	return unspents, nil
}

// part of btc.Wallet interface
func (ew *electrumWallet) lockUnspent(unlock bool, ops []*Output) error {
	eUnspent, err := ew.wallet.ListUnspent(ew.ctx)
	if err != nil {
		return err
	}
	opMap := make(map[OutPoint]struct{}, len(ops))
	for _, op := range ops {
		opMap[op.Pt] = struct{}{}
	}
	// For the ones that appear in listunspent, use (un)freeze_utxo also.
unspents:
	for _, utxo := range eUnspent {
		for op := range opMap {
			if op.Vout == utxo.PrevOutIdx && op.TxHash.String() == utxo.PrevOutHash {
				// FreezeUTXO and UnfreezeUTXO do not error when called
				// repeatedly for the same UTXO.
				if unlock {
					if err = ew.wallet.UnfreezeUTXO(ew.ctx, utxo.PrevOutHash, utxo.PrevOutIdx); err != nil {
						ew.log.Warnf("UnfreezeUTXO(%s:%d) failed: %v", utxo.PrevOutHash, utxo.PrevOutIdx, err)
						// Maybe we lost a race somewhere. Keep going.
					}
					ew.lockedOutpointsMtx.Lock()
					delete(ew.lockedOutpoints, op)
					ew.lockedOutpointsMtx.Unlock()
					delete(opMap, op)
					continue unspents
				}

				if err = ew.wallet.FreezeUTXO(ew.ctx, utxo.PrevOutHash, utxo.PrevOutIdx); err != nil {
					ew.log.Warnf("FreezeUTXO(%s:%d) failed: %v", utxo.PrevOutHash, utxo.PrevOutIdx, err)
				}
				// listunspent returns locked utxos, so we have to track it.
				ew.lockedOutpointsMtx.Lock()
				ew.lockedOutpoints[op] = struct{}{}
				ew.lockedOutpointsMtx.Unlock()
				delete(opMap, op)
				continue unspents
			}
		}
	}

	// If not in the listunspent response, fail if trying to lock, otherwise
	// just remove them from the lockedOutpoints map (unlocking spent UTXOs).
	if len(opMap) > 0 && !unlock {
		return fmt.Errorf("failed to lock some utxos")
	}
	for op := range opMap {
		ew.lockedOutpointsMtx.Lock()
		delete(ew.lockedOutpoints, op)
		ew.lockedOutpointsMtx.Unlock()
	}

	return nil
}

func (ew *electrumWallet) listLockedOutpoints() []*RPCOutpoint {
	ew.lockedOutpointsMtx.RLock()
	defer ew.lockedOutpointsMtx.RUnlock()
	locked := make([]*RPCOutpoint, 0, len(ew.lockedOutpoints))
	for op := range ew.lockedOutpoints {
		locked = append(locked, &RPCOutpoint{
			TxID: op.TxHash.String(),
			Vout: op.Vout,
		})
	}
	return locked
}

// part of btc.Wallet interface
func (ew *electrumWallet) listLockUnspent() ([]*RPCOutpoint, error) {
	return ew.listLockedOutpoints(), nil
}

// externalAddress creates a fresh address beyond the default gap limit, so it
// should be used immediately. Part of btc.Wallet interface.
func (ew *electrumWallet) externalAddress() (btcutil.Address, error) {
	addr, err := ew.wallet.GetUnusedAddress(ew.ctx)
	if err != nil {
		return nil, err
	}
	return ew.decodeAddr(addr, ew.chainParams)
}

// changeAddress creates a fresh address beyond the default gap limit, so it
// should be used immediately. Part of btc.Wallet interface.
func (ew *electrumWallet) changeAddress() (btcutil.Address, error) {
	return ew.externalAddress() // sadly, cannot request internal addresses
}

// part of btc.Wallet interface
func (ew *electrumWallet) signTx(inTx *wire.MsgTx) (*wire.MsgTx, error) {
	// If the wallet's signtransaction RPC ever has a problem with the PSBT, we
	// could attempt to sign the transaction ourselves by pulling the inputs'
	// private keys and using txscript manually, but this can vary greatly
	// between assets.

	packet, err := psbt.NewFromUnsignedTx(inTx)
	if err != nil {
		return nil, err
	}
	psbtB64, err := packet.B64Encode()
	if err != nil {
		return nil, err
	}

	signedB, err := ew.wallet.SignTx(ew.ctx, ew.walletPass(), psbtB64)
	if err != nil {
		return nil, err
	}
	return msgTxFromBytes(signedB)
}

type hash160er interface {
	Hash160() *[20]byte
}

type pubKeyer interface {
	PubKey() *btcec.PublicKey
}

// part of btc.Wallet interface
func (ew *electrumWallet) privKeyForAddress(addr string) (*btcec.PrivateKey, error) {
	addrDec, err := ew.decodeAddr(addr, ew.chainParams)
	if err != nil {
		return nil, err
	}
	wifStr, err := ew.wallet.GetPrivateKeys(ew.ctx, ew.walletPass(), addr)
	if err != nil {
		return nil, err
	}
	wif, err := btcutil.DecodeWIF(wifStr)
	if err != nil {
		return nil, err
	} // wif.PrivKey is the result

	// Sanity check that PrivKey corresponds to the pubkey(hash).
	var pkh []byte
	switch addrT := addrDec.(type) {
	case pubKeyer: // e.g. *btcutil.AddressPubKey:
		// Get same format as wif.SerializePubKey()
		var pk []byte
		if wif.CompressPubKey {
			pk = addrT.PubKey().SerializeCompressed()
		} else {
			pk = addrT.PubKey().SerializeUncompressed()
		}
		pkh = btcutil.Hash160(pk) // addrT.ScriptAddress() would require SetFormat(compress/uncompress)
	case *btcutil.AddressScriptHash, *btcutil.AddressWitnessScriptHash:
		return wif.PrivKey, nil // assume unknown redeem script references this pubkey
	case hash160er: // p2pkh and p2wpkh
		pkh = addrT.Hash160()[:]
	}
	wifPKH := btcutil.Hash160(wif.SerializePubKey())
	if !bytes.Equal(pkh, wifPKH) {
		return nil, errors.New("pubkey mismatch")
	}
	return wif.PrivKey, nil
}

func (ew *electrumWallet) pass() (pw string, unlocked bool) {
	ew.pwMtx.RLock()
	defer ew.pwMtx.RUnlock()
	return ew.pw, ew.unlocked
}

func (ew *electrumWallet) testPass(pw []byte) error {
	addr, err := ew.wallet.GetUnusedAddress(ew.ctx)
	if err != nil {
		return err
	}
	wifStr, err := ew.wallet.GetPrivateKeys(ew.ctx, string(pw), addr)
	if err != nil {
		// When providing a password to an unprotected wallet, and other cases,
		// a cryptic error containing "incorrect padding" is returned.
		if strings.Contains(strings.ToLower(err.Error()), "incorrect padding") {
			return errors.New("incorrect password (no password required?)")
		}
		return fmt.Errorf("GetPrivateKeys: %v", err)
	}
	// That should be enough, but validate the returned keys in case they are
	// empty or invalid.
	if _, err = btcutil.DecodeWIF(wifStr); err != nil {
		return fmt.Errorf("DecodeWIF: %v", err)
	}
	return nil
}

// walletLock locks the wallet. Part of the btc.Wallet interface.
func (ew *electrumWallet) walletLock() error {
	ew.pwMtx.Lock()
	defer ew.pwMtx.Unlock()
	if ew.pw == "" && ew.unlocked {
		// This is an unprotected wallet (can't actually lock it). But confirm
		// the password is still empty in case it changed externally.
		if err := ew.testPass([]byte{}); err == nil {
			return nil
		} // must have changed! "lock" it!
	}
	ew.pw, ew.unlocked = "", false
	return nil
}

// locked indicates if the wallet has been unlocked. Part of the btc.Wallet
// interface.
func (ew *electrumWallet) locked() bool {
	ew.pwMtx.RLock()
	defer ew.pwMtx.RUnlock()
	return !ew.unlocked
}

// walletPass returns the wallet passphrase. Since an empty password is valid,
// use pass or locked to determine if locked. This is for convenience.
func (ew *electrumWallet) walletPass() string {
	pw, _ := ew.pass()
	return pw
}

// walletUnlock attempts to unlock the wallet with the provided password. On
// success, the password is stored and may be accessed via pass or walletPass.
// Part of the btc.Wallet interface.
func (ew *electrumWallet) walletUnlock(pw []byte) error {
	if err := ew.testPass(pw); err != nil {
		return err
	}
	ew.pwMtx.Lock()
	ew.pw, ew.unlocked = string(pw), true
	ew.pwMtx.Unlock()
	return nil
}

// part of the btc.Wallet interface
func (ew *electrumWallet) peerCount() (uint32, error) {
	if ew.chain() == nil { // must work prior to resetChain
		return 0, nil
	}

	info, err := ew.wallet.GetInfo(ew.ctx)
	if err != nil {
		return 0, err
	}
	select {
	case <-ew.chain().Done():
		return 0, errors.New("electrumx server connection down")
	default:
	}

	return uint32(info.Connections), nil
}

// part of the btc.Wallet interface
func (ew *electrumWallet) ownsAddress(addr btcutil.Address) (bool, error) {
	addrStr, err := ew.stringAddr(addr, ew.chainParams)
	if err != nil {
		return false, err
	}
	valid, mine, err := ew.wallet.CheckAddress(ew.ctx, addrStr)
	if err != nil {
		return false, err
	}
	if !valid { // maybe electrum doesn't know all encodings that btcutil does
		return false, nil // an error here may prevent reconfiguring a misconfigured wallet
	}
	return mine, nil
}

// part of the btc.Wallet interface
func (ew *electrumWallet) syncStatus() (*asset.SyncStatus, error) {
	info, err := ew.wallet.GetInfo(ew.ctx)
	if err != nil {
		return nil, err
	}
	return &asset.SyncStatus{
		Synced:       info.Connected && info.SyncHeight >= info.ServerHeight,
		TargetHeight: uint64(info.ServerHeight),
		Blocks:       uint64(info.SyncHeight),
	}, nil
}

// part of the btc.Wallet interface
func (ew *electrumWallet) listTransactionsSinceBlock(blockHeight int32) ([]*ListTransactionsResult, error) {
	bestHeight, err := ew.getBestBlockHeight()
	if err != nil {
		return nil, fmt.Errorf("error getting best block: %v", err)
	}
	if bestHeight < blockHeight {
		return nil, nil
	}
	var txs []*ListTransactionsResult
	from := int64(blockHeight)
	to := int64(blockHeight + 2000)
	for {
		if to > int64(bestHeight) {
			to = int64(bestHeight)
		}
		addTxs, err := ew.wallet.OnchainHistory(ew.ctx, from, to)
		if err != nil {
			return nil, fmt.Errorf("error getting onchain history: %v", err)
		}
		for _, tx := range addTxs {
			ltr := &ListTransactionsResult{
				BlockHeight: uint32(tx.Height),
				BlockTime:   uint64(tx.Timestamp), // Maybe?
				Send:        !tx.Incoming,
				TxID:        tx.TxID,
			}
			if tx.Fee != nil {
				f, err := strconv.ParseFloat(*tx.Fee, 64)
				if err != nil {
					return nil, fmt.Errorf("error parsing fee: %v", err)
				}
				ltr.Fee = &f
			}
			txs = append(txs, ltr)
		}
		if to == int64(bestHeight) {
			break
		}
		from = to
		to += 2000
	}
	return txs, nil
}

// checkWalletTx will get the bytes and confirmations of a wallet transaction.
// For non-wallet transactions, it is normal to see "Exception: Transaction not
// in wallet" in Electrum's parent console, if launched from a terminal.
// Part of the walletTxChecker interface.
func (ew *electrumWallet) checkWalletTx(txid string) ([]byte, uint32, error) {
	// GetWalletTxConfs only works for wallet transactions, while
	// wallet.GetRawTransaction will try the wallet DB first, but fall back to
	// querying a server, so do GetWalletTxConfs first to prevent that.
	confs, err := ew.wallet.GetWalletTxConfs(ew.ctx, txid)
	if err != nil {
		return nil, 0, err
	}
	txRaw, err := ew.wallet.GetRawTransaction(ew.ctx, txid)
	if err != nil {
		return nil, 0, err
	}
	if confs < 0 {
		confs = 0
	}
	return txRaw, uint32(confs), nil
}

// part of the walletTxChecker interface
func (ew *electrumWallet) getWalletTransaction(txHash *chainhash.Hash) (*GetTransactionResult, error) {
	// Try the wallet first. If it is not a wallet transaction or if it is
	// confirmed, fall back to the chain method to get the block info and time
	// fields.
	txid := txHash.String()
	txRaw, confs, err := ew.checkWalletTx(txid)
	if err == nil && confs == 0 {
		return &GetTransactionResult{
			TxID:  txid,
			Bytes: txRaw,
			// Time/TimeReceived? now? needed?
		}, nil
	} // else we have to ask a server for the verbose response with block info

	txInfo, err := ew.chain().GetTransaction(ew.ctx, txid)
	if err != nil {
		return nil, err
	}
	txRaw, err = hex.DecodeString(txInfo.Hex)
	if err != nil {
		return nil, err
	}
	return &GetTransactionResult{
		Confirmations: uint64(txInfo.Confirmations),
		BlockHash:     txInfo.BlockHash,
		// BlockIndex unknown
		BlockTime:    uint64(txInfo.BlockTime),
		TxID:         txInfo.TxID, // txHash.String()
		Time:         uint64(txInfo.Time),
		TimeReceived: uint64(txInfo.Time),
		Bytes:        txRaw,
	}, nil
}

func (ew *electrumWallet) fingerprint() (string, error) {
	return "", fmt.Errorf("fingerprint not implemented")
}

// part of the walletTxChecker interface
func (ew *electrumWallet) swapConfirmations(txHash *chainhash.Hash, vout uint32, contract []byte, startTime time.Time) (confs uint32, spent bool, err error) {
	// To determine if it is spent, we need the address of the output.
	var pkScript []byte
	txid := txHash.String()
	// Try the wallet first in case this is a wallet transaction (own swap).
	txRaw, confs, err := ew.checkWalletTx(txid)
	if err == nil {
		msgTx, err := msgTxFromBytes(txRaw)
		if err != nil {
			return 0, false, err
		}
		if vout >= uint32(len(msgTx.TxOut)) {
			return 0, false, fmt.Errorf("output %d of tx %v does not exists", vout, txid)
		}
		pkScript = msgTx.TxOut[vout].PkScript
	} else {
		// Fall back to the more expensive server request.
		txInfo, err := ew.chain().GetTransaction(ew.ctx, txid)
		if err != nil {
			return 0, false, err
		}
		confs = uint32(txInfo.Confirmations)
		if txInfo.Confirmations < 1 {
			confs = 0
		}
		if vout >= uint32(len(txInfo.Vout)) {
			return 0, false, fmt.Errorf("output %d of tx %v does not exists", vout, txid)
		}
		txOut := &txInfo.Vout[vout]
		pkScript, err = hex.DecodeString(txOut.PkScript.Hex)
		if err != nil {
			return 0, false, fmt.Errorf("invalid pkScript: %w", err)
		}
	}

	spent, err = ew.outputIsSpent(ew.ctx, txHash, vout, pkScript)
	if err != nil {
		return 0, false, err
	}
	return confs, spent, nil
}

// tryRemoveLocalTx attempts to remove a "local" transaction from the Electrum
// wallet. Such a transaction is unbroadcasted. This may be necessary if a
// broadcast of a local txn attempt failed so that the inputs are available for
// other transactions.
func (ew *electrumWallet) tryRemoveLocalTx(ctx context.Context, txid string) {
	if err := ew.wallet.RemoveLocalTx(ctx, txid); err != nil {
		ew.log.Errorf("Failed to remove local transaction %s: %v",
			txid, err)
	}
}

func (ew *electrumWallet) outPointAddress(ctx context.Context, txid string, vout uint32) (string, error) {
	txRaw, err := ew.wallet.GetRawTransaction(ctx, txid)
	if err != nil {
		return "", err
	}
	msgTx, err := msgTxFromBytes(txRaw)
	if err != nil {
		return "", err
	}
	if vout >= uint32(len(msgTx.TxOut)) {
		return "", fmt.Errorf("output %d of tx %v does not exists", vout, txid)
	}
	pkScript := msgTx.TxOut[vout].PkScript
	_, addrs, _, err := txscript.ExtractPkScriptAddrs(pkScript, ew.chainParams)
	if err != nil {
		return "", fmt.Errorf("invalid pkScript: %v", err)
	}
	if len(addrs) != 1 {
		return "", fmt.Errorf("invalid pkScript: %d addresses", len(addrs))
	}
	addrStr, err := ew.stringAddr(addrs[0], ew.chainParams)
	if err != nil {
		return "", err
	}
	return addrStr, nil
}

func (ew *electrumWallet) findOutputSpender(ctx context.Context, txHash *chainhash.Hash, vout uint32) (*wire.MsgTx, uint32, error) {
	txid := txHash.String()
	addr, err := ew.outPointAddress(ctx, txid, vout)
	if err != nil {
		return nil, 0, fmt.Errorf("invalid outpoint address: %w", err)
	}
	// NOTE: Caller should already have determined the output is spent before
	// requesting the entire address history.
	hist, err := ew.wallet.GetAddressHistory(ctx, addr)
	if err != nil {
		return nil, 0, fmt.Errorf("unable to get address history: %w", err)
	}

	sort.Slice(hist, func(i, j int) bool {
		return hist[i].Height > hist[j].Height // descending
	})

	var outHeight int64
	for _, io := range hist {
		if io.TxHash == txid {
			outHeight = io.Height
			continue // same txn
		}
		if io.Height < outHeight {
			break // spender not before the output's txn
		}
		txRaw, err := ew.wallet.GetRawTransaction(ctx, io.TxHash)
		if err != nil {
			ew.log.Warnf("Unable to retrieve transaction %v for address %v: %v",
				io.TxHash, addr, err)
			continue
		}
		msgTx, err := msgTxFromBytes(txRaw)
		if err != nil {
			ew.log.Warnf("Unable to decode transaction %v for address %v: %v",
				io.TxHash, addr, err)
			continue
		}
		for vin, txIn := range msgTx.TxIn {
			prevOut := &txIn.PreviousOutPoint
			if vout == prevOut.Index && prevOut.Hash.IsEqual(txHash) {
				return msgTx, uint32(vin), nil
			}
		}
	}

	return nil, 0, nil // caller should check msgTx (internal method)
}