multi: Create multisig tool.

client/asset/interface.go

@@ -257,6 +257,10 @@ const (
 	// too small to cover the gas fees when using a bundler.
 	ErrBundlerRedemptionLotSizeTooSmall = dex.ErrorKind("bundler redemption lot size too small")
 
+	// ErrMultisigPartialSend is returned when an error occurs after creating
+	// a multisig and sending some amount of funds.
+	ErrMultisigPartialSend = dex.ErrorKind("multisig partially sent")
+
 	// InternalNodeLoggerName is the name for a logger that is used to fine
 	// tune log levels for only loggers using this name.
 	InternalNodeLoggerName = "INTL"
@@ -816,6 +820,36 @@ type Bonder interface {
 	// required for efficient client bond management.
 }
 
+type PaymentMultisig struct {
+	NRequired, Locktime int64
+	AssetID             uint32
+	SignerXpubs         [][]byte
+	AddrToVal           map[string]float64
+	SpendingTx          *PaymentMultisigTx
+}
+
+type PaymentMultisigTx struct {
+	TxHex   string `json:"txhex"`
+	HasSigs []bool `json:"hassigs"`
+}
+
+// Multisigner is a wallet capable of sending payments to multisig addresses.
+type Multisigner interface {
+	Broadcaster
+	// SendFundsToMultisig sends amounts to a multisig address, then creates
+	// a transaction that spends those funds. ErrMultisigPartialSend and
+	// partial results are returned if an error happens after sending funds.
+	SendFundsToMultisig(ctx context.Context, pm *PaymentMultisig) (*PaymentMultisigTx, error)
+	// SignMultisig signs the pmTx with the supplied privateKey and inserts
+	// the signature at idx among the other signatures.
+	SignMultisig(ctx context.Context, pmTx *PaymentMultisigTx, privKey []byte) (*PaymentMultisigTx, error)
+	// RefundMultisig refunds a multisig if it is after the locktime and we
+	// are the sender.
+	RefundMultisig(ctx context.Context, pmTx *PaymentMultisigTx) (txHash string, err error)
+	// ViewPaymentMultisig returns a tx hex in human readable json format.
+	ViewPaymentMultisig(pmTx *PaymentMultisigTx) (string, error)
+}
+
 // Rescanner is a wallet implementation with rescan functionality.
 type Rescanner interface {
 	// Rescan performs a rescan and block until it is done. If no birthday is

client/core/core.go

@@ -1501,9 +1501,10 @@ type Core struct {
 	credMtx     sync.RWMutex
 	credentials *db.PrimaryCredentials
 
-	loginMtx  sync.Mutex
-	loggedIn  bool
-	bondXPriv *hdkeychain.ExtendedKey // derived from creds.EncSeed on login
+	loginMtx      sync.Mutex
+	loggedIn      bool
+	bondXPriv     *hdkeychain.ExtendedKey // derived from creds.EncSeed on login
+	multisigXPriv *hdkeychain.ExtendedKey // derived from creds.EncSeed on login
 
 	seedGenerationTime uint64
 
@@ -4581,6 +4582,10 @@ func (c *Core) Login(pw []byte) error {
 			if err != nil {
 				return false, fmt.Errorf("error deriving mesh private key: %w", err)
 			}
+			c.multisigXPriv, err = deriveMultisigXPriv(seed)
+			if err != nil {
+				return false, fmt.Errorf("error deriving multisig private key: %w", err)
+			}
 
 			if c.cfg.Mesh && c.net == dex.Simnet {
 				mesh, err := mesh.New(&mesh.Config{
@@ -4921,6 +4926,8 @@ func (c *Core) Logout() error {
 
 	c.bondXPriv.Zero()
 	c.bondXPriv = nil
+	c.multisigXPriv.Zero()
+	c.multisigXPriv = nil
 
 	c.loggedIn = false
 

client/core/core_test.go

@@ -666,6 +666,18 @@ func (tdb *TDB) Language() (string, error) {
 	return "en-US", nil
 }
 
+func (tdb *TDB) NextMultisigKeyIndex(assetID uint32) (uint32, error) {
+	return 0, nil
+}
+
+func (tdb *TDB) StoreMultisigIndexForPubkey(assetID, idx uint32, pubkey [33]byte) error {
+	return nil
+}
+
+func (tdb *TDB) MultisigIndexForPubkey(assetID uint32, pubkey [33]byte) (uint32, error) {
+	return 0, nil
+}
+
 type tCoin struct {
 	id []byte