assets+loopdb: implement asset deposit withdrawal

This commit implements the necessary plumbing to enable deposit
withdrawal. Withdrawing reveals the server's internal key for the
deposit, allowing the client to sweep it independently.

Author: bhandras

assets/deposit/manager.go

@@ -1012,3 +1012,76 @@ func (m *Manager) releaseDepositSweepInputs(ctx context.Context,
 
 	return nil
 }
+
+// WithdrawDeposits withdraws the deposits with the given IDs. It will first ask
+// the server for the deposit keys, then initate the withdrawal by updating the
+// deposit state.
+func (m *Manager) WithdrawDeposits(ctx context.Context,
+	depositIDs []string) error {
+
+	done, err := m.scheduleNextCall()
+	if err != nil {
+		return err
+	}
+	defer done()
+
+	for _, depositID := range depositIDs {
+		d, ok := m.deposits[depositID]
+		if !ok {
+			return fmt.Errorf("deposit %v not found", depositID)
+		}
+
+		if d.State != StateConfirmed {
+			return fmt.Errorf("deposit %v is not withdrawable, "+
+				"current state: %v", depositID, d.State)
+		}
+
+		log.Infof("Initiating deposit withdrawal %v: %v",
+			depositID, d.Amount)
+	}
+
+	keys, err := m.depositServiceClient.WithdrawAssetDeposits(
+		ctx, &swapserverrpc.WithdrawAssetDepositsServerReq{
+			DepositIds: depositIDs,
+		},
+	)
+	if err != nil {
+		return fmt.Errorf("unable to request withdrawal: %w", err)
+	}
+
+	for depositID, privKeyBytes := range keys.DepositKeys {
+		d, ok := m.deposits[depositID]
+		if !ok {
+			log.Warnf("Skipping withdrawal of unknown deposit: %v",
+				depositID)
+			continue
+		}
+
+		privKey, pubKey := btcec.PrivKeyFromBytes(privKeyBytes)
+		if !d.CoSignerInternalKey.IsEqual(pubKey) {
+			return fmt.Errorf("revealed co-signer internal key "+
+				"does not match local key for %v", depositID)
+		}
+
+		err := m.store.SetAssetDepositServerKey(ctx, depositID, privKey)
+		if err != nil {
+			return err
+		}
+
+		d.State = StateWithdrawn
+		err = d.GenerateSweepKeys(ctx, m.tapClient)
+		if err != nil {
+			log.Errorf("Unable to generate sweep keys for deposit "+
+				"withdrawal %v: %v", d.ID, err)
+
+			return err
+		}
+
+		err = m.handleDepositStateUpdate(ctx, d)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}

assets/deposit/server.go

@@ -149,5 +149,19 @@ func (s *Server) WithdrawAssetDeposits(ctx context.Context,
 	in *looprpc.WithdrawAssetDepositsRequest) (
 	*looprpc.WithdrawAssetDepositsResponse, error) {
 
-	return nil, status.Error(codes.Unimplemented, "unimplemented")
+	if s.manager == nil {
+		return nil, ErrAssetDepositsUnavailable
+	}
+
+	if len(in.DepositIds) == 0 {
+		return nil, status.Error(codes.InvalidArgument,
+			"at least one deposit id must be provided")
+	}
+
+	err := s.manager.WithdrawDeposits(ctx, in.DepositIds)
+	if err != nil {
+		return nil, status.Error(codes.Internal, err.Error())
+	}
+
+	return &looprpc.WithdrawAssetDepositsResponse{}, nil
 }

assets/deposit/sql_store.go

@@ -35,6 +35,9 @@ type Querier interface {
 
 	GetActiveAssetDeposits(ctx context.Context) (
 		[]sqlc.GetActiveAssetDepositsRow, error)
+
+	SetAssetDepositServerInternalKey(ctx context.Context,
+		arg sqlc.SetAssetDepositServerInternalKeyParams) error
 }
 
 // DepositBaseDB is the interface that contains all the queries generated
@@ -135,6 +138,8 @@ func (s *SQLStore) UpdateDeposit(ctx context.Context, d *Deposit) error {
 			}
 
 		case StateExpired:
+			fallthrough
+		case StateWithdrawn:
 			scriptKey := d.SweepScriptKey.SerializeCompressed()
 			internalKey := d.SweepInternalKey.SerializeCompressed()
 			err := tx.SetAssetDepositSweepKeys(
@@ -310,3 +315,16 @@ func (s *SQLStore) GetActiveDeposits(ctx context.Context) ([]Deposit, error) {
 
 	return deposits, nil
 }
+
+// SetAssetDepositServerKey sets the server's internal key for the give asset
+// deposit.
+func (s *SQLStore) SetAssetDepositServerKey(ctx context.Context,
+	depositID string, key *btcec.PrivateKey) error {
+
+	return s.db.SetAssetDepositServerInternalKey(
+		ctx, sqlc.SetAssetDepositServerInternalKeyParams{
+			DepositID:         depositID,
+			ServerInternalKey: key.Serialize(),
+		},
+	)
+}

loopdb/sqlc/asset_deposits.sql.go

@@ -59,3 +59,8 @@ WHERE u.id = (
 )
 AND u.update_state IN (0, 1, 2, 3, 4, 5, 6);
 
+-- name: SetAssetDepositServerInternalKey :exec
+UPDATE asset_deposits
+SET server_internal_key = $2
+WHERE deposit_id = $1
+AND server_internal_key IS NULL;