staticaddr: use generated change addresses

Author: hieblmi

loopdb/sqlc/migrations/000022_static_loopin_change_address.down.sql

@@ -0,0 +1 @@
+ALTER TABLE static_address_swaps DROP COLUMN change_static_address_id;

loopdb/sqlc/migrations/000022_static_loopin_change_address.up.sql

@@ -0,0 +1,13 @@
+ALTER TABLE static_address_swaps
+    ADD change_static_address_id INT REFERENCES static_addresses(id);
+
+-- Existing fractional swaps sent change back to the legacy static address.
+-- Backfill that relation so in-flight swaps remain recoverable after the
+-- client starts requiring explicit per-swap change metadata.
+UPDATE static_address_swaps
+SET change_static_address_id = (
+    SELECT id FROM static_addresses ORDER BY id ASC LIMIT 1
+)
+WHERE selected_amount > 0
+  AND change_static_address_id IS NULL
+  AND EXISTS (SELECT 1 FROM static_addresses);

loopdb/sqlc/models.go

@@ -10,7 +10,8 @@ INSERT INTO static_address_swaps (
     htlc_tx_fee_rate_sat_kw,
     htlc_timeout_sweep_tx_id,
     htlc_timeout_sweep_address,
-    fast
+    fast,
+    change_static_address_id
 ) VALUES (
     $1,
     $2,
@@ -22,7 +23,8 @@ INSERT INTO static_address_swaps (
     $8,
     $9,
     $10,
-    $11
+    $11,
+    $12
 );
 
 -- name: UpdateStaticAddressLoopIn :exec
@@ -48,27 +50,49 @@ INSERT INTO static_address_swap_updates (
 SELECT
     swaps.*,
     static_address_swaps.*,
-    htlc_keys.*
+    htlc_keys.*,
+    change_address.client_pubkey     change_client_pubkey,
+    change_address.server_pubkey     change_server_pubkey,
+    change_address.expiry            change_expiry,
+    change_address.client_key_family change_client_key_family,
+    change_address.client_key_index  change_client_key_index,
+    change_address.pkscript          change_pkscript,
+    change_address.protocol_version  change_protocol_version,
+    change_address.initiation_height change_initiation_height
 FROM
     swaps
         JOIN
     static_address_swaps ON swaps.swap_hash = static_address_swaps.swap_hash
         JOIN
     htlc_keys ON swaps.swap_hash = htlc_keys.swap_hash
+        LEFT JOIN
+    static_addresses change_address
+        ON static_address_swaps.change_static_address_id = change_address.id
 WHERE
         swaps.swap_hash = $1;
 
 -- name: GetStaticAddressLoopInSwapsByStates :many
 SELECT
     swaps.*,
     static_address_swaps.*,
-    htlc_keys.*
+    htlc_keys.*,
+    change_address.client_pubkey     change_client_pubkey,
+    change_address.server_pubkey     change_server_pubkey,
+    change_address.expiry            change_expiry,
+    change_address.client_key_family change_client_key_family,
+    change_address.client_key_index  change_client_key_index,
+    change_address.pkscript          change_pkscript,
+    change_address.protocol_version  change_protocol_version,
+    change_address.initiation_height change_initiation_height
 FROM
     swaps
         JOIN
     static_address_swaps ON swaps.swap_hash = static_address_swaps.swap_hash
         JOIN
     htlc_keys ON swaps.swap_hash = htlc_keys.swap_hash
+        LEFT JOIN
+    static_addresses change_address
+        ON static_address_swaps.change_static_address_id = change_address.id
         JOIN
     static_address_swap_updates u ON swaps.swap_hash = u.swap_hash
         -- This subquery ensures that we are checking only the latest update for
@@ -158,4 +182,3 @@ WHERE
 
 
 
-

loopdb/sqlc/queries/static_address_loopin.sql

@@ -104,6 +104,29 @@ func (f *FSM) InitHtlcAction(ctx context.Context,
 	}
 	swapInvoiceAmt := swapAmount - f.loopIn.QuotedSwapFee
 
+	var changeOutput *swapserverrpc.StaticAddressChangeOutput
+	if hasChange {
+		changeAmount := f.loopIn.ExpectedChangeAmount()
+		f.loopIn.ChangeAddressParams, err =
+			f.cfg.AddressManager.NewChangeAddress(ctx)
+		if err != nil {
+			err = fmt.Errorf("unable to create static address "+
+				"change output: %w", err)
+
+			return returnError(err)
+		}
+
+		changeOutput, err = staticutil.ChangeOutput(
+			f.loopIn.ChangeAddressParams, changeAmount,
+		)
+		if err != nil {
+			err = fmt.Errorf("unable to prepare static address "+
+				"change output: %w", err)
+
+			return returnError(err)
+		}
+	}
+
 	// Generate random preimage.
 	var swapPreimage lntypes.Preimage
 	if _, err = rand.Read(swapPreimage[:]); err != nil {
@@ -174,6 +197,7 @@ func (f *FSM) InitHtlcAction(ctx context.Context,
 		PaymentTimeoutSeconds:  f.loopIn.PaymentTimeoutSeconds,
 		Fast:                   f.loopIn.Fast,
 		DepositToClientPubkeys: depositClientPubkeys,
+		ChangeOutput:           changeOutput,
 	}
 	if f.loopIn.LastHop != nil {
 		loopInReq.LastHop = f.loopIn.LastHop