Restore any missing psbt metadata that resource constrained signers s…

…trip

Fixes ([#6764])
Changelog-Fixed: Restore any missing metadata that resource constrained signers stripped

bitcoin/psbt.c

@@ -86,6 +86,22 @@ struct wally_psbt *new_psbt(const tal_t *ctx, const struct wally_tx *wtx)
 	return psbt;
 }
 
+struct wally_psbt *combine_psbt(const tal_t *ctx,
+				const struct wally_psbt *psbt0,
+				const struct wally_psbt *psbt1)
+{
+	struct wally_psbt *combined_psbt;
+	tal_wally_start();
+	if (wally_psbt_clone_alloc(psbt0, 0, &combined_psbt) != WALLY_OK)
+		abort();
+	if (wally_psbt_combine(combined_psbt, psbt1) != WALLY_OK) {
+		tal_wally_end_onto(ctx, combined_psbt, struct wally_psbt);
+		return tal_free(combined_psbt);
+	}
+	tal_wally_end_onto(ctx, combined_psbt, struct wally_psbt);
+	return combined_psbt;
+}
+
 bool psbt_is_finalized(const struct wally_psbt *psbt)
 {
 	size_t is_finalized;

bitcoin/psbt.h

@@ -50,6 +50,17 @@ struct wally_psbt *new_psbt(const tal_t *ctx,
  */
 struct wally_psbt *clone_psbt(const tal_t *ctx, struct wally_psbt *psbt);
 
+/**
+ * combine_psbt - Combine two PSBT into a cloned copy
+ *
+ * @ctx - allocation context
+ * @psbt0 - one psbt
+ * @psbt1 - other psbt
+ */
+struct wally_psbt *combine_psbt(const tal_t *ctx,
+				const struct wally_psbt *psbt0,
+				const struct wally_psbt *psbt1);
+
 /**
  * psbt_is_finalized - Check if tx is ready to be extracted
  *

wallet/walletrpc.c

@@ -799,15 +799,28 @@ static struct command_result *json_signpsbt(struct command *cmd,
 				    "HSM gave bad sign_withdrawal_reply %s",
 				    tal_hex(tmpctx, msg));
 
-	if (!psbt_set_version(signed_psbt, psbt_version)) {
+	/* Some signers (VLS) prune the input.utxo data as it's used
+	 * because it is too large to store in the signer. We can
+	 * restore this metadata by combining the signed psbt back
+	 * into a clone of the original psbt. */
+	struct wally_psbt *combined_psbt;
+	combined_psbt = combine_psbt(cmd, psbt, signed_psbt);
+	if (!combined_psbt) {
+		return command_fail(cmd, LIGHTNINGD,
+				    "Unable to combine signed psbt: %s",
+				    type_to_string(tmpctx, struct wally_psbt,
+						   signed_psbt));
+	}
+
+	if (!psbt_set_version(combined_psbt, psbt_version)) {
 		return command_fail(cmd, LIGHTNINGD,
 				    "Signed PSBT unable to have version set: %s",
 					 type_to_string(tmpctx, struct wally_psbt,
-					 	psbt));
+					 	combined_psbt));
 	}
 
 	response = json_stream_success(cmd);
-	json_add_psbt(response, "signed_psbt", signed_psbt);
+	json_add_psbt(response, "signed_psbt", combined_psbt);
 	return command_success(cmd, response);
 }