feat: PoC redeem frontrun protection

packages/sui-indexer/src/redeem-service.ts

@@ -382,9 +382,6 @@ export class RedeemService {
 		const availableUtxos = await this.storage.getAvailableUtxos(req.setup_id);
 		const selectedUtxos = selectUtxos(availableUtxos, req.amount);
 
-		// TODO: we should continue only if our solution is better than the existing one - in case
-		//   someone frontrun us.
-
 		if (!selectedUtxos) {
 			logger.warn({
 				msg: "Insufficient UTXOs for request",
@@ -394,8 +391,33 @@ export class RedeemService {
 			return;
 		}
 
+		const client = this.getSuiClient(req.sui_network);
+
+		try {
+			const existingUtxoCount = await client.getRedeemUtxoCount(
+				req.redeem_id,
+				req.nbtc_pkg,
+				req.nbtc_contract,
+			);
+
+			if (existingUtxoCount > 0 && selectedUtxos.length >= existingUtxoCount) {
+				logger.info({
+					msg: "Existing solution is equal or better, skipping proposal",
+					redeemId: req.redeem_id,
+					existingUtxoCount,
+					ourUtxoCount: selectedUtxos.length,
+				});
+				return;
+			}
+		} catch (e) {
+			logger.warn({
+				msg: "Failed to fetch existing UTXO count, proceeding with proposal",
+				redeemId: req.redeem_id,
+				error: e,
+			});
+		}
+
 		try {
-			const client = this.getSuiClient(req.sui_network);
 			const txDigest = await client.proposeRedeemUtxos({
 				redeemId: req.redeem_id,
 				utxoIds: selectedUtxos.map((u) => u.nbtc_utxo_id),

packages/sui-indexer/src/redeem-sui-client.ts

@@ -39,6 +39,7 @@ export interface SuiClient {
 		nbtcContract: string,
 	): Promise<void>;
 	getRedeemBtcTx(redeemId: number, nbtcPkg: string, nbtcContract: string): Promise<string>;
+	getRedeemUtxoCount(redeemId: number, nbtcPkg: string, nbtcContract: string): Promise<number>;
 }
 
 class SuiClientImp implements SuiClient {
@@ -111,6 +112,50 @@ class SuiClientImp implements SuiClient {
 		return Buffer.from(decoded).toString("hex");
 	}
 
+	async getRedeemUtxoCount(
+		redeemId: number,
+		nbtcPkg: string,
+		nbtcContract: string,
+	): Promise<number> {
+		const tx = new Transaction();
+
+		const redeem = tx.add(
+			nBTCContractModule.redeemRequest({
+				package: nbtcPkg,
+				arguments: {
+					contract: nbtcContract,
+					redeemId: redeemId,
+				},
+			}),
+		);
+
+		tx.add(
+			RedeemRequestModule.inputsLength({
+				package: nbtcPkg,
+				arguments: {
+					r: redeem,
+				},
+			}),
+		);
+
+		const result = await this.#sui.devInspectTransactionBlock({
+			transactionBlock: tx,
+			sender: this.signer.toSuiAddress(),
+		});
+
+		if (result.error) {
+			throw new Error(`DevInspect failed: ${result.error}`);
+		}
+
+		const lengthResult = result.results?.[1]?.returnValues?.[0]?.[0];
+		if (!lengthResult) {
+			throw new Error("Failed to get inputs_length result");
+		}
+		const bytes = Uint8Array.from(lengthResult);
+		const view = new DataView(bytes.buffer);
+		return Number(view.getBigUint64(0, true));
+	}
+
 	async proposeRedeemUtxos(args: ProposeRedeemCall): Promise<string> {
 		const tx = new Transaction();