Add BigNumber transformation utility for typed data signing

Co-authored-by: joaquim.verges <joaquim.verges@gmail.com>

Author: cursoragent

src/server/routes/backend-wallet/sign-typed-data.ts

@@ -6,6 +6,7 @@ import { arbitrumSepolia } from "thirdweb/chains";
 import { isSmartBackendWallet } from "../../../shared/db/wallets/get-wallet-details";
 import { getWalletDetails } from "../../../shared/db/wallets/get-wallet-details";
 import { walletDetailsToAccount } from "../../../shared/utils/account";
+import { transformBigNumbers } from "../../../shared/utils/bignumber";
 import { getChain } from "../../../shared/utils/chain";
 import { createCustomError } from "../../middleware/error";
 import { standardResponseSchema } from "../../schemas/shared-api-schemas";
@@ -47,6 +48,9 @@ export async function signTypedData(fastify: FastifyInstance) {
       const { "x-backend-wallet-address": walletAddress } =
         request.headers as Static<typeof walletHeaderSchema>;
 
+      // Transform any BigNumber objects in the value to stringified bigints
+      const transformedValue = transformBigNumbers(value);
+
       const walletDetails = await getWalletDetails({
         address: walletAddress,
       });
@@ -79,7 +83,7 @@ export async function signTypedData(fastify: FastifyInstance) {
         domain,
         types,
         primaryType: parsedPrimaryType,
-        message: value,
+        message: transformedValue,
       } as never);
 
       reply.status(StatusCodes.OK).send({

src/shared/utils/bignumber.ts

@@ -0,0 +1,66 @@
+/**
+ * Utility functions for handling BigNumber objects in payloads
+ */
+
+/**
+ * Interface representing a BigNumber object as it comes from the frontend
+ */
+interface BigNumberObject {
+  type: "BigNumber";
+  hex: string;
+}
+
+/**
+ * Type guard to check if an object is a BigNumber object
+ */
+function isBigNumberObject(obj: unknown): obj is BigNumberObject {
+  return (
+    typeof obj === "object" &&
+    obj !== null &&
+    "type" in obj &&
+    "hex" in obj &&
+    obj.type === "BigNumber" &&
+    typeof obj.hex === "string"
+  );
+}
+
+/**
+ * Converts a BigNumber object to a stringified bigint
+ */
+function bigNumberToStringifiedBigInt(bigNumberObj: BigNumberObject): string {
+  // Convert hex string to bigint, then to string
+  return BigInt(bigNumberObj.hex).toString();
+}
+
+/**
+ * Recursively transforms all BigNumber objects in an arbitrary object/array
+ * into stringified bigints
+ */
+export function transformBigNumbers(obj: unknown): unknown {
+  // Handle null/undefined
+  if (obj === null || obj === undefined) {
+    return obj;
+  }
+
+  // Handle BigNumber objects
+  if (isBigNumberObject(obj)) {
+    return bigNumberToStringifiedBigInt(obj);
+  }
+
+  // Handle arrays
+  if (Array.isArray(obj)) {
+    return obj.map(transformBigNumbers);
+  }
+
+  // Handle objects
+  if (typeof obj === "object") {
+    const result: Record<string, unknown> = {};
+    for (const [key, value] of Object.entries(obj)) {
+      result[key] = transformBigNumbers(value);
+    }
+    return result;
+  }
+
+  // Handle primitives (string, number, boolean, etc.)
+  return obj;
+}