Add type validation to FT metadata

packages/rpc/src/methods/ftMetadata.ts

@@ -10,9 +10,45 @@ export type FtMetadata = {
   decimals: number;
 }
 
-export const ftBalance = async ({ contractId }): Promise<FtMetadata> => {
-  return callViewMethod<FtMetadata>({
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function isFtMetadata(x: any): x is FtMetadata {
+  if (typeof x.spec !== 'string') {
+    return false;
+  }
+  if (typeof x.name !== 'string') {
+    return false;
+  }
+  if (typeof x.symbol !== 'string') {
+    return false;
+  }
+  if (!isStringOrNull(x.icon)) {
+    return false;
+  }
+  if (!isStringOrNull(x.reference)) {
+    return false;
+  }
+  if (!isStringOrNull(x.reference_hash)) {
+    return false;
+  }
+  return typeof x.decimals === 'number';
+}
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function isStringOrNull(x: any): x is string | null {
+  if (typeof x === 'string') {
+    return true;
+  }
+  if (x === null) {
+    return true;
+  }
+  return false;
+}
+
+export const ftBalance = async ({ contractId }): Promise<FtMetadata | null> => {
+  const res = callViewMethod<FtMetadata>({
     contractId,
     method: 'ft_metadata',
   });
+
+  return isFtMetadata(res) ? res : null;
 };