Return additional error information from decodeU8a (#3540)

CHANGELOG.md

@@ -1,5 +1,12 @@
 # CHANGELOG
 
+## master
+
+Changes:
+
+- Return additional error information from internal u8a decoding failures
+
+
 ## 4.10.1 May 17, 2021
 
 Upgrade priority: Medium. Recommended for uses of Polkadot/Kusama 9010 runtimes.

packages/types/src/codec/Struct.ts

@@ -99,12 +99,13 @@ function decodeStructFromObject <T> (registry: Registry, Types: ConstructorDef,
  */
 function decodeStruct <T> (registry: Registry, Types: ConstructorDef, value: unknown, jsonMap: Map<any, string>): T {
   if (isHex(value)) {
-    return decodeStruct(registry, Types, hexToU8a(value as string), jsonMap);
+    return decodeStruct(registry, Types, hexToU8a(value.toString()), jsonMap);
   } else if (isU8a(value)) {
-    const values = decodeU8a(registry, value, Object.values(Types));
+    const keys = Object.keys(Types);
+    const values = decodeU8a(registry, value, Object.values(Types), keys);
 
     // Transform array of values to {key: value} mapping
-    return Object.keys(Types).reduce((raw, key, index): T => {
+    return keys.reduce((raw, key, index): T => {
       // TS2322: Type 'Codec' is not assignable to type 'T[keyof S]'.
       // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
       (raw as any)[key] = values[index];

packages/types/src/codec/utils/decodeU8a.ts

@@ -10,18 +10,24 @@ import type { Codec, Constructor, Registry } from '../../types';
  * @param u8a - The u8a to decode.
  * @param types - The array of Constructor to decode the U8a against.
  */
-export function decodeU8a (registry: Registry, u8a: Uint8Array, _types: Constructor[] | { [index: string]: Constructor }): Codec[] {
-  const types = Array.isArray(_types)
-    ? _types
-    : Object.values(_types);
+export function decodeU8a (registry: Registry, u8a: Uint8Array, _types: Constructor[] | { [index: string]: Constructor }, _keys?: string[]): Codec[] {
+  const [types, keys]: [Constructor<Codec>[], string[]] = Array.isArray(_types)
+    ? [_types, _keys || []]
+    : [Object.values(_types), Object.keys(_types)];
   const result: Codec[] = [];
   let offset = 0;
 
   for (let i = 0; i < types.length; i++) {
-    const value = new types[i](registry, u8a.subarray(offset));
+    const Type = types[i];
 
-    result.push(value);
-    offset += value.encodedLength;
+    try {
+      const value = new Type(registry, u8a.subarray(offset));
+
+      result.push(value);
+      offset += value.encodedLength;
+    } catch (error) {
+      throw new Error(`decodeU8a: failed on ${keys[i] ? `${keys[i]}: ` : ''}${new Type(registry).toRawType()}:: ${(error as Error).message}`);
+    }
   }
 
   return result;