Handle both prefixed and non-prefixed hex Bytes (#379)

packages/types/src/Bytes.spec.ts

@@ -0,0 +1,23 @@
+// Copyright 2017-2018 @polkadot/types authors & contributors
+// This software may be modified and distributed under the terms
+// of the ISC license. See the LICENSE file for details.
+
+import Bytes from './Bytes';
+
+describe('Bytes', () => {
+  describe('hex decoding', () => {
+    const CODE = new Uint8Array([0x14, 0x3a, 0x63, 0x6f, 0x64, 0x65]);
+
+    it('decodes when hex is length prefixed', () => {
+      expect(
+        new Bytes('0x143a636f6465').toU8a()
+      ).toEqual(CODE);
+    });
+
+    it('decodes when hex is not length prefixed', () => {
+      expect(
+        new Bytes('0x3a636f6465').toU8a()
+      ).toEqual(CODE);
+    });
+  });
+});

packages/types/src/Bytes.ts

@@ -22,15 +22,16 @@ export default class Bytes extends U8a {
     } else if (isHex(value)) {
       // FIXME We manually add the length prefix for hex for now
       // https://github.com/paritytech/substrate/issues/889
-      // Instead of the block below, it should simply be:
-      // return Bytes.decodeBytes(hexToU8a(value as string));
+      // HACK 7 Nov 2018 Some Bytes values are properly encoded, i.e. when
+      // querying storage for code, others are not (yet), i.e. extrinsics.
+      // Here we pull the length, check for matches and add when not
       const u8a = hexToU8a(value as string);
+      const [offset, length] = Compact.decodeU8a(u8a, DEFAULT_LENGTH_BITS);
 
       return Bytes.decodeBytes(
-        u8aConcat(
-          Compact.encodeU8a(u8a.length, DEFAULT_LENGTH_BITS),
-          u8a
-        )
+        u8a.length === (offset + length.toNumber())
+          ? u8a
+          : Compact.addLengthPrefix(u8a)
       );
     } else if (isU8a(value)) {
       const [offset, length] = Compact.decodeU8a(value, DEFAULT_LENGTH_BITS);

packages/types/src/codec/Compact.ts

@@ -56,6 +56,12 @@ export default class Compact extends Base<UInt | Moment> {
     );
   }
 
+  static stripLengthPrefix (u8a: Uint8Array, bitLength: UIntBitLength = DEFAULT_LENGTH_BITS): Uint8Array {
+    const [offset] = Compact.decodeU8a(u8a, bitLength);
+
+    return u8a.subarray(offset);
+  }
+
   static decodeCompact (Type: Constructor<UInt | Moment>, value: AnyNumber): Moment | UInt {
     if (isString(value)) {
       return new Type(