Allow Text to construct from hex (#1018)

* Allow Text to construct from hex

* Simplify decodeText

packages/types/src/primitive/Text.spec.ts

@@ -8,9 +8,9 @@ import Text from './Text';
 
 describe('Text', () => {
   describe('decode', () => {
-    const testDecode = (type: string, input: string | Uint8Array | { toString: () => string }, expected: string) =>
+    const testDecode = (type: string, input: string | Uint8Array | { toString: () => string }, expected: string, toFn: 'toString' | 'toHex' = 'toString') =>
       it(`can decode from ${type}`, () => {
-        expect(new Text(input).toString()).toBe(expected);
+        expect(new Text(input)[toFn]()).toBe(expected);
       });
 
     testDecode('string', 'foo', 'foo');
@@ -18,6 +18,7 @@ describe('Text', () => {
     testDecode('Uint8Array', Uint8Array.from([12, 102, 111, 111]), 'foo');
     testDecode('U8a', new U8a(Uint8Array.from([12, 102, 111, 111])), 'foo');
     testDecode('object with `toString()`', { toString (): string { return 'foo'; } }, 'foo');
+    testDecode('hex input value', new Text('0x12345678'), '0x12345678', 'toHex');
   });
 
   describe('encode', () => {
@@ -26,7 +27,7 @@ describe('Text', () => {
         expect(new Text('foo')[to]()).toEqual(expected);
       });
 
-    testEncode('toHex', '0x0c666f6f');
+    testEncode('toHex', '0x666f6f');
     testEncode('toString', 'foo');
     testEncode('toU8a', Uint8Array.from([12, 102, 111, 111]));
   });

packages/types/src/primitive/Text.ts

@@ -2,7 +2,7 @@
 // This software may be modified and distributed under the terms
 // of the Apache-2.0 license. See the LICENSE file for details.
 
-import { assert, isString, stringToU8a, u8aToString, u8aToHex } from '@polkadot/util';
+import { assert, hexToU8a, isHex, isString, stringToU8a, u8aToString, u8aToHex } from '@polkadot/util';
 
 import { AnyU8a, Codec } from '../types';
 import Compact from '../codec/Compact';
@@ -28,8 +28,8 @@ export default class Text extends String implements Codec {
   }
 
   private static decodeText (value: Text | string | AnyU8a | { toString: () => string }): string {
-    if (isString(value)) {
-      return value.toString();
+    if (isHex(value)) {
+      return u8aToString(hexToU8a(value.toString()));
     } else if (value instanceof Uint8Array) {
       if (!value.length) {
         return '';
@@ -81,7 +81,9 @@ export default class Text extends String implements Codec {
    * @description Returns a hex string representation of the value
    */
   toHex (): string {
-    return u8aToHex(this.toU8a());
+    // like  with Vec<u8>, when we are encoding to hex, we don't actually add
+    // the length prefix (it is already implied by the actual string length)
+    return u8aToHex(this.toU8a(true));
   }
 
   /**