u8a to u8a convenience function (#116)

* Convenience u8aToU8a conversion

* u8aConcat take u8a | hex

packages/util/src/u8a/concat.js

@@ -3,9 +3,11 @@
 // of the ISC license. See the LICENSE file for details.
 // @flow
 
+const u8aToU8a = require('./toU8a');
+
 /**
   @name u8aConcat
-  @signature u8aConcat (...values: Array<Uint8Array>): Uint8Array
+  @signature u8aConcat (...values: Array<Uint8Array | string>): Uint8Array
   @summary Creates a concatenated Uint8Array from the inputs.
   @description
     Concatenates the input arrays into a single `UInt8Array`.
@@ -17,13 +19,13 @@
       new Uint8Array([4, 5, 6])
     ); // [1, 2, 3, 4, 5, 6]
 */
-module.exports = function u8aConcat (...list: Array<Uint8Array>): Uint8Array {
+module.exports = function u8aConcat (...list: Array<Uint8Array | string>): Uint8Array {
   const length = list.reduce((total, item) => total + item.length, 0);
   const result = new Uint8Array(length);
   let offset = 0;
 
   return list.reduce((result, item) => {
-    result.set(item, offset);
+    result.set(u8aToU8a(item), offset);
     offset += item.length;
 
     return result;

packages/util/src/u8a/index.js

@@ -14,6 +14,7 @@ const u8aToBn = require('./toBn');
 const u8aToBuffer = require('./toBuffer');
 const u8aToHex = require('./toHex');
 const u8aToString = require('./toString');
+const u8aToU8a = require('./toU8a');
 const u8aToUtf8 = require('./toUtf8');
 
 /**
@@ -31,5 +32,6 @@ module.exports = {
   u8aToBuffer,
   u8aToHex,
   u8aToString,
+  u8aToU8a,
   u8aToUtf8
 };

packages/util/src/u8a/toU8a.js

@@ -0,0 +1,32 @@
+// Copyright 2017-2018 Jaco Greeff
+// This software may be modified and distributed under the terms
+// of the ISC license. See the LICENSE file for details.
+// @flow
+
+const isU8a = require('../is/u8a');
+const hexToU8a = require('../hex/toU8a');
+
+/**
+  @name u8aToU8a
+  @signature u8aToU8a (value?: Uint8Array | string): Uint8Array
+  @summary Creates a Uint8Array value from a Uint8Array bignumber or hex input.
+  @description
+    `null` inputs returns a `[]` result, Uint8Array values returns the value, hex strings returns a Uint8Array representation.
+  @example
+    import { u8aToU8a } from '@polkadot/util';
+
+    u8aToU8a(new Uint8Array([0x12, 0x34]); // => Uint8Array([0x12, 0x34])
+    u8aToU8a(0x1234); // => Uint8Array([0x12, 0x34])
+*/
+module.exports = function u8aToU8a (value?: Uint8Array | string): Uint8Array {
+  // flowlint-next-line sketchy-null-string:off
+  if (!value) {
+    return new Uint8Array(0);
+  }
+
+  return isU8a(value)
+    // $FlowFixMe type is determined
+    ? value
+    // $FlowFixMe type is determined
+    : hexToU8a(value);
+};

packages/util/src/u8a/toU8a.spec.js

@@ -0,0 +1,29 @@
+// Copyright 2017-2018 Jaco Greeff
+// This software may be modified and distributed under the terms
+// of the ISC license. See the LICENSE file for details.
+
+const { u8aToU8a } = require('./index');
+
+describe('u8aToU8a', () => {
+  it('returns an empty Uint8Array when null provided', () => {
+    expect(
+      u8aToU8a(null)
+    ).toHaveLength(0);
+  });
+
+  it('returns a Uint8Array with the correct values (hex)', () => {
+    expect(
+      u8aToU8a('0x80000a')
+    ).toEqual(
+      new Uint8Array([128, 0, 10])
+    );
+  });
+
+  it('returns a Uint8Array with the correct values (u8a)', () => {
+    expect(
+      u8aToU8a(new Uint8Array([128, 0, 10]))
+    ).toEqual(
+      new Uint8Array([128, 0, 10])
+    );
+  });
+});