fix(ripple-keypairs): hexToBytes should produce [] for empty input, not [0] (#1977)

BN.toArray intentionally returns [0] rather than [] for length zero,
which may make sense for BigNum data, but not for byte strings.

packages/ripple-keypairs/HISTORY.md

@@ -1,6 +1,7 @@
 # ripple-keypairs Release History
 
 ## Unreleased
+- `hexToBytes` now produces empty output for empty input, rather than `[0]`.
 - Extend `bytesToHex` to work correctly with any input type accepted by `Array.from`.
   In particular, it now produces correct output for typed arrays such as `UInt8Array`.
 

packages/ripple-keypairs/src/utils.ts

@@ -11,7 +11,10 @@ function bytesToHex(a: Iterable<number> | ArrayLike<number>): string {
 
 function hexToBytes(a): number[] {
   assert.ok(a.length % 2 === 0)
-  return new BN(a, 16).toArray(null, a.length / 2)
+  // Special-case length zero to return [].
+  // BN.toArray intentionally returns [0] rather than [] for length zero,
+  // which may make sense for BigNum data, but not for byte strings.
+  return a.length === 0 ? [] : new BN(a, 16).toArray(null, a.length / 2)
 }
 
 function computePublicKeyHash(publicKeyBytes: Buffer): Buffer {

packages/ripple-keypairs/test/utils-test.js

@@ -4,6 +4,10 @@ const assert = require('assert')
 const utils = require('../dist/utils')
 
 describe('utils', () => {
+  it('hexToBytes - empty', () => {
+    assert.deepEqual(utils.hexToBytes(''), [])
+  })
+
   it('hexToBytes - zero', () => {
     assert.deepEqual(utils.hexToBytes('000000'), [0, 0, 0])
   })