fix: Add transaction encoding helper functions

web3.js/src/util/encoding.js

@@ -0,0 +1,32 @@
+// @flow
+
+export function decodeLength(bytes: Array<number>): number {
+  let len = 0;
+  let size = 0;
+  // eslint-disable-next-line no-constant-condition
+  while (true) {
+    let elem = bytes.shift();
+    len |= (elem & 0x7f) << (size * 7);
+    size += 1;
+    if ((elem & 0x80) === 0) {
+      break;
+    }
+  }
+  return len;
+}
+
+export function encodeLength(bytes: Array<number>, len: number) {
+  let rem_len = len;
+  // eslint-disable-next-line no-constant-condition
+  while (true) {
+    let elem = rem_len & 0x7f;
+    rem_len >>= 7;
+    if (rem_len == 0) {
+      bytes.push(elem);
+      break;
+    } else {
+      elem |= 0x80;
+      bytes.push(elem);
+    }
+  }
+}

web3.js/test/shortvec-encoding.test.js

@@ -0,0 +1,71 @@
+// @flow
+
+import {decodeLength, encodeLength} from '../src/util/shortvec-encoding';
+
+function checkDecodedArray(array: Array<number>, expectedValue: number) {
+  expect(decodeLength(array)).toEqual(expectedValue);
+  expect(array.length).toEqual(0);
+}
+
+test('shortvec decodeLength', () => {
+  let array = [];
+  checkDecodedArray(array, 0);
+
+  array = [5];
+  checkDecodedArray(array, 5);
+
+  array = [0x7f];
+  checkDecodedArray(array, 0x7f);
+
+  array = [0x80, 0x01];
+  checkDecodedArray(array, 0x80);
+
+  array = [0xff, 0x01];
+  checkDecodedArray(array, 0xff);
+
+  array = [0x80, 0x02];
+  checkDecodedArray(array, 0x100);
+
+  array = [0xff, 0xff, 0x01];
+  checkDecodedArray(array, 0x7fff);
+
+  array = [0x80, 0x80, 0x80, 0x01];
+  checkDecodedArray(array, 0x200000);
+});
+
+function checkEncodedArray(
+  array: Array<number>,
+  len: number,
+  prevLength: number,
+  addedLength: number,
+  expectedArray: Array<number>,
+) {
+  encodeLength(array, len);
+  expect(array.length).toEqual(prevLength);
+  expect(array.slice(-addedLength)).toEqual(expectedArray);
+}
+
+test('shortvec encodeLength', () => {
+  let array = [];
+  let prevLength = 1;
+  checkEncodedArray(array, 0, prevLength, 1, [0]);
+
+  checkEncodedArray(array, 5, (prevLength += 1), 1, [5]);
+
+  checkEncodedArray(array, 0x7f, (prevLength += 1), 1, [0x7f]);
+
+  checkEncodedArray(array, 0x80, (prevLength += 2), 2, [0x80, 0x01]);
+
+  checkEncodedArray(array, 0xff, (prevLength += 2), 2, [0xff, 0x01]);
+
+  checkEncodedArray(array, 0x100, (prevLength += 2), 2, [0x80, 0x02]);
+
+  checkEncodedArray(array, 0x7fff, (prevLength += 3), 3, [0xff, 0xff, 0x01]);
+
+  prevLength = checkEncodedArray(array, 0x200000, (prevLength += 4), 4, [
+    0x80,
+    0x80,
+    0x80,
+    0x01,
+  ]);
+});