readVarInt tests

src/thrift.js

@@ -115,10 +115,7 @@ function readElement(reader, type) {
 /**
  * Var int, also known as Unsigned LEB128.
  * Var ints take 1 to 5 bytes (int32) or 1 to 10 bytes (int64).
- * Takes a Big Endian unsigned integer, left-pads the bit-string to make it a
- * multiple of 7 bits, splits it into 7-bit groups, prefix the most-significant
- * 7-bit group with the 0 bit, prefixing the remaining 7-bit groups with the
- * 1 bit and encode the resulting bit-string as Little Endian.
+ * Reads groups of 7 low bits until high bit is 0.
  *
  * @param {DataReader} reader
  * @returns {number} value

test/helpers.js

@@ -34,3 +34,13 @@ export function fileToJson(filePath) {
   const buffer = fs.readFileSync(filePath)
   return JSON.parse(buffer.toString())
 }
+
+/**
+ * Make a DataReader from bytes
+ *
+ * @param {number[]} bytes
+ * @returns {import('../src/types.js').DataReader}
+ */
+export function reader(bytes) {
+  return { view: new DataView(new Uint8Array(bytes).buffer), offset: 0 }
+}

test/thrift.test.js

@@ -1,5 +1,6 @@
 import { describe, expect, it } from 'vitest'
-import { deserializeTCompactProtocol, toVarInt } from '../src/thrift.js'
+import { deserializeTCompactProtocol, readVarInt, toVarInt } from '../src/thrift.js'
+import { reader } from './helpers.js'
 
 describe('deserializeTCompactProtocol function', () => {
 
@@ -79,3 +80,22 @@ describe('deserializeTCompactProtocol function', () => {
   })
 
 })
+
+describe('readVarInt', () => {
+  it('read single-byte varint', () => {
+    expect(readVarInt(reader([0x01]))).toBe(1)
+    expect(readVarInt(reader([0x7f]))).toBe(127)
+  })
+
+  it('read multi-byte varint', () => {
+    // 129 as varint (0b10000001 00000001)
+    expect(readVarInt(reader([0x81, 0x01]))).toBe(129)
+    // 16515 as varint (0b10000011 10000010 00000001)
+    expect(readVarInt(reader([0x83, 0x82, 0x01]))).toBe(16643)
+  })
+
+  it('read maximum int32 varint', () => {
+    // 2147483647 as varint (0b11111111 11111111 11111111 11111111 00000111)
+    expect(readVarInt(reader([0xff, 0xff, 0xff, 0xff, 0x07]))).toBe(2147483647)
+  })
+})