feat: add optional offset param to varint.decode (#201)

Author: Gozala

src/varint.js

@@ -2,10 +2,11 @@ import varint from '../vendor/varint.js'
 
 /**
  * @param {Uint8Array} data
+ * @param {number} [offset=0]
  * @returns {[number, number]}
  */
-export const decode = (data) => {
-  const code = varint.decode(data)
+export const decode = (data, offset = 0) => {
+  const code = varint.decode(data, offset)
   return [code, varint.decode.bytes]
 }
 

test/test-varint.js

@@ -0,0 +1,28 @@
+/* globals describe, it */
+
+import { varint } from 'multiformats'
+import chai from 'chai'
+import chaiAsPromised from 'chai-as-promised'
+
+chai.use(chaiAsPromised)
+const { assert } = chai
+
+const UTF8 = new TextEncoder()
+
+describe('varint', () => {
+  it('can decode with offset', () => {
+    const message = UTF8.encode('hello-world')
+    const outerTag = 0x55
+    const innerTag = 0xe3
+    const outerTagSize = varint.encodingLength(outerTag)
+    const innerTagSize = varint.encodingLength(innerTag)
+
+    const bytes = new Uint8Array(message.byteLength + outerTagSize + innerTagSize)
+    varint.encodeTo(outerTag, bytes)
+    varint.encodeTo(innerTag, bytes, outerTagSize)
+    bytes.set(message, outerTagSize + innerTagSize)
+
+    assert.deepStrictEqual(varint.decode(bytes), [outerTag, outerTagSize])
+    assert.deepStrictEqual(varint.decode(bytes, outerTagSize), [innerTag, innerTagSize])
+  })
+})