`Type.fromBuffer()` behaves differently when given the original `toBuffer()` result vs. a `Uint8Array` copy of the same bytes.

[simensgreen]

avsc: fromBuffer yields wrong result for Uint8Array copy of toBuffer output (browser)

Environment

• Runtime: Browser (Vite bundled)
• Browser: Microsoft Edge
• avsc: ^5.7.9
• buffer: ^6.0.3 (polyfill)
• Bundler: Vite ^7.3.1

Description

Type.fromBuffer() behaves differently when given the original toBuffer() result vs. a Uint8Array copy of the same bytes. The same byte sequence decodes correctly from the original buffer but produces wrong output from the copy.

Steps to reproduce

import { Type } from "avsc/etc/browser/avsc"

const strArr = Type.forSchema({ type: "array", items: "string" })
const buf1 = strArr.toBuffer(["a", "b", "c"])
const buf2 = new Uint8Array([...buf1])

const left = strArr.fromBuffer(buf1).join("")
const right = strArr.fromBuffer(buf2).join("")

console.log(left, right) // "abc" "979899"

Expected

left === right → both "abc"

Actual

• left === "abc" ✓
• right === "979899" ✗

The string "979899" corresponds to ASCII codes 97, 98, 99 ('a', 'b', 'c') interpreted as decimal strings: "97" + "98" + "99".

Additional notes

• Using the original buf1 in fromBuffer works as expected.
• Creating a fresh buffer with strArr.toBuffer(["a", "b", "c"]) and decoding it also works correctly.
• The issue appears only when decoding a Uint8Array copy of the original buffer.
• Diagnostic output:

  buf1.constructor.name: Buffer
  buf2.constructor.name: Uint8Array
  buf1 instanceof Buffer: true
  buf2 instanceof Buffer: false
  buf1 instanceof Uint8Array: true
  buf2 instanceof Uint8Array: true
  

Possible cause

Different code paths for Buffer vs. plain Uint8Array in avsc’s internal decoding (e.g. instanceof Buffer checks or different handling of .buffer / ArrayBuffer views).

[simensgreen]

Related to #410