fix: prevent stack overflow in toBase64 for large inputs in non-Node environments

[claygeo]

Problem

toBase64 in src/internal/utils/base64.ts crashes with RangeError: Maximum call stack size exceeded when encoding inputs larger than ~100KB in non-Node environments (browsers, Cloudflare Workers, Deno, etc.).

Reproduction:

const large = new Uint8Array(200 * 1024); // 200KB
toBase64(large); // RangeError: Maximum call stack size exceeded

This affects any use case that sends large payloads through the SDK in browser environments, most commonly image uploads via base64 encoding.

Root Cause

Line 18 uses String.fromCharCode.apply(null, data), which spreads the entire Uint8Array as individual function arguments. JavaScript engines have a maximum argument limit (typically ~65,536), so any input larger than ~64KB overflows the call stack.

Node.js environments are unaffected because they hit the Buffer.from() path on line 10, which has no such limitation.

Solution

Process the Uint8Array in 32KB chunks (0x8000 bytes), convert each chunk separately with String.fromCharCode.apply(), then join before passing to btoa(). This stays well within the argument limit while producing identical output.

const CHUNK_SIZE = 0x8000;
const parts: string[] = [];
for (let i = 0; i < data.length; i += CHUNK_SIZE) {
  const chunk = data.subarray(i, i + CHUNK_SIZE);
  parts.push(String.fromCharCode.apply(null, chunk as any));
}
return btoa(parts.join(''));

This is a well-established pattern used by libraries like js-base64, Firebase SDK, and others that need to encode large binary data in browser environments.

Note on Generated Code

This file is marked as generated by Stainless. The fix should ideally be upstreamed to the code generator to persist across regenerations. In the meantime, this patch fixes the bug for current users.

Test Plan

• toBase64(new Uint8Array(0)) → empty string ✅
• toBase64(new Uint8Array(100)) → valid base64 (small input, existing behavior) ✅
• toBase64(new Uint8Array(200 * 1024)) → valid base64 without stack overflow ✅
• toBase64("hello") → string path unaffected ✅
• Node.js environment → uses Buffer path, unaffected ✅

Closes #932