fix: test before using Buffers

[ST-DDT]

Fixes #3285

---

Adds a feature check before committing to use the Buffer methods.

Alternative

Remove the Buffer "shortcut" check and usage from the base64url method.

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[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 99.97%. Comparing base (6f1a0f8) to head (c5cb2c6).
Report is 1 commits behind head on next.

Files with missing lines	Patch %	Lines
src/internal/base64.ts	77.77%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #3400   +/-   ##
=======================================
  Coverage   99.97%   99.97%           
=======================================
  Files        2811     2811           
  Lines      216965   216972    +7     
  Branches      943      944    +1     
=======================================
+ Hits       216912   216919    +7     
  Misses         53       53           

Files with missing lines	Coverage Δ
src/internal/base64.ts	44.00% <77.77%> (+10.66%)	⬆️

... and 1 file with indirect coverage changes

[xDivisionByZerox]

I'm honestly fine with both solutions. Having the explicit check function with documentation linking to the related upstream issues, might remind someone in the future to look into this and remove the workaround. On the other side, most of us are propably suvscribed to the external issues as well and will get notified anyway.

[Shinigami92]

My opinionated solution:

/* eslint-disable no-undef -- This file serves as a compatibility layer between environments */

/**
 * Checks whether the environment supports the given encoding on the `Buffer` class.
 * This is required because some `Buffer` polyfills do not support all encodings.
 *
 * @param encoding The encoding to check.
 *
 * @see https://www.npmjs.com/package/buffer
 * @see https://github.com/feross/buffer/issues/309
 */
function bufferFeatureCheck(encoding: BufferEncoding): boolean {
  try {
    return typeof Buffer.from("test").toString(encoding) === "string";
  } catch {
    return false;
  }
}

const SUPPORTS_BASE64_BUFFER =
  typeof Buffer === "undefined" || !bufferFeatureCheck("base64");
const SUPPORTS_BASE64_URL_BUFFER =
  typeof Buffer === "undefined" || !bufferFeatureCheck("base64url");

/**
 * This works the same as `Buffer.from(input).toString('base64')`
 * to work on both Node.js and browser environment.
 *
 * @internal
 *
 * @param input The string to encode to Base64.
 *
 * @returns Base64 encoded string.
 *
 * @see https://datatracker.ietf.org/doc/html/rfc4648
 *
 * @example const encodedHeader = toBase64(JSON.stringify(header));
 */
export function toBase64(input: string): string {
  if (SUPPORTS_BASE64_BUFFER) {
    return Buffer.from(input).toString("base64");
  }

  const utf8Bytes = new TextEncoder().encode(input);
  const binaryString = Array.from(utf8Bytes, (byte) =>
    String.fromCodePoint(byte)
  ).join("");
  return btoa(binaryString);
}

/**
 * This works the same as `Buffer.from(input).toString('base64url')`
 * to work on both Node.js and browser environment.
 *
 * @internal
 *
 * @param input The string to encode to Base64 URL.
 *
 * @returns Base64 URL encoded string.
 *
 * @see https://datatracker.ietf.org/doc/html/rfc4648
 *
 * @example const encodedHeader = toBase64Url(JSON.stringify(header));
 */
export function toBase64Url(input: string): string {
  if (SUPPORTS_BASE64_URL_BUFFER) {
    return Buffer.from(input).toString("base64url");
  }

  return toBase64(input)
    .replaceAll("+", "-")
    .replaceAll("/", "_")
    .replaceAll(/=+$/g, "");
}

I know this moves the check into the function, but makes it (to me) much more readable. I don't think that the condition has a to bad performance compared to actually craft the base64 string.

Edit: we might even be able to remove the typeof Buffer === "undefined", because the try-catch would catch it anyway 😅