Add streaming base64 encode/decode via TransformStream

[Copilot]

Adds memory-efficient streaming support for base64 encoding and decoding using Web Streams API.

Changes

• New Classes

  • Base64EncoderStream - TransformStream<Uint8Array, string> for streaming encode
  • Base64DecoderStream - TransformStream<string, Uint8Array> for streaming decode
  • Both support standard base64 and base64url via constructor urlMode parameter

• Implementation

  • Automatic chunk boundary handling via internal buffering (3-byte for encode, 4-char for decode)
  • Reuses existing encoding/decoding functions
  • Zero dependencies - uses native TransformStream

• Documentation

  • README, examples.md, and index.md updated with streaming API and usage
  • Version bumped to 3.0.0 (breaking: new major API surface)

Usage

// Encode a large file stream
const encoder = new base64.Base64EncoderStream();
await fileStream.readable
  .pipeThrough(encoder)
  .pipeTo(destination);

// Decode base64 stream
const decoder = new base64.Base64DecoderStream(true); // URL mode
await base64Stream.readable
  .pipeThrough(new TextDecoderStream())
  .pipeThrough(decoder)
  .pipeTo(destination);

Compatibility

Node.js 16.5+, Deno 1.16+, Bun, modern browsers (all with native TransformStream support).

Original prompt

Add cross runtime support for streaming encoding and decoding. Keep it lean.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[Copilot]

🟡 Changes recommended

Formatting fails CI, decoder boundary coverage is incomplete, and examples use an API unavailable in the documented runtime range.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Adds Web Streams-based Base64 encoding and decoding while preserving standard and URL-safe modes.

Changes:

• Adds encoder and decoder TransformStream classes.
• Adds streaming tests and usage documentation.
• Bumps the package to version 3.0.0.

File summaries

File	Description
src/base64.ts	Implements and exports streaming APIs.
tests/base64.test.ts	Adds streaming behavior tests.
README.md	Lists streaming APIs and compatibility.
docs/index.md	Documents stream classes and usage.
docs/examples.md	Adds streaming examples.
deno.json	Bumps the package version.

Review details

Suppressed comments (3)

tests/base64.test.ts:222

• This “multiple chunks” case splits only on four-character boundaries, so it never exercises the decoder's new buffering across a quartet boundary. Use deliberately unaligned chunks so a regression in buffer carry-over is detected.

  const chunks = ["SGVs", "bG8g", "d29y", "bGQ="];

docs/examples.md:66

• ReadableStream.from() is unavailable before Node.js v20.6.0, despite the documented v16.5.0 minimum. Use the baseline stream constructor so this decoding example works on supported Node.js versions.

const decodedStream = ReadableStream.from([base64Data])
  .pipeThrough(decoder);

docs/examples.md:84

• This URL-mode example also relies on ReadableStream.from(), which requires Node.js v20.6.0 rather than the advertised v16.5.0. Build the source with the standard constructor to preserve the stated compatibility.

const urlEncodedStream = ReadableStream.from([textData])
  .pipeThrough(urlEncoder);

• Files reviewed: 6/6 changed files
• Comments generated: 2
• Review effort level: Balanced

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.