browser/api/zip.ts

import { readdirSync, readFileSync, statSync } from 'node:fs';
import { join, relative } from 'node:path';

// A ZIP writer, in about seventy lines, so the extension download can never be stale.
//
// ── Why this exists rather than a file in public/ ──
//
// It was a file in public/: `browser-relay-extension.zip`, built by hand and served as a static asset.
// On 2026-08-21 it was found to be 58 lines behind the source it claimed to be — built in August from
// something that predated a February commit, and never rebuilt since. Anyone who downloaded it got an
// extension missing the multi-session recovery path, which is exactly the failure they would then hit.
//
// A snapshot drifts because nothing makes it not drift. Building from the directory at request time
// removes the class: there is no second copy to fall behind.
//
// ── Why hand-rolled, and why STORED rather than deflated ──
//
// The router's own history says the previous version of this shelled out to `zip`. That works and it
// makes the plugin need a host binary for a convenience feature — this manifest's "nothing to declare"
// is worth more than the compression. Bun ships no zip writer, and the stored format is genuinely small:
// a local header per file, a central directory, and an end record.
//
// Chrome accepts stored entries. The extension is ~50 KB of text; deflate would save perhaps 30 KB on a
// download that happens once.

/** CRC-32, the one thing in the format that is not just bytes in order. */
function crc32(bytes: Uint8Array): number {
  let crc = 0xffffffff;
  for (const byte of bytes) {
    crc ^= byte;
    for (let i = 0; i < 8; i++) crc = crc & 1 ? (crc >>> 1) ^ 0xedb88320 : crc >>> 1;
  }
  return (crc ^ 0xffffffff) >>> 0;
}

type Entry = { name: string; data: Uint8Array; crc: number; offset: number };

const u16 = (v: number) => [v & 0xff, (v >>> 8) & 0xff];
const u32 = (v: number) => [v & 0xff, (v >>> 8) & 0xff, (v >>> 16) & 0xff, (v >>> 24) & 0xff];

/** Every file under `dir`, depth first, with paths relative to it. */
function collect(dir: string, root = dir): { name: string; data: Uint8Array }[] {
  const out: { name: string; data: Uint8Array }[] = [];
  for (const item of readdirSync(dir).sort()) {
    const path = join(dir, item);
    if (statSync(path).isDirectory()) out.push(...collect(path, root));
    else out.push({ name: relative(root, path), data: new Uint8Array(readFileSync(path)) });
  }
  return out;
}

/**
 * Zip a directory, stored, with a fixed timestamp.
 *
 * The timestamp is fixed (1980-01-01, the format's own zero) so the same directory always produces
 * byte-identical output. That makes the download cacheable and, more usefully, makes "did this change"
 * answerable by comparing two files rather than unpacking them.
 */
export function zipDirectory(dir: string): Uint8Array {
  const files = collect(dir);
  const parts: number[] = [];
  const entries: Entry[] = [];

  for (const file of files) {
    const nameBytes = [...new TextEncoder().encode(file.name)];
    const crc = crc32(file.data);
    entries.push({ ...file, crc, offset: parts.length });
    parts.push(
      ...u32(0x04034b50), // local file header
      ...u16(20), // version needed
      ...u16(0), // flags
      ...u16(0), // method 0 = stored
      ...u16(0), // time
      ...u16(0x0021), // date — 1980-01-01
      ...u32(crc),
      ...u32(file.data.length), // compressed size == uncompressed, stored
      ...u32(file.data.length),
      ...u16(nameBytes.length),
      ...u16(0), // extra length
      ...nameBytes,
      ...file.data,
    );
  }

  const centralStart = parts.length;
  for (const entry of entries) {
    const nameBytes = [...new TextEncoder().encode(entry.name)];
    parts.push(
      ...u32(0x02014b50), // central directory header
      ...u16(20), // version made by
      ...u16(20), // version needed
      ...u16(0),
      ...u16(0),
      ...u16(0),
      ...u16(0x0021),
      ...u32(entry.crc),
      ...u32(entry.data.length),
      ...u32(entry.data.length),
      ...u16(nameBytes.length),
      ...u16(0), // extra
      ...u16(0), // comment
      ...u16(0), // disk
      ...u16(0), // internal attrs
      ...u32(0), // external attrs
      ...u32(entry.offset),
      ...nameBytes,
    );
  }

  parts.push(
    ...u32(0x06054b50), // end of central directory
    ...u16(0),
    ...u16(0),
    ...u16(entries.length),
    ...u16(entries.length),
    ...u32(parts.length - centralStart),
    ...u32(centralStart),
    ...u16(0), // comment length
  );

  return new Uint8Array(parts);
}