implemented a lot of features

tests/unit/par2.spec.ts

@@ -0,0 +1,60 @@
+import { test } from '@japa/runner'
+import { createHash } from 'node:crypto'
+import { isPar2, parsePar2 } from '#lib/par2/index'
+
+const md5 = (data: Buffer) => createHash('md5').update(data).digest()
+
+/** Builds one PAR2 packet with a valid checksum. */
+function packet(setId: Buffer, type: string, body: Buffer) {
+  const padded = Buffer.concat([body, Buffer.alloc((4 - (body.length % 4)) % 4)])
+  const length = Buffer.alloc(8)
+  length.writeBigUInt64LE(BigInt(64 + padded.length))
+  const typeBuf = Buffer.alloc(16)
+  typeBuf.write(type, 'latin1')
+  const hashed = Buffer.concat([setId, typeBuf, padded])
+  return Buffer.concat([Buffer.from('PAR2\0PKT', 'latin1'), length, md5(hashed), hashed])
+}
+
+function fileDesc(setId: Buffer, name: string, size: number) {
+  const len = Buffer.alloc(8)
+  len.writeBigUInt64LE(BigInt(size))
+  const md5_16k = md5(Buffer.from(`${name}-16k`))
+  const fileId = md5(Buffer.concat([md5_16k, len, Buffer.from(name)]))
+  const body = Buffer.concat([fileId, md5(Buffer.from(name)), md5_16k, len, Buffer.from(name, 'utf8')])
+  return packet(setId, 'PAR 2.0\0FileDesc', body)
+}
+
+test.group('par2 / parsePar2', () => {
+  const setId = Buffer.alloc(16, 7)
+
+  test('reads file names and sizes from FileDesc packets', ({ assert }) => {
+    const data = Buffer.concat([
+      packet(setId, 'PAR 2.0\0Main', Buffer.alloc(12)),
+      fileDesc(setId, 'Some.Movie.2024.part01.rar', 104857600),
+      fileDesc(setId, 'Some.Movie.2024.part02.rar', 52428800),
+      fileDesc(setId, 'Some.Movie.2024.part01.rar', 104857600), // duplicates are common
+    ])
+    assert.isTrue(isPar2(data))
+    const set = parsePar2(data)!
+    assert.equal(set.recoverySetId, setId.toString('hex'))
+    assert.deepEqual(
+      set.files.map((f) => [f.name, f.length]),
+      [
+        ['Some.Movie.2024.part01.rar', 104857600],
+        ['Some.Movie.2024.part02.rar', 52428800],
+      ]
+    )
+  })
+
+  test('skips corrupted packets and resumes at the next one', ({ assert }) => {
+    const bad = fileDesc(setId, 'bad.bin', 1)
+    bad[100] ^= 0xff
+    const data = Buffer.concat([bad, fileDesc(setId, 'good.bin', 12345)])
+    assert.deepEqual(parsePar2(data)!.files.map((f) => f.name), ['good.bin'])
+  })
+
+  test('returns null for non-par2 data', ({ assert }) => {
+    assert.isFalse(isPar2(Buffer.from('Rar!\x1a\x07\x00', 'latin1')))
+    assert.isNull(parsePar2(Buffer.from('hello world')))
+  })
+})