fix(metadata): support CBZ archive comments

Retry central-directory discovery at the ZIP comment limit when the default scan reaches the end of the file. Preserve the archive comment while rewriting ComicInfo.xml.

Fixes #1272

server/src/modules/file-write/formats/cbx/cbz-zip-patcher.ts

@@ -4,25 +4,42 @@ import * as unzipper from 'unzipper';
 import { replaceFileAtomically } from '../shared/atomic-file-replace';
 import { writeZipArchive, type ZipRewriteEntry } from '../shared/zip-rewrite';
 
+const ZIP_END_OF_CENTRAL_DIRECTORY_SIZE_BYTES = 22;
+const MAX_ZIP_COMMENT_SIZE_BYTES = 0xffff;
+const ZIP_TAIL_SIZE_BYTES = ZIP_END_OF_CENTRAL_DIRECTORY_SIZE_BYTES + MAX_ZIP_COMMENT_SIZE_BYTES;
+
+type ZipCentralDirectory = unzipper.CentralDirectory & { comment?: string };
+
+const openZipFileWithOptions = unzipper.Open.file as (filePath: string, options: { tailSize: number }) => Promise<ZipCentralDirectory>;
+
+async function openZipFile(filePath: string): Promise<ZipCentralDirectory> {
+  try {
+    return await unzipper.Open.file(filePath);
+  } catch (error) {
+    if (!(error instanceof Error) || error.message !== 'FILE_ENDED') throw error;
+    return openZipFileWithOptions(filePath, { tailSize: ZIP_TAIL_SIZE_BYTES });
+  }
+}
+
 function isComicInfoEntry(entryPath: string): boolean {
   const normalized = entryPath.replace(/\\/g, '/').toLowerCase();
   return normalized === 'comicinfo.xml' || normalized.endsWith('/comicinfo.xml');
 }
 
 export async function readComicInfoFromZip(filePath: string): Promise<string | null> {
-  const zip = await unzipper.Open.file(filePath);
+  const zip = await openZipFile(filePath);
   const entry = zip.files.find((f) => isComicInfoEntry(f.path));
   if (!entry) return null;
   return (await entry.buffer()).toString('utf-8');
 }
 
 export async function writeComicInfoToZip(filePath: string, xmlContent: string): Promise<void> {
-  const zip = await unzipper.Open.file(filePath);
+  const zip = await openZipFile(filePath);
   const existing = zip.files.find((f) => isComicInfoEntry(f.path));
   const xmlEntryPath = existing?.path ?? 'ComicInfo.xml';
 
   const tmpPath = join(dirname(filePath), `.cbx-write-${randomUUID()}`);
-  await writeZipArchive(tmpPath, rewriteEntries(zip.files, xmlEntryPath, xmlContent));
+  await writeZipArchive(tmpPath, rewriteEntries(zip.files, xmlEntryPath, xmlContent), { comment: zip.comment });
 
   await replaceFileAtomically(tmpPath, filePath);
 }

server/src/modules/file-write/formats/cbx/cbz-zip-roundtrip.test.ts

@@ -1,6 +1,6 @@
 import { ZipArchive } from 'archiver';
 import { createWriteStream } from 'fs';
-import { mkdtemp, readdir, rm } from 'fs/promises';
+import { mkdtemp, readFile, readdir, rm } from 'fs/promises';
 import { tmpdir } from 'os';
 import { join } from 'path';
 import * as unzipper from 'unzipper';
@@ -9,6 +9,9 @@ import { readComicInfoFromZip, writeComicInfoToZip } from './cbz-zip-patcher';
 
 let testRoot: string;
 
+const MAX_ZIP_COMMENT_BYTES = 0xffff;
+const ZIP_END_OF_CENTRAL_DIRECTORY_SIGNATURE = Buffer.from([0x50, 0x4b, 0x05, 0x06]);
+
 beforeEach(async () => {
   testRoot = await mkdtemp(join(tmpdir(), 'bookorbit-cbz-roundtrip-'));
 });
@@ -23,9 +26,9 @@ function pageBytes(index: number): Buffer {
   return bytes;
 }
 
-async function writeArchive(filePath: string, entries: Array<{ path: string; content: Buffer }>): Promise<void> {
+async function writeArchive(filePath: string, entries: Array<{ path: string; content: Buffer }>, comment = ''): Promise<void> {
   const output = createWriteStream(filePath);
-  const archive = new ZipArchive({ zlib: { level: 6 } });
+  const archive = new ZipArchive({ zlib: { level: 6 }, comment });
 
   await new Promise<void>((resolve, reject) => {
     output.on('close', resolve);
@@ -37,6 +40,15 @@ async function writeArchive(filePath: string, entries: Array<{ path: string; con
   });
 }
 
+async function readArchiveComment(filePath: string): Promise<string> {
+  const contents = await readFile(filePath);
+  const endRecordOffset = contents.lastIndexOf(ZIP_END_OF_CENTRAL_DIRECTORY_SIGNATURE);
+  if (endRecordOffset < 0) throw new Error('ZIP end of central directory record not found');
+
+  const commentLength = contents.readUInt16LE(endRecordOffset + 20);
+  return contents.subarray(endRecordOffset + 22, endRecordOffset + 22 + commentLength).toString('utf-8');
+}
+
 async function readArchive(filePath: string): Promise<Array<{ path: string; content: Buffer }>> {
   const zip = await unzipper.Open.file(filePath);
   return Promise.all(zip.files.map(async (entry) => ({ path: entry.path, content: await entry.buffer() })));
@@ -85,4 +97,15 @@ describe('cbz zip round trip', () => {
 
     await expect(readdir(testRoot)).resolves.toEqual(['volume.cbz']);
   });
+
+  it('updates comic info and preserves an archive comment at the ZIP format limit', async () => {
+    const target = join(testRoot, 'volume.cbz');
+    const archiveComment = 'x'.repeat(MAX_ZIP_COMMENT_BYTES);
+    await writeArchive(target, comicPages(3), archiveComment);
+
+    await writeComicInfoToZip(target, '<ComicInfo><Title>Updated</Title></ComicInfo>');
+
+    await expect(readComicInfoFromZip(target)).resolves.toBe('<ComicInfo><Title>Updated</Title></ComicInfo>');
+    await expect(readArchiveComment(target)).resolves.toBe(archiveComment);
+  });
 });

server/src/modules/file-write/formats/shared/zip-rewrite.ts

@@ -10,14 +10,18 @@ export interface ZipRewriteEntry {
   store?: boolean;
 }
 
+export interface ZipRewriteOptions {
+  comment?: string;
+}
+
 /**
  * Archiver pipes an appended stream into its queue immediately, so appending every entry of a large
  * archive up front holds one descriptor and one decompression buffer per entry until the rewrite
  * finishes. Entries are appended one at a time and their sources opened only once archiver is ready
  * for them, which keeps descriptors and memory flat regardless of entry count.
  */
-export async function writeZipArchive(tmpPath: string, entries: Iterable<ZipRewriteEntry>): Promise<void> {
+export async function writeZipArchive(tmpPath: string, entries: Iterable<ZipRewriteEntry>, options: ZipRewriteOptions = {}): Promise<void> {
-  const archive = new ZipArchive({ zlib: { level: ZLIB_COMPRESSION_LEVEL } });
+  const archive = new ZipArchive({ zlib: { level: ZLIB_COMPRESSION_LEVEL }, comment: options.comment });
   const output = createWriteStream(tmpPath);
 
   let fail!: (error: Error) => void;