Fix leading-slash ZIP entry names breaking ZIP-based publications

[raphi011]

Summary

ZIP archives sometimes store entry names with a leading slash (e.g. /001.jpg). This is spec-noncompliant — APPNOTE.TXT §4.4.17.1 defines an entry name as "the name of the file, with optional relative path" that "MUST NOT contain a drive or device letter, or a leading slash" — but it's common in the wild, especially CBZ comics packed by tools that don't strip the slash, and Internet Archive comic uploads.

Left untouched, the leading slash turns the manifest href into an absolute-path reference: when /001.jpg is resolved against the publication server's base URL (e.g. readium://<uuid>/), the slash replaces the base path entirely, producing a request that no longer maps to the archive entry. Every resource 404s. This is most visible with image-based (Divina/CBZ) publications, which address resources by the entry's path — every page renders as a broken image.

This was discovered while opening a real Pepper&Carrot CBZ from the Internet Archive (entries stored as /001.jpg, …) in a Readium-based reader: import and cover extraction succeeded (direct, symmetric container lookups), but every page 404'd.

Fix

Interpret a stored ZIP entry name as the relative path the format intends, by stripping leading slashes via a new RelativeURL(zipEntryPath:), in both ZIP backends:

• MinizipContainer / ZIPFoundationContainer now key entries under the normalized, slash-free relative URL — so entries and the manifest reading order are slash-free and resolve correctly against the base URL.
• MinizipContainer additionally preserves the original stored name in its entry metadata and locates by it verbatim when reading (unzLocateFile matches the central-directory name exactly), with a slash-stripped fallback. ZIPFoundationContainer already reads via the retained Entry, so it needs no read-path change.

This aligns Swift with the Kotlin toolkit, which strips the prefix for the same reason (Url.fromLegacyHref → fromDecodedPath(href.removePrefix("/")), migration guide: "We dropped the / prefix to avoid issues when resolving to a base URL"), and with the wider ecosystem (Python's ZipFile strips leading slashes on extraction). It also complements #432, which removed the leading-/ prefix for exploded archives but not for compressed ZIP/CBZ containers.

Tests

Adds a forged leading-slash.zip fixture (entries /root.txt, /folder/file.txt, plus a well-formed normal.txt) and, for each backend, tests covering:

• the entries set is exposed slash-free, and
• the read path resolves a leading-slash entry to its bytes.

All MinizipContainerTests + ZIPFoundationContainerTests pass (28/28) on the iOS simulator. Verified end-to-end in a downstream app: the original broken CBZ renders all pages with no re-import.

[Copilot]

Pull request overview

This PR fixes interoperability with ZIP/CBZ archives whose entry names are stored with a leading slash (e.g. /001.jpg). By normalizing entry names to slash-free relative URLs, manifest hrefs resolve correctly against the publication server base URL, preventing widespread 404s (notably in image-based/Divina publications).

Changes:

• Added RelativeURL(zipEntryPath:) to strip leading slashes from stored ZIP entry names.
• Updated both ZIP backends (MinizipContainer, ZIPFoundationContainer) to key entries using normalized, slash-free relative URLs, and added read-path handling for Minizip.
• Added test coverage for leading-slash entry names in both container backends and documented the fix in the changelog.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Tests/SharedTests/Toolkit/ZIP/ZIPFoundationContainerTests.swift	Adds tests ensuring leading-slash ZIP entry names are exposed slash-free and remain readable.
Tests/SharedTests/Toolkit/ZIP/MinizipContainerTests.swift	Adds equivalent leading-slash normalization + read tests for the Minizip backend.
Sources/Shared/Toolkit/ZIP/ZIPFoundation/ZIPFoundationContainer.swift	Switches entry URL creation to RelativeURL(zipEntryPath:) so entries are keyed without leading slashes.
Sources/Shared/Toolkit/ZIP/ZIPEntryURL.swift	Introduces RelativeURL(zipEntryPath:) helper to normalize ZIP entry paths (strip leading /).
Sources/Shared/Toolkit/ZIP/Minizip/MinizipContainer.swift	Keys entries by normalized slash-free URLs while preserving original stored names for reading; adjusts entry location logic.
CHANGELOG.md	Documents the behavior fix under Unreleased.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mickael-menu]

Thank you @raphi011! I've simplified the CHANGELOG a bit, removed the reference to the Internet Archive (as I couldn't observe it), and relaxed the claim that most CBZ files are impacted.