fix(reader): support epub loading without native grouping APIs

Keep EPUB loading functional on browsers without Object.groupBy or Map.groupBy.
Replace the native calls with local helpers and cover missing APIs with EPUB 2
and EPUB 3 metadata regression tests.

Closes #1683

client/public/assets/foliate/epub.js

@@ -181,6 +181,25 @@ const getPropertyURL = (value, prefixes) => {
   return baseURL ? baseURL + reference : null
 }
 
+const groupBy = (items, getKey) => {
+  const groups = Object.create(null)
+  for (const item of items) {
+    const key = getKey(item)
+    ;(groups[key] ??= []).push(item)
+  }
+  return groups
+}
+
+const groupByMap = (items, getKey) => {
+  const groups = new Map()
+  for (const item of items) {
+    const key = getKey(item)
+    if (!groups.has(key)) groups.set(key, [])
+    groups.get(key).push(item)
+  }
+  return groups
+}
+
 const getMetadata = (opf) => {
   const { $ } = childGetter(opf, NS.OPF)
   const $metadata = $(opf.documentElement, 'metadata')
@@ -188,7 +207,7 @@ const getMetadata = (opf) => {
   const opfNS = opf.documentElement.namespaceURI === NS.OPF ? NS.OPF : null
 
   // first pass: convert to JS objects
-  const els = Object.groupBy($metadata.children, (el) =>
+  const els = groupBy($metadata.children, (el) =>
     el.namespaceURI === NS.DC ? 'dc' : el.namespaceURI === opfNS && el.localName === 'meta' ? (el.hasAttribute('name') ? 'legacyMeta' : 'meta') : '',
   )
   const baseLang = $metadata.getAttribute('xml:lang') ?? opf.documentElement.getAttribute('xml:lang') ?? 'und'
@@ -210,13 +229,13 @@ const getMetadata = (opf) => {
       ),
     }
   }
-  const refines = Map.groupBy(els.meta ?? [], (el) => el.getAttribute('refines'))
+  const refines = groupByMap(els.meta ?? [], (el) => el.getAttribute('refines'))
   const getProperties = (el) => {
     const els = refines.get(el ? '#' + el.getAttribute('id') : null)
     if (!els) return null
-    return Object.groupBy(els.map(parse), (x) => x.property)
+    return groupBy(els.map(parse), (x) => x.property)
   }
-  const dc = Object.fromEntries(Object.entries(Object.groupBy(els.dc, (el) => el.localName)).map(([name, els]) => [name, els.map(parse)]))
+  const dc = Object.fromEntries(Object.entries(groupBy(els.dc, (el) => el.localName)).map(([name, els]) => [name, els.map(parse)]))
   const properties = getProperties() ?? {}
   const legacyMeta = Object.fromEntries(els.legacyMeta?.map((el) => [el.getAttribute('name'), el.getAttribute('content')]) ?? [])
 
@@ -268,9 +287,7 @@ const getMetadata = (opf) => {
     }
     return value
   }
-  const belongsTo = Object.groupBy(properties['belongs-to-collection'] ?? [], (x) =>
-    prop(x, 'collection-type') === 'series' ? 'series' : 'collection',
-  )
+  const belongsTo = groupBy(properties['belongs-to-collection'] ?? [], (x) => (prop(x, 'collection-type') === 'series' ? 'series' : 'collection'))
   const mainTitle = dc.title?.find((x) => prop(x, 'title-type') === 'main') ?? dc.title?.[0]
   const metadata = {
     identifier: getIdentifier(opf),

client/src/features/reader/epub/__tests__/metadata-compatibility.spec.ts

@@ -0,0 +1,90 @@
+import { afterEach, describe, expect, it } from 'vitest'
+
+// @ts-expect-error public Foliate asset has no TypeScript declarations.
+import { EPUB } from '../../../../../public/assets/foliate/epub.js'
+
+const objectGroupBy = Object.getOwnPropertyDescriptor(Object, 'groupBy')!
+const mapGroupBy = Object.getOwnPropertyDescriptor(Map, 'groupBy')!
+
+afterEach(() => {
+  Object.defineProperty(Object, 'groupBy', objectGroupBy)
+  Object.defineProperty(Map, 'groupBy', mapGroupBy)
+})
+
+async function openEpub(version: string, extraMetadata: string) {
+  const files: Record<string, string> = {
+    'META-INF/container.xml': `<container xmlns="urn:oasis:names:tc:opendocument:xmlns:container" version="1.0"><rootfiles><rootfile full-path="OPS/book.opf" media-type="application/oebps-package+xml"/></rootfiles></container>`,
+    'OPS/book.opf': `<package xmlns="http://www.idpf.org/2007/opf" version="${version}" unique-identifier="id"><metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:opf="http://www.idpf.org/2007/opf"><dc:identifier id="id">urn:uuid:compatibility-test</dc:identifier><dc:title id="title">Main title</dc:title><dc:creator id="author" opf:role="aut">Test author</dc:creator><dc:language>en</dc:language>${extraMetadata}</metadata><manifest><item id="chapter" href="chapter.xhtml" media-type="application/xhtml+xml"/></manifest><spine><itemref idref="chapter"/></spine></package>`,
+    'OPS/chapter.xhtml': `<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Chapter</title></head><body><p>Readable content.</p></body></html>`,
+  }
+  return new EPUB({
+    loadText: async (uri: string) => files[uri] ?? null,
+    loadBlob: async () => null,
+    getSize: () => 0,
+  }).init()
+}
+
+describe.each([
+  { name: 'native grouping APIs', objectMissing: false, mapMissing: false },
+  { name: 'Object.groupBy unavailable', objectMissing: true, mapMissing: false },
+  { name: 'Map.groupBy unavailable', objectMissing: false, mapMissing: true },
+  { name: 'both grouping APIs unavailable', objectMissing: true, mapMissing: true },
+])('EPUB metadata with $name', ({ objectMissing, mapMissing }) => {
+  function disableGroupingApis() {
+    if (objectMissing) Object.defineProperty(Object, 'groupBy', { ...objectGroupBy, value: undefined })
+    if (mapMissing) Object.defineProperty(Map, 'groupBy', { ...mapGroupBy, value: undefined })
+  }
+
+  it('opens EPUB 3 with grouped values, refinements, rendition and media metadata intact', async () => {
+    const metadata = `<dc:title id="subtitle">Subtitle</dc:title><dc:language>fr</dc:language>
+      <meta refines="#title" property="title-type">main</meta>
+      <meta refines="#title" property="file-as">Title, Main</meta>
+      <meta refines="#subtitle" property="title-type">subtitle</meta>
+      <meta refines="#author" property="file-as">Author, Test</meta>
+      <meta refines="#author" property="role">aut</meta>
+      <meta property="belongs-to-collection" id="collection">Test collection</meta>
+      <meta refines="#collection" property="collection-type">set</meta>
+      <meta refines="#collection" property="group-position">2</meta>
+      <meta property="rendition:layout">pre-paginated</meta>
+      <meta property="media:duration">00:01:30</meta>
+      <meta property="__proto__">Untrusted property</meta>
+      <meta property="constructor">Another untrusted property</meta>`
+    const baseline = await openEpub('3.0', metadata)
+    disableGroupingApis()
+
+    const book = await openEpub('3.0', metadata)
+
+    expect(book.metadata).toEqual(baseline.metadata)
+    expect(book.metadata).toMatchObject({
+      title: 'Main title',
+      sortAs: 'Title, Main',
+      subtitle: 'Subtitle',
+      author: { name: 'Test author', sortAs: 'Author, Test' },
+      language: ['en', 'fr'],
+      belongsTo: { collection: { name: 'Test collection', position: '2' } },
+    })
+    expect(book.rendition).toEqual({ layout: 'pre-paginated' })
+    expect(book.media).toEqual({ duration: 90 })
+    expect(book.sections.map((section: { id: string }) => section.id)).toEqual(['OPS/chapter.xhtml'])
+    const chapter = await book.sections[0].createDocument()
+    expect(chapter.querySelector('p')?.textContent).toBe('Readable content.')
+    expect(Object.getOwnPropertyDescriptor(Object, 'groupBy')?.value).toBe(objectMissing ? undefined : objectGroupBy.value)
+    expect(Object.getOwnPropertyDescriptor(Map, 'groupBy')?.value).toBe(mapMissing ? undefined : mapGroupBy.value)
+  })
+
+  it('opens EPUB 2 without refinement metadata and preserves legacy series metadata', async () => {
+    disableGroupingApis()
+
+    const book = await openEpub('2.0', '<meta name="calibre:series" content="Test series"/><meta name="calibre:series_index" content="3"/>')
+
+    expect(book.metadata).toMatchObject({
+      title: 'Main title',
+      author: { name: 'Test author', role: 'aut' },
+      language: 'en',
+      belongsTo: { series: { name: 'Test series', position: 3 } },
+    })
+    expect(book.rendition).toEqual({})
+    expect(book.media).toEqual({})
+    expect(book.sections).toHaveLength(1)
+  })
+})