From abb98d96666004eb53447e4d3de4e43bd65a0379 Mon Sep 17 00:00:00 2001
From: Weiyi Li <1093656961@qq.com>
Date: Mon, 21 Sep 2026 14:31:26 +0000
Subject: [PATCH] Select a single value from XMP language alternatives

Fixes #20801.

`dc:title`, `dc:description`, `dc:rights` and `xmpRights:UsageTerms` are
language alternatives, so pick the `x-default` entry (compared
case-insensitively, as the XMP specification requires), or the first one
when there is no default, instead of concatenating all of them.

Continues the approach proposed by @nyxsky404 in https://github.com/mozilla/pdf.js/pull/20874.
---
 src/core/metadata_parser.js | 30 ++++++++++++++++++-
 test/unit/metadata_spec.js  | 58 +++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+), 1 deletion(-)

diff --git a/src/core/metadata_parser.js b/src/core/metadata_parser.js
index f50927e43db57..a4cbfa12d59c0 100644
--- a/src/core/metadata_parser.js
+++ b/src/core/metadata_parser.js
@@ -21,7 +21,10 @@ class MetadataParser {
     data = this._repair(data);
 
     // Convert the string to an XML document.
-    const parser = new SimpleXMLParser({ lowerCaseName: true });
+    const parser = new SimpleXMLParser({
+      lowerCaseName: true,
+      hasAttributes: true,
+    });
     const xmlDocument = parser.parseFromString(data);
 
     this._metadataMap = new Map();
@@ -99,6 +102,25 @@ class MetadataParser {
     );
   }
 
+  _parseLangAlt(entry) {
+    const alt = entry.children.find(node => node.nodeName === "rdf:alt");
+    const alternatives = alt ? this._getSequence(alt) : [];
+    // Language alternatives represent the same value in different languages.
+    // Prefer the default value, without changing the string-valued API.
+    const selected =
+      alternatives.find(node =>
+        node.attributes.some(
+          ({ name, value }) =>
+            name === "xml:lang" && value.toLowerCase() === "x-default"
+        )
+      ) || alternatives[0];
+
+    this._metadataMap.set(
+      entry.nodeName,
+      (selected || entry).textContent.trim()
+    );
+  }
+
   _parse(xmlDocument) {
     let rdf = xmlDocument.documentElement;
 
@@ -128,6 +150,12 @@ class MetadataParser {
           case "dc:subject":
             this._parseArray(entry);
             continue;
+          case "dc:title":
+          case "dc:description":
+          case "dc:rights":
+          case "xmprights:usageterms":
+            this._parseLangAlt(entry);
+            continue;
         }
         this._metadataMap.set(name, entry.textContent.trim());
       }
diff --git a/test/unit/metadata_spec.js b/test/unit/metadata_spec.js
index 4bb5afde7cb03..618113907361e 100644
--- a/test/unit/metadata_spec.js
+++ b/test/unit/metadata_spec.js
@@ -37,6 +37,64 @@ describe("metadata", function () {
     expect([...metadata]).toEqual([["dc:title", "Foo bar baz"]]);
   });
 
+  it("should select the default language alternative (issue 20801)", function () {
+    for (const name of [
+      "dc:title",
+      "dc:description",
+      "dc:rights",
+      "xmpRights:UsageTerms",
+    ]) {
+      for (const alternatives of [
+        '<rdf:li xml:lang="x-default">Hello World</rdf:li>' +
+          '<rdf:li xml:lang="en">Hello World</rdf:li>',
+        '<rdf:li xml:lang="fr">Bonjour le monde</rdf:li>' +
+          '<rdf:li xml:lang="x-default">Hello World</rdf:li>',
+        '<rdf:li xml:lang="fr">Bonjour le monde</rdf:li>' +
+          '<rdf:li xml:lang="X-Default">Hello World</rdf:li>',
+      ]) {
+        const data =
+          "<rdf:RDF><rdf:Description>" +
+          `<${name}><rdf:Alt>${alternatives}</rdf:Alt></${name}>` +
+          "</rdf:Description></rdf:RDF>";
+
+        expect(createMetadata(data).get(name.toLowerCase()))
+          .withContext(`${name}: ${alternatives}`)
+          .toEqual("Hello World");
+      }
+    }
+  });
+
+  it("should use the first language alternative if there is no default", function () {
+    for (const name of [
+      "dc:title",
+      "dc:description",
+      "dc:rights",
+      "xmpRights:UsageTerms",
+    ]) {
+      const data =
+        "<rdf:RDF><rdf:Description>" +
+        `<${name}><rdf:Alt>` +
+        '<rdf:li xml:lang="en">Hello World</rdf:li>' +
+        '<rdf:li xml:lang="fr">Bonjour le monde</rdf:li>' +
+        `</rdf:Alt></${name}>` +
+        "</rdf:Description></rdf:RDF>";
+
+      expect(createMetadata(data).get(name.toLowerCase()))
+        .withContext(name)
+        .toEqual("Hello World");
+    }
+  });
+
+  it("should handle whitespace before the language alternatives", function () {
+    const data =
+      "<rdf:RDF><rdf:Description><dc:title>\n  <rdf:Alt>\n" +
+      '  <rdf:li xml:lang="en">English title</rdf:li>\n' +
+      '  <rdf:li xml:lang="x-default"> Default title </rdf:li>\n' +
+      "</rdf:Alt>\n</dc:title></rdf:Description></rdf:RDF>";
+
+    expect(createMetadata(data).get("dc:title")).toEqual("Default title");
+  });
+
   it("should repair and handle invalid metadata", function () {
     const data =
       "<x:xmpmeta xmlns:x='adobe:ns:meta/'>" +