security: fix complete multi-character sanitization for HTML comments in txt.ts (#3806)

* security: fix for code scanning alert no. 11: Incomplete multi-character sanitization

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

* fix: use dotAll flag to match multi-line HTML comments

Add the 's' flag to the comment-stripping regex so '.' matches
newlines, ensuring comments spanning multiple lines are also removed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: iterative dotAll sanitization in extractChaptersFromSegment

Fixes code scanning alert #10 (incomplete multi-character sanitization).
Apply the same fix as alert #11: replace one-shot comment stripping
with an iterative loop using the 's' (dotAll) flag so nested and
multi-line HTML comments are fully removed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: iterative HTML tag sanitization in cleanDescription

Fixes code scanning alert #9 (incomplete multi-character sanitization).
Replace one-shot tag stripping with an iterative loop so crafted inputs
like nested/overlapping tags cannot leave '<script' behind after a single
replacement pass.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

apps/readest-app/src/services/metadata/providers/googlebooks.ts

@@ -208,9 +208,12 @@ export class GoogleBooksProvider extends BaseMetadataProvider {
       return undefined;
     }
 
-    return description
-      .replace(/<[^>]*>/g, '')
-      .replace(/\s+/g, ' ')
-      .trim();
+    let sanitized = description;
+    let previous: string;
+    do {
+      previous = sanitized;
+      sanitized = sanitized.replace(/<[^>]*>/g, '');
+    } while (sanitized !== previous);
+    return sanitized.replace(/\s+/g, ' ').trim();
   }
 }

apps/readest-app/src/utils/txt.ts

@@ -475,7 +475,13 @@ export class TxtToEpubConverter {
   ): Chapter[] {
     const { language } = metadata;
     const { fallbackParagraphsPerChapter } = option;
-    const trimmedSegment = segment.replace(/<!--.*?-->/g, '').trim();
+    let sanitizedSegment = segment;
+    let previousSegment: string;
+    do {
+      previousSegment = sanitizedSegment;
+      sanitizedSegment = sanitizedSegment.replace(/<!--.*?-->/gs, '');
+    } while (sanitizedSegment !== previousSegment);
+    const trimmedSegment = sanitizedSegment.trim();
     if (!trimmedSegment) return [];
 
     const chapterRegexps = this.createChapterRegexps(language);