fix: show "Failed to index" when failing to parse epub (#2556)

lib/I18n/translations/english.yaml

@@ -18,6 +18,7 @@ STR_NO_CHAPTERS: "No chapters"
 STR_END_OF_BOOK: "End of book"
 STR_EMPTY_CHAPTER: "Empty chapter"
 STR_INDEXING: "Indexing"
+STR_INDEX_FAILED: "Failed to index - invalid book"
 STR_MEMORY_ERROR: "Memory error"
 STR_PAGE_LOAD_ERROR: "Page load error"
 STR_EMPTY_FILE: "Empty file"

src/activities/reader/EpubReaderActivity.cpp

@@ -893,6 +893,15 @@ void EpubReaderActivity::render(RenderLock&& lock) {
     GUI.drawPopup(renderer, tr(STR_SAVE_PROGRESS_FAILED));
   };
 
+  // A section build failure (e.g. an invalid/corrupt EPUB that fails XML parsing) leaves the
+  // "Indexing" popup on screen with no way forward. Surface an explicit error instead of hanging.
+  // clearScreen first so the error popup doesn't overlay the stale "Indexing" popup.
+  const auto showBuildError = [this]() {
+    renderer.clearScreen();
+    GUI.drawPopup(renderer, tr(STR_INDEX_FAILED));
+    automaticPageTurnActive = false;
+  };
+
   // edge case handling for sub-zero spine index
   if (currentSpineIndex < 0) {
     currentSpineIndex = 0;
@@ -991,7 +1000,7 @@ void EpubReaderActivity::render(RenderLock&& lock) {
                                         SETTINGS.imageRendering, SETTINGS.focusReadingEnabled, popupFn)) {
           LOG_ERR("ERS", "Failed to persist page data to SD");
           section.reset();
-          showPendingSyncSaveError();
+          showBuildError();
           return;
         }
       } else {
@@ -1033,7 +1042,7 @@ void EpubReaderActivity::render(RenderLock&& lock) {
                                  SETTINGS.imageRendering, SETTINGS.focusReadingEnabled)) {
           LOG_ERR("ERS", "Failed to start section build");
           section.reset();
-          showPendingSyncSaveError();
+          showBuildError();
           return;
         }
         while (!section->isBuildComplete() &&
@@ -1044,7 +1053,7 @@ void EpubReaderActivity::render(RenderLock&& lock) {
           if (!section->buildSomeMore(BUILD_PAGES_PER_CHUNK)) {
             LOG_ERR("ERS", "Failed during incremental section build");
             section.reset();
-            showPendingSyncSaveError();
+            showBuildError();
             return;
           }
         }
@@ -1098,7 +1107,7 @@ void EpubReaderActivity::render(RenderLock&& lock) {
                              SETTINGS.focusReadingEnabled)) {
       LOG_ERR("ERS", "Failed to start partial extension build");
       section.reset();
-      showPendingSyncSaveError();
+      showBuildError();
       return;
     }
     // Extend until either the target page exists or the build completes.
@@ -1106,7 +1115,7 @@ void EpubReaderActivity::render(RenderLock&& lock) {
       if (!section->buildSomeMore(BUILD_PAGES_PER_CHUNK)) {
         LOG_ERR("ERS", "Failed during incremental section build");
         section.reset();
-        showPendingSyncSaveError();
+        showBuildError();
         return;
       }
     }
@@ -1117,7 +1126,7 @@ void EpubReaderActivity::render(RenderLock&& lock) {
       if (!section->buildSomeMore(BUILD_PAGES_PER_CHUNK)) {
         LOG_ERR("ERS", "Failed during incremental section build");
         section.reset();
-        showPendingSyncSaveError();
+        showBuildError();
         return;
       }
     }
@@ -1167,17 +1176,29 @@ void EpubReaderActivity::render(RenderLock&& lock) {
     auto p = section->loadPage(section->currentPage);
     if (!p) {
       LOG_ERR("ERS", "Failed to load page from SD - clearing section cache");
+      automaticPageTurnActive = false;
+      // Retrying rebuilds a transiently corrupt section and usually recovers, but a page that keeps
+      // failing would loop forever on a blank screen, so bound the retries before giving up.
+      const bool giveUp = ++pageLoadRetryCount > MAX_PAGE_LOAD_RETRIES;
       // Abandon (not suspend) any active build BEFORE clearing: clearCache deletes the files,
       // and the destructor's suspend would otherwise commit tables into a deleted handle.
       section->abandonBuild();
       section->clearCache();
       section.reset();
+      if (giveUp) {
+        LOG_ERR("ERS", "Page load retry limit reached, aborting");
+        pageLoadRetryCount = 0;  // Reset so a later user-initiated navigation can try afresh
+        renderer.clearScreen();
+        renderer.drawCenteredText(UI_12_FONT_ID, 300, tr(STR_PAGE_LOAD_ERROR), true, EpdFontFamily::BOLD);
+        renderer.displayBuffer();
+        showPendingSyncSaveError();
+        return;
+      }
       requestUpdate();  // Try again after clearing cache
-                        // TODO: prevent infinite loop if the page keeps failing to load for some reason
-      automaticPageTurnActive = false;
       showPendingSyncSaveError();
       return;
     }
+    pageLoadRetryCount = 0;  // Reset the retry counter once a page loads cleanly
 
     // Collect footnotes from the loaded page
     currentPageFootnotes = std::move(p->footnotes);

src/activities/reader/EpubReaderActivity.h

@@ -32,6 +32,10 @@ class EpubReaderActivity final : public Activity {
   float pendingSpineProgress = 0.0f;
   bool pendingScreenshot = false;
   bool pendingSyncSaveError = false;
+  // Consecutive page-load failures. Each failure drops the section and rebuilds on the next render,
+  // which recovers a transiently corrupt cache; capped so a persistently bad page can't spin forever.
+  uint8_t pageLoadRetryCount = 0;
+  static constexpr uint8_t MAX_PAGE_LOAD_RETRIES = 3;
   bool skipNextButtonCheck = false;  // Skip button processing for one frame after subactivity exit
   bool automaticPageTurnActive = false;
   bool showBookmarkMessage = false;