Fix inconsistent recognition_done_ state on empty pages

src/api/baseapi.cpp

@@ -765,6 +765,7 @@ int TessBaseAPI::Recognize(ETEXT_DESC *monitor) {
   delete page_res_;
   if (block_list_->empty()) {
     page_res_ = new PAGE_RES(false, block_list_, &tesseract_->prev_word_best_choice_);
+    recognition_done_ = true;
     return 0; // Empty page.
   }
 

unittest/baseapi_test.cc

@@ -157,6 +157,37 @@ TEST_F(TesseractTest, HOCRContainsBaseline) {
   src_pix.destroy();
 }
 
+// Tests that all output formats return valid results on an empty page.
+// Regression test for https://github.com/tesseract-ocr/tesseract/issues/4112
+TEST_F(TesseractTest, EmptyPageOutputConsistency) {
+  tesseract::TessBaseAPI api;
+  if (api.Init(TessdataPath().c_str(), "eng", tesseract::OEM_LSTM_ONLY) == -1) {
+    // eng.traineddata not found.
+    GTEST_SKIP();
+  }
+  // Create a blank white image (no text to detect).
+  Image blank_pix = pixCreate(200, 200, 8);
+  CHECK(blank_pix);
+  pixSetAll(blank_pix);
+  api.SetImage(blank_pix);
+  ASSERT_EQ(api.Recognize(nullptr), 0);
+
+  // All output formats should return non-null, even on an empty page.
+  char *hocr = api.GetHOCRText(0);
+  EXPECT_TRUE(hocr != nullptr);
+  delete[] hocr;
+
+  char *utf8 = api.GetUTF8Text();
+  EXPECT_TRUE(utf8 != nullptr);
+  delete[] utf8;
+
+  char *tsv = api.GetTSVText(0);
+  EXPECT_TRUE(tsv != nullptr);
+  delete[] tsv;
+
+  blank_pix.destroy();
+}
+
 // Tests that Tesseract gets exactly the right answer on some page numbers.
 TEST_F(TesseractTest, AdaptToWordStrTest) {
 #ifdef DISABLED_LEGACY_ENGINE