3 files changed, 62 insertions, 0 deletions
diff --git a/fpdfsdk/fpdfannot.cpp b/fpdfsdk/fpdfannot.cpp
index 5c4aae2075..ec748e66ec 100644
--- a/fpdfsdk/fpdfannot.cpp
+++ b/fpdfsdk/fpdfannot.cpp
@@ -727,6 +727,22 @@ FPDFAnnot_GetStringValue(FPDF_ANNOTATION annot,
       buffer, buflen);
 }
 
+FPDF_EXPORT FPDF_ANNOTATION FPDF_CALLCONV
+FPDFAnnot_GetLinkedAnnot(FPDF_ANNOTATION annot, FPDF_WIDESTRING key) {
+  CPDF_AnnotContext* pAnnot = CPDFAnnotContextFromFPDFAnnotation(annot);
+  if (!pAnnot || !pAnnot->GetAnnotDict())
+    return nullptr;
+
+  CPDF_Dictionary* pLinkedDict =
+      pAnnot->GetAnnotDict()->GetDictFor(CFXByteStringFromFPDFWideString(key));
+  if (!pLinkedDict || pLinkedDict->GetStringFor("Type") != "Annot")
+    return nullptr;
+
+  auto pLinkedAnnot = pdfium::MakeUnique<CPDF_AnnotContext>(
+      pLinkedDict, pAnnot->GetPage(), nullptr);
+  return pLinkedAnnot.release();
+}
+
 FPDF_EXPORT int FPDF_CALLCONV FPDFAnnot_GetFlags(FPDF_ANNOTATION annot) {
   if (!annot)
     return FPDF_ANNOT_FLAG_NONE;
diff --git a/fpdfsdk/fpdfannot_embeddertest.cpp b/fpdfsdk/fpdfannot_embeddertest.cpp
index 4aca839226..47b71667b2 100644
--- a/fpdfsdk/fpdfannot_embeddertest.cpp
+++ b/fpdfsdk/fpdfannot_embeddertest.cpp
@@ -914,6 +914,51 @@ TEST_F(FPDFAnnotEmbeddertest, GetSetStringValue) {
   CloseSaved();
 }
 
+TEST_F(FPDFAnnotEmbeddertest, ExtractLinkedAnnotations) {
+  // Open a file with annotations and load its first page.
+  ASSERT_TRUE(OpenDocument("annotation_highlight_square_with_ap.pdf"));
+  FPDF_PAGE page = FPDF_LoadPage(document(), 0);
+  ASSERT_TRUE(page);
+
+  // Retrieve the highlight annotation which has its popup defined.
+  FPDF_ANNOTATION annot = FPDFPage_GetAnnot(page, 0);
+  ASSERT_TRUE(annot);
+  EXPECT_EQ(FPDF_ANNOT_HIGHLIGHT, FPDFAnnot_GetSubtype(annot));
+  std::unique_ptr<unsigned short, pdfium::FreeDeleter> popup_key =
+      GetFPDFWideString(L"Popup");
+  ASSERT_TRUE(FPDFAnnot_HasKey(annot, popup_key.get()));
+  ASSERT_EQ(FPDF_OBJECT_REFERENCE,
+            FPDFAnnot_GetValueType(annot, popup_key.get()));
+
+  // Retrieve and verify the popup of the highlight annotation.
+  FPDF_ANNOTATION popup = FPDFAnnot_GetLinkedAnnot(annot, popup_key.get());
+  ASSERT_TRUE(popup);
+  EXPECT_EQ(FPDF_ANNOT_POPUP, FPDFAnnot_GetSubtype(popup));
+  FS_RECTF rect;
+  ASSERT_TRUE(FPDFAnnot_GetRect(popup, &rect));
+  EXPECT_NEAR(612.0f, rect.left, 0.001f);
+  EXPECT_NEAR(578.792, rect.bottom, 0.001f);
+
+  // Attempting to retrieve |annot|'s "IRT"-linked annotation would fail, since
+  // "IRT" is not a key in |annot|'s dictionary.
+  std::unique_ptr<unsigned short, pdfium::FreeDeleter> irt_key =
+      GetFPDFWideString(L"IRT");
+  ASSERT_FALSE(FPDFAnnot_HasKey(annot, irt_key.get()));
+  EXPECT_FALSE(FPDFAnnot_GetLinkedAnnot(annot, irt_key.get()));
+
+  // Attempting to retrieve |annot|'s parent dictionary as an annotation would
+  // fail, since its parent is not an annotation.
+  std::unique_ptr<unsigned short, pdfium::FreeDeleter> p_key =
+      GetFPDFWideString(L"P");
+  ASSERT_TRUE(FPDFAnnot_HasKey(annot, p_key.get()));
+  EXPECT_EQ(FPDF_OBJECT_REFERENCE, FPDFAnnot_GetValueType(annot, p_key.get()));
+  EXPECT_FALSE(FPDFAnnot_GetLinkedAnnot(annot, p_key.get()));
+
+  FPDFPage_CloseAnnot(popup);
+  FPDFPage_CloseAnnot(annot);
+  UnloadPage(page);
+}
+
 TEST_F(FPDFAnnotEmbeddertest, GetFormFieldFlagsTextField) {
   // Open file with form text fields.
   ASSERT_TRUE(OpenDocument("text_form_multiple.pdf"));
diff --git a/fpdfsdk/fpdfview_c_api_test.c b/fpdfsdk/fpdfview_c_api_test.c
index 4dd4995cd2..b42dc160da 100644
--- a/fpdfsdk/fpdfview_c_api_test.c
+++ b/fpdfsdk/fpdfview_c_api_test.c
@@ -59,6 +59,7 @@ int CheckPDFiumCApi() {
     CHK(FPDFAnnot_HasKey);
     CHK(FPDFAnnot_SetStringValue);
     CHK(FPDFAnnot_GetStringValue);
+    CHK(FPDFAnnot_GetLinkedAnnot);
     CHK(FPDFAnnot_GetFlags);
     CHK(FPDFAnnot_SetFlags);
     CHK(FPDFAnnot_GetFormFieldFlags);