Expose marked content IDs for images and alt text.

 - Adds two new public bits of API:
    - StructElement_GetMCID(STRUCTELEMENT) to return the marked content
      ID of the struct element.
    - IMAGEOBJ_METADATA.mcid to contain the marked content ID of the
      image.
 - Restores ContentMark::GetMCID, which was removed with other dead
   code in https://pdfium-review.googlesource.com/c/pdfium/+/19170.
 - Adds a couple calls to tests, including a simple new PDF to test
   the struct tree marked content ID.

Bug:pdfium:957
Change-Id: I92856e43d741df989e53a575a08258da19a39f22
Reviewed-on: https://pdfium-review.googlesource.com/20632
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

4 files changed, 34 insertions, 0 deletions

diff --git a/fpdfsdk/fpdf_structtree.cpp b/fpdfsdk/fpdf_structtree.cpp
index 30b7c3fce7..676824ef99 100644
--- a/fpdfsdk/fpdf_structtree.cpp
+++ b/fpdfsdk/fpdf_structtree.cpp
@@ -83,6 +83,14 @@ FPDF_StructElement_GetAltText(FPDF_STRUCTELEMENT struct_element,
              : 0;
 }
 
+FPDF_EXPORT int FPDF_CALLCONV
+FPDF_StructElement_GetMarkedContentID(FPDF_STRUCTELEMENT struct_element) {
+  CPDF_StructElement* elem = ToStructTreeElement(struct_element);
+  CPDF_Object* p =
+      (elem && elem->GetDict()) ? elem->GetDict()->GetObjectFor("K") : nullptr;
+  return p && p->IsNumber() ? p->GetInteger() : -1;
+}
+
 FPDF_EXPORT unsigned long FPDF_CALLCONV
 FPDF_StructElement_GetType(FPDF_STRUCTELEMENT struct_element,
                            void* buffer,
diff --git a/fpdfsdk/fpdf_structtree_embeddertest.cpp b/fpdfsdk/fpdf_structtree_embeddertest.cpp
index 05b77fc0f7..7ca81f7b2e 100644
--- a/fpdfsdk/fpdf_structtree_embeddertest.cpp
+++ b/fpdfsdk/fpdf_structtree_embeddertest.cpp
@@ -6,6 +6,7 @@
 #include "public/fpdf_structtree.h"
 #include "testing/embedder_test.h"
 #include "testing/test_support.h"
+#include "third_party/base/optional.h"
 
 class FPDFStructTreeEmbeddertest : public EmbedderTest {};
 
@@ -24,6 +25,7 @@ TEST_F(FPDFStructTreeEmbeddertest, GetAltText) {
   EXPECT_EQ(nullptr, element);
   element = FPDF_StructTree_GetChildAtIndex(struct_tree, 0);
   ASSERT_NE(nullptr, element);
+  EXPECT_EQ(-1, FPDF_StructElement_GetMarkedContentID(element));
   EXPECT_EQ(0U, FPDF_StructElement_GetAltText(element, nullptr, 0));
 
   ASSERT_EQ(1, FPDF_StructElement_CountChildren(element));
@@ -34,6 +36,7 @@ TEST_F(FPDFStructTreeEmbeddertest, GetAltText) {
   EXPECT_EQ(nullptr, child_element);
   child_element = FPDF_StructElement_GetChildAtIndex(element, 0);
   ASSERT_NE(nullptr, child_element);
+  EXPECT_EQ(-1, FPDF_StructElement_GetMarkedContentID(child_element));
   EXPECT_EQ(0U, FPDF_StructElement_GetAltText(child_element, nullptr, 0));
 
   ASSERT_EQ(1, FPDF_StructElement_CountChildren(child_element));
@@ -44,6 +47,7 @@ TEST_F(FPDFStructTreeEmbeddertest, GetAltText) {
   EXPECT_EQ(nullptr, gchild_element);
   gchild_element = FPDF_StructElement_GetChildAtIndex(child_element, 0);
   ASSERT_NE(nullptr, gchild_element);
+  EXPECT_EQ(-1, FPDF_StructElement_GetMarkedContentID(gchild_element));
   ASSERT_EQ(24U, FPDF_StructElement_GetAltText(gchild_element, nullptr, 0));
 
   unsigned short buffer[12];
@@ -54,6 +58,7 @@ TEST_F(FPDFStructTreeEmbeddertest, GetAltText) {
   for (size_t i = 0; i < FX_ArraySize(buffer); ++i)
     EXPECT_EQ(0U, buffer[i]);
 
+  EXPECT_EQ(-1, FPDF_StructElement_GetMarkedContentID(gchild_element));
   ASSERT_EQ(24U, FPDF_StructElement_GetAltText(gchild_element, buffer,
                                                sizeof(buffer)));
   const wchar_t kExpected[] = L"Black Image";
@@ -69,6 +74,22 @@ TEST_F(FPDFStructTreeEmbeddertest, GetAltText) {
   FPDF_ClosePage(page);
 }
 
+TEST_F(FPDFStructTreeEmbeddertest, GetMarkedContentID) {
+  ASSERT_TRUE(OpenDocument("marked_content_id.pdf"));
+  FPDF_PAGE page = LoadPage(0);
+  ASSERT_TRUE(page);
+
+  FPDF_STRUCTTREE struct_tree = FPDF_StructTree_GetForPage(page);
+  ASSERT_TRUE(struct_tree);
+  ASSERT_EQ(1, FPDF_StructTree_CountChildren(struct_tree));
+
+  FPDF_STRUCTELEMENT element = FPDF_StructTree_GetChildAtIndex(struct_tree, 0);
+  EXPECT_EQ(0, FPDF_StructElement_GetMarkedContentID(element));
+
+  FPDF_StructTree_Close(struct_tree);
+  FPDF_ClosePage(page);
+}
+
 TEST_F(FPDFStructTreeEmbeddertest, GetType) {
   ASSERT_TRUE(OpenDocument("tagged_alt_text.pdf"));
   FPDF_PAGE page = LoadPage(0);
diff --git a/fpdfsdk/fpdfedit_embeddertest.cpp b/fpdfsdk/fpdfedit_embeddertest.cpp
index 6cb2771154..ee2fc7eb85 100644
--- a/fpdfsdk/fpdfedit_embeddertest.cpp
+++ b/fpdfsdk/fpdfedit_embeddertest.cpp
@@ -1205,6 +1205,7 @@ TEST_F(FPDFEditEmbeddertest, GetImageMetadata) {
   // |page|, all values are correct, with the last two being default values.
   ASSERT_EQ(FPDF_PAGEOBJ_IMAGE, FPDFPageObj_GetType(obj));
   ASSERT_TRUE(FPDFImageObj_GetImageMetadata(obj, nullptr, &metadata));
+  EXPECT_EQ(7, metadata.marked_content_id);
   EXPECT_EQ(92u, metadata.width);
   EXPECT_EQ(68u, metadata.height);
   EXPECT_NEAR(96.000000, metadata.horizontal_dpi, 0.001);
@@ -1214,6 +1215,7 @@ TEST_F(FPDFEditEmbeddertest, GetImageMetadata) {
 
   // Verify the metadata of a bitmap image with indexed colorspace.
   ASSERT_TRUE(FPDFImageObj_GetImageMetadata(obj, page, &metadata));
+  EXPECT_EQ(7, metadata.marked_content_id);
   EXPECT_EQ(92u, metadata.width);
   EXPECT_EQ(68u, metadata.height);
   EXPECT_NEAR(96.000000, metadata.horizontal_dpi, 0.001);
@@ -1225,6 +1227,7 @@ TEST_F(FPDFEditEmbeddertest, GetImageMetadata) {
   obj = FPDFPage_GetObject(page, 37);
   ASSERT_EQ(FPDF_PAGEOBJ_IMAGE, FPDFPageObj_GetType(obj));
   ASSERT_TRUE(FPDFImageObj_GetImageMetadata(obj, page, &metadata));
+  EXPECT_EQ(9, metadata.marked_content_id);
   EXPECT_EQ(126u, metadata.width);
   EXPECT_EQ(106u, metadata.height);
   EXPECT_NEAR(162.173752, metadata.horizontal_dpi, 0.001);
diff --git a/fpdfsdk/fpdfeditimg.cpp b/fpdfsdk/fpdfeditimg.cpp
index 4842e35c76..0d7ba56559 100644
--- a/fpdfsdk/fpdfeditimg.cpp
+++ b/fpdfsdk/fpdfeditimg.cpp
@@ -267,6 +267,8 @@ FPDFImageObj_GetImageMetadata(FPDF_PAGEOBJECT image_object,
   if (!pImg)
     return false;
 
+  metadata->marked_content_id = pObj->m_ContentMark.GetMarkedContentID();
+
   const int nPixelWidth = pImg->GetPixelWidth();
   const int nPixelHeight = pImg->GetPixelHeight();
   metadata->width = nPixelWidth;