Add APIs for limited use of document tagged code.

fpdfsdk/fpdf_structtree.cpp

Index: fpdfsdk/fpdf_structtree.cpp
diff --git a/fpdfsdk/fpdf_structtree.cpp b/fpdfsdk/fpdf_structtree.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..541c46b378c74561446e96a3516d7bed00c1bce1
--- /dev/null
+++ b/fpdfsdk/fpdf_structtree.cpp
@@ -0,0 +1,88 @@
+// Copyright 2016 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "public/fpdf_structtree.h"
+
+#include "core/fpdfapi/page/cpdf_page.h"
+#include "core/fpdfapi/parser/cpdf_dictionary.h"
+#include "core/fpdfdoc/fpdf_tagged.h"
+#include "fpdfsdk/fsdk_define.h"
+
+namespace {
+
+IPDF_StructTree* ToStructTree(FPDF_STRUCTTREE struct_tree) {
+  return reinterpret_cast<IPDF_StructTree*>(struct_tree);
+}
+
+IPDF_StructElement* ToStructTreeElement(FPDF_STRUCTELEMENT struct_element) {
+  return reinterpret_cast<IPDF_StructElement*>(struct_element);
+}
+
+}  // namespace
+
+DLLEXPORT FPDF_STRUCTTREE STDCALL FPDF_StructTree_GetForPage(FPDF_PAGE page) {
+  CPDF_Page* pPage = CPDFPageFromFPDFPage(page);
+  if (!pPage)
+    return nullptr;
+  return IPDF_StructTree::LoadPage(pPage->m_pDocument, pPage->m_pFormDict);
+}
+
+DLLEXPORT void STDCALL FPDF_StructTree_Close(FPDF_STRUCTTREE struct_tree) {
+  delete ToStructTree(struct_tree);
+}
+
+DLLEXPORT int STDCALL
+FPDF_StructTree_CountChildren(FPDF_STRUCTTREE struct_tree) {
+  IPDF_StructTree* tree = ToStructTree(struct_tree);
+  return tree ? tree->CountTopElements() : -1;
+}
+
+DLLEXPORT FPDF_STRUCTELEMENT STDCALL
+FPDF_StructTree_GetChildAtIndex(FPDF_STRUCTTREE struct_tree, int index) {
+  IPDF_StructTree* tree = ToStructTree(struct_tree);
+  if (!tree || index < 0 || index >= tree->CountTopElements())
+    return nullptr;
+  return tree->GetTopElement(index);
+}
+
+DLLEXPORT unsigned long STDCALL
+FPDF_StructElement_GetAltText(FPDF_STRUCTELEMENT struct_element,
+                              void* buffer,
+                              unsigned long buflen) {
+  IPDF_StructElement* elem = ToStructTreeElement(struct_element);
+  if (!elem)
+    return 0;
+
+  CPDF_Dictionary* dict = elem->GetDict();
+  if (!dict)
+    return 0;
+
+  CFX_WideString str = elem->GetDict()->GetUnicodeTextFor("Alt");
+  if (str.IsEmpty())
+    return 0;
+
+  CFX_ByteString encodedStr = str.UTF16LE_Encode();
+  const unsigned long len = encodedStr.GetLength();
+  if (buffer && len <= buflen)
+    FXSYS_memcpy(buffer, encodedStr.c_str(), len);
+  return len;
+}
+
+DLLEXPORT int STDCALL
+FPDF_StructElement_CountChildren(FPDF_STRUCTELEMENT struct_element) {
+  IPDF_StructElement* elem = ToStructTreeElement(struct_element);
+  return elem ? elem->CountKids() : -1;
+}
+
+DLLEXPORT FPDF_STRUCTELEMENT STDCALL
+FPDF_StructElement_GetChildAtIndex(FPDF_STRUCTELEMENT struct_element,
+                                   int index) {
+  IPDF_StructElement* elem = ToStructTreeElement(struct_element);
+  if (!elem || index < 0 || index >= elem->CountKids())
+    return nullptr;
+
+  CPDF_StructKid kid = elem->GetKid(index);
+  return kid.m_Type == CPDF_StructKid::Element ? kid.m_Element.m_pElement
+                                               : nullptr;
+}