Add API for getting page labels.

core/fpdfdoc/cpdf_pagelabel.cpp

 // 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.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "core/fpdfdoc/cpdf_pagelabel.h"
 
 #include "core/fpdfapi/parser/cpdf_dictionary.h"
 #include "core/fpdfapi/parser/cpdf_document.h"
@@ skipping 57 matching lines @@
     wsNumPortion = MakeLetters(num);
   }
   return wsNumPortion;
 }
 
 }  // namespace
 
 CPDF_PageLabel::CPDF_PageLabel(CPDF_Document* pDocument)
     : m_pDocument(pDocument) {}
 
-CFX_WideString CPDF_PageLabel::GetLabel(int nPage) const {
-  CFX_WideString wsLabel;
+bool CPDF_PageLabel::GetLabel(int nPage, CFX_WideString* wsLabel) const {
   if (!m_pDocument)
-    return wsLabel;
+    return false;
+
+  if (nPage < 0 || nPage >= m_pDocument->GetPageCount())
+    return false;
 
   CPDF_Dictionary* pPDFRoot = m_pDocument->GetRoot();
   if (!pPDFRoot)
-    return wsLabel;
+    return false;
 
   CPDF_Dictionary* pLabels = pPDFRoot->GetDictFor("PageLabels");
+  if (!pLabels)
+    return false;
+
   CPDF_NumberTree numberTree(pLabels);
   CPDF_Object* pValue = nullptr;
   int n = nPage;
   while (n >= 0) {
     pValue = numberTree.LookupValue(n);
     if (pValue)
       break;
     n--;
   }
 
   if (pValue) {
     pValue = pValue->GetDirect();
     if (CPDF_Dictionary* pLabel = pValue->AsDictionary()) {
       if (pLabel->KeyExist("P"))
-        wsLabel += pLabel->GetUnicodeTextFor("P");
+        *wsLabel += pLabel->GetUnicodeTextFor("P");
 
       CFX_ByteString bsNumberingStyle = pLabel->GetStringFor("S", "");
       int nLabelNum = nPage - n + pLabel->GetIntegerFor("St", 1);
       CFX_WideString wsNumPortion =
           GetLabelNumPortion(nLabelNum, bsNumberingStyle);
-      wsLabel += wsNumPortion;
-      return wsLabel;
+      *wsLabel += wsNumPortion;
+      return true;
     }
   }
-  wsLabel.Format(L"%d", nPage + 1);
-  return wsLabel;
+  wsLabel->Format(L"%d", nPage + 1);
+  return true;
 }
 
 int32_t CPDF_PageLabel::GetPageByLabel(const CFX_ByteStringC& bsLabel) const {
   if (!m_pDocument)
     return -1;
 
   CPDF_Dictionary* pPDFRoot = m_pDocument->GetRoot();
   if (!pPDFRoot)
     return -1;
 
   int nPages = m_pDocument->GetPageCount();
   for (int i = 0; i < nPages; i++) {
-    if (PDF_EncodeText(GetLabel(i)).Compare(bsLabel))
+    CFX_WideString str;
+    if (!GetLabel(i, &str))
+      continue;
+    if (PDF_EncodeText(str).Compare(bsLabel))
       return i;
   }
 
   int nPage = FXSYS_atoi(CFX_ByteString(bsLabel).c_str());  // NUL terminate.
   return nPage > 0 && nPage <= nPages ? nPage : -1;
 }
 
 int32_t CPDF_PageLabel::GetPageByLabel(const CFX_WideStringC& wsLabel) const {
   return GetPageByLabel(PDF_EncodeText(wsLabel.c_str()).AsStringC());
 }