Unify parsing of cross ref table v4.

We can use 'Prev' value of first-page cross-reference table trailer
for load main cross-reference table,
instead of 'T' value of Linearized header (Offset of first entry in main cross-reference table).

This is better solution, because this is allow us check entry count in main cross-ref table and
unify loading of main cross-ref table with loading methods of non linearized document.

See PDF specification:
http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/pdf/pdfs/PDF32000_2008.pdf#678
(page 678, Example 3/part 3)

Change-Id: I59dcf3c73a0fb561221ded78e827e40535dbd717
Reviewed-on: https://pdfium-review.googlesource.com/13810
Commit-Queue: Art Snake <art-snake@yandex-team.ru>
Reviewed-by: dsinclair <dsinclair@chromium.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/core/fpdfapi/parser/cpdf_data_avail.cpp b/core/fpdfapi/parser/cpdf_data_avail.cpp
index 38e857f22f..91fc8c1087 100644
--- a/core/fpdfapi/parser/cpdf_data_avail.cpp
+++ b/core/fpdfapi/parser/cpdf_data_avail.cpp
@@ -1171,13 +1171,22 @@ CPDF_DataAvail::DocAvailStatus CPDF_DataAvail::CheckLinearizedData() {
     return DataError;
 
   if (!m_bMainXRefLoadTried) {
+    ASSERT(m_pDocument->GetParser()->GetTrailer());
+    const FX_SAFE_FILESIZE main_xref_offset =
+        m_pDocument->GetParser()->GetTrailer()->GetIntegerFor("Prev");
+    if (!main_xref_offset.IsValid())
+      return DataError;
+
+    if (main_xref_offset.ValueOrDie() == 0)
+      return DataAvailable;
+
     FX_SAFE_SIZE_T data_size = m_dwFileLen;
-    data_size -= m_pLinearized->GetLastXRefOffset();
+    data_size -= main_xref_offset.ValueOrDie();
     if (!data_size.IsValid())
       return DataError;
 
     if (!GetValidator()->CheckDataRangeAndRequestIfUnavailable(
-            m_pLinearized->GetLastXRefOffset(), data_size.ValueOrDie()))
+            main_xref_offset.ValueOrDie(), data_size.ValueOrDie()))
       return DataNotAvailable;
 
     CPDF_Parser::Error eRet =