Merge to XFA: Relax the check on 0 length streams.

CPDF_SyntaxParser::ReadStream() originally created stream objects when
the length is 0. Commit 2526930 tightened the constraint and returned
NULL. This has some adverse affects, as seen in Chromium's print
preview of PDFs.

Instead, relax the constraint a little so when the length is 0, return a
CPDF_Stream with NULL data and size 0.

BUG=531835

Review URL: https://codereview.chromium.org/1394743002 .

(cherry picked from commit 4fa0e27ba39f49ba92fb4c160ab836a6f1dd2893)

Review URL: https://codereview.chromium.org/1400613002 .

1 files changed, 17 insertions, 14 deletions

diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index 1f7a42f48d..3fc8591690 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -2527,28 +2527,31 @@ CPDF_Stream* CPDF_SyntaxParser::ReadStream(CPDF_Dictionary* pDict,
           len -= 1;
         }
       }
-      if (len <= 0) {
+      if (len < 0) {
         return nullptr;
       }
       pDict->SetAtInteger(FX_BSTRC("Length"), len);
     }
     m_Pos = streamStartPos;
   }
-  if (len <= 0) {
+  if (len < 0) {
     return nullptr;
   }
-  uint8_t* pData = FX_Alloc(uint8_t, len);
-  ReadBlock(pData, len);
-  if (pCryptoHandler) {
-    CFX_BinaryBuf dest_buf;
-    dest_buf.EstimateSize(pCryptoHandler->DecryptGetSize(len));
-    void* context = pCryptoHandler->DecryptStart(objnum, gennum);
-    pCryptoHandler->DecryptStream(context, pData, len, dest_buf);
-    pCryptoHandler->DecryptFinish(context, dest_buf);
-    FX_Free(pData);
-    pData = dest_buf.GetBuffer();
-    len = dest_buf.GetSize();
-    dest_buf.DetachBuffer();
+  uint8_t* pData = nullptr;
+  if (len > 0) {
+    pData = FX_Alloc(uint8_t, len);
+    ReadBlock(pData, len);
+    if (pCryptoHandler) {
+      CFX_BinaryBuf dest_buf;
+      dest_buf.EstimateSize(pCryptoHandler->DecryptGetSize(len));
+      void* context = pCryptoHandler->DecryptStart(objnum, gennum);
+      pCryptoHandler->DecryptStream(context, pData, len, dest_buf);
+      pCryptoHandler->DecryptFinish(context, dest_buf);
+      FX_Free(pData);
+      pData = dest_buf.GetBuffer();
+      len = dest_buf.GetSize();
+      dest_buf.DetachBuffer();
+    }
   }
   CPDF_Stream* pStream = new CPDF_Stream(pData, len, pDict);
   if (pContext) {