3 files changed, 67 insertions, 3 deletions
diff --git a/core/fpdfdoc/cpdf_metadata.cpp b/core/fpdfdoc/cpdf_metadata.cpp
index 5ef7312752..b9a92963dd 100644
--- a/core/fpdfdoc/cpdf_metadata.cpp
+++ b/core/fpdfdoc/cpdf_metadata.cpp
@@ -8,7 +8,7 @@
 
 #include "core/fpdfapi/parser/cpdf_stream.h"
 #include "core/fpdfapi/parser/cpdf_stream_acc.h"
-#include "core/fxcrt/cfx_memorystream.h"
+#include "core/fxcrt/cfx_readonlymemorystream.h"
 #include "core/fxcrt/fx_codepage.h"
 #include "core/fxcrt/xml/cfx_xmldocument.h"
 #include "core/fxcrt/xml/cfx_xmlelement.h"
@@ -67,8 +67,8 @@ std::vector<UnsupportedFeature> CPDF_Metadata::CheckForSharedForm() const {
   auto pAcc = pdfium::MakeRetain<CPDF_StreamAcc>(stream_.Get());
   pAcc->LoadAllDataFiltered();
 
-  auto stream = pdfium::MakeRetain<CFX_MemoryStream>(pAcc->GetData(),
-                                                     pAcc->GetSize(), false);
+  auto stream = pdfium::MakeRetain<CFX_ReadOnlyMemoryStream>(pAcc->GetData(),
+                                                             pAcc->GetSize());
   CFX_XMLParser parser(stream);
   std::unique_ptr<CFX_XMLDocument> doc = parser.Parse();
   if (!doc)
diff --git a/core/fxcrt/cfx_readonlymemorystream.cpp b/core/fxcrt/cfx_readonlymemorystream.cpp
new file mode 100644
index 0000000000..1d09759208
--- /dev/null
+++ b/core/fxcrt/cfx_readonlymemorystream.cpp
@@ -0,0 +1,34 @@
+// Copyright 2018 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/fxcrt/cfx_readonlymemorystream.h"
+
+#include "core/fxcrt/fx_safe_types.h"
+
+CFX_ReadOnlyMemoryStream::CFX_ReadOnlyMemoryStream(const uint8_t* pBuf,
+                                                   FX_FILESIZE size)
+    : m_pBuf(pBuf), m_size(size) {}
+
+CFX_ReadOnlyMemoryStream::~CFX_ReadOnlyMemoryStream() = default;
+
+FX_FILESIZE CFX_ReadOnlyMemoryStream::GetSize() {
+  return m_size;
+}
+
+bool CFX_ReadOnlyMemoryStream::ReadBlock(void* buffer,
+                                         FX_FILESIZE offset,
+                                         size_t size) {
+  if (offset < 0)
+    return false;
+
+  FX_SAFE_FILESIZE newPos = pdfium::base::checked_cast<FX_FILESIZE>(size);
+  newPos += offset;
+  if (!newPos.IsValid() || newPos.ValueOrDie() > m_size)
+    return false;
+
+  memcpy(buffer, m_pBuf + offset, size);
+  return true;
+}
diff --git a/core/fxcrt/cfx_readonlymemorystream.h b/core/fxcrt/cfx_readonlymemorystream.h
new file mode 100644
index 0000000000..e9d18222a4
--- /dev/null
+++ b/core/fxcrt/cfx_readonlymemorystream.h
@@ -0,0 +1,30 @@
+// Copyright 2018 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
+
+#ifndef CORE_FXCRT_CFX_READONLYMEMORYSTREAM_H_
+#define CORE_FXCRT_CFX_READONLYMEMORYSTREAM_H_
+
+#include "core/fxcrt/fx_stream.h"
+#include "core/fxcrt/retain_ptr.h"
+
+class CFX_ReadOnlyMemoryStream final : public IFX_SeekableReadStream {
+ public:
+  template <typename T, typename... Args>
+  friend RetainPtr<T> pdfium::MakeRetain(Args&&... args);
+
+  // IFX_SeekableReadStream:
+  FX_FILESIZE GetSize() override;
+  bool ReadBlock(void* buffer, FX_FILESIZE offset, size_t size) override;
+
+ private:
+  CFX_ReadOnlyMemoryStream(const uint8_t* pBuf, FX_FILESIZE size);
+  ~CFX_ReadOnlyMemoryStream() override;
+
+  const uint8_t* const m_pBuf;
+  const FX_FILESIZE m_size;
+};
+
+#endif  // CORE_FXCRT_CFX_READONLYMEMORYSTREAM_H_