Implement CFX_CodecMemory.

This class is much simpler than CFX_MemoryStream and does only what
CFX_BmpDecompressor and CFX_GifContext needs. Swap out CFX_MemoryStream
and remove CFX_MemoryStream::Seek().

BUG=pdfium:263

Change-Id: Ifd8ce4d2b6c9fedd6ec842d46f54fc8e654fbca7
Reviewed-on: https://pdfium-review.googlesource.com/39880
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>

2 files changed, 63 insertions, 0 deletions

diff --git a/core/fxcodec/codec/cfx_codec_memory.cpp b/core/fxcodec/codec/cfx_codec_memory.cpp
new file mode 100644
index 0000000000..8eac02c9ee
--- /dev/null
+++ b/core/fxcodec/codec/cfx_codec_memory.cpp
@@ -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.
+
+#include "core/fxcodec/codec/cfx_codec_memory.h"
+
+#include <algorithm>
+
+CFX_CodecMemory::CFX_CodecMemory(uint8_t* buffer, size_t size)
+    : buffer_(buffer), size_(size) {}
+
+CFX_CodecMemory::~CFX_CodecMemory() = default;
+
+bool CFX_CodecMemory::Seek(size_t pos) {
+  if (pos > size_)
+    return false;
+
+  pos_ = pos;
+  return true;
+}
+
+size_t CFX_CodecMemory::ReadBlock(void* buffer, size_t size) {
+  if (!buffer || !size || IsEOF())
+    return 0;
+
+  size_t bytes_to_read = std::min(size, size_ - pos_);
+  memcpy(buffer, &buffer_[pos_], bytes_to_read);
+  pos_ += bytes_to_read;
+  return bytes_to_read;
+}
diff --git a/core/fxcodec/codec/cfx_codec_memory.h b/core/fxcodec/codec/cfx_codec_memory.h
new file mode 100644
index 0000000000..6eee72a32d
--- /dev/null
+++ b/core/fxcodec/codec/cfx_codec_memory.h
@@ -0,0 +1,33 @@
+// 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.
+
+#ifndef CORE_FXCODEC_CODEC_CFX_CODEC_MEMORY_H_
+#define CORE_FXCODEC_CODEC_CFX_CODEC_MEMORY_H_
+
+#include "core/fxcrt/retain_ptr.h"
+
+class CFX_CodecMemory : public Retainable {
+ public:
+  template <typename T, typename... Args>
+  friend RetainPtr<T> pdfium::MakeRetain(Args&&... args);
+
+  uint8_t* GetBuffer() { return buffer_; }
+  size_t GetSize() const { return size_; }
+  size_t GetPosition() const { return pos_; }
+  bool IsEOF() const { return pos_ >= size_; }
+  size_t ReadBlock(void* buffer, size_t size);
+
+  // Sets the cursor position to |pos| if possible.
+  bool Seek(size_t pos);
+
+ private:
+  CFX_CodecMemory(uint8_t* buffer, size_t size);
+  ~CFX_CodecMemory() override;
+
+  uint8_t* const buffer_;
+  const size_t size_;
+  size_t pos_ = 0;
+};
+
+#endif  // CORE_FXCODEC_CODEC_CFX_CODEC_MEMORY_H_