Mojo: Use new message APIs to reduce copying

mojo/public/cpp/bindings/lib/pickle_buffer.cc

-// Copyright 2015 The Chromium 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 "mojo/public/cpp/bindings/lib/pickle_buffer.h"
-
-#include <stddef.h>
-#include <stdint.h>
-#include <stdlib.h>
-
-#include "base/logging.h"
-#include "base/macros.h"
-#include "base/pickle.h"
-#include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
-
-namespace mojo {
-namespace internal {
-
-class PickleBuffer::Storage : public base::Pickle {
- public:
-  explicit Storage(size_t num_bytes);
-  ~Storage() override {}
-
-  size_t available_capacity() const {
-    return capacity_after_header() - payload_size();
-  }
-
-  void* GetData() { return static_cast<void*>(mutable_payload()); }
-  void* Claim(size_t num_bytes) { return ClaimBytes(num_bytes); }
-
- private:
-  // TODO(rockot): Stop wasting 8 bytes per buffer.
-  //
-  // We don't use Pickle's header at all, but its base header type consumes 4
-  // bytes. We waste another 4 bytes to keep our actual buffer aligned to an
-  // 8-byte boundary.
-  //
-  // The reason we don't use base::Pickle's header is that it stores payload
-  // length in the first 4 bytes. Mojo Messages are packed like mojom structs,
-  // where the first 4 bytes are header size rather than payload size.
-  struct PaddedHeader : public base::Pickle::Header {
-    uint32_t padding;
-  };
-
-  static_assert(sizeof(PaddedHeader) % 8 == 0,
-      "PickleBuffer requires a Pickle header size with 8-byte alignment.");
-
-  DISALLOW_COPY_AND_ASSIGN(Storage);
-};
-
-PickleBuffer::Storage::Storage(size_t num_bytes)
-    : base::Pickle(sizeof(PaddedHeader)) {
-  headerT<PaddedHeader>()->padding = 0;
-  Resize(num_bytes);
-}
-
-PickleBuffer::PickleBuffer(size_t num_bytes, bool zero_initialized)
-    : storage_(new Storage(num_bytes)) {
-  if (zero_initialized)
-    memset(storage_->GetData(), 0, num_bytes);
-}
-
-PickleBuffer::~PickleBuffer() {
-}
-
-const void* PickleBuffer::data() const { return storage_->GetData(); }
-
-size_t PickleBuffer::data_num_bytes() const { return storage_->payload_size(); }
-
-base::Pickle* PickleBuffer::pickle() const {
-  return storage_.get();
-}
-
-void* PickleBuffer::Allocate(size_t num_bytes) {
-  DCHECK(storage_);
-
-  // The last allocation may terminate in between 8-byte boundaries. Pad the
-  // front of this allocation if that's the case.
-  size_t padded_capacity = Align(storage_->payload_size());
-  DCHECK_GE(padded_capacity, storage_->payload_size());
-
-  size_t padding_bytes = padded_capacity - storage_->payload_size();
-  size_t allocation_size = padding_bytes + num_bytes;
-  const void* previous_data_location = storage_->GetData();
-  if (storage_->available_capacity() < allocation_size) {
-    NOTREACHED() <<
-        "Message buffers must be fully allocated before serialization.";
-    return nullptr;
-  }
-  char* p = static_cast<char*>(storage_->Claim(allocation_size));
-  DCHECK_EQ(storage_->GetData(), previous_data_location);
-  return p + padding_bytes;
-}
-
-PickleBuffer* PickleBuffer::AsPickleBuffer() { return this; }
-
-}  // namespace internal
-}  // namespace mojo