Introduce SharedMemoryDataConsumerHandle.

content/child/shared_memory_data_consumer_handle.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 "content/child/shared_memory_data_consumer_handle.h"
+
+#include <algorithm>
+#include <deque>
+#include <vector>
+
+namespace content {
+
+namespace {
+
+class FixedReceivedData final : public RequestPeer::ReceivedData {
+ public:
+  explicit FixedReceivedData(RequestPeer::ReceivedData* data)
+      : data_(data->payload(), data->payload() + data->length()),
+        encoded_length_(data->encoded_length()) {}
+
+  const char* payload() const override {
+    return data_.empty() ? nullptr : &data_[0];
+  }
+  int length() const override { return static_cast<int>(data_.size()); }
+  int encoded_length() const override { return encoded_length_; }
+
+ private:
+  const std::vector<char> data_;
+  const int encoded_length_;
+
+  DISALLOW_COPY_AND_ASSIGN(FixedReceivedData);
+};
+
+}  // namespace
+
+using Result = blink::WebDataConsumerHandle::Result;
+using Data = RequestPeer::ReceivedData;
+
+class SharedMemoryDataConsumerHandle::Context final
+    : public base::RefCountedThreadSafe<Context> {
+ public:
+  Context()
+      : result_(Ok),
+        first_offset_(0),
+        client_(nullptr),
+        is_reader_active_(true) {}
+
+  bool IsEmpty() const { return queue_.empty(); }
+  void Clear() {
+    for (Data* data : queue_) {
+      delete data;
+    }
+    queue_.clear();
+    first_offset_ = 0;
+    client_ = nullptr;
+  }
+  void PopReadData() {
+    Data* top = Top();
+    if (static_cast<size_t>(top->length()) <= first_offset_) {
+      delete top;
+      queue_.pop_front();
+      first_offset_ = 0;
+    }
+  }
+  Data* Top() { return queue_.front(); }
+  void Push(scoped_ptr<Data> data) { queue_.push_back(data.release()); }
+  size_t first_offset() const { return first_offset_; }
+  void AdvanceFirstOffset(size_t s) { first_offset_ += s; }
+  Result result() const { return result_; }
+  void set_result(Result r) { result_ = r; }
+  Client* client() { return client_; }
+  void set_client(Client* client) { client_ = client; }
+  bool is_reader_active() const { return is_reader_active_; }
+  void set_is_reader_active(bool b) { is_reader_active_ = b; }
+
+ private:
+  friend class base::RefCountedThreadSafe<Context>;
+  ~Context() {
+    // This is necessary because the queue stores raw pointers.
+    Clear();
+  }
+
+  // |result_| stores the ultimate state of this handle if it has. Otherwise,
+  // |Ok| is set.
+  Result result_;
+  // TODO(yhirano): Use std::deque<scoped_ptr<ReceivedData>> once it is allowed.
+  std::deque<RequestPeer::ReceivedData*> queue_;
+  size_t first_offset_;
+  Client* client_;
+  bool is_reader_active_;
+
+  DISALLOW_COPY_AND_ASSIGN(Context);
+};
+
+SharedMemoryDataConsumerHandle::Writer::Writer(
+    const scoped_refptr<Context>& context,
+    BackpressureMode mode)
+    : context_(context), mode_(mode) {
+}
+
+SharedMemoryDataConsumerHandle::Writer::~Writer() {
+  Close();
+}
+
+void SharedMemoryDataConsumerHandle::Writer::AddData(scoped_ptr<Data> data) {
+  if (!data->length()) {
+    // We omit empty data.
+    return;
+  }
+
+  if (!context_->is_reader_active()) {
+    // No one is interested in the data.
+    return;
+  }
+
+  bool needs_notification = context_->client() && context_->IsEmpty();
+  scoped_ptr<RequestPeer::ReceivedData> data_to_pass;
+  if (mode_ == kApplyBackpressure) {
+    data_to_pass = data.Pass();
+  } else {
+    data_to_pass = make_scoped_ptr(new FixedReceivedData(data.get()));
+  }
+  context_->Push(data_to_pass.Pass());
+
+  if (needs_notification)
+    context_->client()->didGetReadable();
+}
+
+void SharedMemoryDataConsumerHandle::Writer::Close() {
+  if (context_->result() == Ok) {
+    context_->set_result(Done);
+    if (context_->client() && context_->IsEmpty())
+      context_->client()->didGetReadable();
+  }
+}
+
+SharedMemoryDataConsumerHandle::SharedMemoryDataConsumerHandle(
+    BackpressureMode mode,
+    scoped_ptr<Writer>* writer)
+    : context_(new Context) {
+  writer->reset(new Writer(context_, mode));
+}
+
+SharedMemoryDataConsumerHandle::~SharedMemoryDataConsumerHandle() {
+  context_->set_is_reader_active(false);
+  context_->Clear();
+}
+
+Result SharedMemoryDataConsumerHandle::read(void* data,
+                                            size_t size,
+                                            Flags flags,
+                                            size_t* read_size_to_return) {
+  size_t total_read_size = 0;
+  *read_size_to_return = 0;
+  if (context_->result() != Ok && context_->result() != Done)
+    return context_->result();
+
+  while (!context_->IsEmpty() && total_read_size < size) {
+    const auto& top = context_->Top();
+    size_t readable = top->length() - context_->first_offset();
+    size_t writable = size - total_read_size;
+    size_t read_size = std::min(readable, writable);
+    const char* begin = top->payload() + context_->first_offset();
+    std::copy(begin, begin + read_size,
+              static_cast<char*>(data) + total_read_size);
+    total_read_size += read_size;
+    context_->AdvanceFirstOffset(read_size);

[tyoshino (SeeGerritForStatus), 2015/05/26 08:05:13]

how about exposing only a single method named Consume that does
AdvanceFirstOffset and then PopReadData unless you have use cases in your mind
in which only one of them is used?

Between AdvanceFirstOffset and PopReadData, the context holds a fully consumed
data with which e.g. current IsEmpty() doesn't work correctly.

[yhirano, 2015/05/26 08:19:42]

Done.

+    context_->PopReadData();
+  }
+  *read_size_to_return = total_read_size;
+  return total_read_size ? Ok : context_->result() == Done ? Done : ShouldWait;
+}
+
+Result SharedMemoryDataConsumerHandle::beginRead(const void** buffer,
+                                                 Flags flags,
+                                                 size_t* available) {
+  *buffer = nullptr;
+  *available = 0;
+
+  if (context_->result() != Ok && context_->result() != Done)
+    return context_->result();
+
+  if (context_->IsEmpty())
+    return context_->result() == Done ? Done : ShouldWait;
+
+  const auto& top = context_->Top();
+  *buffer = top->payload() + context_->first_offset();
+  *available = top->length() - context_->first_offset();
+
+  return Ok;
+}
+
+Result SharedMemoryDataConsumerHandle::endRead(size_t read_size) {
+  if (context_->IsEmpty())
+    return UnexpectedError;
+
+  context_->AdvanceFirstOffset(read_size);
+  context_->PopReadData();
+  return Ok;
+}
+
+void SharedMemoryDataConsumerHandle::registerClient(Client* client) {
+  context_->set_client(client);
+
+  if (!context_->IsEmpty())
+    client->didGetReadable();
+}
+
+void SharedMemoryDataConsumerHandle::unregisterClient() {
+  context_->set_client(nullptr);
+}
+
+}  // namespace content