net: Implement canceling of all async operations in FileStream.

net/base/file_stream_win.cc

 // Copyright (c) 2012 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 "net/base/file_stream.h"
+#include "net/base/file_stream_win.h"
 
 #include <windows.h>
 
 #include "base/file_path.h"
 #include "base/logging.h"
-#include "base/message_loop.h"
 #include "base/metrics/histogram.h"
-#include "base/synchronization/waitable_event.h"
-#include "base/threading/thread_restrictions.h"
+#include "base/task_runner_util.h"
 #include "base/threading/worker_pool.h"
-#include "net/base/file_stream_metrics.h"
-#include "net/base/file_stream_net_log_parameters.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 
 namespace net {
 
 // Ensure that we can just use our Whence values directly.
 COMPILE_ASSERT(FROM_BEGIN == FILE_BEGIN, bad_whence_begin);
 COMPILE_ASSERT(FROM_CURRENT == FILE_CURRENT, bad_whence_current);
 COMPILE_ASSERT(FROM_END == FILE_END, bad_whence_end);
 
 namespace {
 
 void SetOffset(OVERLAPPED* overlapped, const LARGE_INTEGER& offset) {
   overlapped->Offset = offset.LowPart;
   overlapped->OffsetHigh = offset.HighPart;
 }
 
 void IncrementOffset(OVERLAPPED* overlapped, DWORD count) {
   LARGE_INTEGER offset;
   offset.LowPart = overlapped->Offset;
   offset.HighPart = overlapped->OffsetHigh;
   offset.QuadPart += static_cast<LONGLONG>(count);
   SetOffset(overlapped, offset);
 }
 
-int RecordAndMapError(int error,
-                      FileErrorSource source,
-                      bool record_uma,
-                      const net::BoundNetLog& bound_net_log) {
-  net::Error net_error = MapSystemError(error);
-
-  bound_net_log.AddEvent(
-      net::NetLog::TYPE_FILE_STREAM_ERROR,
-      base::Bind(&NetLogFileStreamErrorCallback,
-                 source, error, net_error));
-
-  RecordFileError(error, source, record_uma);
-
-  return net_error;
-}
-
-// Opens a file with some network logging.
-// The opened file and the result code are written to |file| and |result|.
-void OpenFile(const FilePath& path,
-              int open_flags,
-              bool record_uma,
-              base::PlatformFile* file,
-              int* result,
-              const net::BoundNetLog& bound_net_log) {
-  std::string file_name = path.AsUTF8Unsafe();
-  bound_net_log.BeginEvent(
-      net::NetLog::TYPE_FILE_STREAM_OPEN,
-      NetLog::StringCallback("file_name", &file_name));
-
-  *file = base::CreatePlatformFile(path, open_flags, NULL, NULL);
-  if (*file == base::kInvalidPlatformFileValue) {
-    DWORD error = GetLastError();
-    LOG(WARNING) << "Failed to open file: " << error;
-    *result = RecordAndMapError(error,
-                                FILE_ERROR_SOURCE_OPEN,
-                                record_uma,
-                                bound_net_log);
-    bound_net_log.EndEvent(net::NetLog::TYPE_FILE_STREAM_OPEN);
-    return;
-  }
-}
-
-// Closes a file with some network logging.
-void CloseFile(base::PlatformFile file,
-               const net::BoundNetLog& bound_net_log) {
-  bound_net_log.AddEvent(net::NetLog::TYPE_FILE_STREAM_CLOSE);
-  if (file == base::kInvalidPlatformFileValue)
-    return;
-
-  CancelIo(file);
-
-  if (!base::ClosePlatformFile(file))
-    NOTREACHED();
-  bound_net_log.EndEvent(net::NetLog::TYPE_FILE_STREAM_OPEN);
-}
-
-// Closes a file with CloseFile() and signals the completion.
-void CloseFileAndSignal(base::PlatformFile* file,
-                        base::WaitableEvent* on_io_complete,
-                        const net::BoundNetLog& bound_net_log) {
-  CloseFile(*file, bound_net_log);
-  *file = base::kInvalidPlatformFileValue;
-  on_io_complete->Signal();
-}
-
-// Invokes a given closure and signals the completion.
-void InvokeAndSignal(const base::Closure& closure,
-                     base::WaitableEvent* on_io_complete) {
-  closure.Run();
-  on_io_complete->Signal();
-}
-
 }  // namespace
 
-// FileStreamWin::AsyncContext ----------------------------------------------
-
-class FileStreamWin::AsyncContext : public MessageLoopForIO::IOHandler {
- public:
-  explicit AsyncContext(const net::BoundNetLog& bound_net_log)
-      : context_(), is_closing_(false),
-        record_uma_(false), bound_net_log_(bound_net_log),
-        error_source_(FILE_ERROR_SOURCE_COUNT) {
-    context_.handler = this;
-  }
-  ~AsyncContext();
-
-  void IOCompletionIsPending(const CompletionCallback& callback,
-                             IOBuffer* buf);
-
-  OVERLAPPED* overlapped() { return &context_.overlapped; }
-  const CompletionCallback& callback() const { return callback_; }
-
-  void set_error_source(FileErrorSource source) { error_source_ = source; }
-
-  void EnableErrorStatistics() {
-    record_uma_ = true;
-  }
-
- private:
-  virtual void OnIOCompleted(MessageLoopForIO::IOContext* context,
-                             DWORD bytes_read, DWORD error) OVERRIDE;
-
-  MessageLoopForIO::IOContext context_;
-  CompletionCallback callback_;
-  scoped_refptr<IOBuffer> in_flight_buf_;
-  bool is_closing_;
-  bool record_uma_;
-  const net::BoundNetLog bound_net_log_;
-  FileErrorSource error_source_;
-};
-
-FileStreamWin::AsyncContext::~AsyncContext() {
-  is_closing_ = true;
-  bool waited = false;
-  base::TimeTicks start = base::TimeTicks::Now();
-  while (!callback_.is_null()) {
-    waited = true;
-    MessageLoopForIO::current()->WaitForIOCompletion(INFINITE, this);
-  }
-  if (waited) {
-    // We want to see if we block the message loop for too long.
-    UMA_HISTOGRAM_TIMES("AsyncIO.FileStreamClose",
-                        base::TimeTicks::Now() - start);
-  }
+FileStream::Context::Context(const BoundNetLog& bound_net_log)
+    : io_context_(),
+      file_(base::kInvalidPlatformFileValue),
+      record_uma_(false),
+      async_in_progress_(false),
+      orphaned_(false),
+      bound_net_log_(bound_net_log),
+      error_source_(FILE_ERROR_SOURCE_COUNT) {
+  io_context_.handler = this;
 }
 
-void FileStreamWin::AsyncContext::IOCompletionIsPending(
-    const CompletionCallback& callback,
-    IOBuffer* buf) {
-  DCHECK(callback_.is_null());
-  callback_ = callback;
-  in_flight_buf_ = buf;  // Hold until the async operation ends.
+FileStream::Context::Context(base::PlatformFile file,
+                             const BoundNetLog& bound_net_log,
+                             int open_flags)
+    : io_context_(),
+      file_(file),
+      record_uma_(false),
+      async_in_progress_(false),
+      orphaned_(false),
+      bound_net_log_(bound_net_log),
+      error_source_(FILE_ERROR_SOURCE_COUNT) {
+  io_context_.handler = this;
+  if (open_flags & base::PLATFORM_FILE_ASYNC)
+    RegisterInMessageLoop();
 }
 
-void FileStreamWin::AsyncContext::OnIOCompleted(
-    MessageLoopForIO::IOContext* context, DWORD bytes_read, DWORD error) {
-  DCHECK_EQ(&context_, context);
-  DCHECK(!callback_.is_null());
-
-  if (is_closing_) {
-    callback_.Reset();
-    in_flight_buf_ = NULL;
-    return;
-  }
-
-  int result = static_cast<int>(bytes_read);
-  if (error && error != ERROR_HANDLE_EOF) {
-    result = RecordAndMapError(error, error_source_, record_uma_,
-                               bound_net_log_);
-  }
-
-  if (bytes_read)
-    IncrementOffset(&context->overlapped, bytes_read);
-
-  CompletionCallback temp_callback = callback_;
-  callback_.Reset();
-  scoped_refptr<IOBuffer> temp_buf = in_flight_buf_;
-  in_flight_buf_ = NULL;
-  temp_callback.Run(result);
+FileStream::Context::~Context() {
 }
 
-// FileStream ------------------------------------------------------------
+void FileStream::Context::SeekAsync(Whence whence,
+                                    int64 offset,
+                                    const Int64CompletionCallback& callback) {
+  DCHECK(!async_in_progress_);
 
-FileStreamWin::FileStreamWin(net::NetLog* net_log)
-    : file_(base::kInvalidPlatformFileValue),
-      open_flags_(0),
-      auto_closed_(true),
-      record_uma_(false),
-      bound_net_log_(net::BoundNetLog::Make(net_log,
-                                            net::NetLog::SOURCE_FILESTREAM)),
-      weak_ptr_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {
-  bound_net_log_.BeginEvent(net::NetLog::TYPE_FILE_STREAM_ALIVE);
+  const bool posted = base::PostTaskAndReplyWithResult(
+      base::WorkerPool::GetTaskRunner(true /* task is slow */),
+      FROM_HERE,
+      base::Bind(&Context::SeekFileImpl,
+                 base::Unretained(this), whence, offset),
+      base::Bind(&Context::OnSeekCompleted,
+                 base::Unretained(this), callback));
+  DCHECK(posted);
+
+  async_in_progress_ = true;
 }
 
-FileStreamWin::FileStreamWin(
-    base::PlatformFile file, int flags, net::NetLog* net_log)
-    : file_(file),
-      open_flags_(flags),
-      auto_closed_(false),
-      record_uma_(false),
-      bound_net_log_(net::BoundNetLog::Make(net_log,
-                                            net::NetLog::SOURCE_FILESTREAM)),
-      weak_ptr_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {
-  bound_net_log_.BeginEvent(net::NetLog::TYPE_FILE_STREAM_ALIVE);
-
-  // If the file handle is opened with base::PLATFORM_FILE_ASYNC, we need to
-  // make sure we will perform asynchronous File IO to it.
-  if (flags & base::PLATFORM_FILE_ASYNC) {
-    async_context_.reset(new AsyncContext(bound_net_log_));
-    MessageLoopForIO::current()->RegisterIOHandler(file_,
-                                                   async_context_.get());
-  }
-}
-
-FileStreamWin::~FileStreamWin() {
-  if (open_flags_ & base::PLATFORM_FILE_ASYNC) {
-    // Block until the in-flight open/close operation is complete.
-    // TODO(satorux): Ideally we should not block. crbug.com/115067
-    WaitForIOCompletion();
-
-    // Block until the last read/write operation is complete.
-    async_context_.reset();
-  }
-
-  if (auto_closed_) {
-    if (open_flags_ & base::PLATFORM_FILE_ASYNC) {
-      // Close the file in the background.
-      if (IsOpen()) {
-        const bool posted = base::WorkerPool::PostTask(
-            FROM_HERE,
-            base::Bind(&CloseFile, file_, bound_net_log_),
-            true /* task_is_slow */);
-        DCHECK(posted);
-      }
-    } else {
-      CloseSync();
-    }
-  }
-
-  bound_net_log_.EndEvent(net::NetLog::TYPE_FILE_STREAM_ALIVE);
-}
-
-void FileStreamWin::Close(const CompletionCallback& callback) {
-  DCHECK(open_flags_ & base::PLATFORM_FILE_ASYNC);
-  DCHECK(!weak_ptr_factory_.HasWeakPtrs());
-  DCHECK(!on_io_complete_.get());
-  on_io_complete_.reset(new base::WaitableEvent(
-      false  /* manual_reset */, false  /* initially_signaled */));
-
-  // Passing &file_ to a thread pool looks unsafe but it's safe here as the
-  // destructor ensures that the close operation is complete with
-  // WaitForIOCompletion(). See also the destructor.
-  const bool posted = base::WorkerPool::PostTaskAndReply(
-      FROM_HERE,
-      base::Bind(&CloseFileAndSignal, &file_, on_io_complete_.get(),
-                 bound_net_log_),
-      base::Bind(&FileStreamWin::OnClosed,
-                 weak_ptr_factory_.GetWeakPtr(),
-                 callback),
-      true /* task_is_slow */);
-  DCHECK(posted);
-}
-
-void FileStreamWin::CloseSync() {
-  // The logic here is similar to CloseFile() but async_context_.reset() is
-  // caled in this function.
-
-  // Block until the in-flight open operation is complete.
-  // TODO(satorux): Replace this with a DCHECK(open_flags & ASYNC) once this
-  // once all async clients are migrated to use Close(). crbug.com/114783
-  WaitForIOCompletion();
-
-  bound_net_log_.AddEvent(net::NetLog::TYPE_FILE_STREAM_CLOSE);
-  if (file_ != base::kInvalidPlatformFileValue)
-    CancelIo(file_);
-
-  // Block until the last read/write operation is complete.
-  async_context_.reset();
-
-  if (file_ != base::kInvalidPlatformFileValue) {
-    if (!base::ClosePlatformFile(file_))
-      NOTREACHED();
-    file_ = base::kInvalidPlatformFileValue;
-
-    bound_net_log_.EndEvent(net::NetLog::TYPE_FILE_STREAM_OPEN);
-  }
-}
-
-int FileStreamWin::Open(const FilePath& path, int open_flags,
-                        const CompletionCallback& callback) {
-  if (IsOpen()) {
-    DLOG(FATAL) << "File is already open!";
-    return ERR_UNEXPECTED;
-  }
-
-  open_flags_ = open_flags;
-  DCHECK(open_flags_ & base::PLATFORM_FILE_ASYNC);
-  DCHECK(!weak_ptr_factory_.HasWeakPtrs());
-  DCHECK(!on_io_complete_.get());
-  on_io_complete_.reset(new base::WaitableEvent(
-      false  /* manual_reset */, false  /* initially_signaled */));
-
-  // Passing &file_ to a thread pool looks unsafe but it's safe here as the
-  // destructor ensures that the open operation is complete with
-  // WaitForIOCompletion().  See also the destructor.
-  int* result = new int(OK);
-  const bool posted = base::WorkerPool::PostTaskAndReply(
-      FROM_HERE,
-      base::Bind(&InvokeAndSignal,
-                 base::Bind(&OpenFile, path, open_flags, record_uma_, &file_,
-                            result, bound_net_log_),
-                 on_io_complete_.get()),
-      base::Bind(&FileStreamWin::OnOpened,
-                 weak_ptr_factory_.GetWeakPtr(),
-                 callback, base::Owned(result)),
-      true /* task_is_slow */);
-  DCHECK(posted);
-  return ERR_IO_PENDING;
-}
-
-int FileStreamWin::OpenSync(const FilePath& path, int open_flags) {
-  if (IsOpen()) {
-    DLOG(FATAL) << "File is already open!";
-    return ERR_UNEXPECTED;
-  }
-
-  open_flags_ = open_flags;
-
-  int result = OK;
-  OpenFile(path, open_flags_, record_uma_, &file_, &result, bound_net_log_);
-  if (result != OK)
-    return result;
-
-  // TODO(satorux): Remove this once all async clients are migrated to use
-  // Open(). crbug.com/114783
-  if (open_flags_ & base::PLATFORM_FILE_ASYNC) {
-    async_context_.reset(new AsyncContext(bound_net_log_));
-    if (record_uma_)
-      async_context_->EnableErrorStatistics();
-    MessageLoopForIO::current()->RegisterIOHandler(file_,
-                                                   async_context_.get());
-  }
-
-  return OK;
-}
-
-bool FileStreamWin::IsOpen() const {
-  return file_ != base::kInvalidPlatformFileValue;
-}
-
-int FileStreamWin::Seek(Whence whence, int64 offset,
-                        const Int64CompletionCallback& callback) {
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
-
-  // Make sure we're async and we have no other in-flight async operations.
-  DCHECK(open_flags_ & base::PLATFORM_FILE_ASYNC);
-  DCHECK(!weak_ptr_factory_.HasWeakPtrs());
-  DCHECK(!on_io_complete_.get());
-
-  int64* result = new int64(-1);
-  on_io_complete_.reset(new base::WaitableEvent(
-      false  /* manual_reset */, false  /* initially_signaled */));
-
-  const bool posted = base::WorkerPool::PostTaskAndReply(
-      FROM_HERE,
-      base::Bind(&InvokeAndSignal,
-                 // Unretained should be fine as we wait for a signal on
-                 // on_io_complete_ at the destructor.
-                 base::Bind(&FileStreamWin::SeekFile, base::Unretained(this),
-                            whence, offset, result),
-                 on_io_complete_.get()),
-      base::Bind(&FileStreamWin::OnSeeked,
-                 weak_ptr_factory_.GetWeakPtr(),
-                 callback, base::Owned(result)),
-      true /* task is slow */);
-  DCHECK(posted);
-  return ERR_IO_PENDING;
-}
-
-int64 FileStreamWin::SeekSync(Whence whence, int64 offset) {
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
-
-  DCHECK(!async_context_.get() || async_context_->callback().is_null());
-  int64 result = -1;
-  SeekFile(whence, offset, &result);
+int64 FileStream::Context::SeekSync(Whence whence, int64 offset) {
+  int64 result = SeekFileImpl(whence, offset);
+  CheckForSeekError(&result);
   return result;
 }
 
-int64 FileStreamWin::Available() {
-  base::ThreadRestrictions::AssertIOAllowed();
-
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
-
-  int64 cur_pos = SeekSync(FROM_CURRENT, 0);
-  if (cur_pos < 0)
-    return cur_pos;
-
+int64 FileStream::Context::GetFileSize() const {
   LARGE_INTEGER file_size;
   if (!GetFileSizeEx(file_, &file_size)) {
     DWORD error = GetLastError();
     LOG(WARNING) << "GetFileSizeEx failed: " << error;
-    return RecordAndMapError(error,
-                             FILE_ERROR_SOURCE_GET_SIZE,
-                             record_uma_,
-                             bound_net_log_);
+    return RecordAndMapError(error, FILE_ERROR_SOURCE_GET_SIZE);
   }
 
-  return file_size.QuadPart - cur_pos;
+  return file_size.QuadPart;
 }
 
-int FileStreamWin::Read(
-    IOBuffer* buf, int buf_len, const CompletionCallback& callback) {
-  DCHECK(async_context_.get());
-
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
-
-  DCHECK(open_flags_ & base::PLATFORM_FILE_READ);
-
-  OVERLAPPED* overlapped = NULL;
-  DCHECK(!callback.is_null());
-  DCHECK(async_context_->callback().is_null());
-  overlapped = async_context_->overlapped();
-  async_context_->set_error_source(FILE_ERROR_SOURCE_READ);
+int FileStream::Context::ReadAsync(IOBuffer* buf,
+                                   int buf_len,
+                                   const CompletionCallback& callback) {
+  DCHECK(!async_in_progress_);
+  error_source_ = FILE_ERROR_SOURCE_READ;
 
   int rv = 0;
 
   DWORD bytes_read;
-  if (!ReadFile(file_, buf->data(), buf_len, &bytes_read, overlapped)) {
+  if (!ReadFile(file_, buf->data(), buf_len,
+                &bytes_read, &io_context_.overlapped)) {
     DWORD error = GetLastError();
     if (error == ERROR_IO_PENDING) {
-      async_context_->IOCompletionIsPending(callback, buf);
+      IOCompletionIsPending(callback, buf);
       rv = ERR_IO_PENDING;
     } else if (error == ERROR_HANDLE_EOF) {
       rv = 0;  // Report EOF by returning 0 bytes read.
     } else {
       LOG(WARNING) << "ReadFile failed: " << error;
-      rv = RecordAndMapError(error,
-                             FILE_ERROR_SOURCE_READ,
-                             record_uma_,
-                             bound_net_log_);
+      rv = RecordAndMapError(error, FILE_ERROR_SOURCE_READ);
     }
-  } else if (overlapped) {
-    async_context_->IOCompletionIsPending(callback, buf);
+  } else {
+    IOCompletionIsPending(callback, buf);
     rv = ERR_IO_PENDING;
-  } else {
-    rv = static_cast<int>(bytes_read);
   }
   return rv;
 }
 
-int FileStreamWin::ReadSync(char* buf, int buf_len) {
-  DCHECK(!async_context_.get());
-  base::ThreadRestrictions::AssertIOAllowed();
-
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
-
-  DCHECK(open_flags_ & base::PLATFORM_FILE_READ);
-
+int FileStream::Context::ReadSync(char* buf, int buf_len) {
   int rv = 0;
 
   DWORD bytes_read;
   if (!ReadFile(file_, buf, buf_len, &bytes_read, NULL)) {
     DWORD error = GetLastError();
     if (error == ERROR_HANDLE_EOF) {
       rv = 0;  // Report EOF by returning 0 bytes read.
     } else {
       LOG(WARNING) << "ReadFile failed: " << error;
-      rv = RecordAndMapError(error,
-                             FILE_ERROR_SOURCE_READ,
-                             record_uma_,
-                             bound_net_log_);
+      rv = RecordAndMapError(error, FILE_ERROR_SOURCE_READ);
     }
   } else {
     rv = static_cast<int>(bytes_read);
   }
   return rv;
 }
 
-int FileStreamWin::ReadUntilComplete(char *buf, int buf_len) {
-  int to_read = buf_len;
-  int bytes_total = 0;
-
-  do {
-    int bytes_read = ReadSync(buf, to_read);
-    if (bytes_read <= 0) {
-      if (bytes_total == 0)
-        return bytes_read;
-
-      return bytes_total;
-    }
-
-    bytes_total += bytes_read;
-    buf += bytes_read;
-    to_read -= bytes_read;
-  } while (bytes_total < buf_len);
-
-  return bytes_total;
-}
-
-int FileStreamWin::Write(
-    IOBuffer* buf, int buf_len, const CompletionCallback& callback) {
-  DCHECK(async_context_.get());
-
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
-
-  DCHECK(open_flags_ & base::PLATFORM_FILE_WRITE);
-
-  OVERLAPPED* overlapped = NULL;
-  DCHECK(!callback.is_null());
-  DCHECK(async_context_->callback().is_null());
-  overlapped = async_context_->overlapped();
-  async_context_->set_error_source(FILE_ERROR_SOURCE_WRITE);
+int FileStream::Context::WriteAsync(IOBuffer* buf,
+                                    int buf_len,
+                                    const CompletionCallback& callback) {
+  error_source_ = FILE_ERROR_SOURCE_WRITE;
 
   int rv = 0;
   DWORD bytes_written = 0;
-  if (!WriteFile(file_, buf->data(), buf_len, &bytes_written, overlapped)) {
+  if (!WriteFile(file_, buf->data(), buf_len,
+                 &bytes_written, &io_context_.overlapped)) {
     DWORD error = GetLastError();
     if (error == ERROR_IO_PENDING) {
-      async_context_->IOCompletionIsPending(callback, buf);
+      IOCompletionIsPending(callback, buf);
       rv = ERR_IO_PENDING;
     } else {
       LOG(WARNING) << "WriteFile failed: " << error;
-      rv = RecordAndMapError(error,
-                             FILE_ERROR_SOURCE_WRITE,
-                             record_uma_,
-                             bound_net_log_);
+      rv = RecordAndMapError(error, FILE_ERROR_SOURCE_WRITE);
     }
-  } else if (overlapped) {
-    async_context_->IOCompletionIsPending(callback, buf);
+  } else {
+    IOCompletionIsPending(callback, buf);
     rv = ERR_IO_PENDING;
+  }
+  return rv;
+}
+
+int FileStream::Context::WriteSync(const char* buf, int buf_len) {
+  int rv = 0;
+  DWORD bytes_written = 0;
+  if (!WriteFile(file_, buf, buf_len, &bytes_written, NULL)) {
+    DWORD error = GetLastError();
+    LOG(WARNING) << "WriteFile failed: " << error;
+    rv = RecordAndMapError(error, FILE_ERROR_SOURCE_WRITE);
   } else {
     rv = static_cast<int>(bytes_written);
   }
   return rv;
 }
 
-int FileStreamWin::WriteSync(
-    const char* buf, int buf_len) {
-  DCHECK(!async_context_.get());
-  base::ThreadRestrictions::AssertIOAllowed();
+int FileStream::Context::Flush() {
+  if (FlushFileBuffers(file_))
+    return OK;
 
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
-
-  DCHECK(open_flags_ & base::PLATFORM_FILE_WRITE);
-
-  int rv = 0;
-  DWORD bytes_written = 0;
-  if (!WriteFile(file_, buf, buf_len, &bytes_written, NULL)) {
-    DWORD error = GetLastError();
-    LOG(WARNING) << "WriteFile failed: " << error;
-    rv = RecordAndMapError(error,
-                           FILE_ERROR_SOURCE_WRITE,
-                           record_uma_,
-                           bound_net_log_);
-  } else {
-    rv = static_cast<int>(bytes_written);
-  }
-  return rv;
+  return RecordAndMapError(GetLastError(), FILE_ERROR_SOURCE_FLUSH);
 }
 
-int FileStreamWin::Flush() {
-  base::ThreadRestrictions::AssertIOAllowed();
+int FileStream::Context::Truncate(int64 bytes) {
+  BOOL result = SetEndOfFile(file_);
+  if (result)
+    return bytes;
 
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
+  DWORD error = GetLastError();
+  LOG(WARNING) << "SetEndOfFile failed: " << error;
+  return RecordAndMapError(error, FILE_ERROR_SOURCE_SET_EOF);
+}
 
-  DCHECK(open_flags_ & base::PLATFORM_FILE_WRITE);
-  if (FlushFileBuffers(file_)) {
-    return OK;
+void FileStream::Context::RegisterInMessageLoop() {
+  if (file_ != base::kInvalidPlatformFileValue)
+    MessageLoopForIO::current()->RegisterIOHandler(file_, this);
+}
+
+int64 FileStream::Context::SeekFileImpl(Whence whence, int64 offset) {
+  LARGE_INTEGER distance, res;
+  distance.QuadPart = offset;
+  DWORD move_method = static_cast<DWORD>(whence);
+  if (SetFilePointerEx(file_, distance, &res, move_method)) {
+    SetOffset(&io_context_.overlapped, res);
+    return res.QuadPart;
   }
 
-  return RecordAndMapError(GetLastError(),
-                           FILE_ERROR_SOURCE_FLUSH,
-                           record_uma_,
-                           bound_net_log_);
+  return -static_cast<int>(GetLastError());
 }
 
-int64 FileStreamWin::Truncate(int64 bytes) {
-  base::ThreadRestrictions::AssertIOAllowed();
-
-  if (!IsOpen())
-    return ERR_UNEXPECTED;
-
-  // We'd better be open for writing.
-  DCHECK(open_flags_ & base::PLATFORM_FILE_WRITE);
-
-  // Seek to the position to truncate from.
-  int64 seek_position = SeekSync(FROM_BEGIN, bytes);
-  if (seek_position != bytes)
-    return ERR_UNEXPECTED;
-
-  // And truncate the file.
-  BOOL result = SetEndOfFile(file_);
-  if (!result) {
-    DWORD error = GetLastError();
-    LOG(WARNING) << "SetEndOfFile failed: " << error;
-    return RecordAndMapError(error,
-                             FILE_ERROR_SOURCE_SET_EOF,
-                             record_uma_,
-                             bound_net_log_);
+void FileStream::Context::CheckForSeekError(int64* result) {
+  if (*result < 0) {
+    *result = RecordAndMapError(static_cast<int>(-(*result)),
+                                FILE_ERROR_SOURCE_SEEK);
   }
-
-  // Success.
-  return seek_position;
 }
 
-void FileStreamWin::EnableErrorStatistics() {
-  record_uma_ = true;
-
-  if (async_context_.get())
-    async_context_->EnableErrorStatistics();
+void FileStream::Context::OnSeekCompleted(
+    const Int64CompletionCallback& callback,
+    int64 result) {
+  CheckForSeekError(&result);
+  OnAsyncCompleted(callback, result);
 }
 
-void FileStreamWin::SetBoundNetLogSource(
-    const net::BoundNetLog& owner_bound_net_log) {
-  if ((owner_bound_net_log.source().id == net::NetLog::Source::kInvalidId) &&
-      (bound_net_log_.source().id == net::NetLog::Source::kInvalidId)) {
-    // Both |BoundNetLog|s are invalid.
+void FileStream::Context::IOCompletionIsPending(
+    const CompletionCallback& callback,
+    IOBuffer* buf) {
+  DCHECK(callback_.is_null());
+  callback_ = callback;
+  in_flight_buf_ = buf;  // Hold until the async operation ends.
+  async_in_progress_ = true;
+}
+
+void FileStream::Context::OnIOCompleted(MessageLoopForIO::IOContext* context,
+                                        DWORD bytes_read,
+                                        DWORD error) {
+  DCHECK_EQ(&io_context_, context);
+  DCHECK(!callback_.is_null());
+
+  if (orphaned_) {
+    callback_.Reset();
+    in_flight_buf_ = NULL;
+    CloseAsync(CompletionCallback());
     return;
   }
 
-  // Should never connect to itself.
-  DCHECK_NE(bound_net_log_.source().id, owner_bound_net_log.source().id);
+  int result = static_cast<int>(bytes_read);
+  if (error && error != ERROR_HANDLE_EOF)
+    result = RecordAndMapError(error, error_source_);
 
-  bound_net_log_.AddEvent(
-      net::NetLog::TYPE_FILE_STREAM_BOUND_TO_OWNER,
-      owner_bound_net_log.source().ToEventParametersCallback());
+  if (bytes_read)
+    IncrementOffset(&io_context_.overlapped, bytes_read);
 
-  owner_bound_net_log.AddEvent(
-      net::NetLog::TYPE_FILE_STREAM_SOURCE,
-      bound_net_log_.source().ToEventParametersCallback());
+  // Reset this before Run() as Run() may issue a new async operation.
+  async_in_progress_ = false;
+  CompletionCallback temp_callback = callback_;
+  callback_.Reset();
+  scoped_refptr<IOBuffer> temp_buf = in_flight_buf_;
+  in_flight_buf_ = NULL;
+  temp_callback.Run(result);
 }
 
-base::PlatformFile FileStreamWin::GetPlatformFileForTesting() {
-  return file_;
-}
-
-void FileStreamWin::OnClosed(const CompletionCallback& callback) {
-  file_ = base::kInvalidPlatformFileValue;
-
-  // Reset this before Run() as Run() may issue a new async operation.
-  ResetOnIOComplete();
-  callback.Run(OK);
-}
-
-void FileStreamWin::SeekFile(Whence whence, int64 offset, int64* result) {
-  LARGE_INTEGER distance, res;
-  distance.QuadPart = offset;
-  DWORD move_method = static_cast<DWORD>(whence);
-  if (!SetFilePointerEx(file_, distance, &res, move_method)) {
-    DWORD error = GetLastError();
-    LOG(WARNING) << "SetFilePointerEx failed: " << error;
-    *result = RecordAndMapError(error,
-                                FILE_ERROR_SOURCE_SEEK,
-                                record_uma_,
-                                bound_net_log_);
-    return;
-  }
-  if (async_context_.get()) {
-    async_context_->set_error_source(FILE_ERROR_SOURCE_SEEK);
-    SetOffset(async_context_->overlapped(), res);
-  }
-  *result = res.QuadPart;
-}
-
-void FileStreamWin::OnOpened(const CompletionCallback& callback, int* result) {
-  if (*result == OK) {
-    async_context_.reset(new AsyncContext(bound_net_log_));
-    if (record_uma_)
-      async_context_->EnableErrorStatistics();
-    MessageLoopForIO::current()->RegisterIOHandler(file_,
-                                                   async_context_.get());
-  }
-
-  // Reset this before Run() as Run() may issue a new async operation.
-  ResetOnIOComplete();
-  callback.Run(*result);
-}
-
-void FileStreamWin::OnSeeked(
-    const Int64CompletionCallback& callback,
-    int64* result) {
-  // Reset this before Run() as Run() may issue a new async operation.
-  ResetOnIOComplete();
-  callback.Run(*result);
-}
-
-void FileStreamWin::ResetOnIOComplete() {
-  on_io_complete_.reset();
-  weak_ptr_factory_.InvalidateWeakPtrs();
-}
-
-void FileStreamWin::WaitForIOCompletion() {
-  // http://crbug.com/115067
-  base::ThreadRestrictions::ScopedAllowWait allow_wait;
-  if (on_io_complete_.get()) {
-    on_io_complete_->Wait();
-    on_io_complete_.reset();
-  }
+template <typename R>
+void FileStream::Context::OnAsyncCompleted(
+    const base::Callback<void(R)>& callback,
+    R result) {
+  // Reset this before Run() as Run() may issue a new async operation. Also it
+  // should be reset before CloseAsync() because it shouldn't run if any async
+  // operation is in progress.
+  async_in_progress_ = false;
+  if (orphaned_)
+    CloseAsync(CompletionCallback());
+  else
+    callback.Run(result);
 }
 
 }  // namespace net