[fsp] Add FileStreamReader for the reading operation.

chrome/browser/chromeos/file_system_provider/fileapi/file_stream_reader.cc

+// Copyright 2014 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 "chrome/browser/chromeos/file_system_provider/fileapi/file_stream_reader.h"
+
+#include "base/files/file.h"
+#include "chrome/browser/chromeos/file_system_provider/fileapi/provider_async_file_util.h"
+#include "chrome/browser/chromeos/file_system_provider/mount_path_util.h"
+#include "chrome/browser/chromeos/file_system_provider/provided_file_system_interface.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/base/net_errors.h"
+
+using content::BrowserThread;
+
+namespace chromeos {
+namespace file_system_provider {
+namespace {
+
+// Dicards the callback from CloseFile().
+void EmptyStatusCallback(base::File::Error /* result */) {
+}
+
+// Converts net::CompletionCallback to net::Int64CompletionCallback.
+void Int64ToIntCompletionCallback(net::CompletionCallback callback,
+                                  int64 result) {
+  callback.Run(static_cast<int>(result));
+}
+
+// Opens a file for reading and calls the completion callback. Must be called
+// on UI thread.
+void OpenFileOnUIThread(
+    const fileapi::FileSystemURL& url,
+    const FileStreamReader::InitializeCompletedCallback& callback) {
+  // TODO(mtomasz): Check if the modification time of the file is as expected.
+  util::FileSystemURLParser parser(url);
+  if (!parser.Parse()) {
+    BrowserThread::PostTask(
+        BrowserThread::IO,
+        FROM_HERE,
+        base::Bind(callback,
+                   base::WeakPtr<ProvidedFileSystemInterface>(),
+                   base::FilePath(),
+                   0 /* file_handle */,
+                   base::File::FILE_ERROR_SECURITY));

[kinaba, 2014/05/16 07:58:00]

I think you can directly do callback.Run() because OnOpenFileCompleteOnUIThread
does it after all.

[mtomasz, 2014/05/16 09:18:20]

Done. I also added some thread checks.

+    return;
+  }
+
+  parser.file_system()->OpenFile(
+      parser.file_path(),
+      ProvidedFileSystemInterface::OPEN_FILE_MODE_READ,
+      false /* create */,
+      base::Bind(
+          callback, parser.file_system()->GetWeakPtr(), parser.file_path()));
+}
+
+// Forwards results of calling OpenFileOnUIThread back to the IO thread.
+void OnOpenFileCompletedOnUIThread(
+    const FileStreamReader::InitializeCompletedCallback& callback,
+    base::WeakPtr<ProvidedFileSystemInterface> file_system,
+    const base::FilePath& file_path,
+    int file_handle,
+    base::File::Error result) {
+  BrowserThread::PostTask(
+      BrowserThread::IO,
+      FROM_HERE,
+      base::Bind(callback, file_system, file_path, file_handle, result));
+}
+
+// Closes a file. Ignores result, since it is called from a constructor.
+// Must be called on UI thread.
+void CloseFileOnUIThread(base::WeakPtr<ProvidedFileSystemInterface> file_system,
+                         int file_handle) {
+  if (file_system.get())
+    file_system->CloseFile(file_handle, base::Bind(&EmptyStatusCallback));
+}
+
+// Requests reading contents of a file. In case of either success or a failure
+// |callback| is executed. It can be called many times, until |has_next| is set
+// to false. This function guarantees that it will succeed only if the file has
+// not been changed while reading. Must be called on UI thread.
+void ReadFileOnUIThread(
+    base::WeakPtr<ProvidedFileSystemInterface> file_system,
+    int file_handle,
+    net::IOBuffer* buffer,
+    int64 offset,
+    int length,
+    const ProvidedFileSystemInterface::ReadChunkReceivedCallback& callback) {
+  // If the file system got unmounted, then abort the reading operation.
+  if (!file_system.get()) {
+    BrowserThread::PostTask(
+        BrowserThread::IO,
+        FROM_HERE,
+        base::Bind(
+            callback, 0, false /* has_next */, base::File::FILE_ERROR_ABORT));

[kinaba, 2014/05/16 07:58:00]

ditto: no need for posting.

[mtomasz, 2014/05/16 09:18:20]

Done.

+    return;
+  }
+
+  file_system->ReadFile(file_handle, buffer, offset, length, callback);
+}
+
+// Forward the completion callback to IO thread.
+void OnReadChunkReceivedOnUIThread(
+    const ProvidedFileSystemInterface::ReadChunkReceivedCallback&
+        chunk_received_callback,
+    int chunk_length,
+    bool has_next,
+    base::File::Error result) {
+  BrowserThread::PostTask(
+      BrowserThread::IO,
+      FROM_HERE,
+      base::Bind(chunk_received_callback, chunk_length, has_next, result));
+}
+
+// TODO(mtomasz): Comment.

[kinaba, 2014/05/16 07:58:00]

Comment.

[mtomasz, 2014/05/16 09:18:20]

Done.

+void GetMetadataOnUIThread(
+    base::WeakPtr<ProvidedFileSystemInterface> file_system,
+    const base::FilePath& file_path,
+    const fileapi::AsyncFileUtil::GetFileInfoCallback& callback) {
+  // If the file system got unmounted, then abort the get length operation.
+  if (!file_system.get()) {
+    BrowserThread::PostTask(
+        BrowserThread::IO,
+        FROM_HERE,
+        base::Bind(callback, base::File::FILE_ERROR_ABORT, base::File::Info()));
+    return;

[kinaba, 2014/05/16 07:58:00]

ditto: no need for posting.

[mtomasz, 2014/05/16 09:18:20]

Done.

+  }
+
+  file_system->GetMetadata(file_path, callback);
+}
+
+// Forward the completion callback to IO thread.
+void OnGetMetadataReceivedOnUIThread(
+    const fileapi::AsyncFileUtil::GetFileInfoCallback& callback,
+    base::File::Error result,
+    const base::File::Info& file_info) {
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE, base::Bind(callback, result, file_info));
+}
+
+}  // namespace
+
+FileStreamReader::FileStreamReader(fileapi::FileSystemContext* context,
+                                   const fileapi::FileSystemURL& url,
+                                   int64 initial_offset,
+                                   const base::Time& expected_modification_time)
+    : context_(context),
+      url_(url),
+      current_offset_(initial_offset),
+      current_length_(0),
+      expected_modification_time_(expected_modification_time),
+      file_handle_(0),
+      weak_ptr_factory_(this) {
+}
+
+FileStreamReader::~FileStreamReader() {
+  CloseFileOnUIThread(file_system_, file_handle_);
+}
+
+void FileStreamReader::Initialize(
+    const base::Closure& pending_closure,
+    const net::Int64CompletionCallback& error_callback) {
+  OpenFileOnUIThread(
+      url_,
+      base::Bind(&OnOpenFileCompletedOnUIThread,
+                 base::Bind(&FileStreamReader::OnInitializeCompleted,
+                            weak_ptr_factory_.GetWeakPtr(),
+                            pending_closure,
+                            error_callback)));
+}
+
+void FileStreamReader::OnInitializeCompleted(
+    const base::Closure& pending_closure,
+    const net::Int64CompletionCallback& error_callback,
+    base::WeakPtr<ProvidedFileSystemInterface> file_system,
+    const base::FilePath& file_path,
+    int file_handle,
+    base::File::Error result) {
+  // In case of an error, return immediately using the |error_callback| of the
+  // Read() or GetLength() pending request.
+  if (result != base::File::FILE_OK) {
+    error_callback.Run(net::FileErrorToNetError(result));
+    return;
+  }
+
+  file_system_ = file_system;
+  file_path_ = file_path;
+  file_handle_ = file_handle;
+  DCHECK_LT(0, file_handle);
+
+  // Run the task waiting for the initialization to be completed.
+  pending_closure.Run();
+}
+
+int FileStreamReader::Read(net::IOBuffer* buffer,
+                           int buffer_length,
+                           const net::CompletionCallback& callback) {
+  // Lazily initialize with the first call to Read().
+  if (!file_system_.get()) {

[kinaba, 2014/05/16 07:58:00]

Dereferencing a weak pointer in different threads (IO here) than its born place
(UI) is not thread safe (see the comments in weak_ptr.h). |file_handle_| should
be used here. Same for other checks on the IO thread.

[mtomasz, 2014/05/16 09:18:20]

Oops. It is also incorrect here, since we don't want to reinitialize once the FS
is gone. Done.

+    Initialize(base::Bind(&FileStreamReader::ReadAfterInitialized,
+                          weak_ptr_factory_.GetWeakPtr(),
+                          buffer,
+                          buffer_length,
+                          callback),
+               base::Bind(&Int64ToIntCompletionCallback, callback));
+    return net::ERR_IO_PENDING;
+  }
+
+  ReadAfterInitialized(buffer, buffer_length, callback);
+  return net::ERR_IO_PENDING;
+}
+
+int64 FileStreamReader::GetLength(
+    const net::Int64CompletionCallback& callback) {
+  // Lazily initialize with the first call to Read().

[kinaba, 2014/05/16 07:58:00]

nit: Read() => GetLength()

[mtomasz, 2014/05/16 09:18:20]

Done.

+  if (!file_system_.get()) {
+    Initialize(base::Bind(&FileStreamReader::GetLengthAfterInitialized,
+                          weak_ptr_factory_.GetWeakPtr(),
+                          callback),
+               callback);
+    return net::ERR_IO_PENDING;
+  }
+
+  GetLengthAfterInitialized(callback);
+  return net::ERR_IO_PENDING;
+}
+
+void FileStreamReader::ReadAfterInitialized(
+    net::IOBuffer* buffer,
+    int buffer_length,
+    const net::CompletionCallback& callback) {
+  // If the file system got unmounted, then abort the reading operation.
+  if (!file_system_.get()) {
+    callback.Run(net::ERR_ABORTED);
+    return;
+  }
+
+  current_length_ = 0;
+  BrowserThread::PostTask(
+      BrowserThread::UI,
+      FROM_HERE,
+      base::Bind(&ReadFileOnUIThread,
+                 file_system_,
+                 file_handle_,
+                 buffer,
+                 current_offset_,
+                 buffer_length,
+                 base::Bind(&OnReadChunkReceivedOnUIThread,
+                            base::Bind(&FileStreamReader::OnReadChunkReceived,
+                                       weak_ptr_factory_.GetWeakPtr(),
+                                       callback))));
+}
+
+void FileStreamReader::GetLengthAfterInitialized(
+    const net::Int64CompletionCallback& callback) {
+  // If the file system got unmounted, then abort the length fetching operation.
+  if (!file_system_.get()) {
+    callback.Run(net::ERR_ABORTED);
+    return;
+  }
+
+  BrowserThread::PostTask(
+      BrowserThread::UI,
+      FROM_HERE,
+      base::Bind(
+          &GetMetadataOnUIThread,
+          file_system_,
+          file_path_,
+          base::Bind(
+              &OnGetMetadataReceivedOnUIThread,
+              base::Bind(&FileStreamReader::OnGetMetadataForGetLengthReceived,
+                         weak_ptr_factory_.GetWeakPtr(),
+                         callback))));
+}
+
+void FileStreamReader::OnReadChunkReceived(
+    const net::CompletionCallback& callback,
+    int chunk_length,
+    bool has_next,
+    base::File::Error result) {
+  current_length_ += chunk_length;
+
+  // If this is the last chunk with a success, then finalize.
+  if (!has_next && result == base::File::FILE_OK) {
+    current_offset_ += current_length_;
+    callback.Run(current_length_);
+    return;
+  }
+
+  // In case of an error, abort.
+  if (result != base::File::FILE_OK) {
+    DCHECK(!has_next);
+    callback.Run(net::FileErrorToNetError(result));

[kinaba, 2014/05/16 07:58:00]

return;

[mtomasz, 2014/05/16 09:18:20]

Done.

+  }
+
+  // More data is about to come, so do not call the callback yet.
+  DCHECK(has_next);
+}
+
+void FileStreamReader::OnGetMetadataForGetLengthReceived(
+    const net::Int64CompletionCallback& callback,
+    base::File::Error result,
+    const base::File::Info& file_info) {
+  // In case of an error, abort.
+  if (result != base::File::FILE_OK) {
+    callback.Run(net::FileErrorToNetError(result));
+    return;
+  }
+
+  DCHECK_EQ(result, base::File::FILE_OK);
+  callback.Run(file_info.size);
+}
+
+}  // namespace file_system_provider
+}  // namespace chromeos