[fsp] First part of support for reading files.

chrome/browser/chromeos/file_system_provider/operations/read_file.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/operations/read_file.h"
+
+#include <limits>
+#include <string>
+
+#include "chrome/common/extensions/api/file_system_provider.h"
+#include "chrome/common/extensions/api/file_system_provider_internal.h"
+
+namespace chromeos {
+namespace file_system_provider {
+namespace operations {
+namespace {
+
+// Convert |value| into |output|. If parsing fails, then returns a negative
+// value. Otherwise returns number of bytes written to the buffer.
+int CopyRequestValueToBuffer(scoped_ptr<RequestValue> value,
+                             net::IOBuffer* buffer,
+                             int buffer_offset,
+                             int buffer_length) {
+  using extensions::api::file_system_provider_internal::
+      ReadFileRequestedSuccess::Params;
+
+  const Params* params = value->read_file_success_params();
+  if (!params)
+    return -1;
+
+  // TODO(mtomasz): Consider using a Blob URL, instead of DOMString.
+  std::string input_data;
+
+  const size_t chunk_size = params->data.length();
+
+  // Check for overflows.
+  if (chunk_size > static_cast<size_t>(buffer_length) - buffer_offset)
+    return -1;
+
+  memcpy(buffer->data() + buffer_offset, params->data.c_str(), chunk_size);
+
+  return chunk_size;
+}
+
+}  // namespace
+
+ReadFile::ReadFile(
+    extensions::EventRouter* event_router,
+    const ProvidedFileSystemInfo& file_system_info,
+    int file_handle,
+    net::IOBuffer* buffer,
+    int64 offset,
+    int length,
+    const ProvidedFileSystemInterface::ReadChunkReceivedCallback& callback)
+    : Operation(event_router, file_system_info),
+      file_handle_(file_handle),
+      buffer_(buffer),
+      offset_(offset),
+      length_(length),
+      callback_(callback) {
+}
+
+ReadFile::~ReadFile() {
+}
+
+bool ReadFile::Execute(int request_id) {
+  scoped_ptr<base::ListValue> values(new base::ListValue);
+  values->AppendInteger(file_handle_);
+  values->AppendDouble(offset_);
+  values->AppendInteger(length_);
+  return SendEvent(
+      request_id,
+      extensions::api::file_system_provider::OnReadFileRequested::kEventName,
+      values.Pass());
+}
+
+void ReadFile::OnSuccess(int /* request_id */,
+                         scoped_ptr<RequestValue> result,
+                         bool has_next) {
+  const int copy_result =
+      CopyRequestValueToBuffer(result.Pass(), buffer_, offset_, length_);

[kinaba, 2014/05/15 08:23:40]

|offset_| seems to be used in two different ways:
as an argument of OnReadFileRequested for indicating the offset in the file, and
as an argument of CopyRequestValueToBuffer for indicating the offset in the
|buffer_|.

Do they coincide? If so it looks strange to me because then we need to allocate
a buffer of the same size as the whole file.

In other words, shouldn't the third argument here be always zero?

[mtomasz, 2014/05/16 01:39:39]

You're right. Good catch. Fixed. 

+  DCHECK_LE(0, copy_result);
+  DCHECK(!has_next || copy_result > 0);
+  callback_.Run(copy_result, has_next, base::File::FILE_OK);
+}
+
+void ReadFile::OnError(int /* request_id */, base::File::Error error) {
+  callback_.Run(0 /* chunk_length */, false /* has_next */, error);
+}
+
+}  // namespace operations
+}  // namespace file_system_provider
+}  // namespace chromeos