Introduce background Download process to android

content/browser/android/download_process_host.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/browser/android/download_process_host.h"
+
+#include <string>
+
+#include "base/command_line.h"
+#include "base/strings/utf_string_conversions.h"
+#include "content/public/common/child_process_host.h"
+#include "content/public/common/content_switches.h"
+#include "content/public/common/process_type.h"
+#include "content/public/common/sandbox_type.h"
+#include "content/public/common/sandboxed_process_launcher_delegate.h"
+#include "ipc/ipc_switches.h"
+
+namespace content {
+
+// Delegate to launch the download child process.
+class DownloadSandboxedProcessLauncherDelegate

[svaldez, 2016/01/25 15:33:43]

Is this actually a Sandboxed process? (We're creatingit NoSandbox)

[qinmin, 2016/01/25 22:48:23]

No. Unfortunately, BrowserChildProcessHost::Launch() needs an instance of
SandboxedProcessLauncherDelegate. However, in SandboxedProcessLauncherDelegate,
the sandbox policy doesn't necessarily needs to be strictly sandboxed. Or we can
define out own sandbox policy in sandbox_type.h

+    : public content::SandboxedProcessLauncherDelegate {
+ public:
+  DownloadSandboxedProcessLauncherDelegate(content::ChildProcessHost* host)
+      : ipc_fd_(host->TakeClientFileDescriptor()) {}
+
+  ~DownloadSandboxedProcessLauncherDelegate() override {}
+
+  base::ScopedFD TakeIpcFd() override { return std::move(ipc_fd_); }
+
+ private:
+  base::ScopedFD ipc_fd_;
+};
+
+DownloadProcessHost::DownloadProcessHost() : started_(false) {}
+
+DownloadProcessHost::~DownloadProcessHost() {}
+
+bool DownloadProcessHost::StartProcess() {
+  if (started_)

[svaldez, 2016/01/25 15:33:43]

Possibly crash if StartProcess is called again.

[qinmin, 2016/01/25 22:48:23]

This function will be called when the first time a download starts in chrome,
and we should terminate the background process when there are no downloads in
progress. As a result, we should either expose a
DownloadProcessHost::IsStarted() call to the caller so that the caller can check
if download service is running, or do nothing when
DownloadProcessHost::startProcess() is called. This CL chooses the latter.

+    return true;
+  started_ = true;
+
+  process_.reset(content::BrowserChildProcessHost::Create(
+      content::PROCESS_TYPE_DOWNLOAD, this));
+  process_->SetName(base::UTF8ToUTF16(switches::kDownloadProcess));
+
+  std::string channel_id = process_->GetHost()->CreateChannel();

[asanka, 2016/01/25 16:44:50]

Do you intend for more than one browser process instance to share a background
download process? The control IPC channel you create here can be bound to only
the initiating browser process instance IIUC.

[qinmin, 2016/01/25 22:48:23]

Yes, the download process can outlive chrome. As a result, if chrome gets killed
and got relauched, we should get a new IPC fd from the browser process.

+  if (channel_id.empty())
+    return false;
+
+  const base::CommandLine& browser_command_line =
+      *base::CommandLine::ForCurrentProcess();
+
+  base::FilePath exe_path = content::ChildProcessHost::GetChildPath(
+      content::ChildProcessHost::CHILD_NORMAL);
+  if (exe_path.empty()) {
+    NOTREACHED() << "Unable to get download process binary name.";
+    return false;
+  }
+
+  base::CommandLine* cmd_line = new base::CommandLine(exe_path);
+  cmd_line->AppendSwitchASCII(switches::kProcessType,
+                              switches::kDownloadProcess);
+  cmd_line->AppendSwitchASCII(switches::kProcessChannelID, channel_id);
+  cmd_line->AppendSwitch(switches::kNoSandbox);
+
+  process_->Launch(
+      new DownloadSandboxedProcessLauncherDelegate(process_->GetHost()),
+      cmd_line, false);
+
+  return true;
+}
+
+bool DownloadProcessHost::OnMessageReceived(const IPC::Message& message) {
+  NOTIMPLEMENTED();
+  return true;
+}
+
+void DownloadProcessHost::OnProcessLaunchFailed() {
+  NOTIMPLEMENTED();
+}
+
+void DownloadProcessHost::OnProcessCrashed(int exit_code) {
+  NOTIMPLEMENTED();
+}
+
+void DownloadProcessHost::OnProcessLaunched() {
+  NOTIMPLEMENTED();
+}
+
+}  // namespace content