Make application shortcuts point to app_host.exe, install App Host during app installation.

chrome/browser/extensions/app_host_installer_impl_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 "chrome/browser/extensions/app_host_installer_impl_win.h"
+
+#include <windows.h>
+#include "base/basictypes.h"
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/logging.h"
+#include "base/process_util.h"
+#include "base/string16.h"
+#include "base/win/object_watcher.h"
+#include "base/win/registry.h"
+#include "chrome/browser/extensions/app_host_installer.h"
+#include "chrome/common/extensions/extension.h"
+#include "chrome/installer/launcher_support/chrome_launcher_support.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace {
+
+// TODO(huangs) Refactor the constants: http://crbug.com/148538
+const wchar_t kGoogleRegClientsKey[] = L"Software\\Google\\Update\\Clients";
+
+// Copied from chrome_appid.cc.
+const wchar_t kBinariesAppGuid[] = L"{4DC8B4CA-1BDA-483e-B5FA-D3C12E15B62D}";
+
+// Copied from google_update_constants.cc
+const wchar_t kRegCommandLineField[] = L"CommandLine";
+const wchar_t kRegCommandsKey[] = L"Commands";
+
+// Copied from util_constants.cc.
+const wchar_t kCmdQuickEnableApplicationHost[] =
+    L"quick-enable-application-host";
+
+class QuickEnableWatcher : public base::win::ObjectWatcher::Delegate {

[erikwright (departed), 2012/10/05 21:18:23]

Add class comments.

[huangs, 2012/10/07 01:42:25]

Done.

+ public:
+  QuickEnableWatcher(const base::Callback<void(bool)>& callback)
+      : callback_(callback) {}
+
+  // base::win::ObjectWatcher::Delegate implementation.
+  virtual void OnObjectSignaled(HANDLE object) OVERRIDE {
+    int exit_code = 0;
+    base::TerminationStatus status(
+        base::GetTerminationStatus(object, &exit_code));
+    if (status == base::TERMINATION_STATUS_NORMAL_TERMINATION) {
+      callback_.Run(true);
+    } else {
+      LOG(ERROR) << "App Host install failed, status = " << status
+                 << ", exit code = " << exit_code;
+      callback_.Run(false);
+    }
+    callback_.Reset();
+  }
+
+ private:
+  base::Callback<void(bool)> callback_;
+
+  DISALLOW_COPY_AND_ASSIGN(QuickEnableWatcher);
+};
+
+// Reads the path to app_host.exe from the value "UninstallString" within the
+// App Host's "ClientState" registry key.  Returns an empty string if the path
+// does not exist or cannot be read.
+string16 GetQuickEnableAppHostCommand(bool system_level) {
+  HKEY root_key = system_level ? HKEY_LOCAL_MACHINE : HKEY_CURRENT_USER;
+  string16 subkey(kGoogleRegClientsKey);
+  subkey.append(1, L'\\').append(kBinariesAppGuid)
+      .append(1, L'\\').append(kRegCommandsKey)
+      .append(1, L'\\').append(kCmdQuickEnableApplicationHost);
+  base::win::RegKey reg_key;
+  string16 cmd;
+  if (reg_key.Open(root_key, subkey.c_str(),
+                   KEY_QUERY_VALUE) == ERROR_SUCCESS) {
+    // If read is unsuccessful, |cmd| remains empty.
+    reg_key.ReadValue(kRegCommandLineField, &cmd);
+  }
+  return cmd;
+}
+
+// Launches the Google Update command to quick-enable App Host.
+// Returns true if the command is launched.
+bool LaunchQuickEnableAppHost(base::win::ScopedHandle* process) {
+  DCHECK(!process->IsValid());
+  bool success = false;
+
+  string16 cmd_str(GetQuickEnableAppHostCommand(true));
+  if (cmd_str.empty()) {  // Try user-level if absent from system-level.
+    cmd_str = GetQuickEnableAppHostCommand(false);
+  }
+  if (!cmd_str.empty()) {
+    VLOG(1) << "Quick-enabling application host: " << cmd_str;
+    if (!base::LaunchProcess(cmd_str, base::LaunchOptions(),
+                             process->Receive())) {
+      LOG(ERROR) << "Failed to quick-enable application host.";
+    }
+    success = process->IsValid();
+  }
+  return success;
+}
+
+}  // namespace
+
+namespace extensions {
+
+using content::BrowserThread;
+
+AppHostInstallerImpl::AppHostInstallerImpl() {}
+
+// (1) is checked here. If true, proceeds to (2), else signals success.
+void AppHostInstallerImpl::InstallAppHostIfNecessary(
+    const Extension& extension,
+    const base::Callback<void(bool)>& completion_callback) {
+  if (!BrowserThread::GetCurrentThreadIdentifier(&caller_thread_id_)) {

[erikwright (departed), 2012/10/05 21:18:23]

DCHECK completion_callback_.IsNull()

[huangs, 2012/10/07 01:42:25]

I don't understand this (callback.h has no IsNull()); please clarify!

+    NOTREACHED();
+    return;
+  }
+  completion_callback_ = completion_callback;
+
+  if (extension.is_platform_app())
+    InstallAppHostIfNecessaryInternal();
+  else
+    Finish(true);
+}
+
+// (2) is checked here. If false, signals success, else installs App Host.
+void AppHostInstallerImpl::InstallAppHostIfNecessaryInternal() {
+  if (BrowserThread::CurrentlyOn(BrowserThread::FILE)) {
+    if (chrome_launcher_support::IsAppHostPresent())
+      Finish(true);
+    else
+      InstallAppHost();
+  } else {  // Redo on FILE thread.
+    BrowserThread::PostTask(BrowserThread::FILE, FROM_HERE, base::Bind(
+        &AppHostInstallerImpl::InstallAppHostIfNecessaryInternal,
+        base::Unretained(this)));

[erikwright (departed), 2012/10/05 21:18:23]

Can't the impl potentially be deleted before this callback is invoked? Then
you'll have a use-after-free?

[huangs, 2012/10/07 01:42:25]

I'm letting AppHostInstallerImpl manage its own lifecycle; we'll iterate on
this!

+  }
+}
+
+void AppHostInstallerImpl::InstallAppHost() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  DCHECK(!process_.IsValid());
+  if (!LaunchQuickEnableAppHost(&process_)) {
+    Finish(false);
+  } else {
+    DCHECK(process_.IsValid());
+    DCHECK(!delegate_.get());
+    watcher_.StopWatching();
+    delegate_.reset(new QuickEnableWatcher(
+        base::Bind(&AppHostInstallerImpl::Finish, base::Unretained(this))));

[erikwright (departed), 2012/10/05 21:18:23]

Here I think the Unretained is probably safe, but you need to check and document
that if it stays this way.

[huangs, 2012/10/07 01:42:25]

If AppHostInstallerImpl deletes itself, then this is safe.  
Note that both callers (CrxInstaller and UnpackedInstaller) extend
base::RefCountedThreadSafe<>, so I think they are guaranteed to live while
AppHostInstallerImpl is running (please verify).

+    watcher_.StartWatching(process_, delegate_.get());
+  }
+}
+
+void AppHostInstallerImpl::Finish(bool success) {
+  if (BrowserThread::CurrentlyOn(caller_thread_id_)) {
+    completion_callback_.Run(success);
+  } else {  // Redo on caller thread.
+    BrowserThread::PostTask(caller_thread_id_, FROM_HERE, base::Bind(
+        &AppHostInstallerImpl::Finish, base::Unretained(this), success));

[erikwright (departed), 2012/10/05 21:18:23]

Same concern here about Unretained.

[huangs, 2012/10/07 01:42:25]

Ditto.

+  }
+}
+
+}  // namespace extensions