Adding a DBus signal for printers changed

A system daemon needs a signal that indicate the printers list has
changed so it can query Chrome again.  This generates the
PrintersChanged signal from org.chromium.PrintersService.

Bug: b:143242799
Change-Id: I4424603b05f89691d568f03f220e7eaf37bd0cf9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1949041Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Commit-Queue: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743291}

chrome/browser/chromeos/BUILD.gn

@@ -955,6 +955,8 @@ source_set("chromeos") {
     "dbus/metrics_event_service_provider.h",
     "dbus/plugin_vm_service_provider.cc",
     "dbus/plugin_vm_service_provider.h",
+    "dbus/printers_service_provider.cc",
+    "dbus/printers_service_provider.h",
     "dbus/proxy_resolution_service_provider.cc",
     "dbus/proxy_resolution_service_provider.h",
     "dbus/screen_lock_service_provider.cc",
@@ -2482,6 +2484,7 @@ action("dbus_service_files") {
     "dbus/org.chromium.MetricsEventService.conf",
     "dbus/org.chromium.NetworkProxyService.conf",
     "dbus/org.chromium.PluginVmService.conf",
+    "dbus/org.chromium.PrintersService.conf",
     "dbus/org.chromium.ScreenLockService.conf",
     "dbus/org.chromium.SmbFsService.conf",
     "dbus/org.chromium.VirtualFileRequestService.conf",

chrome/browser/chromeos/chrome_browser_main_chromeos.cc

@@ -57,6 +57,7 @@
 #include "chrome/browser/chromeos/dbus/machine_learning_decision_service_provider.h"
 #include "chrome/browser/chromeos/dbus/metrics_event_service_provider.h"
 #include "chrome/browser/chromeos/dbus/plugin_vm_service_provider.h"
+#include "chrome/browser/chromeos/dbus/printers_service_provider.h"
 #include "chrome/browser/chromeos/dbus/proxy_resolution_service_provider.h"
 #include "chrome/browser/chromeos/dbus/screen_lock_service_provider.h"
 #include "chrome/browser/chromeos/dbus/smb_fs_service_provider.h"
@@ -304,6 +305,12 @@ class DBusServices {
         CrosDBusService::CreateServiceProviderList(
             std::make_unique<ChromeFeaturesServiceProvider>()));
 
+    printers_service_ = CrosDBusService::Create(
+        system_bus, kPrintersServiceName,
+        dbus::ObjectPath(kPrintersServicePath),
+        CrosDBusService::CreateServiceProviderList(
+            std::make_unique<PrintersServiceProvider>()));
+
     vm_applications_service_ = CrosDBusService::Create(
         system_bus, vm_tools::apps::kVmApplicationsServiceName,
         dbus::ObjectPath(vm_tools::apps::kVmApplicationsServicePath),
@@ -384,6 +391,7 @@ class DBusServices {
     kiosk_info_service_.reset();
     metrics_event_service_.reset();
     plugin_vm_service_.reset();
+    printers_service_.reset();
     virtual_file_request_service_.reset();
     component_updater_service_.reset();
     chrome_features_service_.reset();
@@ -407,6 +415,7 @@ class DBusServices {
   std::unique_ptr<CrosDBusService> kiosk_info_service_;
   std::unique_ptr<CrosDBusService> metrics_event_service_;
   std::unique_ptr<CrosDBusService> plugin_vm_service_;
+  std::unique_ptr<CrosDBusService> printers_service_;
   std::unique_ptr<CrosDBusService> screen_lock_service_;
   std::unique_ptr<CrosDBusService> virtual_file_request_service_;
   std::unique_ptr<CrosDBusService> component_updater_service_;

chrome/browser/chromeos/dbus/org.chromium.PrintersService.conf

+<!DOCTYPE busconfig PUBLIC "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
+  "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
+<!--
+  Copyright 2020 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.
+-->
+
+<busconfig>
+  <policy user="chronos">
+    <allow own="org.chromium.PrintersService"/>
+  </policy>
+</busconfig>

chrome/browser/chromeos/dbus/printers_service_provider.cc

+// Copyright 2020 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/dbus/printers_service_provider.h"
+
+#include "chrome/browser/chromeos/printing/cups_printers_manager_factory.h"
+#include "chrome/browser/chromeos/printing/cups_printers_manager_proxy.h"
+#include "chrome/browser/profiles/profile_manager.h"
+#include "dbus/message.h"
+#include "third_party/cros_system_api/dbus/service_constants.h"
+
+namespace chromeos {
+
+PrintersServiceProvider::PrintersServiceProvider() = default;
+
+PrintersServiceProvider::~PrintersServiceProvider() = default;
+
+void PrintersServiceProvider::Start(
+    scoped_refptr<dbus::ExportedObject> exported_object) {
+  exported_object_ = exported_object;
+  auto* proxy = CupsPrintersManagerFactory::GetInstance()->GetProxy();
+  DCHECK(proxy);
+  printers_manager_observer_.Add(proxy);
+}
+
+void PrintersServiceProvider::OnPrintersChanged(
+    PrinterClass printer_class,
+    const std::vector<Printer>& /*printers*/) {
+  // Signal is suppressed for discovered printers because they require setup
+  // before being usable.
+  if (printer_class == PrinterClass::kDiscovered) {
+    return;
+  }
+  DVLOG(1) << "Emitting printers changed DBus event";
+  EmitSignal();
+}
+
+void PrintersServiceProvider::EmitSignal() {
+  DCHECK(exported_object_);
+
+  dbus::Signal signal(chromeos::kPrintersServiceInterface,
+                      chromeos::kPrintersServicePrintersChangedSignal);
+  exported_object_->SendSignal(&signal);
+}
+
+}  // namespace chromeos

chrome/browser/chromeos/dbus/printers_service_provider.h

+// Copyright 2020 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.
+
+#ifndef CHROME_BROWSER_CHROMEOS_DBUS_PRINTERS_SERVICE_PROVIDER_H_
+#define CHROME_BROWSER_CHROMEOS_DBUS_PRINTERS_SERVICE_PROVIDER_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/scoped_observer.h"
+#include "chrome/browser/chromeos/printing/cups_printers_manager.h"
+#include "chrome/browser/chromeos/printing/cups_printers_manager_proxy.h"
+#include "chromeos/dbus/services/cros_dbus_service.h"
+#include "dbus/exported_object.h"
+
+namespace chromeos {
+
+// Provides a DBus service which emits a signal to indicate that the available
+// printers has changed.  Clients are intended to listen for the signal then
+// make a request for more printers through a side channel e.g. cups_proxy.
+class PrintersServiceProvider
+    : public CrosDBusService::ServiceProviderInterface,
+      public chromeos::CupsPrintersManager::Observer {
+ public:
+  PrintersServiceProvider();
+  ~PrintersServiceProvider() override;
+
+  // CrosDBusService::ServiceProviderInterface overrides:
+  void Start(scoped_refptr<dbus::ExportedObject> exported_object) override;
+
+  // CupsPrintersManager::Observer overrides:
+  void OnPrintersChanged(PrinterClass printers_class,
+                         const std::vector<Printer>& printers) override;
+
+ private:
+  // Emits the D-Bus signal for this event.
+  void EmitSignal();
+
+  // A reference on ExportedObject for sending signals.
+  scoped_refptr<dbus::ExportedObject> exported_object_;
+
+  ScopedObserver<chromeos::CupsPrintersManagerProxy,
+                 chromeos::CupsPrintersManager::Observer>
+      printers_manager_observer_{this};
+
+  DISALLOW_COPY_AND_ASSIGN(PrintersServiceProvider);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_DBUS_PRINTERS_SERVICE_PROVIDER_H_