extensions/browser/api/vpn_provider/vpn_service.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 "extensions/browser/api/vpn_provider/vpn_service.h"

#include <stdint.h>
#include <utility>
#include <vector>

#include "base/bind.h"
#include "base/callback_helpers.h"
#include "base/containers/contains.h"
#include "base/guid.h"
#include "base/location.h"
#include "base/logging.h"
#include "base/macros.h"
#include "base/memory/ptr_util.h"
#include "base/optional.h"
#include "base/single_thread_task_runner.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "base/threading/thread_task_runner_handle.h"
#include "base/values.h"
#include "chromeos/dbus/shill/shill_third_party_vpn_driver_client.h"
#include "chromeos/dbus/shill/shill_third_party_vpn_observer.h"
#include "chromeos/network/network_configuration_handler.h"
#include "chromeos/network/network_profile.h"
#include "chromeos/network/network_profile_handler.h"
#include "chromeos/network/network_state.h"
#include "chromeos/network/network_state_handler.h"
#include "chromeos/network/network_type_pattern.h"
#include "content/public/browser/pepper_vpn_provider_resource_host_proxy.h"
#include "content/public/browser/vpn_service_proxy.h"
#include "crypto/sha2.h"
#include "extensions/browser/event_router.h"
#include "extensions/browser/extension_registry.h"
#include "extensions/browser/unloaded_extension_reason.h"
#include "third_party/cros_system_api/dbus/service_constants.h"

namespace chromeos {

namespace {

namespace api_vpn = extensions::api::vpn_provider;

void DoNothingFailureCallback(const std::string& error_name,
                              const std::string& error_message) {
  LOG(ERROR) << error_name << ": " << error_message;
}

}  // namespace

class VpnService::VpnConfiguration : public ShillThirdPartyVpnObserver {
 public:
  VpnConfiguration(const std::string& extension_id,
                   const std::string& configuration_name,
                   const std::string& key,
                   base::WeakPtr<VpnService> vpn_service);
  ~VpnConfiguration() override;

  const std::string& extension_id() const { return extension_id_; }
  const std::string& configuration_name() const { return configuration_name_; }
  const std::string& key() const { return key_; }
  const std::string& service_path() const { return service_path_; }
  void set_service_path(const std::string& service_path) {
    service_path_ = service_path;
  }
  const std::string& object_path() const { return object_path_; }
  void set_pepper_proxy(
      std::unique_ptr<content::PepperVpnProviderResourceHostProxy>
          pepper_vpn_provider_proxy) {
    pepper_vpn_provider_proxy_ = std::move(pepper_vpn_provider_proxy);
  }

  // ShillThirdPartyVpnObserver:
  void OnPacketReceived(const std::vector<char>& data) override;
  void OnPlatformMessage(uint32_t message) override;

 private:
  const std::string extension_id_;
  const std::string configuration_name_;
  const std::string key_;
  const std::string object_path_;

  std::unique_ptr<content::PepperVpnProviderResourceHostProxy>
      pepper_vpn_provider_proxy_;

  std::string service_path_;

  base::WeakPtr<VpnService> vpn_service_;

  DISALLOW_COPY_AND_ASSIGN(VpnConfiguration);
};

VpnService::VpnConfiguration::VpnConfiguration(
    const std::string& extension_id,
    const std::string& configuration_name,
    const std::string& key,
    base::WeakPtr<VpnService> vpn_service)
    : extension_id_(extension_id),
      configuration_name_(configuration_name),
      key_(key),
      object_path_(shill::kObjectPathBase + key_),
      vpn_service_(vpn_service) {}

VpnService::VpnConfiguration::~VpnConfiguration() {}

void VpnService::VpnConfiguration::OnPacketReceived(
    const std::vector<char>& data) {
  if (!vpn_service_) {
    return;
  }
  // Pass packet to the Pepper API if the connection is bound to it.
  if (pepper_vpn_provider_proxy_) {
    pepper_vpn_provider_proxy_->SendOnPacketReceived(data);
  } else {
    std::unique_ptr<base::ListValue> event_args =
        api_vpn::OnPacketReceived::Create(
            std::vector<uint8_t>(data.begin(), data.end()));
    vpn_service_->SendSignalToExtension(
        extension_id_, extensions::events::VPN_PROVIDER_ON_PACKET_RECEIVED,
        api_vpn::OnPacketReceived::kEventName, std::move(event_args));
  }
}

void VpnService::VpnConfiguration::OnPlatformMessage(uint32_t message) {
  if (!vpn_service_) {
    return;
  }
  DCHECK_GE(api_vpn::PLATFORM_MESSAGE_LAST, message);

  api_vpn::PlatformMessage platform_message =
      static_cast<api_vpn::PlatformMessage>(message);

  if (platform_message == api_vpn::PLATFORM_MESSAGE_CONNECTED) {
    vpn_service_->SetActiveConfiguration(this);
  } else if (platform_message == api_vpn::PLATFORM_MESSAGE_DISCONNECTED ||
             platform_message == api_vpn::PLATFORM_MESSAGE_ERROR) {
    vpn_service_->SetActiveConfiguration(nullptr);

    // Disconnect Pepper-bound configuration.
    if (pepper_vpn_provider_proxy_) {
      pepper_vpn_provider_proxy_->SendOnUnbind();
      pepper_vpn_provider_proxy_.reset();
    }
  }

  // TODO(kaliamoorthi): Update the lower layers to get the error message and
  // pass in the error instead of std::string().
  std::unique_ptr<base::ListValue> event_args =
      api_vpn::OnPlatformMessage::Create(configuration_name_, platform_message,
                                         std::string());

  vpn_service_->SendSignalToExtension(
      extension_id_, extensions::events::VPN_PROVIDER_ON_PLATFORM_MESSAGE,
      api_vpn::OnPlatformMessage::kEventName, std::move(event_args));
}

class VpnService::VpnServiceProxyImpl : public content::VpnServiceProxy {
 public:
  VpnServiceProxyImpl(base::WeakPtr<VpnService> vpn_service);

  void Bind(const std::string& extension_id,
            const std::string& configuration_id,
            const std::string& configuration_name,
            SuccessCallback success,
            FailureCallback failure,
            std::unique_ptr<content::PepperVpnProviderResourceHostProxy>
                pepper_vpn_provider_proxy) override;
  void SendPacket(const std::string& extension_id,
                  const std::vector<char>& data,
                  SuccessCallback success,
                  FailureCallback failure) override;

 private:
  base::WeakPtr<VpnService> vpn_service_;

  DISALLOW_COPY_AND_ASSIGN(VpnServiceProxyImpl);
};

VpnService::VpnServiceProxyImpl::VpnServiceProxyImpl(
    base::WeakPtr<VpnService> vpn_service)
    : vpn_service_(vpn_service) {}

void VpnService::VpnServiceProxyImpl::Bind(
    const std::string& extension_id,
    const std::string& configuration_id,
    const std::string& configuration_name,
    SuccessCallback success,
    FailureCallback failure,
    std::unique_ptr<content::PepperVpnProviderResourceHostProxy>
        pepper_vpn_provider_proxy) {
  if (!vpn_service_) {
    NOTREACHED();
    return;
  }

  vpn_service_->Bind(extension_id, configuration_id, configuration_name,
                     std::move(success), std::move(failure),
                     std::move(pepper_vpn_provider_proxy));
}

void VpnService::VpnServiceProxyImpl::SendPacket(
    const std::string& extension_id,
    const std::vector<char>& data,
    SuccessCallback success,
    FailureCallback failure) {
  if (!vpn_service_) {
    NOTREACHED();
    return;
  }

  vpn_service_->SendPacket(extension_id, data, std::move(success),
                           std::move(failure));
}

VpnService::VpnService(
    content::BrowserContext* browser_context,
    const std::string& userid_hash,
    extensions::ExtensionRegistry* extension_registry,
    extensions::EventRouter* event_router,
    ShillThirdPartyVpnDriverClient* shill_client,
    NetworkConfigurationHandler* network_configuration_handler,
    NetworkProfileHandler* network_profile_handler,
    NetworkStateHandler* network_state_handler)
    : browser_context_(browser_context),
      userid_hash_(userid_hash),
      extension_registry_(extension_registry),
      event_router_(event_router),
      shill_client_(shill_client),
      network_configuration_handler_(network_configuration_handler),
      network_profile_handler_(network_profile_handler),
      network_state_handler_(network_state_handler),
      active_configuration_(nullptr) {
  extension_registry_->AddObserver(this);
  network_state_handler_->AddObserver(this, FROM_HERE);
  network_configuration_handler_->AddObserver(this);
  base::ThreadTaskRunnerHandle::Get()->PostTask(
      FROM_HERE, base::BindOnce(&VpnService::NetworkListChanged,
                                weak_factory_.GetWeakPtr()));
}

VpnService::~VpnService() {
  network_configuration_handler_->RemoveObserver(this);
  network_state_handler_->RemoveObserver(this, FROM_HERE);
  extension_registry_->RemoveObserver(this);
}

void VpnService::SendShowAddDialogToExtension(const std::string& extension_id) {
  SendSignalToExtension(extension_id,
                        extensions::events::VPN_PROVIDER_ON_UI_EVENT,
                        api_vpn::OnUIEvent::kEventName,
                        api_vpn::OnUIEvent::Create(
                            api_vpn::UI_EVENT_SHOWADDDIALOG, std::string()));
}

void VpnService::SendShowConfigureDialogToExtension(
    const std::string& extension_id,
    const std::string& configuration_id) {
  SendSignalToExtension(
      extension_id, extensions::events::VPN_PROVIDER_ON_UI_EVENT,
      api_vpn::OnUIEvent::kEventName,
      api_vpn::OnUIEvent::Create(api_vpn::UI_EVENT_SHOWCONFIGUREDIALOG,
                                 configuration_id));
}

void VpnService::SendPlatformError(const std::string& extension_id,
                                   const std::string& configuration_id,
                                   const std::string& error_message) {
  SendSignalToExtension(
      extension_id, extensions::events::VPN_PROVIDER_ON_PLATFORM_MESSAGE,
      api_vpn::OnPlatformMessage::kEventName,
      api_vpn::OnPlatformMessage::Create(
          configuration_id, api_vpn::PLATFORM_MESSAGE_ERROR, error_message));
}

std::string VpnService::GetKey(const std::string& extension_id,
                               const std::string& name) {
  const std::string key = crypto::SHA256HashString(extension_id + name);
  return base::HexEncode(key.data(), key.size());
}

void VpnService::OnConfigurationRemoved(const std::string& service_path,
                                        const std::string& guid) {
  if (service_path_to_configuration_map_.find(service_path) ==
      service_path_to_configuration_map_.end()) {
    // Ignore removal of a configuration unknown to VPN service, which means the
    // configuration was created internally by the platform or already removed
    // by the extension.
    return;
  }

  VpnConfiguration* configuration =
      service_path_to_configuration_map_[service_path];
  std::unique_ptr<base::ListValue> event_args =
      api_vpn::OnConfigRemoved::Create(configuration->configuration_name());
  SendSignalToExtension(configuration->extension_id(),
                        extensions::events::VPN_PROVIDER_ON_CONFIG_REMOVED,
                        api_vpn::OnConfigRemoved::kEventName,
                        std::move(event_args));

  DestroyConfigurationInternal(configuration);
}

void VpnService::OnGetShillProperties(const std::string& service_path,
                                      base::Optional<base::Value> dictionary) {
  if (!dictionary || service_path_to_configuration_map_.find(service_path) !=
                         service_path_to_configuration_map_.end()) {
    return;
  }
  const std::string* vpn_type =
      dictionary->FindStringPath(shill::kProviderTypeProperty);
  const std::string* extension_id =
      dictionary->FindStringPath(shill::kProviderHostProperty);
  const std::string* type = dictionary->FindStringPath(shill::kTypeProperty);
  const std::string* configuration_name =
      dictionary->FindStringPath(shill::kNameProperty);
  if (!vpn_type || !extension_id || !type || !configuration_name ||
      *vpn_type != shill::kProviderThirdPartyVpn || *type != shill::kTypeVPN) {
    return;
  }

  if (!extension_registry_->GetExtensionById(
          *extension_id, extensions::ExtensionRegistry::ENABLED)) {
    // Does not belong to this instance of VpnService.
    return;
  }

  const std::string key = GetKey(*extension_id, *configuration_name);
  VpnConfiguration* configuration =
      CreateConfigurationInternal(*extension_id, *configuration_name, key);
  configuration->set_service_path(service_path);
  service_path_to_configuration_map_[service_path] = configuration;
  shill_client_->AddShillThirdPartyVpnObserver(configuration->object_path(),
                                               configuration);
}

void VpnService::NetworkListChanged() {
  NetworkStateHandler::NetworkStateList network_list;
  network_state_handler_->GetVisibleNetworkListByType(NetworkTypePattern::VPN(),
                                                      &network_list);
  for (auto* iter : network_list) {
    if (service_path_to_configuration_map_.find(iter->path()) !=
        service_path_to_configuration_map_.end()) {
      continue;
    }

    network_configuration_handler_->GetShillProperties(
        iter->path(), base::BindOnce(&VpnService::OnGetShillProperties,
                                     weak_factory_.GetWeakPtr()));
  }
}

void VpnService::CreateConfiguration(const std::string& extension_id,
                                     const std::string& extension_name,
                                     const std::string& configuration_name,
                                     SuccessCallback success,
                                     FailureCallback failure) {
  if (configuration_name.empty()) {
    std::move(failure).Run(std::string(),
                           std::string("Empty name not supported."));
    return;
  }

  const std::string key = GetKey(extension_id, configuration_name);
  if (base::Contains(key_to_configuration_map_, key)) {
    std::move(failure).Run(std::string(), std::string("Name not unique."));
    return;
  }

  const NetworkProfile* profile =
      network_profile_handler_->GetProfileForUserhash(userid_hash_);
  if (!profile) {
    std::move(failure).Run(
        std::string(),
        std::string("No user profile for unshared network configuration."));
    return;
  }

  VpnConfiguration* configuration =
      CreateConfigurationInternal(extension_id, configuration_name, key);

  base::DictionaryValue properties;
  properties.SetKey(shill::kTypeProperty, base::Value(shill::kTypeVPN));
  properties.SetKey(shill::kNameProperty, base::Value(configuration_name));
  properties.SetKey(shill::kProviderHostProperty, base::Value(extension_id));
  properties.SetKey(shill::kObjectPathSuffixProperty,
                    base::Value(configuration->key()));
  properties.SetKey(shill::kProviderTypeProperty,
                    base::Value(shill::kProviderThirdPartyVpn));
  properties.SetKey(shill::kProfileProperty, base::Value(profile->path));

  // Note: This will not create an entry in |policy_util|. TODO(pneubeck):
  // Determine the correct thing to do here, crbug.com/459278.
  std::string guid = base::GenerateGUID();
  properties.SetKey(shill::kGuidProperty, base::Value(guid));

  network_configuration_handler_->CreateShillConfiguration(
      properties,
      base::BindOnce(&VpnService::OnCreateConfigurationSuccess,
                     weak_factory_.GetWeakPtr(), std::move(success),
                     configuration),
      base::BindOnce(&VpnService::OnCreateConfigurationFailure,
                     weak_factory_.GetWeakPtr(), std::move(failure),
                     configuration));
}

void VpnService::DestroyConfiguration(const std::string& extension_id,
                                      const std::string& configuration_id,
                                      SuccessCallback success,
                                      FailureCallback failure) {
  // The ID is the configuration name for now. This may change in the future.
  const std::string key = GetKey(extension_id, configuration_id);
  if (!base::Contains(key_to_configuration_map_, key)) {
    std::move(failure).Run(std::string(), std::string("Unauthorized access."));
    return;
  }

  VpnConfiguration* configuration = key_to_configuration_map_[key].get();
  const std::string service_path = configuration->service_path();
  if (service_path.empty()) {
    std::move(failure).Run(std::string(), std::string("Pending create."));
    return;
  }
  if (active_configuration_ == configuration) {
    configuration->OnPlatformMessage(api_vpn::PLATFORM_MESSAGE_DISCONNECTED);
  }
  DestroyConfigurationInternal(configuration);

  network_configuration_handler_->RemoveConfiguration(
      service_path,
      /*remove_confirmer=*/base::nullopt,
      base::BindOnce(&VpnService::OnRemoveConfigurationSuccess,
                     weak_factory_.GetWeakPtr(), std::move(success)),
      base::BindOnce(&VpnService::OnRemoveConfigurationFailure,
                     weak_factory_.GetWeakPtr(), std::move(failure)));
}

void VpnService::SetParameters(const std::string& extension_id,
                               const base::DictionaryValue& parameters,
                               StringCallback success,
                               FailureCallback failure) {
  if (!DoesActiveConfigurationExistAndIsAccessAuthorized(extension_id)) {
    std::move(failure).Run(std::string(), std::string("Unauthorized access."));
    return;
  }

  shill_client_->SetParameters(active_configuration_->object_path(), parameters,
                               std::move(success), std::move(failure));
}

void VpnService::SendPacket(const std::string& extension_id,
                            const std::vector<char>& data,
                            SuccessCallback success,
                            FailureCallback failure) {
  if (!DoesActiveConfigurationExistAndIsAccessAuthorized(extension_id)) {
    std::move(failure).Run(std::string(), std::string("Unauthorized access."));
    return;
  }

  if (data.empty()) {
    std::move(failure).Run(std::string(),
                           std::string("Can't send an empty packet."));
    return;
  }

  shill_client_->SendPacket(active_configuration_->object_path(), data,
                            std::move(success), std::move(failure));
}

void VpnService::NotifyConnectionStateChanged(const std::string& extension_id,
                                              api_vpn::VpnConnectionState state,
                                              SuccessCallback success,
                                              FailureCallback failure) {
  if (!DoesActiveConfigurationExistAndIsAccessAuthorized(extension_id)) {
    std::move(failure).Run(std::string(), std::string("Unauthorized access."));
    return;
  }

  shill_client_->UpdateConnectionState(active_configuration_->object_path(),
                                       static_cast<uint32_t>(state),
                                       std::move(success), std::move(failure));
}

bool VpnService::VerifyConfigExistsForTesting(
    const std::string& extension_id,
    const std::string& configuration_name) {
  const std::string key = GetKey(extension_id, configuration_name);
  return base::Contains(key_to_configuration_map_, key);
}

bool VpnService::VerifyConfigIsConnectedForTesting(
    const std::string& extension_id) {
  return DoesActiveConfigurationExistAndIsAccessAuthorized(extension_id);
}

void VpnService::DestroyConfigurationsForExtension(
    const extensions::Extension* extension) {
  std::vector<VpnConfiguration*> to_be_destroyed;
  for (const auto& iter : key_to_configuration_map_) {
    if (iter.second->extension_id() == extension->id()) {
      to_be_destroyed.push_back(iter.second.get());
    }
  }

  for (auto* iter : to_be_destroyed) {
    DestroyConfiguration(extension->id(),             // Extension ID
                         iter->configuration_name(),  // Configuration name
                         base::DoNothing(),
                         base::BindOnce(DoNothingFailureCallback));
  }
}

void VpnService::OnExtensionUninstalled(
    content::BrowserContext* browser_context,
    const extensions::Extension* extension,
    extensions::UninstallReason reason) {
  if (browser_context != browser_context_) {
    NOTREACHED();
    return;
  }

  DestroyConfigurationsForExtension(extension);
}

void VpnService::OnExtensionUnloaded(
    content::BrowserContext* browser_context,
    const extensions::Extension* extension,
    extensions::UnloadedExtensionReason reason) {
  if (browser_context != browser_context_) {
    NOTREACHED();
    return;
  }

  if (active_configuration_ &&
      active_configuration_->extension_id() == extension->id()) {
    shill_client_->UpdateConnectionState(
        active_configuration_->object_path(),
        static_cast<uint32_t>(api_vpn::VPN_CONNECTION_STATE_FAILURE),
        base::DoNothing(), base::BindOnce(DoNothingFailureCallback));
  }
  if (reason == extensions::UnloadedExtensionReason::DISABLE ||
      reason == extensions::UnloadedExtensionReason::BLOCKLIST) {
    DestroyConfigurationsForExtension(extension);
  }
}

void VpnService::OnCreateConfigurationSuccess(
    VpnService::SuccessCallback callback,
    VpnConfiguration* configuration,
    const std::string& service_path,
    const std::string& guid) {
  configuration->set_service_path(service_path);
  service_path_to_configuration_map_[service_path] = configuration;
  shill_client_->AddShillThirdPartyVpnObserver(configuration->object_path(),
                                               configuration);
  std::move(callback).Run();
}

void VpnService::OnCreateConfigurationFailure(
    VpnService::FailureCallback callback,
    VpnConfiguration* configuration,
    const std::string& error_name,
    std::unique_ptr<base::DictionaryValue> error_data) {
  DestroyConfigurationInternal(configuration);
  std::move(callback).Run(error_name, std::string());
}

void VpnService::OnRemoveConfigurationSuccess(
    VpnService::SuccessCallback callback) {
  std::move(callback).Run();
}

void VpnService::OnRemoveConfigurationFailure(
    VpnService::FailureCallback callback,
    const std::string& error_name,
    std::unique_ptr<base::DictionaryValue> error_data) {
  std::move(callback).Run(error_name, std::string());
}

void VpnService::SendSignalToExtension(
    const std::string& extension_id,
    extensions::events::HistogramValue histogram_value,
    const std::string& event_name,
    std::unique_ptr<base::ListValue> event_args) {
  std::unique_ptr<extensions::Event> event(new extensions::Event(
      histogram_value, event_name, std::move(event_args), browser_context_));

  event_router_->DispatchEventToExtension(extension_id, std::move(event));
}

void VpnService::SetActiveConfiguration(
    VpnService::VpnConfiguration* configuration) {
  active_configuration_ = configuration;
}

VpnService::VpnConfiguration* VpnService::CreateConfigurationInternal(
    const std::string& extension_id,
    const std::string& configuration_name,
    const std::string& key) {
  VpnConfiguration* configuration = new VpnConfiguration(
      extension_id, configuration_name, key, weak_factory_.GetWeakPtr());
  key_to_configuration_map_[key] = base::WrapUnique(configuration);
  return configuration;
}

void VpnService::DestroyConfigurationInternal(VpnConfiguration* configuration) {
  std::unique_ptr<VpnConfiguration> configuration_ptr =
      std::move(key_to_configuration_map_[configuration->key()]);
  key_to_configuration_map_.erase(configuration->key());
  if (active_configuration_ == configuration) {
    active_configuration_ = nullptr;
  }
  if (!configuration->service_path().empty()) {
    shill_client_->RemoveShillThirdPartyVpnObserver(
        configuration->object_path());
    service_path_to_configuration_map_.erase(configuration->service_path());
  }
}

bool VpnService::DoesActiveConfigurationExistAndIsAccessAuthorized(
    const std::string& extension_id) {
  return active_configuration_ &&
         active_configuration_->extension_id() == extension_id;
}

void VpnService::Bind(
    const std::string& extension_id,
    const std::string& configuration_id,
    const std::string& configuration_name,
    SuccessCallback success,
    FailureCallback failure,
    std::unique_ptr<content::PepperVpnProviderResourceHostProxy>
        pepper_vpn_provider_proxy) {
  // The ID is the configuration name for now. This may change in the future.
  const std::string key = GetKey(extension_id, configuration_id);
  if (!base::Contains(key_to_configuration_map_, key)) {
    std::move(failure).Run(std::string(),
                           std::string("Unauthorized access. "
                                       "The configuration does not exist."));
    return;
  }

  VpnConfiguration* configuration = key_to_configuration_map_[key].get();
  if (active_configuration_ != configuration) {
    std::move(failure).Run(std::string(),
                           std::string("Unauthorized access. "
                                       "The configuration is not active."));
    return;
  }

  if (configuration->extension_id() != extension_id ||
      configuration->configuration_name() != configuration_name) {
    std::move(failure).Run(
        std::string(),
        std::string("Unauthorized access. "
                    "Configuration name or extension ID mismatch."));
    return;
  }

  const std::string service_path = configuration->service_path();
  if (service_path.empty()) {
    std::move(failure).Run(std::string(), std::string("Pending create."));
    return;
  }

  // Connection authorized. All packets will be routed through the Pepper API.
  configuration->set_pepper_proxy(std::move(pepper_vpn_provider_proxy));

  std::move(success).Run();
}

std::unique_ptr<content::VpnServiceProxy> VpnService::GetVpnServiceProxy() {
  return base::WrapUnique(new VpnServiceProxyImpl(weak_factory_.GetWeakPtr()));
}

const std::string VpnService::GetSingleServicepathForTesting() {
  if (service_path_to_configuration_map_.size() == 1)
    return service_path_to_configuration_map_.begin()->first;
  return std::string();
}

}  // namespace chromeos