Service Manager: Remove ServiceContext* arg from Service::OnStart()

services/service_manager/public/cpp/service.h

 // 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.
 
 #ifndef SERVICES_SERVICE_MANAGER_PUBLIC_CPP_SERVICE_H_
 #define SERVICES_SERVICE_MANAGER_PUBLIC_CPP_SERVICE_H_
 
 namespace service_manager {
 
 class InterfaceRegistry;
 class ServiceContext;
 struct ServiceInfo;
 
 // The primary contract between a Service and the Service Manager, receiving
-// lifecycle notifications and connection requests. Every Service must minimally
-// implement OnConnect().
+// lifecycle notifications and connection requests.
 class Service {
  public:
+  Service();
   virtual ~Service();
 
-  // Called once a bidirectional connection with the Service Manager has been
-  // established.
-  //
-  // |context| is the ServiceContext for this instance of the service. It's
-  // guaranteed to outlive the Service instance and therefore may be retained by
-  // it.
-  //
-  // Use the context to retrieve information about the service instance, make
-  // outgoing service connections, and issue other requests to the Service
-  // Manager on behalf of this instance.
-  //
-  // Called exactly once before any calls to OnConnect().
-  virtual void OnStart(ServiceContext* context);
+  // Called exactly once, when a bidirectional connection with the Service
+  // Manager has been established. No calls to OnConnect() will be received
+  // before this.
+  virtual void OnStart();
 
   // Called each time a connection to this service is brokered by the Service
   // Manager. Implement this to expose interfaces to other services.
   //
   // Return true if the connection should succeed or false if the connection
   // should be rejected.
+  //
+  // The default implementation returns false.
   virtual bool OnConnect(const ServiceInfo& remote_info,
-                         InterfaceRegistry* registry) = 0;
+                         InterfaceRegistry* registry);
 
   // Called when the Service Manager has stopped tracking this instance. The
   // service should use this as a signal to shut down, and in fact its process
   // may be reaped shortly afterward if applicable.
   //
   // Return true from this method to tell the ServiceContext to signal its
   // shutdown extenrally (i.e. to invoke it's "connection lost" closure if set),
   // or return false to defer the signal. If deferred, the Service should
   // explicitly call QuitNow() on the ServiceContext when it's ready to be
   // torn down.
   //
   // The default implementation returns true.
   //
   // While it's possible for this to be invoked before either OnStart() or
   // OnConnect() is invoked, neither will be invoked at any point after this
   // OnStop().
   virtual bool OnStop();
+
+ protected:
+  // Access the ServiceContext associated with this Service. Note that this is
+  // only valid to call during or after OnStart(), but never before! As such,
+  // it's always safe to call in OnStart() and OnConnect(), but should generally
+  // be avoided in OnStop().
+  ServiceContext* context() const;
+
+ private:
+  friend class ForwardingService;
+  friend class ServiceContext;
+
+  // NOTE: This is guaranteed to be called before OnStart().
+  void set_context(ServiceContext* context) { service_context_ = context; }
+
+  ServiceContext* service_context_ = nullptr;
+};
+
+// TODO(rockot): Remove this. It's here to satisfy a few remaining use cases
+// where a Service impl is owned by something other than its ServiceContext.
+class ForwardingService : public Service {
+ public:
+  // |target| must outlive this object.
+  explicit ForwardingService(Service* target);
+  ~ForwardingService() override;
+
+ private:
+  // Service:
+  void OnStart() override;
+  bool OnConnect(const ServiceInfo& remote_info,
+                 InterfaceRegistry* registry) override;
+  bool OnStop() override;
+
+  Service* const target_ = nullptr;
 };
 
 }  // namespace service_manager
 
 #endif  // SERVICES_SERVICE_MANAGER_PUBLIC_CPP_SERVICE_H_