service.h

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// Protocol Buffers - Google's data interchange format
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// https://developers.google.com/protocol-buffers/
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// Author: [email protected] (Kenton Varda)
// Based on original Protocol Buffers design by
// Sanjay Ghemawat, Jeff Dean, and others.
//
// DEPRECATED: This module declares the abstract interfaces underlying proto2
// RPC services. These are intented to be independent of any particular RPC
// implementation, so that proto2 services can be used on top of a variety
// of implementations. Starting with version 2.3.0, RPC implementations should
// not try to build on these, but should instead provide code generator plugins
// which generate code specific to the particular RPC implementation. This way
// the generated code can be more appropriate for the implementation in use
// and can avoid unnecessary layers of indirection.
//
//
// When you use the protocol compiler to compile a service definition, it
// generates two classes: An abstract interface for the service (with
// methods matching the service definition) and a "stub" implementation.
// A stub is just a type-safe wrapper around an RpcChannel which emulates a
// local implementation of the service.
//
// For example, the service definition:
// service MyService {
// rpc Foo(MyRequest) returns(MyResponse);
// }
// will generate abstract interface "MyService" and class "MyService::Stub".
// You could implement a MyService as follows:
// class MyServiceImpl : public MyService {
// public:
// MyServiceImpl() {}
// ~MyServiceImpl() {}
//
// // implements MyService ---------------------------------------
//
// void Foo(google::protobuf::RpcController* controller,
// const MyRequest* request,
// MyResponse* response,
// Closure* done) {
// // ... read request and fill in response ...
// done->Run();
// }
// };
// You would then register an instance of MyServiceImpl with your RPC server
// implementation. (How to do that depends on the implementation.)
//
// To call a remote MyServiceImpl, first you need an RpcChannel connected to it.
// How to construct a channel depends, again, on your RPC implementation.
// Here we use a hypothentical "MyRpcChannel" as an example:
// MyRpcChannel channel("rpc:hostname:1234/myservice");
// MyRpcController controller;
// MyServiceImpl::Stub stub(&channel);
// FooRequest request;
// FooRespnose response;
//
// // ... fill in request ...
//
// stub.Foo(&controller, request, &response, NewCallback(HandleResponse));
//
// On Thread-Safety:
//
// Different RPC implementations may make different guarantees about what
// threads they may run callbacks on, and what threads the application is
// allowed to use to call the RPC system. Portable software should be ready
// for callbacks to be called on any thread, but should not try to call the
// RPC system from any thread except for the ones on which it received the
// callbacks. Realistically, though, simple software will probably want to
// use a single-threaded RPC system while high-end software will want to
// use multiple threads. RPC implementations should provide multiple
// choices.

#ifndef GOOGLE_PROTOBUF_SERVICE_H__
#define GOOGLE_PROTOBUF_SERVICE_H__

#include <string>
#include <google/protobuf/stubs/common.h>

namespace google {
namespace protobuf {

// Defined in this file.
class Service;
class RpcController;
class RpcChannel;

// Defined in other files.
class Descriptor; // descriptor.h
class ServiceDescriptor; // descriptor.h
class MethodDescriptor; // descriptor.h
class Message; // message.h

// Abstract base interface for protocol-buffer-based RPC services. Services
// themselves are abstract interfaces (implemented either by servers or as
// stubs), but they subclass this base interface. The methods of this
// interface can be used to call the methods of the Service without knowing
// its exact type at compile time (analogous to Reflection).
class LIBPROTOBUF_EXPORT Service {
 public:
 inline Service() {}
 virtual ~Service();

 // When constructing a stub, you may pass STUB_OWNS_CHANNEL as the second
 // parameter to the constructor to tell it to delete its RpcChannel when
 // destroyed.
 enum ChannelOwnership {
 STUB_OWNS_CHANNEL,
 STUB_DOESNT_OWN_CHANNEL
 };

 // Get the ServiceDescriptor describing this service and its methods.
 virtual const ServiceDescriptor* GetDescriptor() = 0;

 // Call a method of the service specified by MethodDescriptor. This is
 // normally implemented as a simple switch() that calls the standard
 // definitions of the service's methods.
 //
 // Preconditions:
 // * method->service() == GetDescriptor()
 // * request and response are of the exact same classes as the objects
 // returned by GetRequestPrototype(method) and
 // GetResponsePrototype(method).
 // * After the call has started, the request must not be modified and the
 // response must not be accessed at all until "done" is called.
 // * "controller" is of the correct type for the RPC implementation being
 // used by this Service. For stubs, the "correct type" depends on the
 // RpcChannel which the stub is using. Server-side Service
 // implementations are expected to accept whatever type of RpcController
 // the server-side RPC implementation uses.
 //
 // Postconditions:
 // * "done" will be called when the method is complete. This may be
 // before CallMethod() returns or it may be at some point in the future.
 // * If the RPC succeeded, "response" contains the response returned by
 // the server.
 // * If the RPC failed, "response"'s contents are undefined. The
 // RpcController can be queried to determine if an error occurred and
 // possibly to get more information about the error.
 virtual void CallMethod(const MethodDescriptor* method,
 RpcController* controller,
 const Message* request,
 Message* response,
 Closure* done) = 0;

 // CallMethod() requires that the request and response passed in are of a
 // particular subclass of Message. GetRequestPrototype() and
 // GetResponsePrototype() get the default instances of these required types.
 // You can then call Message::New() on these instances to construct mutable
 // objects which you can then pass to CallMethod().
 //
 // Example:
 // const MethodDescriptor* method =
 // service->GetDescriptor()->FindMethodByName("Foo");
 // Message* request = stub->GetRequestPrototype (method)->New();
 // Message* response = stub->GetResponsePrototype(method)->New();
 // request->ParseFromString(input);
 // service->CallMethod(method, *request, response, callback);
 virtual const Message& GetRequestPrototype(
 const MethodDescriptor* method) const = 0;
 virtual const Message& GetResponsePrototype(
 const MethodDescriptor* method) const = 0;

 private:
 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(Service);
};

// An RpcController mediates a single method call. The primary purpose of
// the controller is to provide a way to manipulate settings specific to the
// RPC implementation and to find out about RPC-level errors.
//
// The methods provided by the RpcController interface are intended to be a
// "least common denominator" set of features which we expect all
// implementations to support. Specific implementations may provide more
// advanced features (e.g. deadline propagation).
class LIBPROTOBUF_EXPORT RpcController {
 public:
 inline RpcController() {}
 virtual ~RpcController();

 // Client-side methods ---------------------------------------------
 // These calls may be made from the client side only. Their results
 // are undefined on the server side (may crash).

 // Resets the RpcController to its initial state so that it may be reused in
 // a new call. Must not be called while an RPC is in progress.
 virtual void Reset() = 0;

 // After a call has finished, returns true if the call failed. The possible
 // reasons for failure depend on the RPC implementation. Failed() must not
 // be called before a call has finished. If Failed() returns true, the
 // contents of the response message are undefined.
 virtual bool Failed() const = 0;

 // If Failed() is true, returns a human-readable description of the error.
 virtual string ErrorText() const = 0;

 // Advises the RPC system that the caller desires that the RPC call be
 // canceled. The RPC system may cancel it immediately, may wait awhile and
 // then cancel it, or may not even cancel the call at all. If the call is
 // canceled, the "done" callback will still be called and the RpcController
 // will indicate that the call failed at that time.
 virtual void StartCancel() = 0;

 // Server-side methods ---------------------------------------------
 // These calls may be made from the server side only. Their results
 // are undefined on the client side (may crash).

 // Causes Failed() to return true on the client side. "reason" will be
 // incorporated into the message returned by ErrorText(). If you find
 // you need to return machine-readable information about failures, you
 // should incorporate it into your response protocol buffer and should
 // NOT call SetFailed().
 virtual void SetFailed(const string& reason) = 0;

 // If true, indicates that the client canceled the RPC, so the server may
 // as well give up on replying to it. The server should still call the
 // final "done" callback.
 virtual bool IsCanceled() const = 0;

 // Asks that the given callback be called when the RPC is canceled. The
 // callback will always be called exactly once. If the RPC completes without
 // being canceled, the callback will be called after completion. If the RPC
 // has already been canceled when NotifyOnCancel() is called, the callback
 // will be called immediately.
 //
 // NotifyOnCancel() must be called no more than once per request.
 virtual void NotifyOnCancel(Closure* callback) = 0;

 private:
 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RpcController);
};

// Abstract interface for an RPC channel. An RpcChannel represents a
// communication line to a Service which can be used to call that Service's
// methods. The Service may be running on another machine. Normally, you
// should not call an RpcChannel directly, but instead construct a stub Service
// wrapping it. Example:
// RpcChannel* channel = new MyRpcChannel("remotehost.example.com:1234");
// MyService* service = new MyService::Stub(channel);
// service->MyMethod(request, &response, callback);
class LIBPROTOBUF_EXPORT RpcChannel {
 public:
 inline RpcChannel() {}
 virtual ~RpcChannel();

 // Call the given method of the remote service. The signature of this
 // procedure looks the same as Service::CallMethod(), but the requirements
 // are less strict in one important way: the request and response objects
 // need not be of any specific class as long as their descriptors are
 // method->input_type() and method->output_type().
 virtual void CallMethod(const MethodDescriptor* method,
 RpcController* controller,
 const Message* request,
 Message* response,
 Closure* done) = 0;

 private:
 GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(RpcChannel);
};

} // namespace protobuf

} // namespace google
#endif // GOOGLE_PROTOBUF_SERVICE_H__