在《用最少的代码模拟gRPC四种消息交换模式》中，我使用很简单的代码模拟了gRPC四种消息交换模式（Unary、Client Streaming、Server Streaming和Duplex Streaming），现在我们更近一步，试着使用极简的方式打造一个gRPC框架（github地址）。这个gRPC是对ASP.NET Core gRPC实现原理的模拟，并不是想重新造一个轮子。
一、“标准”的gRPC定义、承载和调用
二、将gRPC方法抽象成委托
三、将委托转换成RequestDelegate
UnaryCallHandler
ClientStreamingCallHandler
ServerStreamingCallHandler
DuplexStreamingCallHandler
四、路由注册
五、为gRPC服务定义一个接口
六、重新定义和承载服务
一、“标准”的gRPC定义、承载和调用
可能有些读者朋友们对ASP.NET Core gRPC还不是太熟悉，所以我们先来演示一下如何在一个ASP.NET Core应用中如何定义和承载一个简单的gRPC服务，并使用自动生成的客户端代码进行调用。我们新建一个空的解决方案，并在其中添加如下所示的三个项目。
我们在类库项目Proto中定义了如下所示Greeter服务，并利用其中定义的四个操作分别模拟四种消息交换模式。HelloRequest 和HelloReply 是它们涉及的两个ProtoBuf消息。
syntax = "proto3"; import "google/protobuf/empty.proto"; service Greeter { rpc SayHelloUnary (HelloRequest) returns ( HelloReply); rpc SayHelloServerStreaming (google.protobuf.Empty) returns (stream HelloReply); rpc SayHelloClientStreaming (stream HelloRequest) returns (HelloReply); rpc SayHelloDuplexStreaming (stream HelloRequest) returns (stream HelloReply); } message HelloRequest { string name = 1; } message HelloReply { string message = 1; }
ASP.NET Core项目中定义了如下的GreeterServce服务实现了定义的四个操作，基类GreeterBase是针对上面这个.proto文件生成的类型。
public class GreeterService: GreeterBase { public override Task<HelloReply> SayHelloUnary(HelloRequest request, ServerCallContext context) => Task.FromResult(new HelloReply { Message = $"Hello, {request.Name}" }); public override async Task<HelloReply> SayHelloClientStreaming(IAsyncStreamReader<HelloRequest> reader, ServerCallContext context) { var list = new List<string>(); while (await reader.MoveNext(CancellationToken.None)) { list.Add(reader.Current.Name); } return new HelloReply { Message = $"Hello, {string.Join(",", list)}" }; } public override async Task SayHelloServerStreaming(Empty request, IServerStreamWriter<HelloReply> responseStream, ServerCallContext context) { await responseStream.WriteAsync(new HelloReply { Message = "Hello, Foo!" }); await Task.Delay(1000); await responseStream.WriteAsync(new HelloReply { Message = "Hello, Bar!" }); await Task.Delay(1000); await responseStream.WriteAsync(new HelloReply { Message = "Hello, Baz!" }); } public override async Task SayHelloDuplexStreaming(IAsyncStreamReader<HelloRequest> reader, IServerStreamWriter<HelloReply> writer, ServerCallContext context) { while (await reader.MoveNext()) { await writer.WriteAsync(new HelloReply { Message = $"Hello {reader.Current.Name}" }); } } }
具体的服务承载代码如下。我们采用Minimal API的形式，通过调用IServiceCollection接口的AddGrpc扩展方法注册相关服务，并调用MapGrpcService<TService>将定义在GreeterServce中的四个方法映射我对应的路由终结点。
var builder = WebApplication.CreateBuilder(args); builder.Services.AddGrpc(); builder.WebHost.ConfigureKestrel(kestrel => kestrel.ConfigureEndpointDefaults(options => options.Protocols = HttpProtocols.Http2)); var app = builder.Build(); app.MapGrpcService<GreeterService>(); app.Run();
在控制台项目Client中，我们利用生成出来的客户端类型GreeterClient分别一对应的服务交换模式调用了四个gRPC方法。
var channel = GrpcChannel.ForAddress("http://localhost:5000"); var client = new GreeterClient(channel); Console.WriteLine("Unary"); await UnaryCallAsync();
Console.WriteLine("nServer Streaming"); await ServerStreamingCallAsync();
Console.WriteLine("nClient Streaming"); await ClientStreamingCallAsync();
Console.WriteLine("nDuplex Streaming"); await DuplexStreamingCallAsync();
Console.ReadLine();
async Task UnaryCallAsync() { var request = new HelloRequest { Name = "foobar" }; var reply = await client.SayHelloUnaryAsync(request); Console.WriteLine(reply.Message); }
async Task ServerStreamingCallAsync() { var streamingCall = client.SayHelloServerStreaming(new Empty()); var reader = streamingCall.ResponseStream; while (await reader.MoveNext(CancellationToken.None)) { Console.WriteLine(reader.Current.Message); } }
async Task ClientStreamingCallAsync() { var streamingCall = client.SayHelloClientStreaming(); var writer = streamingCall.RequestStream; await writer.WriteAsync(new HelloRequest { Name = "Foo" }); await Task.Delay(1000); await writer.WriteAsync(new HelloRequest { Name = "Bar" }); await Task.Delay(1000); await writer.WriteAsync(new HelloRequest { Name = "Baz" }); await writer.CompleteAsync(); var reply = await streamingCall.ResponseAsync; Console.WriteLine(reply.Message); }
async Task DuplexStreamingCallAsync() { var streamingCall = client.SayHelloDuplexStreaming(); var writer = streamingCall.RequestStream; var reader = streamingCall.ResponseStream; _ = Task.Run(async () => { await writer.WriteAsync(new HelloRequest { Name = "Foo" }); await Task.Delay(1000); await writer.WriteAsync(new HelloRequest { Name = "Bar" }); await Task.Delay(1000); await writer.WriteAsync(new HelloRequest { Name = "Baz" }); await writer.CompleteAsync(); }); await foreach (var reply in reader.ReadAllAsync()) { Console.WriteLine(reply.Message); } }
如下所示的是客户端控制台上的输出结果。
二、将gRPC方法抽象成委托
通过上面的演示我们也知道，承载的gRPC类型最终会将其实现的方法注册成路由终结点，这一点其实和MVC是一样的。但是gRPC的方法和定义在Controller类型中的Action方法不同之处在于，前者的签名其实是固定的。如果我们将请求和响应消息类型使用Request和Reply来表示，四种消息交换模式的方法签名就可以写成如下的形式。
Task<Reply> Unary(Request request, ServerCallContext context); Task<Reply> ClientStreaming(IAsyncStreamReader<Request> reader, ServerCallContext context); Task ServerStreaming(Empty request, IServerStreamWriter<Reply> responseStream, ServerCallContext context); Task DuplexStreaming(IAsyncStreamReader<Request> reader, IServerStreamWriter<Reply> writer, ServerCallContext context);
“流式”方法中用来读取请求和写入响应的IAsyncStreamReader<T>和IServerStreamWriter<T>定义如下。
public interface IAsyncStreamReader<out T> { T Current { get; } Task<bool> MoveNext(CancellationToken cancellationToken = default); }
public interface IAsyncStreamWriter<in T> { Task WriteAsync(T message, CancellationToken cancellationToken = default); }
public interface IServerStreamWriter<in T> : IAsyncStreamWriter<T> { }
public interface IClientStreamWriter<in T> : IAsyncStreamWriter<T> { Task CompleteAsync(); }
表示服务端调用上下文的ServerCallContext 类型具有丰富的成员，但是它的本质就是对HttpContext上下文的封装，所以我们对它进行了简化。如下面的代码片段所示，我们给予这个上下文类型两个属性成员，一个是表示请求上下文的HttpContext，另一个则是用来设置响应状态StatusCode，后者对应的枚举定义了完整的gRPC状态码。
public class ServerCallContext { public StatusCode StatusCode { get; set; } = StatusCode.OK; public HttpContext HttpContext { get; } public ServerCallContext(HttpContext httpContext)=> HttpContext = httpContext; } public enum StatusCode { OK = 0, Cancelled = 1, Unknown = 2, InvalidArgument = 3, DeadlineExceeded = 4, NotFound = 5, AlreadyExists = 6, PermissionDenied = 7, Unauthenticated = 0x10, ResourceExhausted = 8, FailedPrecondition = 9, Aborted = 10, OutOfRange = 11, Unimplemented = 12, Internal = 13, Unavailable = 14, DataLoss = 0xF }
既然方法签名固定，意味着我们可以将四种gRPC方法定义成如下四个对应的委托，泛型参数TService、TRequest和TResponse分别表示服务、请求和响应类型。
public delegate Task<TResponse> UnaryMethod<TService, TRequest, TResponse>(TService service, TRequest request, ServerCallContext context) where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; public delegate Task<TResponse> ClientStreamingMethod<TService, TRequest, TResponse>(TService service, IAsyncStreamReader<TRequest> reader, ServerCallContext context) where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; public delegate Task ServerStreamingMethod<TService, TRequest, TResponse>(TService service, TRequest request, IServerStreamWriter<TResponse> writer, ServerCallContext context) where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; public delegate Task DuplexStreamingMethod<TService, TRequest, TResponse>(TService service, IAsyncStreamReader<TRequest> reader, IServerStreamWriter<TResponse> writer, ServerCallContext context) where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>;
我们知道路由的本质就是创建一组路由模式（Pattern）和对应处理器之间的映射关系。路由模式很简单，对应的路由模板为“{ServiceName}/{MethodName}”，并且采用Post请求方法。对应的处理器最终体现为一个RequestDelegate。那么只要我们能够将上述四种委托类型都转换成RequestDelegate委托，一切都迎刃而解了。
三、将委托转换成RequestDelegate
为了将四种委托类型转化成RequestDelegate，我们将后者实现为一个ServiceCallHandler类型，并为其定义了如下两个基类。ServerCallHandlerBase的HandleCallAsync方法正好与RequestDelegate委托的签名一致，所以这个方法最终会用来处理gRPC请求。不同的消息交换模式采用不同的请求处理方式，只需实现抽象方法HandleCallAsyncCore就可以了。HandleCallAsync方法在调用此抽象方法之前将响应的ContentType设置成gRPC标准的响应类型“application/grpc”。在此之后将状态码设置为“grpc-status”首部，它将在HTTP2的DATA帧发送完毕后，以HEADERS帧发送到客户端。这两项操作都是gRPC协议的一部分。
public abstract class ServerCallHandlerBase { public async Task HandleCallAsync(HttpContext httpContext) { try { var serverCallContext = new ServerCallContext(httpContext); var response = httpContext.Response; response.ContentType = "application/grpc"; await HandleCallAsyncCore(serverCallContext); SetStatus(serverCallContext.StatusCode); } catch { SetStatus(StatusCode.Unknown); } void SetStatus(StatusCode statusCode) { httpContext.Response.AppendTrailer("grpc-status", ((int)statusCode).ToString()); } } protected abstract Task HandleCallAsyncCore(ServerCallContext serverCallContext); } public abstract class ServerCallHandler<TService, TRequest, TResponse> : ServerCallHandlerBase where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { protected ServerCallHandler(MessageParser<TRequest> requestParser)=> RequestParser = requestParser; public MessageParser<TRequest> RequestParser { get; } }
ServerCallHandler<TService, TRequest, TResponse>派生自ServerCallHandlerBase，并利用三个泛型参数TService、TRequest、TResponse来表示服务、请求和响应类型，RequestParser用来提供发序列化请求消息的MessageParser<TRequest>对象。针对四种消息交换模式的ServiceCallHandler类型均继承这个泛型基类。
UnaryCallHandler
基于Unary消息交换模式的ServerCallHandler的具体类型为UnaryCallHandler<TService, TRequest, TResponse>，它由上述的UnaryMethod<TService, TRequest, TResponse>委托构建而成。在重写的HandleCallAsyncCore方法中，我们利用HttpContext提供的IServiceProvider对象将服务实例创建出来后，从请求主体中将请求消息读取出来，然后交给指定的委托对象进行处理并得到响应消息，该响应消息最终用来对当前请求予以回复。
internal class UnaryCallHandler<TService, TRequest, TResponse> : ServerCallHandler<TService, TRequest, TResponse> where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { private readonly UnaryMethod<TService, TRequest, TResponse> _handler; public UnaryCallHandler(UnaryMethod<TService, TRequest, TResponse> handler, MessageParser<TRequest> requestParser):base(requestParser) => _handler = handler; protected override async Task HandleCallAsyncCore(ServerCallContext serverCallContext) { using var scope = serverCallContext.HttpContext.RequestServices.CreateScope(); var service = ActivatorUtilities.CreateInstance<TService>(scope.ServiceProvider); var httpContext = serverCallContext.HttpContext; var request = await httpContext.Request.BodyReader.ReadSingleMessageAsync<TRequest>(RequestParser); var reply = await _handler(service, request!, serverCallContext); await httpContext.Response.BodyWriter.WriteMessageAsync(reply); } }
请求消息是通过如下这个ReadSingleMessageAsync<TMessage>方法读取出来的。按照gRPC协议，通过网络传输的请求和响应消息都会在前面追加5个字节，第一个字节表示消息是否经过加密，后面四个字节是一个以大端序表示的整数，表示消息的长度。对于其他消息交换模式，也是调用Buffers的TryReadMessage<TRequest>方法从缓冲区中读取请求消息。
public static async Task<TMessage> ReadSingleMessageAsync<TMessage>(this PipeReader reader, MessageParser<TMessage> parser) where TMessage:IMessage<TMessage> { while (true) { var result = await reader.ReadAsync(); var buffer = result.Buffer; if (Buffers.TryReadMessage(parser, ref buffer, out var message)) { return message!; } reader.AdvanceTo(buffer.Start, buffer.End); if (result.IsCompleted) { break; } } throw new IOException("Fails to read message."); } internal static class Buffers { public static readonly int HeaderLength = 5; public static bool TryReadMessage<TRequest>(MessageParser<TRequest> parser, ref ReadOnlySequence<byte> buffer, out TRequest? message) where TRequest: IMessage<TRequest> { if (buffer.Length < HeaderLength) { message = default; return false; } Span<byte> lengthBytes = stackalloc byte[4]; buffer.Slice(1, 4).CopyTo(lengthBytes); var length = BinaryPrimitives.ReadInt32BigEndian(lengthBytes); if (buffer.Length < length + HeaderLength) { message = default; return false; } message = parser.ParseFrom(buffer.Slice(HeaderLength, length)); buffer = buffer.Slice(length + HeaderLength); return true; } }
如下这个WriteMessageAsync扩展方法负责输出响应消息。
public static ValueTask<FlushResult> WriteMessageAsync(this PipeWriter writer, IMessage message) { var length = message.CalculateSize(); var span = writer.GetSpan(5 + length); span[0] = 0; BinaryPrimitives.WriteInt32BigEndian(span.Slice(1, 4), length); message.WriteTo(span.Slice(5, length)); writer.Advance(5 + length); return writer.FlushAsync(); }
ClientStreamingCallHandler
ClientStreamingCallHandler<TService, TRequest, TResponse>代表Client Streaming模式下的ServerCallHandler，它由对应的ClientStreamingMethod<TService, TRequest, TResponse>委托创建而成。在重写的HandleCallAsyncCore方法中，除了服务实例，它还需要一个用来以“流”的方式读取请求的IAsyncStreamReader<TRequest>对象，它们都将作为参数传递给指定的委托，后者执行后会返回最终的响应消息。此消息同样通过上面这个WriteMessageAsync扩展方法予以回复。
internal class ClientStreamingCallHandler<TService, TRequest, TResponse> : ServerCallHandler<TService, TRequest, TResponse> where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { private readonly ClientStreamingMethod<TService, TRequest, TResponse> _handler; public ClientStreamingCallHandler(ClientStreamingMethod<TService, TRequest, TResponse> handler, MessageParser<TRequest> requestParser) :base(requestParser) { _handler = handler; } protected override async Task HandleCallAsyncCore(ServerCallContext serverCallContext) { using var scope = serverCallContext.HttpContext.RequestServices.CreateScope(); var service = ActivatorUtilities.CreateInstance<TService>(scope.ServiceProvider); var reader = serverCallContext.HttpContext.Request.BodyReader; var writer = serverCallContext.HttpContext.Response.BodyWriter; var streamReader = new HttpContextStreamReader<TRequest>(serverCallContext.HttpContext, RequestParser); var response = await _handler(service, streamReader, serverCallContext); await writer.WriteMessageAsync(response); } }
IAsyncStreamReader<T>接口的实现类型为如下这个HttpContextStreamReader<T>。在了解了请求消息在网络中的结构之后，对于实现在该类型中针对请求的读取操作，应该不难理解。
public class HttpContextStreamReader<T> : IAsyncStreamReader<T> where T : IMessage<T> { private readonly PipeReader _reader; private readonly MessageParser<T> _parser; private ReadOnlySequence<byte> _buffer; public HttpContextStreamReader(HttpContext httpContext, MessageParser<T> parser) { _reader = httpContext.Request.BodyReader; _parser = parser; } public T Current { get; private set; } = default!; public async Task<bool> MoveNext(CancellationToken cancellationToken) { var completed = false; if (_buffer.IsEmpty) { var result = await _reader.ReadAsync(cancellationToken); _buffer = result.Buffer; completed = result.IsCompleted; } if (Buffers.TryReadMessage(_parser, ref _buffer, out var mssage)) { Current = mssage!; _reader.AdvanceTo(_buffer.Start, _buffer.End); return true; } _reader.AdvanceTo(_buffer.Start, _buffer.End); _buffer = default; return !completed && await MoveNext(cancellationToken); } }
ServerStreamingCallHandler
ServerStreamingCallHandler<TService, TRequest, TResponse>代表Server Streaming模式下的ServerCallHandler，它由对应的ServerStreamingMethod<TService, TRequest, TResponse>委托创建而成。在重写的HandleCallAsyncCore方法中，除了服务实例，它还需要一个用来以“流”的方式写入响应的IAsyncStreamWriter<TResponse>对象，它们都将作为参数传递给指定的委托。
internal class ServerStreamingCallHandler<TService, TRequest, TResponse> : ServerCallHandler<TService, TRequest, TResponse> where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { private readonly ServerStreamingMethod<TService, TRequest, TResponse> _handler; public ServerStreamingCallHandler(ServerStreamingMethod<TService, TRequest, TResponse> handler, MessageParser<TRequest> requestParser):base(requestParser) => _handler = handler; protected override async Task HandleCallAsyncCore(ServerCallContext serverCallContext) { using var scope = serverCallContext.HttpContext.RequestServices.CreateScope(); var service = ActivatorUtilities.CreateInstance<TService>(scope.ServiceProvider); var httpContext = serverCallContext.HttpContext; var streamWriter = new HttpContextStreamWriter<TResponse>(httpContext); var request = await httpContext.Request.BodyReader.ReadSingleMessageAsync(RequestParser); await _handler(service, request, streamWriter, serverCallContext); } }
IAsyncStreamWriter<T>接口的实现类型为如下这个HttpContextStreamWriter<T>，它直接调用上面定义的WriteMessageAsync扩展方法将指定的消息写入响应主体的输出流。
public class HttpContextStreamWriter<T> : IServerStreamWriter<T> where T : IMessage<T> { private readonly PipeWriter _writer; public HttpContextStreamWriter(HttpContext httpContext) => _writer = httpContext.Response.BodyWriter; public Task WriteAsync(T message, CancellationToken cancellationToken = default) { cancellationToken.ThrowIfCancellationRequested(); return _writer.WriteMessageAsync(message).AsTask(); } }
DuplexStreamingCallHandler
DuplexStreamingCallHandler<TService, TRequest, TResponse>代表Duplex Streaming模式下的ServerCallHandler，它由对应的DuplexStreamingMethod<TService, TRequest, TResponse>委托创建而成。在重写的HandleCallAsyncCore方法中，除了服务实例，它还需要分别创建以“流”的方式读/写请求/响应的IAsyncStreamReader<TRequest>和IAsyncStreamWriter<TResponse>对象，对应的类型分别为上面定义的HttpContextStreamReader<TRequest>和HttpContextStreamWriter<TResponse>。
internal class DuplexStreamingCallHandler<TService, TRequest, TResponse> : ServerCallHandler<TService, TRequest, TResponse> where TService : class where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { private readonly DuplexStreamingMethod<TService, TRequest, TResponse> _handler; public DuplexStreamingCallHandler(DuplexStreamingMethod<TService, TRequest, TResponse> handler, MessageParser<TRequest> requestParser) :base(requestParser) => _handler = handler; protected override async Task HandleCallAsyncCore(ServerCallContext serverCallContext) { using var scope = serverCallContext.HttpContext.RequestServices.CreateScope(); var service = ActivatorUtilities.CreateInstance<TService>(scope.ServiceProvider); var reader = serverCallContext.HttpContext.Request.BodyReader; var writer = serverCallContext.HttpContext.Response.BodyWriter; var streamReader = new HttpContextStreamReader<TRequest>(serverCallContext.HttpContext, RequestParser); var streamWriter = new HttpContextStreamWriter<TResponse>(serverCallContext.HttpContext); await _handler(service, streamReader, streamWriter, serverCallContext); } }
四、路由注册
目前我们将针对四种消息交换模式的gRPC方法抽象成对应的泛型委托，并且可以利用它们创建ServerCallHandler，后者可以提供作为路由终结点处理器的RequestDelegate委托。枚举和对应ServerCallHandler之间的映射关系如下所示：
- UnaryMethod<TService, TRequest, TResponse>：UnaryCallHandler<TService, TRequest, TResponse>
- ClientStreamingMethod<TService, TRequest, TResponse>：ClientStreamingCallHandler<TService, TRequest, TResponse>
- ServerStreamingMethod<TService, TRequest, TResponse>：ServerStreamingCallHandler<TService, TRequest, TResponse>
- DuplexStreamingMethod<TService, TRequest, TResponse>：DuplexStreamingCallHandler<TService, TRequest, TResponse>
现在我们将整个路由注册的流程串起来，为此我们定义了如下这个IServiceBinder<TService>接口，它提供了两种方式将定义在服务类型TService中的gRPC方法注册成对应的路由终结点。
public interface IServiceBinder<TService> where TService : class { IServiceBinder<TService> AddUnaryMethod<TRequest, TResponse>(string methodName, Func<TService, Func<TRequest, ServerCallContext, Task<TResponse>>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; IServiceBinder<TService> AddClientStreamingMethod<TRequest, TResponse>(string methodName, Func<TService, Func<IAsyncStreamReader<TRequest>, ServerCallContext, Task<TResponse>>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; IServiceBinder<TService> AddServerStreamingMethod<TRequest, TResponse>(string methodName, Func<TService, Func<TRequest, IServerStreamWriter<TResponse>, ServerCallContext, Task>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; IServiceBinder<TService> AddDuplexStreamingMethod<TRequest, TResponse>(string methodName, Func<TService, Func<IAsyncStreamReader<TRequest>, IServerStreamWriter<TResponse>, ServerCallContext, Task>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; IServiceBinder<TService> AddUnaryMethod<TRequest, TResponse>(Expression<Func<TService, Task<TResponse>>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; IServiceBinder<TService> AddClientStreamingMethod<TRequest, TResponse>( Expression<Func<TService, Task<TResponse>>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; IServiceBinder<TService> AddServerStreamingMethod<TRequest, TResponse>( Expression<Func<TService, Task>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; IServiceBinder<TService> AddDuplexStreamingMethod<TRequest, TResponse>( Expression<Func<TService, Task>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse>; }
路由终结点由路由模式和处理器两个元素组成，路由模式主要体现在由gRPC服务和操作名称组成的路由模板，我们默认使用服务类型的名称和方法名称（提出Async后缀）。为了能够对这两个名称进行定制，我们定义了如下两个特性GrpcServiceAttribute和GrpcMethodAttribute，它们可以分别标注在服务类型和操作方法上来指定一个任意的名称。
[AttributeUsage(AttributeTargets.Class)] public class GrpcServiceAttribute: Attribute { public string? ServiceName { get; set; } } [AttributeUsage(AttributeTargets.Method)] public class GrpcMethodAttribute : Attribute { public string? MethodName { get; set; } }
如下所示的ServiceBinder<TService> 是对IServiceBinder<TService> 接口的实现，它是对一个IEndpointRouteBuilder 对象的封装。对于实现的第一组方法，我们利用提供的方法名称与解析TService类型得到的服务名称合并，进而得到路由终结点的URL模板。这些方法还提供了一个针对gRPC方法签名的Func<TService,Func<…>>委托，我们利用它来将提供用于构建对应ServiceCallHandler的委托。我们最终利用IEndpointRouteBuilder 对象完成针对路由终结点的注册。
public class ServiceBinder<TService> : IServiceBinder<TService> where TService : class { private readonly IEndpointRouteBuilder _routeBuilder; public ServiceBinder(IEndpointRouteBuilder routeBuilder) => _routeBuilder = routeBuilder; public IServiceBinder<TService> AddUnaryMethod<TRequest, TResponse>(string methodName, Func<TService, Func<TRequest, ServerCallContext, Task<TResponse>>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { Task<TResponse> GetMethod(TService service, TRequest request, ServerCallContext context) => methodAccessor(service)(request, context); var callHandler = new UnaryCallHandler<TService, TRequest, TResponse>(GetMethod, parser); _routeBuilder.MapPost(ServiceBinder<TService>.GetPath(methodName), callHandler.HandleCallAsync); return this; } public IServiceBinder<TService> AddClientStreamingMethod<TRequest, TResponse>(string methodName, Func<TService, Func<IAsyncStreamReader<TRequest>, ServerCallContext, Task<TResponse>>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { Task<TResponse> GetMethod(TService service, IAsyncStreamReader<TRequest> reader, ServerCallContext context) => methodAccessor(service)(reader, context); var callHandler = new ClientStreamingCallHandler<TService, TRequest, TResponse>(GetMethod, parser); _routeBuilder.MapPost(ServiceBinder<TService>.GetPath(methodName), callHandler.HandleCallAsync); return this; } public IServiceBinder<TService> AddServerStreamingMethod<TRequest, TResponse>(string methodName, Func<TService, Func<TRequest, IServerStreamWriter<TResponse>, ServerCallContext, Task>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { ServerStreamingMethod<TService, TRequest, TResponse> handler = (service, request, writer, context) => methodAccessor(service)(request, writer, context); var callHandler = new ServerStreamingCallHandler<TService, TRequest, TResponse>(handler, parser); _routeBuilder.MapPost(ServiceBinder<TService>.GetPath(methodName), callHandler.HandleCallAsync); return this; } public IServiceBinder<TService> AddDuplexStreamingMethod<TRequest, TResponse>(string methodName, Func<TService, Func<IAsyncStreamReader<TRequest>, IServerStreamWriter<TResponse>, ServerCallContext, Task>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { DuplexStreamingMethod<TService, TRequest, TResponse> handler = (service, reader, writer, context) => methodAccessor(service)(reader, writer, context); var callHandler = new DuplexStreamingCallHandler<TService, TRequest, TResponse>(handler, parser); _routeBuilder.MapPost(ServiceBinder<TService>.GetPath(methodName), callHandler.HandleCallAsync); return this; } private static string GetPath(string methodName) { var serviceName = typeof(TService).GetCustomAttribute<GrpcServiceAttribute>()?.ServiceName ?? typeof(TService).Name; if (methodName.EndsWith("Async")) { methodName = methodName.Substring(0, methodName.Length - 5); } return $"{serviceName}/{methodName}"; } public IServiceBinder<TService> AddUnaryMethod<TRequest, TResponse>(Expression<Func<TService, Task<TResponse>>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { var method = CreateDelegate<UnaryMethod<TService, TRequest,TResponse>>(methodAccessor, out var methodName); var serviceName = typeof(TService).GetCustomAttribute<GrpcServiceAttribute>()?.ServiceName ?? typeof(TService).Name; var callHandler = new UnaryCallHandler<TService, TRequest, TResponse>(method, parser); _routeBuilder.MapPost(ServiceBinder<TService>.GetPath(methodName), callHandler.HandleCallAsync); return this; } public IServiceBinder<TService> AddClientStreamingMethod<TRequest, TResponse>( Expression<Func<TService, Task<TResponse>>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { var method = CreateDelegate<ClientStreamingMethod<TService, TRequest, TResponse>>(methodAccessor, out var methodName); var serviceName = typeof(TService).GetCustomAttribute<GrpcServiceAttribute>()?.ServiceName ?? typeof(TService).Name; var callHandler = new ClientStreamingCallHandler<TService, TRequest, TResponse>(method, parser); _routeBuilder.MapPost(ServiceBinder<TService>.GetPath(methodName), callHandler.HandleCallAsync); return this; } public IServiceBinder<TService> AddServerStreamingMethod<TRequest, TResponse>(Expression<Func<TService, Task>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { var method = CreateDelegate<ServerStreamingMethod<TService, TRequest, TResponse>>(methodAccessor, out var methodName); var serviceName = typeof(TService).GetCustomAttribute<GrpcServiceAttribute>()?.ServiceName ?? typeof(TService).Name; var callHandler = new ServerStreamingCallHandler<TService, TRequest, TResponse>(method, parser); _routeBuilder.MapPost(ServiceBinder<TService>.GetPath(methodName), callHandler.HandleCallAsync); return this; } public IServiceBinder<TService> AddDuplexStreamingMethod<TRequest, TResponse>(Expression<Func<TService, Task>> methodAccessor, MessageParser<TRequest> parser) where TRequest : IMessage<TRequest> where TResponse : IMessage<TResponse> { var method = CreateDelegate<DuplexStreamingMethod<TService, TRequest, TResponse>>(methodAccessor, out var methodName); var serviceName = typeof(TService).GetCustomAttribute<GrpcServiceAttribute>()?.ServiceName ?? typeof(TService).Name; var callHandler = new DuplexStreamingCallHandler<TService, TRequest, TResponse>(method, parser); _routeBuilder.MapPost(ServiceBinder<TService>.GetPath(methodName), callHandler.HandleCallAsync); return this; } private TDelegate CreateDelegate<TDelegate>(LambdaExpression expression, out string methodName) where TDelegate : Delegate { var method = ((MethodCallExpression)expression.Body).Method; methodName = method.GetCustomAttribute<GrpcMethodAttribute>()?.MethodName ?? method.Name; return (TDelegate)Delegate.CreateDelegate(typeof(TDelegate), method); } }
由于第二组方法提供的针对gRPC方法调用的表达式，所以我们可以得到描述方法的MethodInfo对象，该对象不但解决了委托对象的创建问题，还可以提供方法的名称，所以这组方法无需提供gRPC方法的名称。但是提供的表达式并不能严格匹配方法的签名，所以无法提供编译时的错误检验，所以各有优缺点。
五、为gRPC服务定义一个接口
由于路由终结点的注册是针对服务类型进行的，所以我们决定让服务类型自身来完成所有的路由注册工作。在这里我们使用C# 11中一个叫做“静态接口方法”的特性，为服务类型定义如下这个IGrpcService<TService>接口，服务类型TService定义的所有gRPC方法的路由注册全部在静态方法Bind中完成，该方法将上述的IServiceBinder<TService>作为参数。
public interface IGrpcService<TService> where TService:class { static abstract void Bind(IServiceBinder<TService> binder); }
我们定义了如下这个针对IEndpointRouteBuilder 接口的扩展方法完成针对指定服务类型的路由注册。为了与现有的方法区别开来，我特意将其命名为MapGrpcService2。该方法根据指定的IEndpointRouteBuilder 对象将ServiceBinder<TService>对象创建出来，并作为参数调用服务类型的静态Bind方法。到此为止，整个Mini版的gRPC服务端框架就构建完成了，接下来我们看看它能否工作。
public static class EndpointRouteBuilderExtensions { public static IEndpointRouteBuilder MapGrpcService2<TService>(this IEndpointRouteBuilder routeBuilder) where TService : class, IGrpcService<TService> { var binder = new ServiceBinder<TService>(routeBuilder); TService.Bind(binder); return routeBuilder; } }
六、重新定义和承载服务
我们开篇演示了ASP.NET Core gRPC的服务定义、承载和调用。如果我们上面构建的Mini版gRPC框架能够正常工作，意味着客户端代码可以保持不变，我们现在就来试试看。我们在Server项目中将GreeterService服务类型改成如下的形式，它不再继承任何基类，只实现IGrpcService<GreeterService>接口。针对四种消息交换模式的四个方法的实现方法保持不变，在实现的静态Bind方法中，我们采用两种形式完成了针对这四个方法的路由注册。
[GrpcService(ServiceName = "Greeter")] public class GreeterService: IGrpcService<GreeterService> { public Task<HelloReply> SayHelloUnaryAsync(HelloRequest request, ServerCallContext context) => Task.FromResult(new HelloReply { Message = $"Hello, {request.Name}" }); public async Task<HelloReply> SayHelloClientStreamingAsync(IAsyncStreamReader<HelloRequest> reader, ServerCallContext context) { var list = new List<string>(); while (await reader.MoveNext(CancellationToken.None)) { list.Add(reader.Current.Name); } return new HelloReply { Message = $"Hello, {string.Join(",", list)}" }; } public async Task SayHelloServerStreamingAsync(Empty request, IServerStreamWriter<HelloReply> responseStream, ServerCallContext context) { await responseStream.WriteAsync(new HelloReply { Message = "Hello, Foo!" }); await Task.Delay(1000); await responseStream.WriteAsync(new HelloReply { Message = "Hello, Bar!" }); await Task.Delay(1000); await responseStream.WriteAsync(new HelloReply { Message = "Hello, Baz!" }); } public async Task SayHelloDuplexStreamingAsync(IAsyncStreamReader<HelloRequest> reader, IServerStreamWriter<HelloReply> writer, ServerCallContext context) { while (await reader.MoveNext()) { await writer.WriteAsync(new HelloReply { Message = $"Hello {reader.Current.Name}" }); } } public static void Bind(IServiceBinder<GreeterService> binder) { binder
.AddUnaryMethod<HelloRequest, HelloReply>(it =>it.SayHelloUnaryAsync(default!,default!), HelloRequest.Parser) .AddClientStreamingMethod<HelloRequest, HelloReply>(it => it.SayHelloClientStreamingAsync(default!, default!), HelloRequest.Parser)
.AddServerStreamingMethod<Empty, HelloReply>(nameof(SayHelloServerStreamingAsync), it => it.SayHelloServerStreamingAsync, Empty.Parser) .AddDuplexStreamingMethod<HelloRequest, HelloReply>(nameof(SayHelloDuplexStreamingAsync), it => it.SayHelloDuplexStreamingAsync, HelloRequest.Parser); }
}
服务承载程序直接将针对MapGrpcService<GreeterService>方法的调用换成MapGrpcService2<GreeterService>。由于整个框架根本不需要预先注册任何的服务，所以针对AddGrpc扩展方法的调用也可以删除。
using GrpcMini; using Microsoft.AspNetCore.Server.Kestrel.Core; var builder = WebApplication.CreateBuilder(args); builder.WebHost.ConfigureKestrel(kestrel => kestrel.ConfigureEndpointDefaults(options => options.Protocols = HttpProtocols.Http2)); var app = builder.Build(); app.MapGrpcService2<Server.Greeter>(); app.Run();
再次运行我们的程序，客户端依然可以得到相同的输出。
![洛谷 P11345 [KTSC 2023 R2] 基地简化 题解](http://www.itfaba.com/wp-content/themes/kemi/timthumb.php?src=http://www.itfaba.com/wp-content/themes/kemi/img/random/2.jpg&w=218&h=124&zc=1)
