Unary gRPC on Reactor Netty: Event Loop Serialization, Trailers, and Cancellation

With protocol values and message framing complete, Stage 2 delivered the first end-to-end call: plaintext h2c unary RPC. This is already on main , and Stage 3 and Stage 4 subsequently completed all four RPC cardinalities on the same transport primitive. Previous: Building a Leak-Safe gRPC Frame Decoder on Reactor Netty Method Descriptor Is Where Protocol Meets Types A method requires a precise service name, method name, cardinality, and request/response marshallers: var echo = new GrpcMethod <>( "testing.EchoService" , "Echo" , GrpcMethod . Cardinality . UNARY , new ProtobufMarshaller <>( StringValue . parser ()), new ProtobufMarshaller <>( StringValue . parser ())); The generated path must be: /testing.EchoService/Echo The service registry matches by exact full path. An unknown path returns UNIMPLEMENTED ; registering the same path twice fails immediately when building the service definition. Server Validates Protocol Before Subscribing to Business Logic ReactorGrpcServer uses Reactor Netty h2c: DisposableServer bound = HttpServer . create () . host ( host ) . port ( port ) . protocol ( HttpProtocol . H2C ) . handle ( handler: : handle ) . bindNow ( Duration . ofSeconds ( 10 )); Incoming requests are validated in order: HTTP method must be POST; content-type must be application/grpc or application/grpc+... ; te must declare trailers; path must exist; currently only unary cardinality is allowed; metadata and message size must not exceed limits. Only after validation passes does it create a GrpcCallContext and subscribe to the request body, preventing invalid requests from entering the business handler. HTTP 200 Does Not Mean RPC Success The server writes a compatible content-type first; the final status comes from trailing headers: response . status ( 200 ) . header ( HttpHeaderNames . CONTENT_TYPE , "application/grpc+proto" ); response . trailerHeaders ( trailers -> { GrpcException error = terminal . get (); if ( error == null ) { writeStatus ( trailers , GrpcStatu