Overview

gRPC can use protocol buffers as both its Interface Definition Language (IDL) and as its underlying message interchange format.

In gRPC, a client application can directly call a method on a server application on a different machine as if it were a local object, making it easier for you to create distributed applications and services. As in many RPC systems, gRPC is based around the idea of defining a service, specifying the methods that can be called remotely with their parameters and return types. On the server side, the server implements this interface and runs a gRPC server to handle client calls. On the client side, the client has a stub (referred to as just a client in some languages) that provides the same methods as the server.

Trial

# get packages
dart pub get

# run the server
dart bin/server.dart

# open another terminal, run the client
dart bin/client.dart

Basic Tutorial

Define the Service

• simple RPC
• server-side streaming RPC
• client-side streaming RPC
• bidirectional streaming RPC

service RouteGuide {
    # simple RPC
    rpc GetFeature(Point) returns (Feature) {}

    # server to client streaming RPC
    rpc ListFeatures(Rectangle) returns (stream Feature) {}

    # client to server streaming RPC
    rpc RecordRoute(stream Point) returns (RouteSummary) {}

    # bidirectional streaming RPC
    rpm RouteChat(stream RouteNote) returns (stream RouteNote) {}
}

Create the Server

• implementing service interface generated from service definition: doing actual work of our service
• running a gRPC server to listen for requests from clients and dispatch them to the right service implementation

Start the Server

• Create instance of the gRPC server using grpc.Server(), giving list of service implementation
• Call serve() on server to start lisenting for requests, optionally passing in the address and port to listen on. Server will continue to server requests async until shutdown() is called on it

Create the Client

• need to create gRPC channel to communicate with server
• use ChannelOptions to set TLS options for the channel
• need a client stub to perform RPCs
• use CallOptions to set auth credentials when a service require

final channel = ClientChannel(
    '127.0.0.1', 
    port: 8080, 
    options: const ChannelOptions(credentials: ChannelCredentials.insecure())
);
stub = RouteGuideClient(channel, options: CallOptions(timeout: Duration(seconds: 30)));

References

• https://grpc.io/docs/what-is-grpc/introduction/
• Test code: https://github.com/HevaWu/TryProtocolBuffer/tree/main/gRPC/grpc-dart-master/example