In this section we are going to learn the essential of RSocket-RPC and its implementation in Java
RSocket RPC is an easy to use RPC layer that sits on top of RSocket. RSocket is a binary protocol for use on byte stream transports such as TCP, WebSockets, and Aeron. RSocket RPC is able to leverage RSocket’s unique features allowing you develop complex realtime, streaming applications without needing Kafka, Spark, etc. It is completely non-blocking and reactive making it responsive and high performance.
RSocket RPC uses Protobuf 3 as its IDL. Protobuf works well with RSocket because they are both binary. Using Protobuf makes it easy to switch from gRPC. You only need to replace the gRPC compiler with the RSocket RPC compiler to start using RSocket RPC.
RSocket RPC is built with a full duplex protocol RSocket. An application that initiates a connection (traditionally a client) can actually serve requests from the application it is connecting with (traditionally the server). In other words a client can connect to a server, and the server can call a RSocket RPC service located on the client. The server does not have to wait for the client to initiate a call, only the connection is necessary.
RSocket RPC's Java implementation is built using a Reactive Streams compliant library, Reactor-core. RSocket RPC generated code returns either a Flux, which is a stream of many, or a Mono, which is a stream of one. RSocket RPC is compatible with any Reactive Streams implementation including RXJava 2 and Akka Streams.
RSocket RPC respects both RSocket and Reactive Streams back-pressure. Back-pressure is where the consumer of a stream sends the stream's producer a message indicating how many messages it can handle. This makes RSocket RPC services very reliable, and not overwhelmed with demand.
RSocket RPC has five interaction models. They are modeled using a Protobuf 3 IDL. This section details the interaction models, and gives an example Protobuf IDL definition. The interaction models are request/response, request/stream, fire-and-forget, streaming request/one response, and streaming request/streaming response.
Request-response is analogous to a HTTP Rest call. A major difference is that because this is non-blocking the caller can wait for the response for a long time without blocking other requests on the same connection.
rpc RequestReply (SimpleRequest) returns (SimpleResponse) {}
Fire-and-forget sends a request without expecting a response. This is not just ignoring the response; the underlying protocol does not send anything back to the caller. To make a request fire-and-forget with RSocket RPC you need to return google.protobuf.Empty in your IDL. This will generate fire-and-forget code.
import "google/protobuf/empty.proto";
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rpc FireAndForget (SimpleRequest) returns (google.protobuf.Empty) {}
This interaction model sends a single request and then receives multiple responses. This can be used to model subscriptions to topics and queues. It can be also used to do things like page from a database. To generate this, mark the response with the stream keyword.
rpc RequestStream (SimpleRequest) returns (stream SimpleResponse) {}
This interaction model sends a stream of requests and then receives a single response. This can be used to model transactions. You can send multiple requests over a logic channel, and then receive a single response indicating whether they were processed correctly or not. Mark the request with the stream keyword to create this interaction model.
rpc StreamingRequestSingleResponse (stream SimpleRequest) returns (SimpleResponse) {}
This interaction model sends a request stream and returns a response stream. This models a fully-duplex interaction. Mark the request and response with the stream keyword to create this interaction model.
rpc StreamingRequestAndResponse (stream SimpleRequest) returns (stream SimpleResponse) {}
- JDK 1.8
- Gradle 2.x
- Protobuf Compiler 3.x
Mac users can easily install the Protobuf compiler using Homebrew:
$ brew install Protobuf
Ubuntu users can install Protobuf using apt-get:
$ sudo apt-get install libProtobuf-java Protobuf-compiler
RSocket RPC Java uses a Protobuf plugin to generate application code. Add the following code to your project's Gradle file so that it will generate code from your Protobuf IDL when your application is compiled.
protobuf {
protoc {
artifact = 'com.google.protobuf:protoc:3.6.1'
}
plugins {
rsocketRpc {
artifact = 'io.rsocket.rpc:rsocket-rpc-protobuf:0.2.5'
}
}
generateProtoTasks {
all()*.plugins {
rsocketRpc {}
}
}
}
// If you use Intellij add this so it can find the generated classes
idea {
module {
sourceDirs += file("src/main/proto")
sourceDirs += file("src/generated/main/java")
sourceDirs += file("src/generated/main/rsocketRpc")
generatedSourceDirs += file('src/generated/main/java')
generatedSourceDirs += file('src/generated/main/rsocketRpc')
}
}
// clean generated code
clean {
delete 'src/generated/main'
}
After you have installed Protobuf and configured Gradle you need to create a Protobuf IDL to define your service. The following is a simple Protobuf example that defines all the interaction model varieties:
syntax = "proto3";
package io.rsocket.rpc.testing;
import "google/protobuf/empty.proto";
option java_package = "io.rsocket.rpc.testing.protobuf";
option java_outer_classname = "SimpleServiceProto";
option java_multiple_files = true;
service SimpleService {
// Request / Response
rpc RequestReply (SimpleRequest) returns (SimpleResponse) {}
// Fire-and-Forget
rpc FireAndForget (SimpleRequest) returns (google.protobuf.Empty) {}
// Single Request / Streaming Response
rpc RequestStream (SimpleRequest) returns (stream SimpleResponse) {}
// Streaming Request / Single Response
rpc StreamingRequestSingleResponse (stream SimpleRequest) returns (SimpleResponse) {}
// Streaming Request / Streaming Response
rpc StreamingRequestAndResponse (stream SimpleRequest) returns (stream SimpleResponse) {}
}
message SimpleRequest {
string requestMessage = 1;
}
message SimpleResponse {
string responseMessage = 1;
}
After you have configured your Protobuf IDL, use the Protobuf compiler via the Gradle plugin to generate your files:
$ gradlew generateProto
The Protobuf compiler will generate Protobuf builders for the message, and then use the RSocket RPC compiler to generate an interface for the service defined in the IDL. It will also generate a client that implements the interface, and a server takes an implementation of the interface. This is what serves the requests.
Using the above IDL as an example RSocket RPC will generate several classes from the above example, but the ones that you need to concern yourself with are:
SimpleRequestSimpleResponseSimpleServiceSimpleServiceClientSimpleServiceServer
Here is an example implementation of SimpleService, the service contract from the IDL. The SimpleService interface needs to be implemented in order to handle requests:
class DefaultSimpleService implements SimpleService {
@Override
public Mono<Empty> fireAndForget(SimpleRequest message, ByteBuf metadata) {
System.out.println("got message -> " + message.getRequestMessage());
return Mono.just(Empty.getDefaultInstance());
}
@Override
public Mono<SimpleResponse> requestReply(SimpleRequest message, ByteBuf metadata) {
return Mono.fromCallable(
() ->
SimpleResponse.newBuilder()
.setResponseMessage("we got the message -> " + message.getRequestMessage())
.build());
}
@Override
public Mono<SimpleResponse> streamingRequestSingleResponse(Publisher<SimpleRequest> messages, ByteBuf metadata) {
return Flux.from(messages)
.windowTimeout(10, Duration.ofSeconds(500))
.take(1)
.flatMap(Function.identity())
.reduce(
new ConcurrentHashMap<Character, AtomicInteger>(),
(map, s) -> {
char[] chars = s.getRequestMessage().toCharArray();
for (char c : chars) {
map.computeIfAbsent(c, _c -> new AtomicInteger()).incrementAndGet();
}
return map;
})
.map(
map -> {
StringBuilder builder = new StringBuilder();
map.forEach(
(character, atomicInteger) -> {
builder
.append("character -> ")
.append(character)
.append(", count -> ")
.append(atomicInteger.get())
.append("\n");
});
String s = builder.toString();
return SimpleResponse.newBuilder().setResponseMessage(s).build();
});
}
@Override
public Flux<SimpleResponse> requestStream(SimpleRequest message, ByteBuf metadata) {
String requestMessage = message.getRequestMessage();
return Flux.interval(Duration.ofMillis(200))
.onBackpressureDrop()
.map(i -> i + " - got message - " + requestMessage)
.map(s -> SimpleResponse.newBuilder().setResponseMessage(s).build());
}
@Override
public Flux<SimpleResponse> streamingRequestAndResponse(Publisher<SimpleRequest> messages, ByteBuf metadata) {
return Flux.from(messages).flatMap(e -> requestReply(e, metadata));
}
}
The RSocket RPC Compiler generates a client and server interface for you. After you have implemented these generated interfaces you need to hand the implementation to the server. See the below example:
SimpleServiceServer serviceServer = new SimpleServiceServer(new DefaultSimpleService(), Optional.empty(), Optional.empty());
Once you have created an instance of the the server, you need to configure RSocket. The following is a RSocket server configuration
CloseableChannel closeableChannel = RSocketFactory
.receive()
.acceptor((setup, sendingSocket) -> Mono.just(
new RequestHandlingRSocket(serviceServer)
))
.transport(TcpServerTransport.create(8081))
.start()
.block();The RSocket RPC compiler generates a client as well as a server. The client implements the generated interface. You can configure the client either from an RSocket client connection, or server connection. The following shows how to configure an initiator of a connection, typically a client, to send requests to the SimpleService implementation.
RSocket rSocket = RSocketFactory
.connect()
.transport(TcpClientTransport.create(8081))
.start()
.block();
SimpleServiceClient serviceClient = new SimpleServiceClient(rSocket);This configures the receiver of a connection, typically a server, to call the remote SimpleService. Notice that the client is created inside the closure in the acceptor method. The method passes in a variable called sendingSocket. This is the RSocket that is the connection to the client. You can make calls to the client without receiving requests first, or ever.
RSocketFactory.receive()
.acceptor(
(setup, sendingSocket) -> {
SimpleServiceClient client = new SimpleServiceClient(sendingSocket);
// Trivial example - this could also be an RSocket RPC service.
return Mono.just(
new AbstractRSocket() {
@Override
public Mono<Void> fireAndForget(Payload payload) {
return client.fireAndForget(
SimpleRequest.newBuilder()
.setRequestMessage(payload.getDataUtf8())
.build());
}
});
})
.transport(TcpServerTransport.create(8081))
.start()
.block();
Once the client is created, it can be called like any other method. Here is an example call to the streamingRequestSingleResponse method.
SimpleServiceClient client = new SimpleServiceClient(rSocket);
Flux<SimpleRequest> requests =
Flux.range(1, 11)
.map(i -> "sending -> " + i)
.map(s -> SimpleRequest.newBuilder().setRequestMessage(s).build());
SimpleResponse response = client.streamingRequestSingleResponse(requests).block();
System.out.println(response.getResponseMessage());
The above example streams in 11 items to a server. The server receives the stream, counts the most common words, and then returns a message detailing the data received.
See rsocket-rpc-examples for more examples and use-cases.