Introduction
Spring Cloud Function allows you to invoke function via gRPC. While you can read more about gRPC in te provided link, this section will describe the parts relevant to Spring Cloud Function integration.
As with all other Spring-boot based frameworks all you need to do is add spring-cloud-function-grpc dependency to your POM.
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-function-grpc</artifactId>
<version>${current.version}</version>
</dependency>
Programming model
Spring Cloud Function gRPC support provides two modes of operation - client and server. In other words when you add spring-cloud-function-grpc dependency to your POM you may or may not want the gRPC server as you may
only be interested in client-side utilities to invoke a function exposed via gRPC server running on some host/port.
To support these two modes Spring Cloud Function provides spring.cloud.function.grpc.server which defaults to true.
This means that the default mode of operation is server, since the core imtention of gRPC support is to expose user Function via gRPC. However, if you're only inteersted in using client-side utilities (e.g., GrpcUtils to help to invoke a function or convert GrpcMessage to Spring Message and vice versa), you can set this property to false.
Hoever if you intention is to
At the center of gRPC and Spring Cloud Function integration is a canonical protobuff structure - GrpcMessage. It is modeled after Spring Message.
message GrpcMessage {
bytes payload = 1;
map<string, string> headers = 2;
}
As you can see it is a very generic structure which can support any type of data amd metadata you wish to exchange.
It alos defines a MessagingService allowing you to generate required stubs to support true plolyglot nature of gRPC.
service MessagingService {
rpc biStream(stream GrpcMessage) returns (stream GrpcMessage);
rpc clientStream(stream GrpcMessage) returns (GrpcMessage);
rpc serverStream(GrpcMessage) returns (stream GrpcMessage);
rpc requestReply(GrpcMessage) returns (GrpcMessage);
}
That said, when using Java, you do not need to generate anything, rather identify function definition and send and receive Spring Messages.
You can get a pretty good idea from this test case.
4 Interaction Modes
The gRPC provides 4 interaction modes
- Reques/Repply
- Server-side streaming
- Client-side streaming
- Bi-directional streaming
Spring Cloud Function provides support for all 4 of them.
Request Reply
The most straight forward interaction mode is Request/Reply. Suppose you have a function
@EnableAutoConfiguration
public static class SampleConfiguration {
@Bean
public Function<String, String> uppercase() {
return v -> v.toUpperCase();
}
}
You can invoke it using utility method(s) provided in GrpcUtils class
Message<byte[]> message = MessageBuilder.withPayload("\"hello gRPC\"".getBytes())
.setHeader("foo", "bar")
.build();
Message<byte[]> reply = GrpcUtils.requestReply(message);