196 lines
8.8 KiB
Markdown
196 lines
8.8 KiB
Markdown
### Introduction
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Spring Cloud Function allows you to invoke function via [gRPC](https://grpc.io/). While you can read more about gRPC in te provided link, this section will describe the parts relevant to Spring Cloud Function integration.
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As with all other Spring-boot based frameworks all you need to do is add `spring-cloud-function-grpc` dependency to your POM.
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```xml
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<dependency>
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<groupId>org.springframework.cloud</groupId>
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<artifactId>spring-cloud-function-grpc</artifactId>
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<version>${current.version}</version>
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</dependency>
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```
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### Programming model
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#### Two operation modes (client/server)
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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
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only be interested in client-side utilities to invoke a function exposed via gRPC server running on some host/port.
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To support these two modes Spring Cloud Function provides `spring.cloud.function.grpc.server` which defaults to `true`.
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This means that the default mode of operation is _server_, since the core intention of our current gRPC support is to expose user Functions 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`.
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In the server (default) mode, te gRPC server would be bound to te default port ***6048***. You can change it by providing
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`spring.cloud.function.grpc.port` property.
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#### Core Data and Service
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At the center of gRPC and Spring Cloud Function integration is a canonical protobuff structure - `GrpcMessage`. It is modeled after Spring [Message](https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/messaging/Message.html).
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```
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message GrpcMessage {
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bytes payload = 1;
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map<string, string> headers = 2;
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}
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```
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As you can see it is a very generic structure which can support any type of data amd metadata you wish to exchange.
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It alos defines a `MessagingService` allowing you to generate required stubs to support true plolyglot nature of gRPC.
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```
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service MessagingService {
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rpc biStream(stream GrpcMessage) returns (stream GrpcMessage);
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rpc clientStream(stream GrpcMessage) returns (GrpcMessage);
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rpc serverStream(GrpcMessage) returns (stream GrpcMessage);
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rpc requestReply(GrpcMessage) returns (GrpcMessage);
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}
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```
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That said, when using Java, you do not need to generate anything, rather identify function definition and send and receive Spring `Messages`.
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You can get a pretty good idea from this [test case](https://github.com/spring-cloud/spring-cloud-function/blob/82e2583acd7c8aaaf2bc5ec935d486a336e97ae7/spring-cloud-function-grpc/src/test/java/org/springframework/cloud/function/grpc/GrpcInteractionTests.java#L49).
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#### 4 Interaction RPC Modes
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The gRPC provides 4 interaction modes
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* Reques/Repply RPC
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* Server-side streaming RPC
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* Client-side streaming RPC
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* Bi-directional streaming RPC
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Spring Cloud Function provides support for all 4 of them.
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##### Request Reply RPC
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The most straight forward interaction mode is _Request/Reply_.
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Suppose you have a function
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```java
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@EnableAutoConfiguration
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public static class SampleConfiguration {
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@Bean
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public Function<String, String> uppercase() {
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return v -> v.toUpperCase();
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}
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}
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```
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After identifying this function via `spring.cloud.function.definition` property (see example [here](https://github.com/spring-cloud/spring-cloud-function/blob/ded02fec0a6d3d66b8ec00f99f28be2a4bbec668/spring-cloud-function-grpc/src/test/java/org/springframework/cloud/function/grpc/GrpcInteractionTests.java)),
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you can invoke it using utility method(s) provided in `GrpcUtils` class
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```java
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Message<byte[]> message = MessageBuilder.withPayload("\"hello gRPC\"".getBytes())
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.setHeader("foo", "bar")
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.build();
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Message<byte[]> reply = GrpcUtils.requestReply(message);
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```
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You can also provide `spring.cloud.function.definition` property via `Message` headers, to support more dynamic cases.
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```java
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Message<byte[]> message = MessageBuilder.withPayload("\"hello gRPC\"".getBytes())
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.setHeader("foo", "bar")
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.setHeader("spring.cloud.function.definition", "reverse")
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.build();
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```
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##### Server-side streaming RPC
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The Server-side streaming RPC allows you to reply with the stream of data.
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```java
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@EnableAutoConfiguration
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public static class SampleConfiguration {
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@Bean
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public Function<String, Flux<String>> stringInStreamOut() {
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return value -> Flux.just(value, value.toUpperCase());
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}
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}
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```
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After identifying this function via `spring.cloud.function.definition` property (see example [here](https://github.com/spring-cloud/spring-cloud-function/blob/ded02fec0a6d3d66b8ec00f99f28be2a4bbec668/spring-cloud-function-grpc/src/test/java/org/springframework/cloud/function/grpc/GrpcInteractionTests.java)),
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you can invoke it using utility method(s) provided in `GrpcUtils` class
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```java
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Message<byte[]> message = MessageBuilder.withPayload("\"hello gRPC\"".getBytes()).setHeader("foo", "bar").build();
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Flux<Message<byte[]>> reply =
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GrpcUtils.serverStream("localhost", FunctionGrpcProperties.GRPC_PORT, message);
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List<Message<byte[]>> results = reply.collectList().block(Duration.ofSeconds(5));
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```
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You can see that gRPC stream is mapped to instance of `Flux` from [project reactor](https://projectreactor.io/)
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Similarly to the _request/reply_ you can also provide `spring.cloud.function.definition` property via `Message` headers, to support more dynamic cases.
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```java
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Message<byte[]> message = MessageBuilder.withPayload("\"hello gRPC\"".getBytes())
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.setHeader("foo", "bar")
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.setHeader("spring.cloud.function.definition", "reverse")
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.build();
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```
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##### Client-side streaming RPC
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The Client-side streaming RPC allows you to stream input data and receive a single reply.
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```java
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@EnableAutoConfiguration
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public static class SampleConfiguration {
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@Bean
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public Function<Flux<String>, String> streamInStringOut() {
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return flux -> flux.doOnNext(v -> {
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try {
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// do something useful
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Thread.sleep(new Random().nextInt(2000)); // artificial delay
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}
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catch (Exception e) {
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// ignore
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}
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}).collectList().block().toString();
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}
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}
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```
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After identifying this function via `spring.cloud.function.definition` property (see example [here](https://github.com/spring-cloud/spring-cloud-function/blob/ded02fec0a6d3d66b8ec00f99f28be2a4bbec668/spring-cloud-function-grpc/src/test/java/org/springframework/cloud/function/grpc/GrpcInteractionTests.java)),
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you can invoke it using utility method(s) provided in `GrpcUtils` class
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```java
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List<Message<byte[]>> messages = new ArrayList<>();
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messages.add(MessageBuilder.withPayload("\"Ricky\"".getBytes()).setHeader("foo", "bar")
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.build());
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messages.add(MessageBuilder.withPayload("\"Julien\"".getBytes()).setHeader("foo", "bar")
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.build());
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messages.add(MessageBuilder.withPayload("\"Bubbles\"".getBytes()).setHeader("foo", "bar")
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.build());
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Message<byte[]> reply =
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GrpcUtils.clientStream("localhost", FunctionGrpcProperties.GRPC_PORT, Flux.fromIterable(messages));
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```
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You can see that gRPC stream is mapped to instance of `Flux` from [project reactor](https://projectreactor.io/)
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Unlike the _request/reply_ and _server-side streaming_, you can ONLY pass function definition via property or environment variable.
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##### Bi-Directional streaming RPC
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The bi-directional streaming RPC allows you to stream input and output data.
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```java
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@EnableAutoConfiguration
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public static class SampleConfiguration {
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@Bean
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public Function<Flux<String>, Flux<String>> uppercaseReactive() {
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return flux -> flux.map(v -> v.toUpperCase());
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}
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}
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```
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After identifying this function via `spring.cloud.function.definition` property (see example [here](https://github.com/spring-cloud/spring-cloud-function/blob/ded02fec0a6d3d66b8ec00f99f28be2a4bbec668/spring-cloud-function-grpc/src/test/java/org/springframework/cloud/function/grpc/GrpcInteractionTests.java)),
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you can invoke it using utility method(s) provided in `GrpcUtils` class
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```java
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List<Message<byte[]>> messages = new ArrayList<>();
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messages.add(MessageBuilder.withPayload("\"Ricky\"".getBytes()).setHeader("foo", "bar")
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.build());
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messages.add(MessageBuilder.withPayload("\"Julien\"".getBytes()).setHeader("foo", "bar")
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.build());
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messages.add(MessageBuilder.withPayload("\"Bubbles\"".getBytes()).setHeader("foo", "bar")
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.build());
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Flux<Message<byte[]>> clientResponseObserver =
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GrpcUtils.biStreaming("localhost", FunctionGrpcProperties.GRPC_PORT, Flux.fromIterable(messages));
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List<Message<byte[]>> results = clientResponseObserver.collectList().block(Duration.ofSeconds(1));
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```
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You can see that gRPC stream is mapped to instance of `Flux` from [project reactor](https://projectreactor.io/)
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Unlike the _request/reply_ and _server-side streaming_, you can ONLY pass function definition via property or environment variable.
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