Add stream (kafka, Rabbit) and Rsocket examples for Cloud Event

spring-cloud-function-samples/function-sample-cloudevent-stream/README.adoc

@@ -0,0 +1,53 @@
+## Examples of Cloud Events with Spring via AMQP and Apache Kafka
+
+### Introduction
+The current example uses spring-cloud-function framework as its core which allows users to only worry about functional aspects of 
+their requirement while taking care-off non-functional aspects. For more information on Spring Cloud Function please visit 
+our https://spring.io/projects/spring-cloud-function[project page].
+
+The example consists of a Spring boot configuration class 
+https://github.com/spring-cloud/spring-cloud-function/blob/master/spring-cloud-function-samples/function-sample-cloudevent/src/main/java/io/spring/cloudevent/DemoApplication.java[DemoApplication]
+which contains a sample function which you can interact with following via AMQP and Apache Kafka.
+
+### Function as message handler (From RabbitMQ to Apache Kafka)
+
+Assuming you have RabbitMQ and Kafka running, start the application and send a Message to RabbitMQ. You can use RabbitMQ dashboard (if you have it installed)
+and send message to `hire-in-0` exchange.
+To stay compliant with Cloud Event specification you should provide attributes with AMQP appropriate prefixes (i.e., cloudEvents:). For example:
+
+```
+cloudEvents:specversion=1.0
+cloudEvents:type=hire
+cloudEvents:source:spring.io/spring-event
+cloudEvents:id=0001
+```
+
+And your data:
+```
+{"firstName":"John", "lastName":"Doe"}
+```
+
+To simplify this demo part we included a test case which effectively automates this demo by sending Cloud Event to RabbitMQ and receives one from Apache Kafka.
+
+```
+Message<byte[]> messageToAMQP = CloudEventMessageBuilder
+	.withData("{\"firstName\":\"John\", \"lastName\":\"Doe\"}".getBytes())
+	.setSource("https://cloudevent.demo")
+	.setHeader(MessageHeaders.CONTENT_TYPE, MimeTypeUtils.APPLICATION_JSON)
+	.build(CloudEventMessageUtils.AMQP_ATTR_PREFIX);
+
+rabbitTemplate.send("hire-in-0", "#", messageToAMQP);
+Message<String> resultFromKafka = queue.poll(2000, TimeUnit.MILLISECONDS);
+System.out.println("Result Message: " + resultFromKafka);
+. . .
+```
+
+Note how we are using CloudEventMessageBuilder here to only set source as Cloud Event attribute while relying on default values for the rest of the 
+required Cloud Event attributes. We’re also using build(CloudEventMessageUtils.AMQP_ATTR_PREFIX) to ensure that the attributes are prefixed with `cloudEvents:` 
+prefix (see Cloud Events AMQP protocol bindings).
+Also note that on the receiving end Cloud Events attributes are now prefixed with `ce_` prefix (see Cloud Events Kafka protocol bindings), 
+since it was determined by the framework that the target destination is Apache Kafka.
+This last point is worth elaborating a bit. We already established that setting Cloud Event attributes is a non-functional aspect and because 
+of it we’ve exposed a mechanism for you to deal with it outside of your business logic. But what about attribute prefixes? Note that we are running the 
+same code in different execution contexts. This means that the attribute prefixes actually depend on the execution context. So by being aware of the execution 
+context, the framework ensures the correctness of the Cloud Event attribute prefixes.