GH-731 Add support for SDK CloudEvent type

The type itself comes form cloud event sdk. And while s-c-function provides native support for cloud events, this is necessary for cases when user uses CloudEvent type in the signature of a function

Resolves #731

spring-cloud-function-context/pom.xml

@@ -98,6 +98,12 @@
 			<version>${avro.version}</version>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+		    <groupId>io.cloudevents</groupId>
+		    <artifactId>cloudevents-spring</artifactId>
+		    <version>2.2.0</version>
+		    <optional>true</optional>
+		</dependency>
 	</dependencies>
 	<build>
 		<plugins>

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/cloudevent/CloudEventMessageUtils.java

@@ -234,6 +234,9 @@ public final class CloudEventMessageUtils {
 	static Message<?> toCanonical(Message<?> inputMessage, MessageConverter messageConverter) {
 		Map<String, Object> headers = (Map<String, Object>) ReflectionUtils.getField(MESSAGE_HEADERS, inputMessage.getHeaders());
 		canonicalizeHeaders(headers, false);
+		if (isCloudEvent(inputMessage) && headers.containsKey("content-type")) {
+			inputMessage = MessageBuilder.fromMessage(inputMessage).setHeader(MessageHeaders.CONTENT_TYPE, headers.get("content-type")).build();
+		}
 
 		String inputContentType = (String) inputMessage.getHeaders().get(DATACONTENTTYPE);
 		// first check the obvious and see if content-type is `cloudevents`

spring-cloud-function-context/src/main/java/org/springframework/cloud/function/context/config/ContextFunctionCatalogAutoConfiguration.java

@@ -26,6 +26,7 @@ import java.util.stream.Collectors;
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.gson.Gson;
+import io.cloudevents.spring.messaging.CloudEventMessageConverter;
 
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
@@ -142,6 +143,13 @@ public class ContextFunctionCatalogAutoConfiguration {
 		return new AvroSchemaMessageConverter(new AvroSchemaServiceManagerImpl());
 	}
 
+	@Bean
+	@ConditionalOnMissingBean
+	@ConditionalOnClass(name = "io.cloudevents.spring.messaging.CloudEventMessageConverter")
+	public MessageConverter cloudEventMessageConverter() {
+		return new CloudEventMessageConverter();
+	}
+
 	@Bean(RoutingFunction.FUNCTION_NAME)
 	RoutingFunction functionRouter(FunctionCatalog functionCatalog, FunctionProperties functionProperties,
 								BeanFactory beanFactory, @Nullable MessageRoutingCallback routingCallback) {