GH-944 Remove deprecations and update documentation for MessageRoutingCallback

Resolves #944

docs/src/main/asciidoc/spring-cloud-function.adoc

@@ -193,17 +193,6 @@ public MessageRoutingCallback customRouter() {
 In the preceding example you can see a very simple implementation of `MessageRoutingCallback` which determines the function definition from 
 `func_name` Message header of the incoming Message and returns the instance of `FunctionRoutingResult` containing the definition of function to invoke.
 
-Additionally, the `FunctionRoutingResult` provides another constructor allowing you to provide an instance of `Message` as second argument to be used down stream. 
-This is primarily for runtime optimizations. To better understand this case let's look at the following scenario. 
-You need to route based on the payoload type. However, an input Message typically comes in as let's say JSON payload (as `byte[]`) . In order 
-to determine the route-to function definition you need to first process such JSON and potentially create an instance of the target type.
-Once that determination is done you can pass it to `RoutingFunction` which still has a reference to the original Message with un-processed payload
-This means that somewhere downstream, type conversion/transformation would need to be repeated. 
-
-Allowing you to create a new `Message` with converted payload as part of the `FunctionRoutingResult` will instruct `RoutingFunction` to use such `Message` 
-downstream. So effectively you letting the framework to benefit from the work you already did. 
-
-
 *Message Headers*
 
 If the input argument is of type `Message<?>`, you can communicate routing instruction by setting one of

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

@@ -32,17 +32,9 @@ import org.springframework.messaging.Message;
  */
 public interface MessageRoutingCallback {
 
-	/**
-	 * @deprecated in 3.1 in favor of {@link #routingResult(Message)}
-	 */
-	@Deprecated
-	default String functionDefinition(Message<?> message) {
-		return null;
-	}
-
 	/**
 	 * Computes and returns the instance of {@link FunctionRoutingResult} which encapsulates,
-	 * at the very minimum, function definition and optionally Message to be used downstream.
+	 * at the very minimum, function definition.
 	 * <br><br>
 	 * Providing such message is primarily an optimization feature. It could be useful for cases
 	 * where routing procedure is complex and results in, let's say, conversion of the payload to
@@ -52,39 +44,7 @@ public interface MessageRoutingCallback {
 	 * @param message input message
 	 * @return instance of {@link FunctionRoutingResult} containing the result of the routing computation
 	 */
-	default FunctionRoutingResult routingResult(Message<?> message) {
-		return new FunctionRoutingResult(functionDefinition(message));
-	}
-
-	/**
-	 * Domain object that represents the result of the {@link MessageRoutingCallback#routingResult(Message)}
-	 * computation. It consists of function definition and optional Message to be used downstream
-	 * (see {@link MessageRoutingCallback#routingResult(Message)} for more details.
-	 *
-	 * @author Oleg Zhurakousky
-	 *
-	 */
-	final class FunctionRoutingResult {
-
-		private final String functionDefinition;
-
-		private final Message<?> message;
-
-		FunctionRoutingResult(String functionDefinition, Message<?> message) {
-			this.functionDefinition = functionDefinition;
-			this.message = message;
-		}
-
-		public FunctionRoutingResult(String functionDefinition) {
-			this(functionDefinition, null);
-		}
-
-		public String getFunctionDefinition() {
-			return functionDefinition;
-		}
-
-		public Message<?> getMessage() {
-			return message;
-		}
+	default String routingResult(Message<?> message) {
+		return (String) message.getHeaders().get(FunctionProperties.FUNCTION_DEFINITION);
 	}
 }

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

@@ -28,7 +28,6 @@ import reactor.core.publisher.Mono;
 import org.springframework.cloud.function.context.FunctionCatalog;
 import org.springframework.cloud.function.context.FunctionProperties;
 import org.springframework.cloud.function.context.MessageRoutingCallback;
-import org.springframework.cloud.function.context.MessageRoutingCallback.FunctionRoutingResult;
 import org.springframework.cloud.function.context.catalog.SimpleFunctionRegistry.FunctionInvocationWrapper;
 import org.springframework.cloud.function.context.message.MessageUtils;
 import org.springframework.context.expression.MapAccessor;
@@ -123,14 +122,9 @@ public class RoutingFunction implements Function<Object, Object> {
 		if (input instanceof Message) {
 			Message<?> message = (Message<?>) input;
 			if (this.routingCallback != null) {
-				FunctionRoutingResult routingResult = this.routingCallback.routingResult(message);
-				if (routingResult != null) {
-					if (StringUtils.hasText(routingResult.getFunctionDefinition())) {
-						function = this.functionFromDefinition(routingResult.getFunctionDefinition());
-					}
-					if (routingResult.getMessage() != null) {
-						message = routingResult.getMessage();
-					}
+				String functionDefinition = this.routingCallback.routingResult(message);
+				if (StringUtils.hasText(functionDefinition)) {
+					function = this.functionFromDefinition(functionDefinition);
 				}
 			}
 			if (function == null) {

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/MessageRoutingCallbackTests.java

@@ -80,7 +80,7 @@ public class MessageRoutingCallbackTests {
 			return new MessageRoutingCallback() {
 
 				@Override
-				public FunctionRoutingResult routingResult(Message<?> message) {
+				public String routingResult(Message<?> message) {
 					String payload = new String((byte[]) message.getPayload());
 
 					MessageBuilder<?> builder;
@@ -95,8 +95,7 @@ public class MessageRoutingCallbackTests {
 					}
 					Message<?> m = builder.copyHeaders(message.getHeaders()).build();
 					createdMessageIds.put(functionDefinition, m.getHeaders().getId());
-					FunctionRoutingResult functionRoutingResult = new FunctionRoutingResult(functionDefinition, m);
-					return functionRoutingResult;
+					return functionDefinition;
 				}
 			};
 		}

spring-cloud-function-rsocket/src/test/java/org/springframework/cloud/function/rsocket/MessageRoutingCallbackRSocketTests.java

@@ -109,7 +109,7 @@ public class MessageRoutingCallbackRSocketTests {
 		public MessageRoutingCallback customRouter() {
 			return new MessageRoutingCallback() {
 				@Override
-				public String functionDefinition(Message<?> message) {
+				public String routingResult(Message<?> message) {
 					return (String) message.getHeaders().get("func_name");
 				}
 			};