Adds routing keys in message headers

If the incoming message has a stream_routekey header, we use that
to route the message to a named function. Also adding the header
to messages coming out of suppliers.

The biggest change here is sort of orthogonal: it fixes a bug where
Spring Integration would subscribe twice to the same input channel
if the FunctionCatalog contains both functions and consumers. Then
when a message comes in it is dispatched to one or the other, but not
both. So the routing key couldn't work without fixing that
problem.

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/StreamConfiguration.java

@@ -132,6 +132,12 @@ public class StreamConfiguration {
 		@Override
 		public ConditionOutcome getMatchOutcome(ConditionContext context,
 				AnnotatedTypeMetadata metadata) {
+			return getMatchOutcomeForType(this.type, context, metadata);
+
+		}
+
+		protected ConditionOutcome getMatchOutcomeForType(Class<?> type,
+				ConditionContext context, AnnotatedTypeMetadata metadata) {
 			if (context.getBeanFactory().getBeanNamesForType(type, false,
 					false).length > 0) {
 				String endpoint = new RelaxedPropertyResolver(context.getEnvironment(),
@@ -175,5 +181,15 @@ public class StreamConfiguration {
 		public ConsumerCondition() {
 			super(Consumer.class);
 		}
+
+		@Override
+		public ConditionOutcome getMatchOutcome(ConditionContext context,
+				AnnotatedTypeMetadata metadata) {
+			if (getMatchOutcomeForType(Function.class, context, metadata).isMatch()) {
+				return ConditionOutcome
+						.noMatch(String.format("bean of type Function detected"));
+			}
+			return super.getMatchOutcome(context, metadata);
+		}
 	}
 }

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/StreamConfigurationProperties.java

@@ -27,11 +27,13 @@ public class StreamConfigurationProperties {
 	private String endpoint;
 
 	/**
-	 * Interval to be used for the Duration (in milliseconds) of a non-Flux producing Supplier.
-	 * Default is 0, which means the Supplier will only be invoked once. 
+	 * Interval to be used for the Duration (in milliseconds) of a non-Flux producing
+	 * Supplier. Default is 0, which means the Supplier will only be invoked once.
 	 */
 	private long interval = 0L;
 
+	public static final String ROUTE_KEY = "stream_routekey";
+
 	public String getEndpoint() {
 		return endpoint;
 	}

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/StreamListeningConsumerInvoker.java

@@ -83,12 +83,22 @@ public class StreamListeningConsumerInvoker implements SmartInitializingSingleto
 				name = names.iterator().next();
 			}
 			else {
-				for (String candidate : names) {
-					Class<?> inputType = functionInspector.getInputType(candidate);
-					Object value = this.converter.fromMessage(input, inputType);
-					if (value != null && inputType.isInstance(value)) {
-						name = candidate;
-						break;
+				if (input.getHeaders()
+						.containsKey(StreamConfigurationProperties.ROUTE_KEY)) {
+					String key = (String) input.getHeaders()
+							.get(StreamConfigurationProperties.ROUTE_KEY);
+					if (functionCatalog.lookupFunction(key) != null) {
+						return key;
+					}
+				}
+				else {
+					for (String candidate : names) {
+						Class<?> inputType = functionInspector.getInputType(candidate);
+						Object value = this.converter.fromMessage(input, inputType);
+						if (value != null && inputType.isInstance(value)) {
+							name = candidate;
+							break;
+						}
 					}
 				}
 			}

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/StreamListeningFunctionInvoker.java

@@ -16,7 +16,14 @@
 
 package org.springframework.cloud.function.stream;
 
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Function;
 
 import org.springframework.beans.factory.SmartInitializingSingleton;
@@ -27,11 +34,13 @@ import org.springframework.cloud.stream.annotation.Output;
 import org.springframework.cloud.stream.annotation.StreamListener;
 import org.springframework.cloud.stream.converter.CompositeMessageConverterFactory;
 import org.springframework.cloud.stream.messaging.Processor;
+import org.springframework.cloud.stream.reactive.FluxSender;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.converter.MessageConverter;
 import org.springframework.messaging.support.MessageBuilder;
 
 import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
 
 /**
  * @author Mark Fisher
@@ -49,7 +58,11 @@ public class StreamListeningFunctionInvoker implements SmartInitializingSingleto
 
 	private final String defaultEndpoint;
 
-	private static final String NOENDPOINT = "__NOENDPOINT__";
+	private final Map<String, FluxMessageProcessor> processors = new HashMap<>();
+
+	private int count = -1;
+
+	private static final FluxMessageProcessor NOENDPOINT = flux -> Flux.empty();
 
 	public StreamListeningFunctionInvoker(FunctionCatalog functionCatalog,
 			FunctionInspector functionInspector,
@@ -66,40 +79,110 @@ public class StreamListeningFunctionInvoker implements SmartInitializingSingleto
 	}
 
 	@StreamListener
-	@Output(Processor.OUTPUT)
-	public Flux<?> handle(@Input(Processor.INPUT) Flux<Message<?>> input) {
-		return input.groupBy(this::select)
-				.filter(group -> functionCatalog.lookupFunction(group.key()) != null)
-				.flatMap(group -> process(group.key(), group));
+	public Mono<Void> handle(@Input(Processor.INPUT) Flux<Message<?>> input,
+			@Output(Processor.OUTPUT) FluxSender output) {
+		return output.send(
+				input.groupBy(this::select).flatMap(group -> group.key().process(group)));
 	}
 
-	private Flux<?> process(String name, Flux<Message<?>> flux) {
-		return (Flux<?>) functionCatalog.lookupFunction(name)
-				.apply(flux.map(message -> convertInput(name).apply(message)));
+	private Flux<Message<?>> function(String name, Flux<Message<?>> flux) {
+		// TODO: the routing key could be added here, but really it should be added in
+		// Spring Cloud Stream
+		// (https://github.com/spring-cloud/spring-cloud-stream/issues/1010)
+		AtomicReference<Map<String, Object>> headers = new AtomicReference<Map<String, Object>>(
+				new LinkedHashMap<>());
+		return ((Flux<?>) functionCatalog.lookupFunction(name).apply(flux.map(message -> {
+			Object applied = convertInput(name).apply(message);
+			headers.set(message.getHeaders());
+			return applied;
+		}))).map(result -> message(result, headers.get()));
 	}
 
-	private String select(Message<?> input) {
+	private Message<?> message(Object result, Map<String, Object> headers) {
+		return result instanceof Message ? (Message<?>) result
+				: MessageBuilder.withPayload(result).copyHeadersIfAbsent(headers).build();
+	}
+
+	private Flux<Message<?>> consumer(String name, Flux<Message<?>> flux) {
+		functionCatalog.lookupConsumer(name)
+				.accept(flux.map(message -> convertInput(name).apply(message)));
+		return Flux.empty();
+	}
+
+	private Flux<Message<?>> balance(List<String> names, Flux<Message<?>> flux) {
+		if (names.isEmpty()) {
+			return Flux.empty();
+		}
+		String name = choose(names);
+		if (functionCatalog.lookupConsumer(name) != null) {
+			return consumer(name, flux);
+		}
+		return function(name, flux);
+	}
+
+	private synchronized String choose(List<String> names) {
+		if (++count >= names.size() || count < 0) {
+			count = 0;
+		}
+		return names.get(count);
+	}
+
+	private FluxMessageProcessor select(Message<?> input) {
 		String name = defaultEndpoint;
+		if (name != null) {
+			name = stash(name);
+		}
 		if (name == null) {
-			Set<String> names = functionCatalog.getFunctionNames();
+			if (input.getHeaders().containsKey(StreamConfigurationProperties.ROUTE_KEY)) {
+				String key = (String) input.getHeaders()
+						.get(StreamConfigurationProperties.ROUTE_KEY);
+				name = stash(key);
+			}
+		}
+		if (name == null) {
+			Set<String> names = new LinkedHashSet<>(functionCatalog.getFunctionNames());
+			names.addAll(functionCatalog.getConsumerNames());
+			List<String> matches = new ArrayList<>();
 			if (names.size() == 1) {
-				name = names.iterator().next();
+				String key = names.iterator().next();
+				name = stash(key);
 			}
 			else {
 				for (String candidate : names) {
 					Class<?> inputType = functionInspector.getInputType(candidate);
 					Object value = this.converter.fromMessage(input, inputType);
 					if (value != null && inputType.isInstance(value)) {
-						name = candidate;
-						break;
+						matches.add(candidate);
 					}
 				}
+				if (matches.size() == 1) {
+					name = stash(matches.iterator().next());
+				}
+				else {
+					return flux -> balance(matches, flux);
+				}
 			}
 		}
 		if (name == null) {
 			return NOENDPOINT;
 		}
-		return name;
+		return processors.get(name);
+	}
+
+	private String stash(String key) {
+		if (functionCatalog.lookupFunction(key) != null) {
+			if (!processors.containsKey(key)) {
+				processors.put(key, flux -> function(key, flux));
+			}
+			return key;
+		}
+		else if (functionCatalog.lookupConsumer(key) != null) {
+			if (!processors.containsKey(key)) {
+				processors.put(key, flux -> consumer(key, flux));
+			}
+			return key;
+		}
+		return null;
 	}
 
 	private Function<Message<?>, Object> convertInput(String name) {
@@ -123,4 +206,9 @@ public class StreamListeningFunctionInvoker implements SmartInitializingSingleto
 			return this.converter.fromMessage(m, inputType);
 		}
 	}
+
+	interface FluxMessageProcessor {
+		Flux<Message<?>> process(Flux<Message<?>> flux);
+	}
+
 }

spring-cloud-function-stream/src/main/java/org/springframework/cloud/function/stream/SupplierInvokingMessageProducer.java

@@ -21,6 +21,7 @@ import java.util.function.Supplier;
 import org.springframework.cloud.function.registry.FunctionCatalog;
 import org.springframework.cloud.stream.messaging.Source;
 import org.springframework.integration.endpoint.MessageProducerSupport;
+import org.springframework.messaging.Message;
 import org.springframework.messaging.support.MessageBuilder;
 import org.springframework.util.Assert;
 
@@ -40,17 +41,19 @@ public class SupplierInvokingMessageProducer<T> extends MessageProducerSupport {
 
 	@Override
 	protected void doStart() {
-		supplier()
-				.subscribe(m -> this.sendMessage(MessageBuilder.withPayload(m).build()));
+		supplier().subscribe(m -> this.sendMessage(m));
 	}
 
-	private Flux<?> supplier() {
+	private Flux<Message<?>> supplier() {
 		Supplier<Flux<?>> supplier = null;
-		Flux<?> result = Flux.empty();
+		Flux<Message<?>> result = Flux.empty();
 		for (String name : functionCatalog.getSupplierNames()) {
 			supplier = functionCatalog.lookupSupplier(name);
 			Assert.notNull(supplier, "Supplier must not be null");
-			result = Flux.merge(result, supplier.get());
+			result = Flux.merge(result,
+					supplier.get().map(payload -> MessageBuilder.withPayload(payload)
+							.setHeader(StreamConfigurationProperties.ROUTE_KEY, name)
+							.build()));
 		}
 		return result;
 	}

spring-cloud-function-stream/src/test/java/org/springframework/cloud/function/stream/mixed/PojoStreamingMixedTests.java

@@ -22,12 +22,14 @@ import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.cloud.function.stream.StreamConfigurationProperties;
 import org.springframework.cloud.stream.messaging.Processor;
 import org.springframework.cloud.stream.test.binder.MessageCollector;
 import org.springframework.context.annotation.Bean;
@@ -53,8 +55,13 @@ public class PojoStreamingMixedTests {
 	@Autowired
 	List<Bar> collector;
 
+	@Before
+	public void init() {
+		collector.clear();
+	}
+
 	@Test
-	public void test() throws Exception {
+	public void balance() throws Exception {
 		processor.input()
 				.send(MessageBuilder.withPayload("{\"name\":\"hello\"}").build());
 		processor.input()
@@ -66,6 +73,19 @@ public class PojoStreamingMixedTests {
 		assertThat(collector).hasSize(1);
 	}
 
+	@Test
+	public void routing() throws Exception {
+		processor.input().send(MessageBuilder.withPayload("{\"name\":\"hello\"}")
+				.setHeader(StreamConfigurationProperties.ROUTE_KEY, "uppercase").build());
+		processor.input().send(MessageBuilder.withPayload("{\"name\":\"world\"}")
+				.setHeader(StreamConfigurationProperties.ROUTE_KEY, "uppercase").build());
+		Message<?> result = messageCollector.forChannel(processor.output()).poll(1000,
+				TimeUnit.MILLISECONDS);
+		assertThat(result.getPayload()).isInstanceOf(Foo.class);
+		// routing key sends messages to the function, not the consumer
+		assertThat(collector).hasSize(0);
+	}
+
 	@SpringBootApplication
 	public static class StreamingFunctionApplication {
 

spring-cloud-function-stream/src/test/java/org/springframework/cloud/function/stream/supplier/StreamSupplierTests.java

@@ -25,6 +25,7 @@ import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.cloud.function.stream.StreamConfigurationProperties;
 import org.springframework.cloud.stream.messaging.Source;
 import org.springframework.cloud.stream.test.binder.MessageCollector;
 import org.springframework.context.annotation.Bean;
@@ -48,8 +49,11 @@ public class StreamSupplierTests {
 
 	@Test
 	public void test() throws Exception {
-		Message<?> result = messageCollector.forChannel(source.output()).poll(1000, TimeUnit.MILLISECONDS);
+		Message<?> result = messageCollector.forChannel(source.output()).poll(1000,
+				TimeUnit.MILLISECONDS);
 		assertThat(result.getPayload()).isEqualTo("foo");
+		assertThat(result.getHeaders().get(StreamConfigurationProperties.ROUTE_KEY))
+				.isEqualTo("simpleSupplier");
 	}
 
 	@SpringBootApplication