GH-460 Add support for function filtering

Added support for function filtering in the event there are more then one function in catalog. This is primarily to ensure that
we have a mechanism to specify which functions to export as web enpoints (instead of all)

Resolves #460

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

@@ -24,6 +24,7 @@ import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
@@ -51,6 +52,7 @@ import org.springframework.aop.support.AopUtils;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.FactoryBean;
+import org.springframework.beans.factory.InitializingBean;
 import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.cloud.function.context.FunctionCatalog;
@@ -94,7 +96,7 @@ import org.springframework.util.StringUtils;
  * @since 3.0
  */
 public class BeanFactoryAwareFunctionRegistry
-	implements FunctionRegistry, FunctionInspector, ApplicationContextAware {
+	implements FunctionRegistry, FunctionInspector, ApplicationContextAware, InitializingBean {
 
 	private static Log logger = LogFactory.getLog(BeanFactoryAwareFunctionRegistry.class);
 
@@ -118,10 +120,22 @@ public class BeanFactoryAwareFunctionRegistry
 
 	private final CompositeMessageConverter messageConverter;
 
+	private List<String> declaredFunctionDefinitions;
+
 	public BeanFactoryAwareFunctionRegistry(ConversionService conversionService,
 		@Nullable CompositeMessageConverter messageConverter) {
 		this.conversionService = conversionService;
 		this.messageConverter = messageConverter;
+
+	}
+
+	@Override
+	public void afterPropertiesSet() throws Exception {
+		String userDefinition = this.applicationContext.getEnvironment().getProperty("spring.cloud.function.definition");
+		this.declaredFunctionDefinitions = StringUtils.hasText(userDefinition) ? Arrays.asList(userDefinition.split(";")) : Collections.emptyList();
+		if (this.declaredFunctionDefinitions.contains(RoutingFunction.FUNCTION_NAME)) {
+			Assert.isTrue(this.declaredFunctionDefinitions.size() == 1, "It is illegal to declare more then one function when using RoutingFunction");
+		}
 	}
 
 	@Override
@@ -139,9 +153,36 @@ public class BeanFactoryAwareFunctionRegistry
 	@Override
 	@SuppressWarnings("unchecked")
 	public <T> T lookup(String definition, String... acceptedOutputTypes) {
-		if (!StringUtils.hasText(definition)) {
-			definition = this.applicationContext.getEnvironment().getProperty("spring.cloud.function.definition");
+		definition = StringUtils.hasText(definition) ? definition.replaceAll(",", "|") : "";
+
+		boolean routing = definition.contains(RoutingFunction.FUNCTION_NAME)
+				|| this.declaredFunctionDefinitions.contains(RoutingFunction.FUNCTION_NAME);
+
+		if (!routing && this.declaredFunctionDefinitions.size() > 0) {
+			if (StringUtils.hasText(definition)) {
+				if (this.declaredFunctionDefinitions.size() > 1 &&!this.declaredFunctionDefinitions.contains(definition)) {
+					logger.warn("Attempted to access un-declared function definition '" + definition + "'. Declared functions are '" + this.declaredFunctionDefinitions
+							+ "' specified via `spring.cloud.function.definition` property. If the intention is to access "
+							+ "any function available in FunctionCatalog, please remove `spring.cloud.function.definition` property.");
+					return null;
+				}
+			}
+			else {
+				if (this.declaredFunctionDefinitions.size() == 1) {
+					definition = this.declaredFunctionDefinitions.get(0);
+				}
+				else if (this.declaredFunctionDefinitions.size() > 1) {
+					logger.warn("Default function can not be mapped since multiple functions are declared " + this.declaredFunctionDefinitions);
+					return null;
+				}
+				else {
+					logger.warn("Default function can not be mapped since multiple functions are available in FunctionCatalog. "
+							+ "Please use 'spring.cloud.function.definition' property.");
+					return null;
+				}
+			}
 		}
+
 		Object function = this
 			.proxyInvokerIfNecessary((FunctionInvocationWrapper) this.compose(null, definition, acceptedOutputTypes));
 		return (T) function;

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

@@ -28,6 +28,7 @@ import java.util.function.Function;
 import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
+import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Test;
 import reactor.core.publisher.Flux;
@@ -77,6 +78,11 @@ public class BeanFactoryAwareFunctionRegistryTests {
 		return catalog;
 	}
 
+	@Before
+	public void before() {
+		System.clearProperty("spring.cloud.function.definition");
+	}
+
 	@Test
 	public void testDefaultLookup() throws Exception {
 		FunctionCatalog catalog = this.configureCatalog();
@@ -84,6 +90,7 @@ public class BeanFactoryAwareFunctionRegistryTests {
 		assertThat(function).isNull();
 		//==
 		System.setProperty("spring.cloud.function.definition", "uppercase");
+		catalog = this.configureCatalog();
 		function = catalog.lookup("");
 		assertThat(function).isNotNull();
 		Field field = ReflectionUtils.findField(FunctionInvocationWrapper.class, "composed");
@@ -91,6 +98,7 @@ public class BeanFactoryAwareFunctionRegistryTests {
 		assertThat(((boolean) field.get(function))).isFalse();
 		//==
 		System.setProperty("spring.cloud.function.definition", "uppercase|uppercaseFlux");
+		catalog = this.configureCatalog();
 		function = catalog.lookup("", "application/json");
 		Function<Flux<String>, Flux<Message<String>>> typedFunction = (Function<Flux<String>, Flux<Message<String>>>) function;
 		Object blockFirst = typedFunction.apply(Flux.just("hello")).blockFirst();
@@ -354,7 +362,7 @@ public class BeanFactoryAwareFunctionRegistryTests {
 		FunctionCatalog catalog = this.configureCatalog(CollectionOutConfiguration.class);
 		FunctionInvocationWrapper function = catalog.lookup("parseToList", "application/json");
 		assertThat(function).isNotNull();
-		Object result = (Message) function.apply(MessageBuilder.withPayload("1, 2, 3".getBytes()).setHeader(MessageHeaders.CONTENT_TYPE, "text/plain").build());
+		Object result = function.apply(MessageBuilder.withPayload("1, 2, 3".getBytes()).setHeader(MessageHeaders.CONTENT_TYPE, "text/plain").build());
 		assertThat(result instanceof Message).isTrue();
 
 		function = catalog.lookup("parseToListOfMessages", "application/json");