GH-1106 Fix RoutingFunction fail when "spring.cloud.function.definition" header contains a List value instead of a String value (GCP-specific)

Resolves #1106
Resolves #1146

Author: akenra

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

@@ -16,9 +16,11 @@
 
 package org.springframework.cloud.function.context.config;
 
+import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.function.Function;
+import java.util.stream.Collectors;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -193,11 +195,31 @@ else if (StringUtils.hasText(functionProperties.getRoutingExpression())) {
 
 	private FunctionInvocationWrapper locateFunctionFromDefinitionOrExpression(Message<?> message) {
 		for (Entry<String, Object> headerEntry : message.getHeaders().entrySet()) {
-			if (headerEntry.getKey().equalsIgnoreCase(FunctionProperties.FUNCTION_DEFINITION)) {
-				return functionFromDefinition((String) headerEntry.getValue());
+			String headerKey = headerEntry.getKey();
+			Object headerValue = headerEntry.getValue();
+
+			if (headerKey == null || headerValue == null) {
+				continue;
+			}
+
+			boolean isFunctionDefinition = FunctionProperties.FUNCTION_DEFINITION.equalsIgnoreCase(headerKey);
+			boolean isRoutingExpression = FunctionProperties.ROUTING_EXPRESSION.equalsIgnoreCase(headerKey);
+
+			if (isFunctionDefinition) {
+				if (headerValue instanceof String definition) {
+					return functionFromDefinition(definition);
+				}
+				else if (headerValue instanceof List<?> definitions && !definitions.isEmpty()) {
+					return functionFromDefinition(definitions.stream().map(Object::toString).collect(Collectors.joining(",")));
+				}
 			}
-			else if (headerEntry.getKey().equalsIgnoreCase(FunctionProperties.ROUTING_EXPRESSION)) {
-				return this.functionFromExpression((String) headerEntry.getValue(), message, true);
+			else if (isRoutingExpression) {
+				if (headerValue instanceof String expression) {
+					return functionFromExpression(expression, message, true);
+				}
+				else if (headerValue instanceof List<?> expressions && !expressions.isEmpty()) {
+					return functionFromExpression(expressions.get(0).toString(), message, true);
+				}
 			}
 		}
 		return null;

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

@@ -17,6 +17,7 @@
 package org.springframework.cloud.function.context.config;
 
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.function.Function;
 
@@ -98,7 +99,7 @@ public void testDefaultRouting() {
 
 	@SuppressWarnings({ "unchecked", "rawtypes" })
 	@Test
-	public void testInvocationWithMessageAndHeader() {
+	public void testInvocationWithMessageAndStringHeader() {
 		FunctionCatalog functionCatalog = this.configureCatalog();
 		Function function = functionCatalog.lookup(RoutingFunction.FUNCTION_NAME);
 		assertThat(function).isNotNull();
@@ -107,6 +108,57 @@ public void testInvocationWithMessageAndHeader() {
 		assertThat(function.apply(message)).isEqualTo("olleh");
 	}
 
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	@Test
+	public void testInvocationWithMessageAndListOfSingleElementHeader() {
+		FunctionCatalog functionCatalog = this.configureCatalog();
+		Function function = functionCatalog.lookup(RoutingFunction.FUNCTION_NAME);
+		assertThat(function).isNotNull();
+		Message<String> message = MessageBuilder.withPayload("hello")
+				.setHeader(FunctionProperties.PREFIX + ".definition", List.of("reverse"))
+				.build();
+		assertThat(function.apply(message)).isEqualTo("olleh");
+	}
+
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	@Test
+	public void testCompositionWithMessageAndListOfMultipleElementsHeader() {
+		FunctionCatalog functionCatalog = this.configureCatalog();
+		Function function = functionCatalog.lookup(RoutingFunction.FUNCTION_NAME);
+		assertThat(function).isNotNull();
+		Message<String> message = MessageBuilder.withPayload("hello")
+				.setHeader(FunctionProperties.PREFIX + ".definition",
+						List.of("reverse", "uppercase"))
+				.build();
+		assertThat(function.apply(message)).isEqualTo("OLLEH");
+	}
+
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	@Test
+	public void testInvocationWithMessageAndListOfSingleRoutingExpression() {
+		FunctionCatalog functionCatalog = this.configureCatalog();
+		Function function = functionCatalog.lookup(RoutingFunction.FUNCTION_NAME);
+		assertThat(function).isNotNull();
+		Message<String> message = MessageBuilder.withPayload("hello")
+				.setHeader(FunctionProperties.PREFIX + ".routing-expression",
+						List.of("'reverse'"))
+				.build();
+		assertThat(function.apply(message)).isEqualTo("olleh");
+	}
+
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	@Test
+	public void testInvocationWithMessageAndListOfMultipleRoutingExpressions() {
+		FunctionCatalog functionCatalog = this.configureCatalog();
+		Function function = functionCatalog.lookup(RoutingFunction.FUNCTION_NAME);
+		assertThat(function).isNotNull();
+		Message<String> message = MessageBuilder.withPayload("hello")
+				.setHeader(FunctionProperties.PREFIX + ".routing-expression",
+						List.of("'uppercase'", "'reverse'"))
+				.build();
+		assertThat(function.apply(message)).isEqualTo("HELLO");
+	}
+
 	@SuppressWarnings({ "unchecked", "rawtypes" })
 	@Test
 	public void testRoutingSimpleInputWithReactiveFunctionWithMessageHeader() {