Adds reproducer for protobuf msg conversion issue (spring-cloud#1094)

Conversion of protobuf messages fails if the encoded message
looks like a JSON string. Added a test that reproduces the
issue.

Author: simonzn

spring-cloud-function-context/pom.xml

@@ -109,6 +109,14 @@
 			<optional>true</optional>
 		</dependency>
 
+		<!-- Protobuf -->
+		<dependency>
+			<groupId>com.google.protobuf</groupId>
+			<artifactId>protobuf-java</artifactId>
+			<version>3.25.1</version>
+			<scope>test</scope>
+		</dependency>
+
 		<!-- Actuator -->
 		<dependency>
 			<groupId>org.springframework.boot</groupId>

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

@@ -16,6 +16,8 @@
 
 package org.springframework.cloud.function.context.catalog;
 
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
 import java.lang.reflect.Field;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
@@ -37,13 +39,15 @@
 
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.gson.Gson;
+import com.google.protobuf.StringValue;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 import org.reactivestreams.Publisher;
+import org.springframework.messaging.converter.ProtobufMessageConverter;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -78,6 +82,7 @@
 import org.springframework.util.ReflectionUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 
 /**
  * @author Oleg Zhurakousky
@@ -97,6 +102,7 @@ public void before() {
 		messageConverters.add(new JsonMessageConverter(jsonMapper));
 		messageConverters.add(new ByteArrayMessageConverter());
 		messageConverters.add(new StringMessageConverter());
+		messageConverters.add(new ProtobufMessageConverter());
 		this.messageConverter = new SmartCompositeMessageConverter(messageConverters);
 
 		this.conversionService = new DefaultConversionService();
@@ -207,6 +213,34 @@ void textContentTypeWithValueWrappedBracketsIsOk(String inputMessagePayloadValue
 		assertThat(functionResult).isEqualTo(inputMessagePayloadValue);
 	}
 
+	@ParameterizedTest
+	@ValueSource(strings = {
+		"aaaaaaaaaa", // no problem
+		"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa]" // protobuf encoder prepends '[' for length (91 bytes)
+	})
+	public void testSCF1094(String stringValue) throws IOException {
+
+		Function<StringValue, String> getValue = msg -> msg != null ? msg.getValue() : null;
+		Type functionType = ResolvableType.forClassWithGenerics(Function.class, ResolvableType.forClass(StringValue.class), ResolvableType.forClass(String.class)).getType();
+
+		var catalog = new SimpleFunctionRegistry(this.conversionService, this.messageConverter, new JacksonMapper(new ObjectMapper()));
+		catalog.register(new FunctionRegistration<>(getValue, "getValue").type(functionType));
+		FunctionInvocationWrapper lookedUpFunction = catalog.lookup("getValue");
+
+		ByteArrayOutputStream payload = new ByteArrayOutputStream();
+		StringValue.newBuilder()
+			.setValue(stringValue)
+			.build()
+			.writeTo(payload);
+
+		var inputMessage = MessageBuilder.withPayload(payload.toByteArray())
+			.setHeader("contentType", "application/x-protobuf")
+			.build();
+
+		Object result = assertDoesNotThrow(() -> lookedUpFunction.apply(inputMessage));
+		assertThat(result).isEqualTo(stringValue);
+	}
+
 	@SuppressWarnings("unchecked")
 	@Test
 	public void testSCF762() {