Only expose Publisher via FunctionCatalog

Flux.from() is cheap and can be used to marshal the inputs everywhere
internally. With this change users ought to be able to register any
function of any Publisher type.

spring-cloud-function-adapters/spring-cloud-function-adapter-azure/src/main/java/org/springframework/cloud/function/adapter/azure/AzureSpringBootRequestHandler.java

@@ -22,6 +22,8 @@ import java.util.List;
 
 import com.microsoft.azure.serverless.functions.ExecutionContext;
 
+import org.reactivestreams.Publisher;
+
 import reactor.core.publisher.Flux;
 
 /**
@@ -44,7 +46,7 @@ public class AzureSpringBootRequestHandler<I, O> extends AzureSpringFunctionInit
 		initialize(context);
 
 		Object convertedEvent = convertEvent(foo);
-		Flux<?> output = apply(extract(convertedEvent));
+		Publisher<?> output = apply(extract(convertedEvent));
 		return result(convertedEvent, output);
 	}
 
@@ -59,9 +61,9 @@ public class AzureSpringBootRequestHandler<I, O> extends AzureSpringFunctionInit
 		return Flux.just(input);
 	}
 
-	private O result(Object input, Flux<?> output) {
+	private O result(Object input, Publisher<?> output) {
 		List<Object> result = new ArrayList<>();
-		for (Object value : output.toIterable()) {
+		for (Object value : Flux.from(output).toIterable()) {
 			result.add(convertOutput(value));
 		}
 		if (isSingleValue(input) && result.size() == 1) {

spring-cloud-function-adapters/spring-cloud-function-adapter-azure/src/main/java/org/springframework/cloud/function/adapter/azure/AzureSpringFunctionInitializer.java

@@ -28,7 +28,8 @@ import java.util.function.Function;
 import java.util.jar.Manifest;
 
 import com.microsoft.azure.serverless.functions.ExecutionContext;
-import reactor.core.publisher.Flux;
+
+import org.reactivestreams.Publisher;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
@@ -37,12 +38,14 @@ import org.springframework.cloud.function.context.FunctionCatalog;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.util.ClassUtils;
 
+import reactor.core.publisher.Flux;
+
 /**
  * @author Soby Chacko
  */
 public class AzureSpringFunctionInitializer implements Closeable {
 
-	private Function<Flux<?>, Flux<?>> function;
+	private Function<Publisher<?>, Publisher<?>> function;
 
 	private AtomicBoolean initialized = new AtomicBoolean();
 
@@ -110,7 +113,7 @@ public class AzureSpringFunctionInitializer implements Closeable {
 		}
 	}
 
-	protected Flux<?> apply(Flux<?> input) {
+	protected Publisher<?> apply(Publisher<?> input) {
 		if (this.function != null) {
 			return function.apply(input);
 		}