Add support for server-side events and tests

User can POST to web endpoint in SSE style, i.e:

HTTP/1.1
Content-Type: text/event-stream

data:foo

data:bar

Will be converted to a Flux with values foo and bar

spring-cloud-function-web/src/main/java/org/springframework/cloud/function/web/FunctionController.java

@@ -18,10 +18,10 @@ package org.springframework.cloud.function.web;
 import java.util.function.Function;
 
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.context.embedded.ReactiveServerProperties;
 import org.springframework.cloud.function.registry.FunctionCatalog;
-import org.springframework.http.MediaType;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.PostMapping;
@@ -38,6 +38,9 @@ import reactor.core.publisher.Flux;
 @ConditionalOnClass({ RestController.class, ReactiveServerProperties.class })
 public class FunctionController {
 
+	@Value("${debug:${DEBUG:false}}")
+	private boolean debug = false;
+
 	private final FunctionCatalog functions;
 
 	@Autowired
@@ -45,7 +48,7 @@ public class FunctionController {
 		this.functions = catalog;
 	}
 
-	@PostMapping(path = "/{name}", consumes = MediaType.TEXT_PLAIN_VALUE)
+	@PostMapping(path = "/{name}")
 	public Flux<String> function(@PathVariable String name,
 			@RequestBody Flux<String> body) {
 		Function<Object, Object> function;
@@ -57,14 +60,14 @@ public class FunctionController {
 		}
 		@SuppressWarnings("unchecked")
 		Flux<String> result = (Flux<String>) function.apply(body);
-		return result;
+		return debug ? result.log() : result;
 	}
 
-	@GetMapping("/{name}")
+	@GetMapping(path = "/{name}")
 	public Flux<String> supplier(@PathVariable String name) {
 		@SuppressWarnings("unchecked")
 		Flux<String> result = (Flux<String>) functions.lookupSupplier(name).get();
-		return result;
+		return debug ? result.log() : result;
 	}
 
 }

spring-cloud-function-web/src/main/java/org/springframework/cloud/function/web/RestApplication.java

@@ -16,16 +16,97 @@
 
 package org.springframework.cloud.function.web;
 
+import java.nio.CharBuffer;
+import java.nio.charset.Charset;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.function.IntPredicate;
+
+import org.reactivestreams.Publisher;
+
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.core.ResolvableType;
+import org.springframework.core.codec.StringDecoder;
+import org.springframework.core.io.buffer.DataBuffer;
+import org.springframework.core.io.buffer.DataBufferUtils;
+import org.springframework.http.MediaType;
+import org.springframework.http.codec.DecoderHttpMessageReader;
+import org.springframework.http.codec.HttpMessageReader;
+import org.springframework.util.MimeType;
+import org.springframework.web.reactive.config.WebReactiveConfigurer;
+
+import reactor.core.publisher.Flux;
 
 /**
  * @author Mark Fisher
  */
 @SpringBootApplication
-public class RestApplication {
+public class RestApplication implements WebReactiveConfigurer {
+
+	@Override
+	public void extendMessageReaders(List<HttpMessageReader<?>> readers) {
+		readers.add(0, new DecoderHttpMessageReader<>(new SseDecoder()));
+	}
 
 	public static void main(String[] args) {
 		SpringApplication.run(RestApplication.class, args);
 	}
 }
+
+class SseDecoder extends StringDecoder {
+
+	private static final IntPredicate NEWLINE_DELIMITER = b -> b == '\n' || b == '\r';
+
+	@Override
+	public boolean canDecode(ResolvableType elementType, MimeType mimeType) {
+		return super.canDecode(elementType, mimeType)
+				&& MediaType.TEXT_EVENT_STREAM.isCompatibleWith(mimeType);
+	}
+
+	@Override
+	public Flux<String> decode(Publisher<DataBuffer> inputStream,
+			ResolvableType elementType, MimeType mimeType, Map<String, Object> hints) {
+
+		Flux<DataBuffer> inputFlux = Flux.from(inputStream);
+		inputFlux = Flux.from(inputStream).flatMap(SseDecoder::splitOnNewline);
+		return inputFlux.map(buffer -> decodeDataBuffer(buffer, mimeType));
+	}
+
+	private static Flux<DataBuffer> splitOnNewline(DataBuffer dataBuffer) {
+		List<DataBuffer> results = new ArrayList<>();
+		int startIdx = 0;
+		int endIdx;
+		final int limit = dataBuffer.readableByteCount();
+		do {
+			endIdx = dataBuffer.indexOf(NEWLINE_DELIMITER, startIdx);
+			endIdx = dataBuffer.indexOf(NEWLINE_DELIMITER, endIdx + 1);
+			int length = (endIdx != -1 ? endIdx - startIdx + 1 : limit - startIdx) - 7;
+			if (length > 0) {
+				DataBuffer token = dataBuffer.slice(startIdx + 5, length);
+				results.add(DataBufferUtils.retain(token));
+			}
+			startIdx = endIdx + 1;
+		}
+		while (startIdx < limit && endIdx != -1);
+		DataBufferUtils.release(dataBuffer);
+		return Flux.fromIterable(results);
+	}
+
+	private String decodeDataBuffer(DataBuffer dataBuffer, MimeType mimeType) {
+		Charset charset = getCharset(mimeType);
+		CharBuffer charBuffer = charset.decode(dataBuffer.asByteBuffer());
+		DataBufferUtils.release(dataBuffer);
+		return charBuffer.toString();
+	}
+
+	private Charset getCharset(MimeType mimeType) {
+		if (mimeType != null && mimeType.getCharset() != null) {
+			return mimeType.getCharset();
+		}
+		else {
+			return DEFAULT_CHARSET;
+		}
+	}
+}