Fix releasing bug in StringDecoder

This commit fixes an issue in StringDecoder, where, if the buffer did
not contain any delimiters, it was released before it was relayed to
any subscribers.

Closes gh-29119

Author: poutsma

spring-core/src/main/java/org/springframework/core/codec/StringDecoder.java

@@ -143,13 +143,14 @@ private byte[][] getDelimiterBytes(@Nullable MimeType mimeType) {
 	private Collection<DataBuffer> processDataBuffer(
 			DataBuffer buffer, DataBufferUtils.Matcher matcher, LimitedDataBufferList chunks) {
 
+		boolean release = true;
 		try {
 			List<DataBuffer> result = null;
 			do {
 				int endIndex = matcher.match(buffer);
 				if (endIndex == -1) {
 					chunks.add(buffer);
-					DataBufferUtils.retain(buffer); // retain after add (may raise DataBufferLimitException)
+					release = false;
 					break;
 				}
 				DataBuffer split = buffer.split(endIndex + 1);
@@ -177,7 +178,9 @@ private Collection<DataBuffer> processDataBuffer(
 			return (result != null ? result : Collections.emptyList());
 		}
 		finally {
-			DataBufferUtils.release(buffer);
+			if (release) {
+				DataBufferUtils.release(buffer);
+			}
 		}
 	}
 

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/WebClientIntegrationTests.java

@@ -1258,6 +1258,26 @@ void malformedResponseChunksOnEntityWithBody(ClientHttpConnector connector) {
 				.verify();
 	}
 
+	@ParameterizedWebClientTest
+	void retrieveTextDecodedToFlux(ClientHttpConnector connector) {
+		startServer(connector);
+
+		prepareResponse(response -> response
+				.setHeader("Content-Type", "text/plain")
+				.setBody("Hey now"));
+
+		Flux<String> result = this.webClient.get()
+				.uri("/")
+				.accept(MediaType.TEXT_PLAIN)
+				.retrieve()
+				.bodyToFlux(String.class);
+
+		StepVerifier.create(result)
+				.expectNext("Hey now")
+				.expectComplete()
+				.verify(Duration.ofSeconds(3));
+	}
+
 	private <T> Mono<T> doMalformedChunkedResponseTest(
 			ClientHttpConnector connector, Function<ResponseSpec, Mono<T>> handler) {