Polishing contribution and fix failing test

The failing test is for Apache HttpComponents where we cannot apply the
Content-Length together with other headers, and must pass it instead
explicitly to ReactiveEntityProducer when writing at which point it gets
set in the native headers.

Closes gh-27768

spring-web/src/main/java/org/springframework/http/client/reactive/AbstractClientHttpRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -74,6 +74,7 @@ public abstract class AbstractClientHttpRequest implements ClientHttpRequest {
 		this.cookies = new LinkedMultiValueMap<>();
 	}
 
+
 	@Override
 	public HttpHeaders getHeaders() {
 		if (this.readOnlyHeaders != null) {
@@ -88,6 +89,16 @@ public abstract class AbstractClientHttpRequest implements ClientHttpRequest {
 		}
 	}
 
+	/**
+	 * Initialize the read-only headers after the request is committed.
+	 * <p>By default, this method simply applies a read-only wrapper.
+	 * Subclasses can do the same for headers from the native request.
+	 * @since 5.3.15
+	 */
+	protected HttpHeaders initReadOnlyHeaders() {
+		return HttpHeaders.readOnlyHttpHeaders(this.headers);
+	}
+
 	@Override
 	public MultiValueMap<String, HttpCookie> getCookies() {
 		if (State.COMMITTED.equals(this.state.get())) {
@@ -143,14 +154,6 @@ public abstract class AbstractClientHttpRequest implements ClientHttpRequest {
 		return Flux.concat(actions).then();
 	}
 
-	/**
-	 * Initialize read-only headers with underlying request headers.
-	 * @return read-only headers
-	 */
-	protected HttpHeaders initReadOnlyHeaders() {
-		return HttpHeaders.readOnlyHttpHeaders(this.headers);
-	}
-
 
 	/**
 	 * Apply header changes from {@link #getHeaders()} to the underlying request.

spring-web/src/main/java/org/springframework/http/client/reactive/HttpComponentsClientHttpRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -62,6 +62,8 @@ class HttpComponentsClientHttpRequest extends AbstractClientHttpRequest {
 	@Nullable
 	private Flux<ByteBuffer> byteBufferFlux;
 
+	private transient long contentLength = -1;
+
 
 	public HttpComponentsClientHttpRequest(HttpMethod method, URI uri, HttpClientContext context,
 			DataBufferFactory dataBufferFactory) {
@@ -118,11 +120,6 @@ class HttpComponentsClientHttpRequest extends AbstractClientHttpRequest {
 		return doCommit();
 	}
 
-	@Override
-	protected HttpHeaders initReadOnlyHeaders() {
-		return HttpHeaders.readOnlyHttpHeaders(new HttpComponentsHeadersAdapter(this.httpRequest));
-	}
-
 	@Override
 	protected void applyHeaders() {
 		HttpHeaders headers = getHeaders();
@@ -135,6 +132,8 @@ class HttpComponentsClientHttpRequest extends AbstractClientHttpRequest {
 		if (!this.httpRequest.containsHeader(HttpHeaders.ACCEPT)) {
 			this.httpRequest.addHeader(HttpHeaders.ACCEPT, ALL_VALUE);
 		}
+
+		this.contentLength = headers.getContentLength();
 	}
 
 	@Override
@@ -156,6 +155,11 @@ class HttpComponentsClientHttpRequest extends AbstractClientHttpRequest {
 				});
 	}
 
+	@Override
+	protected HttpHeaders initReadOnlyHeaders() {
+		return HttpHeaders.readOnlyHttpHeaders(new HttpComponentsHeadersAdapter(this.httpRequest));
+	}
+
 	public AsyncRequestProducer toRequestProducer() {
 		ReactiveEntityProducer reactiveEntityProducer = null;
 
@@ -165,8 +169,8 @@ class HttpComponentsClientHttpRequest extends AbstractClientHttpRequest {
 			if (getHeaders().getContentType() != null) {
 				contentType = ContentType.parse(getHeaders().getContentType().toString());
 			}
-			reactiveEntityProducer = new ReactiveEntityProducer(this.byteBufferFlux, getHeaders().getContentLength(),
-					contentType, contentEncoding);
+			reactiveEntityProducer = new ReactiveEntityProducer(
+					this.byteBufferFlux, this.contentLength, contentType, contentEncoding);
 		}
 
 		return new BasicRequestProducer(this.httpRequest, reactiveEntityProducer);

spring-web/src/main/java/org/springframework/http/client/reactive/JettyClientHttpRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -126,11 +126,6 @@ class JettyClientHttpRequest extends AbstractClientHttpRequest {
 		});
 	}
 
-	@Override
-	protected HttpHeaders initReadOnlyHeaders() {
-		return HttpHeaders.readOnlyHttpHeaders(new JettyHeadersAdapter(this.jettyRequest.getHeaders()));
-	}
-
 	@Override
 	protected void applyCookies() {
 		getCookies().values().stream().flatMap(Collection::stream)
@@ -147,9 +142,13 @@ class JettyClientHttpRequest extends AbstractClientHttpRequest {
 		}
 	}
 
+	@Override
+	protected HttpHeaders initReadOnlyHeaders() {
+		return HttpHeaders.readOnlyHttpHeaders(new JettyHeadersAdapter(this.jettyRequest.getHeaders()));
+	}
+
 	public ReactiveRequest toReactiveRequest() {
 		return this.builder.build();
 	}
 
-
 }

spring-web/src/main/java/org/springframework/http/client/reactive/ReactorClientHttpRequest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -122,11 +122,6 @@ class ReactorClientHttpRequest extends AbstractClientHttpRequest implements Zero
 		return doCommit(this.outbound::then);
 	}
 
-	@Override
-	protected HttpHeaders initReadOnlyHeaders() {
-		return HttpHeaders.readOnlyHttpHeaders(new NettyHeadersAdapter(this.request.requestHeaders()));
-	}
-
 	@Override
 	protected void applyHeaders() {
 		getHeaders().forEach((key, value) -> this.request.requestHeaders().set(key, value));
@@ -139,4 +134,9 @@ class ReactorClientHttpRequest extends AbstractClientHttpRequest implements Zero
 				.forEach(this.request::addCookie);
 	}
 
+	@Override
+	protected HttpHeaders initReadOnlyHeaders() {
+		return HttpHeaders.readOnlyHttpHeaders(new NettyHeadersAdapter(this.request.requestHeaders()));
+	}
+
 }