Handle zero readTimeout in JdkClientHttpConnector

Prior to this commit, JdkClientHttpConnector#setReadTimeout(Duration)
passed Duration.ZERO through to HttpRequest.Builder#timeout, which
rejects non-positive durations. As a result, every request failed with
an IllegalArgumentException ("Invalid duration: PT0S").

gh-37234 already treats a zero read timeout as an infinite timeout in
JdkClientHttpRequestFactory, which is backed by the same JDK HttpClient
API.

This commit applies the same handling to the reactive
JdkClientHttpConnector so that a zero Duration results in no timeout
being set on the underlying request.

See gh-37232
Closes gh-37412

Signed-off-by: lejuho <52308082+lejuho@users.noreply.github.com>

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

@@ -101,13 +101,14 @@ public class JdkClientHttpConnector implements ClientHttpConnector {
 
 	/**
 	 * Set the underlying {@code HttpClient} read timeout as a {@code Duration}.
+	 * A timeout value of 0 specifies an infinite timeout.
 	 * <p>Default is the system's default timeout.
 	 * @since 6.2
 	 * @see java.net.http.HttpRequest.Builder#timeout
 	 */
 	public void setReadTimeout(Duration readTimeout) {
 		Assert.notNull(readTimeout, "readTimeout is required");
-		this.readTimeout = readTimeout;
+		this.readTimeout = (Duration.ZERO.equals(readTimeout) ? null : readTimeout);
 	}
 
 	/**

spring-web/src/test/java/org/springframework/http/client/reactive/ClientHttpConnectorTests.java

@@ -241,6 +241,19 @@ class ClientHttpConnectorTests {
 
 	}
 
+	@Test
+	void readTimeoutZeroWithJdk() {
+		JdkClientHttpConnector connector = new JdkClientHttpConnector();
+		connector.setReadTimeout(Duration.ZERO);
+
+		prepareResponse(builder -> builder.code(200));
+		Mono<ClientHttpResponse> futureResponse =
+				connector.connect(HttpMethod.GET, this.server.url("/").uri(), ReactiveHttpOutputMessage::setComplete);
+		StepVerifier.create(futureResponse)
+				.assertNext(response -> assertThat(response.getStatusCode()).isEqualTo(HttpStatus.OK))
+				.verifyComplete();
+	}
+
 	private Buffer randomBody(int size) {
 		Buffer responseBody = new Buffer();
 		Random rnd = new Random();