Check response code in SimpleClientHttpResponse::getBody

The error stream can be null with an empty body, so check the response
code instead.

Closes gh-33020

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -85,8 +85,15 @@ final class SimpleClientHttpResponse implements ClientHttpResponse {
 
 	@Override
 	public InputStream getBody() throws IOException {
-		InputStream errorStream = this.connection.getErrorStream();
-		this.responseStream = (errorStream != null ? errorStream : this.connection.getInputStream());
+		if (this.responseStream == null) {
+			if (this.connection.getResponseCode() >= 400) {
+				InputStream errorStream = this.connection.getErrorStream();
+				this.responseStream = (errorStream != null) ? errorStream : InputStream.nullInputStream();
+			}
+			else {
+				this.responseStream = this.connection.getInputStream();
+			}
+		}
 		return this.responseStream;
 	}
 

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

@@ -49,7 +49,7 @@ class SimpleClientHttpResponseTests {
 	@Test  // SPR-14040
 	public void shouldNotCloseConnectionWhenResponseClosed() throws Exception {
 		TestByteArrayInputStream is = new TestByteArrayInputStream("Spring".getBytes(StandardCharsets.UTF_8));
-		given(this.connection.getErrorStream()).willReturn(null);
+		given(this.connection.getResponseCode()).willReturn(200);
 		given(this.connection.getInputStream()).willReturn(is);
 
 		InputStream responseStream = this.response.getBody();
@@ -64,7 +64,7 @@ class SimpleClientHttpResponseTests {
 	public void shouldDrainStreamWhenResponseClosed() throws Exception {
 		byte[] buf = new byte[6];
 		TestByteArrayInputStream is = new TestByteArrayInputStream("SpringSpring".getBytes(StandardCharsets.UTF_8));
-		given(this.connection.getErrorStream()).willReturn(null);
+		given(this.connection.getResponseCode()).willReturn(200);
 		given(this.connection.getInputStream()).willReturn(is);
 
 		InputStream responseStream = this.response.getBody();
@@ -82,6 +82,7 @@ class SimpleClientHttpResponseTests {
 	public void shouldDrainErrorStreamWhenResponseClosed() throws Exception {
 		byte[] buf = new byte[6];
 		TestByteArrayInputStream is = new TestByteArrayInputStream("SpringSpring".getBytes(StandardCharsets.UTF_8));
+		given(this.connection.getResponseCode()).willReturn(404);
 		given(this.connection.getErrorStream()).willReturn(is);
 
 		InputStream responseStream = this.response.getBody();
@@ -98,6 +99,7 @@ class SimpleClientHttpResponseTests {
 	@Test  // SPR-16773
 	public void shouldNotDrainWhenErrorStreamClosed() throws Exception {
 		InputStream is = mock();
+		given(this.connection.getResponseCode()).willReturn(404);
 		given(this.connection.getErrorStream()).willReturn(is);
 		willDoNothing().given(is).close();
 		given(is.transferTo(any())).willCallRealMethod();
@@ -115,7 +117,7 @@ class SimpleClientHttpResponseTests {
 	@Test // SPR-17181
 	public void shouldDrainResponseEvenIfResponseNotRead() throws Exception {
 		TestByteArrayInputStream is = new TestByteArrayInputStream("SpringSpring".getBytes(StandardCharsets.UTF_8));
-		given(this.connection.getErrorStream()).willReturn(null);
+		given(this.connection.getResponseCode()).willReturn(200);
 		given(this.connection.getInputStream()).willReturn(is);
 
 		this.response.close();