Honor Content-[Type|Length] headers from wrapped response again

Commit 375e0e6 introduced a regression in
ContentCachingResponseWrapper (CCRW). Specifically, CCRW no longer
honors Content-Type and Content-Length headers that have been set on
the wrapped response and returns null for those header values if they
have not been set directly on the CCRW.

This commit fixes this regression as follows.

- The Content-Type and Content-Length headers set in the wrapped
  response are honored in getContentType(), containsHeader(),
  getHeader(), and getHeaders() unless those headers have been set
  directly on the CCRW.

- In copyBodyToResponse(), the Content-Type in the wrapped response is
  only overridden if the the Content-Type has been set directly on the
  CCRW.

See spring-projectsgh-32039
Closes spring-projectsgh-32317

spring-web/src/main/java/org/springframework/web/util/ContentCachingResponseWrapper.java

@@ -43,6 +43,7 @@
  * <p>Used e.g. by {@link org.springframework.web.filter.ShallowEtagHeaderFilter}.
  *
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 4.1.3
  * @see ContentCachingRequestWrapper
  */
@@ -157,16 +158,19 @@ public void setContentType(@Nullable String type) {
 	@Override
 	@Nullable
 	public String getContentType() {
-		return this.contentType;
+		if (this.contentType != null) {
+			return this.contentType;
+		}
+		return super.getContentType();
 	}
 
 	@Override
 	public boolean containsHeader(String name) {
-		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
-			return this.contentLength != null;
+		if (this.contentLength != null && HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			return true;
 		}
-		else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
-			return this.contentType != null;
+		else if (this.contentType != null && HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
+			return true;
 		}
 		else {
 			return super.containsHeader(name);
@@ -222,10 +226,10 @@ public void addIntHeader(String name, int value) {
 	@Override
 	@Nullable
 	public String getHeader(String name) {
-		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
-			return (this.contentLength != null) ? this.contentLength.toString() : null;
+		if (this.contentLength != null && HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			return this.contentLength.toString();
 		}
-		else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
+		else if (this.contentType != null && HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
 			return this.contentType;
 		}
 		else {
@@ -235,12 +239,11 @@ else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
 
 	@Override
 	public Collection<String> getHeaders(String name) {
-		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
-			return this.contentLength != null ? Collections.singleton(this.contentLength.toString()) :
-					Collections.emptySet();
+		if (this.contentLength != null && HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			return Collections.singleton(this.contentLength.toString());
 		}
-		else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
-			return this.contentType != null ? Collections.singleton(this.contentType) : Collections.emptySet();
+		else if (this.contentType != null && HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
+			return Collections.singleton(this.contentType);
 		}
 		else {
 			return super.getHeaders(name);
@@ -330,7 +333,7 @@ protected void copyBodyToResponse(boolean complete) throws IOException {
 					}
 					this.contentLength = null;
 				}
-				if (complete || this.contentType != null) {
+				if (this.contentType != null) {
 					rawResponse.setContentType(this.contentType);
 					this.contentType = null;
 				}

spring-web/src/test/java/org/springframework/web/filter/ContentCachingResponseWrapperTests.java

@@ -19,19 +19,22 @@
 import jakarta.servlet.http.HttpServletResponse;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.http.MediaType;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.web.testfixture.servlet.MockHttpServletResponse;
 import org.springframework.web.util.ContentCachingResponseWrapper;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.springframework.http.HttpHeaders.CONTENT_LENGTH;
+import static org.springframework.http.HttpHeaders.CONTENT_TYPE;
 import static org.springframework.http.HttpHeaders.TRANSFER_ENCODING;
 
 /**
  * Tests for {@link ContentCachingResponseWrapper}.
  *
  * @author Rossen Stoyanchev
+ * @author Sam Brannen
  */
 class ContentCachingResponseWrapperTests {
 
@@ -50,6 +53,79 @@ void copyBodyToResponse() throws Exception {
 		assertThat(response.getContentAsByteArray()).isEqualTo(responseBody);
 	}
 
+	@Test
+	void copyBodyToResponseWithPresetHeaders() throws Exception {
+		String PUZZLE = "puzzle";
+		String ENIGMA = "enigma";
+		String NUMBER = "number";
+		String MAGIC = "42";
+
+		byte[] responseBody = "Hello World".getBytes(UTF_8);
+		String responseLength = Integer.toString(responseBody.length);
+		String contentType = MediaType.APPLICATION_JSON_VALUE;
+
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		response.setContentType(contentType);
+		response.setContentLength(999);
+		response.setHeader(PUZZLE, ENIGMA);
+		response.setIntHeader(NUMBER, 42);
+
+		ContentCachingResponseWrapper responseWrapper = new ContentCachingResponseWrapper(response);
+		responseWrapper.setStatus(HttpServletResponse.SC_OK);
+
+		assertThat(responseWrapper.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+		assertThat(responseWrapper.getContentSize()).isZero();
+		assertThat(responseWrapper.getHeaderNames())
+				.containsExactlyInAnyOrder(PUZZLE, NUMBER, CONTENT_TYPE, CONTENT_LENGTH);
+
+		assertThat(responseWrapper.containsHeader(PUZZLE)).as(PUZZLE).isTrue();
+		assertThat(responseWrapper.getHeader(PUZZLE)).as(PUZZLE).isEqualTo(ENIGMA);
+		assertThat(responseWrapper.getHeaders(PUZZLE)).as(PUZZLE).containsExactly(ENIGMA);
+
+		assertThat(responseWrapper.containsHeader(NUMBER)).as(NUMBER).isTrue();
+		assertThat(responseWrapper.getHeader(NUMBER)).as(NUMBER).isEqualTo(MAGIC);
+		assertThat(responseWrapper.getHeaders(NUMBER)).as(NUMBER).containsExactly(MAGIC);
+
+		assertThat(responseWrapper.containsHeader(CONTENT_TYPE)).as(CONTENT_TYPE).isTrue();
+		assertThat(responseWrapper.getHeader(CONTENT_TYPE)).as(CONTENT_TYPE).isEqualTo(contentType);
+		assertThat(responseWrapper.getHeaders(CONTENT_TYPE)).as(CONTENT_TYPE).containsExactly(contentType);
+		assertThat(responseWrapper.getContentType()).as(CONTENT_TYPE).isEqualTo(contentType);
+
+		assertThat(responseWrapper.containsHeader(CONTENT_LENGTH)).as(CONTENT_LENGTH).isTrue();
+		assertThat(responseWrapper.getHeader(CONTENT_LENGTH)).as(CONTENT_LENGTH).isEqualTo("999");
+		assertThat(responseWrapper.getHeaders(CONTENT_LENGTH)).as(CONTENT_LENGTH).containsExactly("999");
+
+		FileCopyUtils.copy(responseBody, responseWrapper.getOutputStream());
+		responseWrapper.copyBodyToResponse();
+
+		assertThat(responseWrapper.getHeaderNames())
+				.containsExactlyInAnyOrder(PUZZLE, NUMBER, CONTENT_TYPE, CONTENT_LENGTH);
+
+		assertThat(response.getStatus()).isEqualTo(HttpServletResponse.SC_OK);
+		assertThat(response.getContentType()).isEqualTo(contentType);
+		assertThat(response.getContentLength()).isEqualTo(responseBody.length);
+		assertThat(response.getContentAsByteArray()).isEqualTo(responseBody);
+		assertThat(response.getHeaderNames())
+				.containsExactlyInAnyOrder(PUZZLE, NUMBER, CONTENT_TYPE, CONTENT_LENGTH);
+
+		assertThat(response.containsHeader(PUZZLE)).as(PUZZLE).isTrue();
+		assertThat(response.getHeader(PUZZLE)).as(PUZZLE).isEqualTo(ENIGMA);
+		assertThat(response.getHeaders(PUZZLE)).as(PUZZLE).containsExactly(ENIGMA);
+
+		assertThat(response.containsHeader(NUMBER)).as(NUMBER).isTrue();
+		assertThat(response.getHeader(NUMBER)).as(NUMBER).isEqualTo(MAGIC);
+		assertThat(response.getHeaders(NUMBER)).as(NUMBER).containsExactly(MAGIC);
+
+		assertThat(response.containsHeader(CONTENT_TYPE)).as(CONTENT_TYPE).isTrue();
+		assertThat(response.getHeader(CONTENT_TYPE)).as(CONTENT_TYPE).isEqualTo(contentType);
+		assertThat(response.getHeaders(CONTENT_TYPE)).as(CONTENT_TYPE).containsExactly(contentType);
+		assertThat(response.getContentType()).as(CONTENT_TYPE).isEqualTo(contentType);
+
+		assertThat(response.containsHeader(CONTENT_LENGTH)).as(CONTENT_LENGTH).isTrue();
+		assertThat(response.getHeader(CONTENT_LENGTH)).as(CONTENT_LENGTH).isEqualTo(responseLength);
+		assertThat(response.getHeaders(CONTENT_LENGTH)).as(CONTENT_LENGTH).containsExactly(responseLength);
+	}
+
 	@Test
 	void copyBodyToResponseWithTransferEncoding() throws Exception {
 		byte[] responseBody = "6\r\nHello 5\r\nWorld0\r\n\r\n".getBytes(UTF_8);