Handle Content-Length in ShallowEtagHeaderFilter more robustly

This commit ensures that setting the Content-Length through
setHeader("Content-Length", x") has the same effect as calling
setContentLength in the ShallowEtagHeaderFilter. It also filters out
Content-Type headers similarly to Content-Length.

Closes gh-32039

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 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.
@@ -21,6 +21,10 @@ import java.io.InputStream;
 import java.io.OutputStreamWriter;
 import java.io.PrintWriter;
 import java.io.UnsupportedEncodingException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
 
 import jakarta.servlet.ServletOutputStream;
 import jakarta.servlet.WriteListener;
@@ -55,6 +59,9 @@ public class ContentCachingResponseWrapper extends HttpServletResponseWrapper {
 	@Nullable
 	private Integer contentLength;
 
+	@Nullable
+	private String contentType;
+
 
 	/**
 	 * Create a new ContentCachingResponseWrapper for the given servlet response.
@@ -139,6 +146,122 @@ public class ContentCachingResponseWrapper extends HttpServletResponseWrapper {
 		this.contentLength = lenInt;
 	}
 
+	@Override
+	public void setContentType(String type) {
+		this.contentType = type;
+	}
+
+	@Override
+	@Nullable
+	public String getContentType() {
+		return this.contentType;
+	}
+
+	@Override
+	public boolean containsHeader(String name) {
+		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			return this.contentLength != null;
+		}
+		else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
+			return this.contentType != null;
+		}
+		else {
+			return super.containsHeader(name);
+		}
+	}
+
+	@Override
+	public void setHeader(String name, String value) {
+		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			this.contentLength = Integer.valueOf(value);
+		}
+		else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
+			this.contentType = value;
+		}
+		else {
+			super.setHeader(name, value);
+		}
+	}
+
+	@Override
+	public void addHeader(String name, String value) {
+		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			this.contentLength = Integer.valueOf(value);
+		}
+		else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
+			this.contentType = value;
+		}
+		else {
+			super.addHeader(name, value);
+		}
+	}
+
+	@Override
+	public void setIntHeader(String name, int value) {
+		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			this.contentLength = Integer.valueOf(value);
+		}
+		else {
+			super.setIntHeader(name, value);
+		}
+	}
+
+	@Override
+	public void addIntHeader(String name, int value) {
+		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			this.contentLength = Integer.valueOf(value);
+		}
+		else {
+			super.addIntHeader(name, value);
+		}
+	}
+
+	@Override
+	@Nullable
+	public String getHeader(String name) {
+		if (HttpHeaders.CONTENT_LENGTH.equalsIgnoreCase(name)) {
+			return (this.contentLength != null) ? this.contentLength.toString() : null;
+		}
+		else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
+			return this.contentType;
+		}
+		else {
+			return super.getHeader(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();
+		}
+		else if (HttpHeaders.CONTENT_TYPE.equalsIgnoreCase(name)) {
+			return this.contentType != null ? Collections.singleton(this.contentType) : Collections.emptySet();
+		}
+		else {
+			return super.getHeaders(name);
+		}
+	}
+
+	@Override
+	public Collection<String> getHeaderNames() {
+		Collection<String> headerNames = super.getHeaderNames();
+		if (this.contentLength != null || this.contentType != null) {
+			List<String> result = new ArrayList<>(headerNames);
+			if (this.contentLength != null) {
+				result.add(HttpHeaders.CONTENT_LENGTH);
+			}
+			if (this.contentType != null) {
+				result.add(HttpHeaders.CONTENT_TYPE);
+			}
+			return result;
+		}
+		else {
+			return headerNames;
+		}
+	}
+
 	@Override
 	public void setBufferSize(int size) {
 		if (size > this.content.size()) {
@@ -197,12 +320,18 @@ public class ContentCachingResponseWrapper extends HttpServletResponseWrapper {
 	protected void copyBodyToResponse(boolean complete) throws IOException {
 		if (this.content.size() > 0) {
 			HttpServletResponse rawResponse = (HttpServletResponse) getResponse();
-			if ((complete || this.contentLength != null) && !rawResponse.isCommitted()) {
+			if (!rawResponse.isCommitted()) {
+				if (complete || this.contentLength != null) {
 					if (rawResponse.getHeader(HttpHeaders.TRANSFER_ENCODING) == null) {
 						rawResponse.setContentLength(complete ? this.content.size() : this.contentLength);
 					}
 					this.contentLength = null;
 				}
+				if (complete || this.contentType != null) {
+					rawResponse.setContentType(this.contentType);
+					this.contentType = null;
+				}
+			}
 			this.content.writeTo(rawResponse.getOutputStream());
 			this.content.reset();
 			if (complete) {

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

@@ -23,6 +23,7 @@ import jakarta.servlet.FilterChain;
 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.MockHttpServletRequest;
 import org.springframework.web.testfixture.servlet.MockHttpServletResponse;
@@ -68,6 +69,7 @@ class ShallowEtagHeaderFilterTests {
 		FilterChain filterChain = (filterRequest, filterResponse) -> {
 			assertThat(filterRequest).as("Invalid request passed").isEqualTo(request);
 			((HttpServletResponse) filterResponse).setStatus(HttpServletResponse.SC_OK);
+			filterResponse.setContentType(MediaType.TEXT_PLAIN_VALUE);
 			FileCopyUtils.copy(responseBody, filterResponse.getOutputStream());
 		};
 		filter.doFilter(request, response, filterChain);
@@ -75,6 +77,7 @@ class ShallowEtagHeaderFilterTests {
 		assertThat(response.getStatus()).as("Invalid status").isEqualTo(200);
 		assertThat(response.getHeader("ETag")).as("Invalid ETag").isEqualTo("\"0b10a8db164e0754105b7a99be72e3fe5\"");
 		assertThat(response.getContentLength()).as("Invalid Content-Length header").isGreaterThan(0);
+		assertThat(response.getContentType()).as("Invalid Content-Type header").isEqualTo(MediaType.TEXT_PLAIN_VALUE);
 		assertThat(response.getContentAsByteArray()).as("Invalid content").isEqualTo(responseBody);
 	}
 
@@ -88,6 +91,7 @@ class ShallowEtagHeaderFilterTests {
 		FilterChain filterChain = (filterRequest, filterResponse) -> {
 			assertThat(filterRequest).as("Invalid request passed").isEqualTo(request);
 			((HttpServletResponse) filterResponse).setStatus(HttpServletResponse.SC_OK);
+			filterResponse.setContentType(MediaType.TEXT_PLAIN_VALUE);
 			FileCopyUtils.copy(responseBody, filterResponse.getOutputStream());
 		};
 		filter.doFilter(request, response, filterChain);
@@ -95,6 +99,7 @@ class ShallowEtagHeaderFilterTests {
 		assertThat(response.getStatus()).as("Invalid status").isEqualTo(200);
 		assertThat(response.getHeader("ETag")).as("Invalid ETag").isEqualTo("W/\"0b10a8db164e0754105b7a99be72e3fe5\"");
 		assertThat(response.getContentLength()).as("Invalid Content-Length header").isGreaterThan(0);
+		assertThat(response.getContentType()).as("Invalid Content-Type header").isEqualTo(MediaType.TEXT_PLAIN_VALUE);
 		assertThat(response.getContentAsByteArray()).as("Invalid content").isEqualTo(responseBody);
 	}
 
@@ -108,14 +113,16 @@ class ShallowEtagHeaderFilterTests {
 		FilterChain filterChain = (filterRequest, filterResponse) -> {
 			assertThat(filterRequest).as("Invalid request passed").isEqualTo(request);
 			byte[] responseBody = "Hello World".getBytes(StandardCharsets.UTF_8);
-			FileCopyUtils.copy(responseBody, filterResponse.getOutputStream());
 			filterResponse.setContentLength(responseBody.length);
+			filterResponse.setContentType(MediaType.TEXT_PLAIN_VALUE);
+			FileCopyUtils.copy(responseBody, filterResponse.getOutputStream());
 		};
 		filter.doFilter(request, response, filterChain);
 
 		assertThat(response.getStatus()).as("Invalid status").isEqualTo(304);
 		assertThat(response.getHeader("ETag")).as("Invalid ETag").isEqualTo("\"0b10a8db164e0754105b7a99be72e3fe5\"");
 		assertThat(response.containsHeader("Content-Length")).as("Response has Content-Length header").isFalse();
+		assertThat(response.containsHeader("Content-Type")).as("Response has Content-Type header").isFalse();
 		byte[] expecteds = new byte[0];
 		assertThat(response.getContentAsByteArray()).as("Invalid content").isEqualTo(expecteds);
 	}