ShallowEtagHeaderFilter writes body early on sendError/sendRedirect and interprets setContentLength/setBufferSize as a hint for capacity increase

Issue: SPR-11705
Issue: SPR-11717

spring-web/src/main/java/org/springframework/web/filter/ShallowEtagHeaderFilter.java

@@ -72,14 +72,15 @@ public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
 	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
 			throws ServletException, IOException {
 
+		HttpServletResponse responseToUse = response;
 		if (!isAsyncDispatch(request)) {
-			response = new ShallowEtagResponseWrapper(response);
+			responseToUse = new ShallowEtagResponseWrapper(response);
 		}
 
-		filterChain.doFilter(request, response);
+		filterChain.doFilter(request, responseToUse);
 
 		if (!isAsyncStarted(request)) {
-			updateResponse(request, response);
+			updateResponse(request, responseToUse);
 		}
 	}
 
@@ -88,41 +89,44 @@ public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
 				WebUtils.getNativeResponse(response, ShallowEtagResponseWrapper.class);
 		Assert.notNull(responseWrapper, "ShallowEtagResponseWrapper not found");
 
-		response = (HttpServletResponse) responseWrapper.getResponse();
-		byte[] body = responseWrapper.toByteArray();
+		HttpServletResponse rawResponse = (HttpServletResponse) responseWrapper.getResponse();
 		int statusCode = responseWrapper.getStatusCode();
+		byte[] body = responseWrapper.toByteArray();
 
-		if (isEligibleForEtag(request, responseWrapper, statusCode, body)) {
+		if (rawResponse.isCommitted()) {
+			if (body.length > 0) {
+				StreamUtils.copy(body, rawResponse.getOutputStream());
+			}
+		}
+		else if (isEligibleForEtag(request, responseWrapper, statusCode, body)) {
 			String responseETag = generateETagHeaderValue(body);
-			response.setHeader(HEADER_ETAG, responseETag);
-
+			rawResponse.setHeader(HEADER_ETAG, responseETag);
 			String requestETag = request.getHeader(HEADER_IF_NONE_MATCH);
 			if (responseETag.equals(requestETag)) {
 				if (logger.isTraceEnabled()) {
 					logger.trace("ETag [" + responseETag + "] equal to If-None-Match, sending 304");
 				}
-				response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
+				rawResponse.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
 			}
 			else {
 				if (logger.isTraceEnabled()) {
 					logger.trace("ETag [" + responseETag + "] not equal to If-None-Match [" + requestETag +
 							"], sending normal response");
 				}
-				copyBodyToResponse(body, response);
+				if (body.length > 0) {
+					rawResponse.setContentLength(body.length);
+					StreamUtils.copy(body, rawResponse.getOutputStream());
+				}
 			}
 		}
 		else {
 			if (logger.isTraceEnabled()) {
 				logger.trace("Response with status code [" + statusCode + "] not eligible for ETag");
 			}
-			copyBodyToResponse(body, response);
-		}
-	}
-
-	private void copyBodyToResponse(byte[] body, HttpServletResponse response) throws IOException {
-		if (body.length > 0) {
-			response.setContentLength(body.length);
-			StreamUtils.copy(body, response.getOutputStream());
+			if (body.length > 0) {
+				rawResponse.setContentLength(body.length);
+				StreamUtils.copy(body, rawResponse.getOutputStream());
+			}
 		}
 	}
 
@@ -202,19 +206,22 @@ public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
 
 		@Override
 		public void sendError(int sc) throws IOException {
+			copyBodyToResponse();
 			super.sendError(sc);
 			this.statusCode = sc;
 		}
 
 		@Override
 		public void sendError(int sc, String msg) throws IOException {
+			copyBodyToResponse();
 			super.sendError(sc, msg);
 			this.statusCode = sc;
 		}
 
 		@Override
-		public void setContentLength(int len) {
-			this.content.resize(len);
+		public void sendRedirect(String location) throws IOException {
+			copyBodyToResponse();
+			super.sendRedirect(location);
 		}
 
 		@Override
@@ -233,9 +240,17 @@ public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
 		}
 
 		@Override
-		public void reset() {
-			super.reset();
-			resetBuffer();
+		public void setContentLength(int len) {
+			if (len > this.content.capacity()) {
+				this.content.resize(len);
+			}
+		}
+
+		@Override
+		public void setBufferSize(int size) {
+			if (size > this.content.capacity()) {
+				this.content.resize(size);
+			}
 		}
 
 		@Override
@@ -243,6 +258,12 @@ public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
 			this.content.reset();
 		}
 
+		@Override
+		public void reset() {
+			super.reset();
+			this.content.reset();
+		}
+
 		public int getStatusCode() {
 			return this.statusCode;
 		}
@@ -251,6 +272,14 @@ public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
 			return this.content.toByteArray();
 		}
 
+		private void copyBodyToResponse() throws IOException {
+			if (this.content.size() > 0) {
+				getResponse().setContentLength(this.content.size());
+				StreamUtils.copy(this.content.toByteArray(), getResponse().getOutputStream());
+				this.content.reset();
+			}
+		}
+
 
 		private class ResponseServletOutputStream extends ServletOutputStream {