Add Vary: Accept-Encoding if response MIME type is compressible

Author: JunTaoLuo

src/Microsoft.AspNetCore.ResponseCompression/BodyWrapperStream.cs

@@ -211,6 +211,24 @@ private void OnWrite()
                 _compressionChecked = true;
                 if (_provider.ShouldCompressResponse(_context))
                 {
+                    // If the MIME type indicates that the response could be compressed, caches will need to vary by the Accept-Encoding header
+                    var varyValues = _context.Response.Headers.GetCommaSeparatedValues(HeaderNames.Vary);
+                    var varyByAcceptEncoding = false;
+
+                    for (var i = 0; i < varyValues.Length; i++)
+                    {
+                        if (string.Equals(varyValues[i], HeaderNames.AcceptEncoding, StringComparison.OrdinalIgnoreCase))
+                        {
+                            varyByAcceptEncoding = true;
+                            break;
+                        }
+                    }
+
+                    if (!varyByAcceptEncoding)
+                    {
+                        _context.Response.Headers.Append(HeaderNames.Vary, HeaderNames.AcceptEncoding);
+                    }
+
                     var compressionProvider = ResolveCompressionProvider();
                     if (compressionProvider != null)
                     {

test/Microsoft.AspNetCore.ResponseCompression.Tests/BodyWrapperStreamTests.cs

@@ -7,13 +7,33 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
+using Microsoft.Net.Http.Headers;
 using Moq;
 using Xunit;
 
 namespace Microsoft.AspNetCore.ResponseCompression.Tests
 {
     public class BodyWrapperStreamTests
     {
+        [Theory]
+        [InlineData(null, "Accept-Encoding")]
+        [InlineData("", "Accept-Encoding")]
+        [InlineData("AnotherHeader", "AnotherHeader,Accept-Encoding")]
+        [InlineData("Accept-Encoding", "Accept-Encoding")]
+        [InlineData("accepT-encodinG", "accepT-encodinG")]
+        [InlineData("accept-encoding,AnotherHeader", "accept-encoding,AnotherHeader")]
+        public void OnWrite_AppendsAcceptEncodingToVaryHeader_IfNotPresent(string providedVaryHeader, string expectedVaryHeader)
+        {
+            var httpContext = new DefaultHttpContext();
+            httpContext.Response.Headers[HeaderNames.Vary] = providedVaryHeader;
+            var stream = new BodyWrapperStream(httpContext, new MemoryStream(), new MockResponseCompressionProvider(flushable: true), null, null);
+
+            stream.Write(new byte[] { }, 0, 0);
+
+
+            Assert.Equal(expectedVaryHeader, httpContext.Response.Headers[HeaderNames.Vary]);
+        }
+
         [Theory]
         [InlineData(true)]
         [InlineData(false)]

test/Microsoft.AspNetCore.ResponseCompression.Tests/ResponseCompressionMiddlewareTest.cs

@@ -36,7 +36,7 @@ public async Task Request_NoAcceptEncoding_Uncompressed()
         {
             var response = await InvokeMiddleware(100, requestAcceptEncodings: null, responseType: TextPlain);
 
-            CheckResponseNotCompressed(response, expectedBodyLength: 100);
+            CheckResponseNotCompressed(response, expectedBodyLength: 100, sendVaryHeader: false);
         }
 
         [Fact]
@@ -52,7 +52,7 @@ public async Task Request_AcceptUnknown_NotCompressed()
         {
             var response = await InvokeMiddleware(100, requestAcceptEncodings: new string[] { "unknown" }, responseType: TextPlain);
 
-            CheckResponseNotCompressed(response, expectedBodyLength: 100);
+            CheckResponseNotCompressed(response, expectedBodyLength: 100, sendVaryHeader: true);
         }
 
         [Theory]
@@ -149,7 +149,7 @@ public async Task MimeTypes_OtherContentTypes_NoMatch(string contentType)
 
             var response = await client.SendAsync(request);
 
-            CheckResponseNotCompressed(response, expectedBodyLength: 100);
+            CheckResponseNotCompressed(response, expectedBodyLength: 100, sendVaryHeader: false);
         }
 
         [Theory]
@@ -185,7 +185,7 @@ public async Task NoBody_NotCompressed(string contentType)
 
             var response = await client.SendAsync(request);
 
-            CheckResponseNotCompressed(response, expectedBodyLength: 0);
+            CheckResponseNotCompressed(response, expectedBodyLength: 0, sendVaryHeader: false);
         }
 
         [Fact]
@@ -201,7 +201,7 @@ public async Task Request_AcceptIdentity_NotCompressed()
         {
             var response = await InvokeMiddleware(100, requestAcceptEncodings: new string[] { "identity" }, responseType: TextPlain);
 
-            CheckResponseNotCompressed(response, expectedBodyLength: 100);
+            CheckResponseNotCompressed(response, expectedBodyLength: 100, sendVaryHeader: true);
         }
 
         [Theory]
@@ -221,15 +221,15 @@ public async Task Request_AcceptWithhigherIdentityQuality_NotCompressed(string[]
         {
             var response = await InvokeMiddleware(100, requestAcceptEncodings: acceptEncodings, responseType: TextPlain);
 
-            CheckResponseNotCompressed(response, expectedBodyLength: expectedBodyLength);
+            CheckResponseNotCompressed(response, expectedBodyLength: expectedBodyLength, sendVaryHeader: true);
         }
 
         [Fact]
         public async Task Response_UnknownMimeType_NotCompressed()
         {
             var response = await InvokeMiddleware(100, requestAcceptEncodings: new string[] { "gzip" }, responseType: "text/custom");
 
-            CheckResponseNotCompressed(response, expectedBodyLength: 100);
+            CheckResponseNotCompressed(response, expectedBodyLength: 100, sendVaryHeader: false);
         }
 
         [Fact]
@@ -240,7 +240,7 @@ public async Task Response_WithContentRange_NotCompressed()
                 r.Headers[HeaderNames.ContentRange] = "1-2/*";
             });
 
-            CheckResponseNotCompressed(response, expectedBodyLength: 50);
+            CheckResponseNotCompressed(response, expectedBodyLength: 50, sendVaryHeader: false);
         }
 
         [Fact]
@@ -446,7 +446,7 @@ public async Task FlushAsyncBody_CompressesAndFlushes()
             request.Headers.AcceptEncoding.ParseAdd("gzip");
 
             var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead);
-            
+
             IEnumerable<string> contentMD5 = null;
             Assert.False(response.Headers.TryGetValues(HeaderNames.ContentMD5, out contentMD5));
             Assert.Single(response.Content.Headers.ContentEncoding, "gzip");
@@ -662,7 +662,7 @@ public async Task SendFileAsync_DifferentContentType_NotBypassed()
 
             var response = await client.SendAsync(request);
 
-            CheckResponseNotCompressed(response, expectedBodyLength: 1024);
+            CheckResponseNotCompressed(response, expectedBodyLength: 1024, sendVaryHeader: false);
 
             Assert.True(fakeSendFile.Invoked);
         }
@@ -793,13 +793,40 @@ private void CheckResponseCompressed(HttpResponseMessage response, int expectedB
         {
             IEnumerable<string> contentMD5 = null;
 
+            var containsVaryAcceptEncoding = false;
+            foreach (var value in response.Headers.GetValues(HeaderNames.Vary))
+            {
+                if (value.Contains(HeaderNames.AcceptEncoding))
+                {
+                    containsVaryAcceptEncoding = true;
+                    break;
+                }
+            }
+            Assert.True(containsVaryAcceptEncoding);
             Assert.False(response.Headers.TryGetValues(HeaderNames.ContentMD5, out contentMD5));
             Assert.Single(response.Content.Headers.ContentEncoding, "gzip");
             Assert.Equal(expectedBodyLength, response.Content.Headers.ContentLength);
         }
 
-        private void CheckResponseNotCompressed(HttpResponseMessage response, int expectedBodyLength)
+        private void CheckResponseNotCompressed(HttpResponseMessage response, int expectedBodyLength, bool sendVaryHeader)
         {
+            if (sendVaryHeader)
+            {
+                var containsVaryAcceptEncoding = false;
+                foreach (var value in response.Headers.GetValues(HeaderNames.Vary))
+                {
+                    if (value.Contains(HeaderNames.AcceptEncoding))
+                    {
+                        containsVaryAcceptEncoding = true;
+                        break;
+                    }
+                }
+                Assert.True(containsVaryAcceptEncoding);
+            }
+            else
+            {
+                Assert.False(response.Headers.Contains(HeaderNames.Vary));
+            }
             Assert.NotNull(response.Headers.GetValues(HeaderNames.ContentMD5));
             Assert.Empty(response.Content.Headers.ContentEncoding);
             Assert.Equal(expectedBodyLength, response.Content.Headers.ContentLength);