Add Content to all HttpResponseMessages

- also, do _not_ require `Stream.CanSeek` when calculating `HttpMessageContent.ContentLength` value
  - this changes behaviour slightly for both requests and responses
    - observable as `HttpMessageContent.Headers.ContentLength!=null` for empty messages
  - for responses, avoids `ContentLength==null` versus `ContentLength==0` inconsistencies (depending on platform)
  - `ContentLength==null` may still occur in some corner cases (which existed before)
    - e.g. when inner `HttpContent` doesn't know its length and `ReadAsStreamAsync()` hasn't completed
- main change means `HttpResponseMessage`s we expose to user code are consistent across platforms
  - note: user code won't see `EmptyContent` in `HttpResponseMessage`s we create

Author: dougbu

src/System.Net.Http.Formatting/HttpContentMessageExtensions.cs

@@ -451,7 +451,7 @@ private static HttpContent CreateHeaderFields(HttpHeaders source, HttpHeaders de
             Contract.Assert(destination != null, "destination headers cannot be null");
             Contract.Assert(contentStream != null, "contentStream must be non null");
             HttpContentHeaders contentHeaders = null;
-            HttpContent content = null;
+            HttpContent content;
 
             // Set the header fields
             foreach (KeyValuePair<string, IEnumerable<string>> header in source)
@@ -481,6 +481,10 @@ private static HttpContent CreateHeaderFields(HttpHeaders source, HttpHeaders de
                 content = new StreamContent(contentStream);
                 contentHeaders.CopyTo(content.Headers);
             }
+            else
+            {
+                content = new StreamContent(Stream.Null);
+            }
 
             return content;
         }

src/System.Net.Http.Formatting/HttpMessageContent.cs

@@ -190,7 +190,7 @@ protected override async Task SerializeToStreamAsync(Stream stream, TransportCon
             if (Content != null)
             {
                 Stream readStream = await _streamTask.Value;
-                ValidateStreamForReading(readStream);
+                ValidateStreamForReading(readStream); // ???
                 await Content.CopyToAsync(stream);
             }
         }
@@ -205,6 +205,7 @@ protected override async Task SerializeToStreamAsync(Stream stream, TransportCon
         protected override bool TryComputeLength(out long length)
         {
             // We have four states we could be in:
+            //   0. We have content and it knows its ContentLength.
             //   1. We have content, but the task is still running or finished without success
             //   2. We have content, the task has finished successfully, and the stream came back as a null or non-seekable
             //   3. We have content, the task has finished successfully, and the stream is seekable, so we know its length
@@ -214,11 +215,13 @@ protected override bool TryComputeLength(out long length)
             // For #3, we return true & the size of our headers + the content length
             // For #4, we return true & the size of our headers
 
-            bool hasContent = _streamTask.Value != null;
             length = 0;
 
-            // Cases #1, #2, #3
-            if (hasContent)
+            if (Content?.Headers.ContentLength is not null)
+            {
+                length = (long)Content.Headers.ContentLength; // Case #0
+            }
+            else if (_streamTask.Value is not null)
             {
                 Stream readStream;
                 if (!_streamTask.Value.TryGetResult(out readStream) // Case #1
@@ -354,7 +357,7 @@ private byte[] SerializeHeader()
             return Encoding.UTF8.GetBytes(message.ToString());
         }
 
-        private void ValidateStreamForReading(Stream stream)
+        private void ValidateStreamForReading(Stream stream) // ???
         {
             // If the content needs to be written to a target stream a 2nd time, then the stream must support
             // seeking (e.g. a FileStream), otherwise the stream can't be copied a second time to a target

src/System.Net.Http.Formatting/HttpRequestMessageExtensions.cs

@@ -3,6 +3,7 @@
 
 using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
+using System.IO;
 using System.Web.Http;
 
 namespace System.Net.Http
@@ -29,6 +30,7 @@ public static HttpResponseMessage CreateResponse(this HttpRequestMessage request
 
             return new HttpResponseMessage
             {
+                Content = new StreamContent(Stream.Null),
                 StatusCode = statusCode,
                 RequestMessage = request
             };
@@ -49,6 +51,7 @@ public static HttpResponseMessage CreateResponse(this HttpRequestMessage request
 
             return new HttpResponseMessage
             {
+                Content = new StreamContent(Stream.Null),
                 RequestMessage = request
             };
         }

test/System.Net.Http.Formatting.Test/Formatting/JsonMediaTypeFormatterTests.cs

@@ -11,12 +11,10 @@
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.TestCommon;
-using Moq;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 
-namespace System.Net.Http.Formatting
-{
+namespace System.Net.Http.Formatting {
     public class JsonMediaTypeFormatterTests : MediaTypeFormatterTestBase<JsonMediaTypeFormatter>
     {
         // Test data which should round-trip without type information in the serialization.  Contains an exhaustive
@@ -588,7 +586,7 @@ public override async Task WriteToStreamAsync_WhenObjectIsNull_WritesDataButDoes
             // Arrange
             JsonMediaTypeFormatter formatter = CreateFormatter();
             Stream stream = new MemoryStream();
-            HttpContent content = new StringContent(String.Empty);
+            HttpContent content = new StreamContent(Stream.Null);
 
             // Act
             await formatter.WriteToStreamAsync(typeof(SampleType), null, stream, content, null);

test/System.Net.Http.Formatting.Test/Handlers/ProgressMessageHandlerTest.cs

@@ -84,15 +84,8 @@ public async Task SendAsync_InsertsReceiveProgressWhenResponseEntityPresent(bool
                 }
                 else
                 {
-#if NET6_0_OR_GREATER
-                    // Test initialization (request.CreateResponse() near the end of this file) for this case leaves
-                    // response.Content non-null (an EmptyContent or StreamContent instance). Those types are internal.
-                    // Just confirm the length matches expectations.
                     Assert.NotNull(response.Content);
                     Assert.Equal(0L, response.Content.Headers.ContentLength);
-#else
-                    Assert.Null(response.Content);
-#endif
                 }
             }
         }

test/System.Net.Http.Formatting.Test/Handlers/ProgressStreamTest.cs

@@ -274,7 +274,7 @@ internal static ProgressStream CreateProgressStream(
             Stream iStream = innerStream ?? new Mock<Stream>().Object;
             ProgressMessageHandler pHandler = progressMessageHandler ?? new ProgressMessageHandler();
             HttpRequestMessage req = request ?? new HttpRequestMessage();
-            HttpResponseMessage rsp = response ?? new HttpResponseMessage();
+            HttpResponseMessage rsp = response ?? new HttpResponseMessage() { Content = new StreamContent(Stream.Null) };
             return new ProgressStream(iStream, pHandler, req, rsp);
         }
 

test/System.Net.Http.Formatting.Test/HttpMessageContentTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System.IO;
 using System.Net.Http.Headers;
 using System.Threading.Tasks;
 using Microsoft.TestCommon;
@@ -39,10 +40,8 @@ private static HttpResponseMessage CreateResponse(bool containsEntity)
             httpResponse.ReasonPhrase = ParserData.HttpReasonPhrase;
             httpResponse.Version = new Version("1.2");
             AddMessageHeaders(httpResponse.Headers);
-            if (containsEntity)
-            {
-                httpResponse.Content = new StringContent(ParserData.HttpMessageEntity);
-            }
+            httpResponse.Content =
+                containsEntity ? new StringContent(ParserData.HttpMessageEntity) : new StreamContent(Stream.Null);
 
             return httpResponse;
         }
@@ -77,20 +76,6 @@ private static async Task ValidateResponse(HttpContent content, bool containsEnt
         {
             Assert.Equal(ParserData.HttpResponseMediaType, content.Headers.ContentType);
 
-#if NET6_0_OR_GREATER
-            // Test initialization leaves the inner HttpContent (EmptyContent or StreamContent) w/ a non-null but
-            // unseekable Stream (EmptyReadStream). HttpMessageContent believes the message has content but is unable
-            // to calculate the message length correctly in this case. Overriding the Content e.g. w/ a StringContent
-            // makes things worse because the serialized content then contains unexpected Content-Type and
-            // Content-Length headers i.e. ParserData.HttpResponseWithEntity looks _smaller_ than
-            // ParserData.HttpResponse  though the opposite would be true in any real scenario. Buffer the
-            // HttpMessageContent to give it a better chance at calculating the length.
-            if (!containsEntity)
-            {
-                await content.LoadIntoBufferAsync();
-            }
-#endif
-
             long? length = content.Headers.ContentLength;
             Assert.NotNull(length);
 

test/System.Net.Http.Formatting.Test/ParserData.cs

@@ -198,14 +198,15 @@ public static TheoryDataSet<string> InvalidStatusCodes
             ((int)HttpStatus).ToString() +
             " " +
             HttpReasonPhrase +
-            "\r\nN1: V1a, V1b, V1c, V1d, V1e\r\nN2: V2\r\n\r\n";
+            "\r\nN1: V1a, V1b, V1c, V1d, V1e\r\nN2: V2\r\nContent-Length: 0\r\n\r\n";
 
         public static readonly string HttpRequestWithEntity =
             HttpMethod +
             " /some/path HTTP/1.2\r\nHost: " +
             HttpHostName +
             "\r\nN1: V1a, V1b, V1c, V1d, V1e\r\nN2: V2\r\nContent-Type: " +
             TextContentType +
+            "\r\nContent-Length: 100" +
             "\r\n\r\n" +
             HttpMessageEntity;
 
@@ -216,6 +217,7 @@ public static TheoryDataSet<string> InvalidStatusCodes
             HttpReasonPhrase +
             "\r\nN1: V1a, V1b, V1c, V1d, V1e\r\nN2: V2\r\nContent-Type: " +
             TextContentType +
+            "\r\nContent-Length: 100" +
             "\r\n\r\n" +
             HttpMessageEntity;
     }

test/System.Web.Http.Test/Controllers/VoidResultConverterTest.cs

@@ -31,7 +31,8 @@ public void Convert_ReturnsResponseMessageWithRequestAssignedAndNoContentToRefle
             var result = _converter.Convert(_context, null);
 
             Assert.Equal(HttpStatusCode.NoContent, result.StatusCode);
-            Assert.Null(result.Content);
+            Assert.NotNull(result.Content);
+            Assert.Equal(0L, result.Content.Headers.ContentLength);
             Assert.Same(_request, result.RequestMessage);
         }
     }

test/System.Web.Http.WebHost.Test/WebHostExceptionHandlerTests.cs

@@ -220,7 +220,8 @@ public async Task HandleAsync_IfCatchBlockIsWebHostBufferedContent_WithCreateExc
                 {
                     Assert.NotNull(response);
                     Assert.Equal(HttpStatusCode.InternalServerError, response.StatusCode);
-                    Assert.Null(response.Content);
+                    Assert.NotNull(response.Content);
+                    Assert.Equal(0L, response.Content.Headers.ContentLength);
                     Assert.Same(expectedRequest, response.RequestMessage);
                 }
             }