runtime: HttpClient no longer sends header 'Accept-Encoding:"gzip, deflate"' and decompress 'gzip/deflate' content by default in .NET Core 2.0

This is a breaking change compared to netcoreapp1.1. In netcoreapp1.1, HttpClient automatically sends header "Accept-Encoding": "gzip, deflate" in the request, and automatically decompress ‘gzip/deflate’ content from the response. However, with netcoreapp2.0, HttpClient doesn’t send the header and stop automatically decompressing ‘gzip/deflate’ content.

Repro Steps

// Program.cs
using System;
using System.Net.Http;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var client = new HttpClient())
            {
                using (var request = new HttpRequestMessage(HttpMethod.Get, @"http://httpbin.org/headers"))
                {
                    var result = client.SendAsync(request).Result;
                    var payload = result.Content.ReadAsStringAsync().Result;
                    Console.WriteLine("Header Dict:\n{0}", payload);
                }
                
                using (var request = new HttpRequestMessage(HttpMethod.Get, @"http://httpbin.org/gzip"))
                {
                    var result = client.SendAsync(request).Result;
                    var payload = result.Content.ReadAsStringAsync().Result;
                    Console.WriteLine("Decompressed Content:\n{0}", payload);
                }
            }
        }
    }
}

With netcoreapp1.1 http://httpbin.org/headers just echos the request headers. You can see Accept-Encoding was sent by HttpClient. http://httpbin.org/gzip returns gzip-encoded data. You can see the content was automatically decompressed by HttpClient.

PS> dotnet restore
PS> dotnet run
Header Dict:
{
  "headers": {
    "Accept-Encoding": "gzip, deflate",
    "Connection": "close",
    "Host": "httpbin.org"
  }
}

Decompressed Content:
{
  "gzipped": true,
  "headers": {
    "Accept-Encoding": "gzip, deflate",
    "Connection": "close",
    "Host": "httpbin.org"
  },
  "method": "GET",
  "origin": "131.107.147.177"
}

With netcoreapp2.0 Accept-Encoding was not sent by HttpClient and the gzip-encoded data was not automatically decompressed.

PS> dotnet restore
PS> dotnet run
Header Dict:
{
  "headers": {
    "Connection": "close",
    "Host": "httpbin.org"
  }
}

Decompressed Content:
 W??X?%?A
?0E?9E???
nE? ^??C2????K??]??????r?.V?O?????*[5*?rJ8qR?+?>???U?"?E?q      ??v?>(?????
.h7??;??????
??

Environment

netcoreapp1.1

.NET Command Line Tools (1.0.1)

Product Information:
 Version:            1.0.1
 Commit SHA-1 hash:  005db40cd1

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.14393
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   ...\AppData\Local\Microsoft\dotnet\sdk\1.0.1

netcoreapp2.0

.NET Command Line Tools (2.0.0-preview1-005724)

Product Information:
 Version:            2.0.0-preview1-005724
 Commit SHA-1 hash:  e391b5d5f3

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.14393
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   ...\AppData\Local\Microsoft\dotnet\sdk\2.0.0-preview1-005724\