http - 在 .Net 中将 HTTP 2 与 HttpClient 结合使用

Question

我正在尝试通过 HTTP 2.0 请求数据。我正在使用 .Net Core 2.2 中的 HttpClient。我在 Windows 10 上，但在生产环境中将在 Linux 上运行。问题是响应中的版本似乎总是“1.1”。我做错了什么？

using (var client = new HttpClient())
{
    using (var request = new HttpRequestMessage(new HttpMethod("GET"),
    "https://duckduckgo.com/"
    ))
    {
        request.Version = new Version(2, 0);
        var response = await client.SendAsync(request);

        Console.WriteLine(response.Version);
    }
}

Answer 1

更新 - .NET Core 3.0

.NET Core 3.0 现在 supports HTTP/2 .以下代码将打印 2.0 :

var client = new HttpClient();

var req = new HttpRequestMessage(HttpMethod.Get, "https://http2.akamai.com/demo"){
             Version = new Version(2, 0) 
             };

var x = await client.SendAsync(req);
var version = x.Version;

Console.WriteLine(version);

原始答案

你 can't use HTTP/2 with HttpClient in .NET Core 2.1 or 2.2 ，即使您在请求中明确设置了版本。您必须显式配置 .NET Core 以使用 .NET Core 2.0 附带的旧 HttpClientHandler 实例，方法是通过以下方式设置 App Context 开关:

AppContext.SetSwitch("System.Net.Http.UseSocketsHttpHandler", false);

或者通过将 DOTNET_SYSTEM_NET_HTTP_USESOCKETSHTTPHANDLER 环境变量设置为 0 或 false。

this Github issue 中的讨论表明 .NET Core 3.0 计划支持 HTTP/2。 Microsoft Connect 2018 上发布的 3.0 Preview 1 尚不支持 HTTP/2。

HttpClientHandler 使用到 .NET Core 2.0 支持 HTTP/2。以下代码将在以 Core 2.0 为目标的项目中返回 2.0:

var client = new HttpClient();

var req = new HttpRequestMessage(HttpMethod.Get, "https://http2.akamai.com/demo")
{
    Version = new Version(2, 0)
};

var x = await client.SendAsync(req);
var version = x.Version;

Console.WriteLine(version);

只要确保在更改目标运行时时彻底清理项目 - 删除 bin、obj 和 所有目标文件，或者您可能最终会像我一样运行错误的运行时。

在 2.1 中，默认添加了一个新的、更快的 SocketsHttpClientHandler。新的处理程序尚不支持 HTTP/2。相同的代码将返回 1.1 作为协议(protocol)版本。

如果在创建 HttpClient 之前设置了应用上下文切换，则使用 HTTP/2。此代码将返回 2.0。有趣的是，无需指定 HTTP 版本。当 HTTP/2 可用时，将协商实际的协议(protocol)版本。 Akamai URL 和 https://www.google.com 都将使用 HTTP/2，即使未指定版本也是如此:

AppContext.SetSwitch("System.Net.Http.UseSocketsHttpHandler", false);
var client = new HttpClient();

var req = new HttpRequestMessage(HttpMethod.Get, "https://http2.akamai.com/demo");
var x = await client.SendAsync(req);

var version = x.Version;

switch和环境变量在官方公告中有说明.NET Core 2.1 SDK Preview 2 :

Sockets Performance and SocketsHttpHandler

We made major improvements to sockets in .NET Core 2.1. Sockets are the basis of both outgoing and incoming networking communication. The higher-level networking APIs in .NET Core 2.1, including HttpClient and Kestrel, are now based on .NET sockets. In earlier versions, these higher-level APIs were based on native networking implementations.

...

You can use one of the following mechanisms to configure a process to use the older HttpClientHandler:

From code, use the AppContext class:

AppContext.SetSwitch("System.Net.Http.UseSocketsHttpHandler", false);

The AppContext switch can also be set by config file.

The same can be achieved via the environment variable DOTNET_SYSTEM_NET_HTTP_USESOCKETSHTTPHANDLER. To opt out, set the value to either false or 0.