我正在尝试通过HTTP 2.0请求数据。我正在使用来自.Net Core 2.2的HttpClient。我正在使用Windows 10，但将在生产中运行Linux。问题是响应中的版本似乎始终为“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);
}
}
更新- .NET Core 3.0
.NET Core 3.0现在支持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);
原始回答
即使你在请求中明确设置了版本号，也无法在.NET Core 2.1或2.2中使用HttpClient的HTTP/2。你需要显式配置.NET Core以使用随.NET Core 2.0一起提供的旧HttpClientHandler实例，可以通过设置App Context开关来实现：
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。
这个Github问题中的讨论显示，.NET Core 3.0计划支持HTTP/2。在Microsoft Connect 2018发布的3.0 Preview 1尚不支持HTTP/2。
HttpClientHandler在.NET Core 2.0之前使用支持HTTP/2。以下代码将在针对Core 2.0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);
如果更改目标运行时，请确保彻底清理项目-删除bin，obj和所有目标文件，否则可能会像我一样使用错误的运行时。
在2.1中，默认添加了一个新的、速度更快的SocketsHttpClientHandler。这个新的处理程序尚不支持HTTP/2。相同的代码将返回协议版本1.1。
但是，如果在创建HttpClient之前设置应用程序上下文切换，则会使用HTTP/2。此代码将返回协议版本2.0。有趣的是，无需指定HTTP版本。当HTTP/2可用时，实际协议版本是经过协商的。即使未指定版本，Akamai URL和https://www.google.com都将使用HTTP/2：
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;
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.
目前建议的模式是在ConfigureServices方法中注册HttpClient依赖项: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/http-requests.
以下是使用类型化客户端注册默认HttpClient并配置其使用HTTP/2的示例:
public void ConfigureServices(IServiceCollection services)
{
...
services.AddHttpClient<ExampleService>()
.ConfigureHttpClient((client) =>
{
client.DefaultRequestVersion = new Version(2, 0);
});
...
}