ASP.NET Core 的 HttpContex

HttpContext

HttpContext 类封装了HTTP Request 和 HTTP Response。
当收到一条HTTP Request 请求时，就会实例化一个HttpContext对象。HttpContext对象可以被中间件访问。
注意：HttpContext 不是线程安全的。

读取 HttpContext 的值

从Razer Page 读取

public class IndexModel : PageModel
{
    public void OnGet()
    {
        var message = HttpContext.Request.PathBase;
    }
}

从Razer Page 的cshtml 读取

@page
@model IndexModel
@{
    var message = HttpContext.Request.PathBase;
}

从 Controller 读取

public class HomeController : Controller
{
    public IActionResult About()
    {
        var pathBase = HttpContext.Request.PathBase;
        return View();
    }
}

从 Minimal API 读取

app.MapGet("/", (HttpContext context) => context.Response.WriteAsync("Hello World"));

修改 HttpContext.Request

HttpContext.Request 可以获取客户端发来的 HttpRequest 请求，并且可以修改其中的值，包括：

• HttpRequest.Path
• HttpRequest.Method
• HttpRequest.Headers
• HttpRequest.RouteValues
• HttpRequest.Query
• HttpRequest.ReadFormAsync()
• HttpRequest.Body

例如下面的代码：

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();
app.MapGet("/", (HttpRequest request) =>
{
    var userAgent = request.Headers.UserAgent;
    var customHeader = request.Headers["x-custom-header"];
    return Results.Ok(new { userAgent = userAgent, customHeader = customHeader });
});

app.Run();

修改 HttpContext.Response

除了能修改接收到的 HttpRequest，返回给客户端的 Response也可以修改。包括：

• HttpResponse.StatusCode
• HttpResponse.ContentType
• HttpResponse.Headers
• HttpResponse.Body

例子代码如下：

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", (HttpResponse response) =>
{
    response.Headers.CacheControl = "no-cache";
    response.Headers["x-custom-header"] = "Custom value";
    return Results.File(File.OpenRead("helloworld.txt"));
});

app.Run();

设置 Response 尾巴

HTTP/2 和 HTTP/3 支持 Response 尾巴，可以在返回 Response 后设置Response 尾巴。
例子代码如下：

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();
app.MapGet("/", (HttpResponse response) =>
{
    // Write body
    response.WriteAsync("Hello world");
    if (response.SupportsTrailers())
    {
        response.AppendTrailer("trailername", "TrailerValue");
    }
});
app.Run();

终止 HttpRequest

HttpContext.RequestAborted cancellation token 可以用于通知HttpRequest 已经被终止。
在请求时：

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

var httpClient = new HttpClient();
app.MapPost("/books/{bookId}", async (int bookId, HttpContext context) =>
{
    var stream = await httpClient.GetStreamAsync(
        $"http://consoto/books/{bookId}.json", context.RequestAborted);
    return Results.Stream(stream, "application/json");
});
app.Run();