ASP.NET Core使用中间件修改HTTP请求标头

Question

All I need to do is to modify [Connection] HTTP Header from "Keep-alive" to lowercase "keep-alive".

I wrote the class,

public class PreRequestModifications
{

    private readonly RequestDelegate _next;

    public PreRequestModifications(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        // Does not get called when making an HTTPWebRequest.   
        await _next.Invoke(context);              
    }
}

and registered on startup,

 public void Configure(IApplicationBuilder app, IHostingEnvironment env)
 {    
     app.UseMiddleware<PreRequestModifications>();
 }

but the Invoke method does not get called when I execute await httpWebRequest.GetResponseAsync();

Answer 1

So middleware gets hit when a request is made and when a response is sent back. Effectively this means you can move through the Invoke method twice like so:

public async Task Invoke(HttpContext context)
{
  ModifyRequest(context);
  await _next(context);
  ModifyResponse(context);
}

So you can modify the response in the ModifyResponse method.

Microsoft's documentation will make it clearer: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/middleware/?view=aspnetcore-2.1

Hopefully this helps.

Answer 2

Have you registered your middleware in the DI system? You need to do so in your Startup class, ConfigureServices method:

services.AddScoped<IMiddleware, SomeMiddleware>();