C# How to set HttpClient Keep-Alive to false

问题:

I had a low performance problem with HTTP requests on .NET. The HTTP GET request to a REST API on the localhost took about 500 ms to complete. I spent a lot of time to fix it. I have tried many ways: HttpClient, HttpWebRequest, WebClient and RestSharp. None of them work. Most solutions on the Internet said to set Proxy parameter to null but it still won't work faster.

The only way I found to reduce this time is to set the Keep-Alive parameter of request to false:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
request.Method = "GET";
request.KeepAlive = false;

HttpWebResponse response = (HttpWebResponse)request.GetResponse();

This works great. Time is reduced to 7-10 ms. But now in some reasons I need to use HttpClient instead of HttpWebRequest. And I can't find how to set Keep-Alive to false for HttpClient. The only thing I found is how to set it to true by setting a "connection" header to "Keep-Alive".

I am using this code for POST request by HttpClient:

        HttpClient _http = new HttpClient();
        _http.DefaultRequestHeaders.Accept.Clear();
        _http.DefaultRequestHeaders.Add("Connection", "Keep-Alive");
        _http.DefaultRequestHeaders.Add("Keep-Alive", "timeout=600");

        var content = new StringContent(
            request, Encoding.UTF8, "application/%appname%+xml");
        content.Headers.ContentType.Parameters.Add(
            new NameValueHeaderValue("type", "payload"));

        HttpResponseMessage response = await _http.PostAsync(uri, content);

And it still takes about 500-600 ms to complete.

回答1:

When you set HttpWebRequest.KeepAlive = true the header set is Connection: keep-alive

When you set HttpWebRequest.KeepAlive = false the header set is Connection: close

So you will need

_http.DefaultRequestHeaders.Add("Connection", "close");

回答2:

Use this code to disable HTTP Keep-Alive on the client:

_http.DefaultRequestHeaders.ConnectionClose = true;

This will set Connection request header to close.

回答3:

See code below:

HttpClient cli;
...
cli.DefaultRequestHeaders.Add("Connection", "keep-alive");
cli.DefaultRequestHeaders.Add("Keep-Alive", "600");

回答4:

I hope this can help you, I have tested

_client.DefaultRequestHeaders.Connection.Add("Keep-Alive");

回答5:

I wrote HttpClientHandler, and in the handler just before the request I deleted the header "Connection". In this case, it sets the default "Connection: keep-alive". Even if before that you put it in the HttpClient by default, set properties, etc. Check your handlers.