HttpWebRequest突然停止工作，几个请求后没有收到响应

Question

I'm working with a WPF .net 4.0 Application. I have a search bar. For each search token I need to do 8 http request to 8 separate URLs to get search results. I send 8 requests to server after 400 milliseconds once the user stops typing in search bar. Searching for 6 to 7 search-tokens results comes very nicely. But after that suddenly HttpWebRequest stops working silently. No exception was thrown, no response was received. I'm working with Windows 7, I disabled the firewall too. I don't know where the subsequent http requests are lost.

Can anyone show me lights to fix this issue?

Below is my code for HttpWebRequest call.

public static void SendReq(string url)
{
    // Create a new HttpWebRequest object.
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);

    request.ContentType = "application/x-www-form-urlencoded";
    request.Proxy = new WebProxy("192.168.1.1", 8000);

    // Set the Method property to 'POST' to post data to the URI.
    request.Method = "POST";

    // start the asynchronous operation
    request.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), request);

}

private static void GetRequestStreamCallback(IAsyncResult asynchronousResult)
{
    HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;

    // End the operation
    Stream postStream = request.EndGetRequestStream(asynchronousResult);

    string postData = this.PostData;

    // Convert the string into a byte array. 
    byte[] byteArray = Encoding.UTF8.GetBytes(postData);

    // Write to the request stream.
    postStream.Write(byteArray, 0, byteArray.Length);
    postStream.Close();

    // Start the asynchronous operation to get the response
    request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
}

private static void GetResponseCallback(IAsyncResult asynchronousResult)
{
    HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;

    // End the operation
    using(HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult))
    {
        using(Stream streamResponse = response.GetResponseStream())
        {
             using(StreamReader streamRead = new StreamReader(streamResponse))
             {
                 string responseString = streamRead.ReadToEnd();
                 Debug.WriteLine(responseString);
             }
        }
    }
}

Answer 1

I think i am very late, but i still want to answer your question, may be it can be helpful to others. By default HTTP Request you make are HTTP 1.1 requests. And HTTP 1.1 Request by default has Keep-Alive connection. so when you make too many request to same server .net framework only make x no. of request.

you should close all your response by response.Close()

you can also specify how many simultaneous requests you can make.

ServicePointManager.DefaultConnectionLimit = 20;

Note that you have to set DefaultConnectionLimit before the first request you make. you can find more information here on msdn .

Answer 2

All i can see is that in GetRequestStreamCallback you should replace

postStream.Write(byteArray, 0, postData.Length);

by

postStream.Write(byteArray, 0, byteArray.Length);

since these length aren't necessarily equal.

Answer 3

@Somnath I am not sure if you found this answer, but if anyone else stumbles across this post with the same issue that Somnath and I were having.

We all try to do our due diligence in keeping memory clean and clear, but with streams we always will save unexplained issues if we make sure to flush the stream before we close it.

Replace This :

postStream.Write(byteArray, 0, byteArray.Length);
postStream.Close();

With This :

postStream.Write(byteArray, 0, byteArray.Length);
postStream.Flush();
postStream.Close();

Answer 4

I followed all suggestion provide by all of you but couldn't stop the silent failure of HTTP request. But I found a workaround. Even myself could not reach to a final conclusion till now.

But my workaround is working well as off now without any failure.

In SendReq(string url) function i have added the following lines of code

System.Net.ServicePointManager.DefaultConnectionLimit = 100; // Just selected a random number for testing greater than 2
System.Net.ServicePointManager.SetTcpKeepAlive(true, 30, 30); // 30 is based on my server i'm hitting
System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;

request.KeepAlive = true;