如何通过相同的Web客户端（带有Cookie）实例发出序列HTTP请求

Question

Please consider my situation:

I am developing an windows phone 7 application which send HTTP POST request to one of server in our school to get some information from it. When you access to the website, it show you an verify code image, you should input your school number, password along with the verify code to login it. Then you can get access to whatever you want.

I have make experiences to comfirm that, the server will write on cookie to client to make sure that you are logged in. But we know that no matter the WebClient or the HttpWebRequest class in windows phone are both only support async operation. If I want implement the log in process, I must write code in getVerifyCode() method's uploadStringCompleted method. I think it's not the best practice. For example:

(NOTICE：this is just an example, not the real code, because to get the verify code I just need a GET method HTTP request, I think it can illustrate the problem confuse me well)

public void getVerifyCode()
{
    webClient.uploadStringCompleted += new uploadStringCompleted(getVerifyCodeCompleted);
    webClient.uploadStringAsync(balabala, balabala, balabala);
}

private void getVerifyCodeCompleted(object sender, uploadStringCompletedArgs e)
{
    if(e.Error == null)
    {
        webClient.uploadStringCompleted -= getVerifyCodeCompleted;

        // start log in 
        // I don't submit a new request inside last request's completed event handler
        // but I can't find a more elegent way to do this.
        webClient.uploadStringCompleted += loginCompleted;
        webClient.uploadStringAsync(balabala, balabala, balabala);
    }
}

So in a nutshell, I wanna to know what is the best practice or design pattern to solve the problem such as above?

Thanks a lot in advance.

Answer 1

Here is a code snippet using HttpWebRequest.BeginGetRequestStream / EndRequestStream :

HttpWebRequest webRequest = WebRequest.Create(@"https://www.somedomain.com/etc") as HttpWebRequest;
webRequest.ContentType = @"application/x-www-form-urlencoded";
webRequest.Method = "POST";

// Prepare the post data into a byte array
string formValues = string.Format(@"login={0}&password={1}", "someLogin", "somePassword");
byte[] byteArray = Encoding.UTF8.GetBytes(formValues);

// Set the "content-length" header 
webRequest.Headers["Content-Length"] = byteArray.Length.ToString();

// Write POST data
IAsyncResult ar = webRequest.BeginGetRequestStream((ac) => { }, null);
using (Stream requestStream = webRequest.EndGetRequestStream(ar) as Stream)
{
    requestStream.Write(byteArray, 0, byteArray.Length);
    requestStream.Close();
}

// Retrieve the response
string responseContent;    

ar = webRequest.BeginGetResponse((ac) => { }, null);
WebResponse webResponse = webRequest.EndGetResponse(ar) as HttpWebResponse;
try
{
    // do something with the response ...
    using (StreamReader sr = new StreamReader(webResponse.GetResponseStream()))
    {
        responseContent = sr.ReadToEnd();
        sr.Close();
    }
}
finally
{
    webResponse.Close();
}

Please note that you should execute it with a ThreadPool.QueueUserWorkItem in order to keep the UI/main thread responsive.