C#: descargar una URL con tiempo de espera

httpwebrequest timeout

Question

¿Cuál es la mejor manera de hacerlo en .NET? Siempre olvido lo que necesito para Dispose() (o envolver con using ).

EDITAR: después de mucho tiempo usando WebRequest , descubrí sobre la personalización de WebClient . Mucho mejor.

Answer 1

Ejecute System.Net.WebClient en un hilo separado, configure un temporizador para matarlo después de su tiempo máximo.

Answer 2

Esto es lo que uso, parece funcionar, pero no sé si es la mejor manera:

public string GetRequest(Uri uri, int timeoutMilliseconds)
{
    var request = System.Net.WebRequest.Create(uri);
    request.Timeout = timeoutMilliseconds;
    using (var response = request.GetResponse())
    using (var stream = response.GetResponseStream())
    using (var reader = new System.IO.StreamReader(stream))
    {
        return reader.ReadToEnd();
    }
}

Answer 3

Manera sincrónica:

var request = HttpWebRequest.Create("http://www.contoso.com");
request.Timeout = 50000;
using (var response = request.GetResponse())
{
    //your code here
}

También puede tener la forma asíncrona:

using System;
using System.Net;
using System.IO;
using System.Text;
using System.Threading;


public class RequestState
{
  // This class stores the State of the request.
  const int BUFFER_SIZE = 1024;
  public StringBuilder requestData;
  public byte[] BufferRead;
  public HttpWebRequest request;
  public HttpWebResponse response;
  public Stream streamResponse;
  public RequestState()
  {
    BufferRead = new byte[BUFFER_SIZE];
    requestData = new StringBuilder("");
    request = null;
    streamResponse = null;
  }
}

class HttpWebRequest_BeginGetResponse
{
    public static ManualResetEvent allDone = new ManualResetEvent(false);
    const int BUFFER_SIZE = 1024;
    const int DefaultTimeout = 2 * 60 * 1000; // 2 minutes timeout

    // Abort the request if the timer fires.
    private static void TimeoutCallback(object state, bool timedOut)
    {
        if (timedOut)
        {
            HttpWebRequest request = state as HttpWebRequest;
            if (request != null)
            {
                request.Abort();
            }
        }
    }

    static void Main()
    {

        try
        {
            // Create a HttpWebrequest object to the desired URL. 
            HttpWebRequest myHttpWebRequest = (HttpWebRequest)WebRequest.Create("http://www.contoso.com");
            myHttpWebRequest.ReadWriteTimeout = DefaultTimeout;


            // Create an instance of the RequestState and assign the previous myHttpWebRequest
            // object to its request field.  
            RequestState myRequestState = new RequestState();
            myRequestState.request = myHttpWebRequest;


            // Start the asynchronous request.
            IAsyncResult result =
              (IAsyncResult)myHttpWebRequest.BeginGetResponse(new AsyncCallback(RespCallback), myRequestState);

            // this line implements the timeout, if there is a timeout, the callback fires and the request becomes aborted
            ThreadPool.RegisterWaitForSingleObject(result.AsyncWaitHandle, new WaitOrTimerCallback(TimeoutCallback), myHttpWebRequest, DefaultTimeout, true);

            // The response came in the allowed time. The work processing will happen in the 
            // callback function.
            allDone.WaitOne();

            // Release the HttpWebResponse resource.
            myRequestState.response.Close();
        }
        catch (WebException e)
        {
            Console.WriteLine("/nMain Exception raised!");
            Console.WriteLine("/nMessage:{0}", e.Message);
            Console.WriteLine("/nStatus:{0}", e.Status);
            Console.WriteLine("Press any key to continue..........");
        }
        catch (Exception e)
        {
            Console.WriteLine("/nMain Exception raised!");
            Console.WriteLine("Source :{0} ", e.Source);
            Console.WriteLine("Message :{0} ", e.Message);
            Console.WriteLine("Press any key to continue..........");
            Console.Read();
        }
    }
    private static void RespCallback(IAsyncResult asynchronousResult)
    {
        try
        {
            // State of request is asynchronous.
            RequestState myRequestState = (RequestState)asynchronousResult.AsyncState;
            HttpWebRequest myHttpWebRequest = myRequestState.request;
            myRequestState.response = (HttpWebResponse)myHttpWebRequest.EndGetResponse(asynchronousResult);

            // Read the response into a Stream object.
            Stream responseStream = myRequestState.response.GetResponseStream();
            myRequestState.streamResponse = responseStream;

            // Begin the Reading of the contents of the HTML page and print it to the console.
            IAsyncResult asynchronousInputRead = responseStream.BeginRead(myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
            return;
        }
        catch (WebException e)
        {
            Console.WriteLine("/nRespCallback Exception raised!");
            Console.WriteLine("/nMessage:{0}", e.Message);
            Console.WriteLine("/nStatus:{0}", e.Status);
        }
        allDone.Set();
    }
    private static void ReadCallBack(IAsyncResult asyncResult)
    {
        try
        {

            RequestState myRequestState = (RequestState)asyncResult.AsyncState;
            Stream responseStream = myRequestState.streamResponse;
            int read = responseStream.EndRead(asyncResult);
            // Read the HTML page and then print it to the console.
            if (read > 0)
            {
                myRequestState.requestData.Append(Encoding.ASCII.GetString(myRequestState.BufferRead, 0, read));
                IAsyncResult asynchronousResult = responseStream.BeginRead(myRequestState.BufferRead, 0, BUFFER_SIZE, new AsyncCallback(ReadCallBack), myRequestState);
                return;
            }
            else
            {
                Console.WriteLine("/nThe contents of the Html page are : ");
                if (myRequestState.requestData.Length > 1)
                {
                    string stringContent;
                    stringContent = myRequestState.requestData.ToString();
                    Console.WriteLine(stringContent);
                }
                Console.WriteLine("Press any key to continue..........");
                Console.ReadLine();

                responseStream.Close();
            }

        }
        catch (WebException e)
        {
            Console.WriteLine("/nReadCallBack Exception raised!");
            Console.WriteLine("/nMessage:{0}", e.Message);
            Console.WriteLine("/nStatus:{0}", e.Status);
        }
        allDone.Set();

    }
}

Answer 4

Siguiendo el comentario de Thomas Levesque aquí , hay una solución más simple y más genérica.

Creamos una subclase WebClient con soporte de tiempo de espera y obtenemos toda la bondad de WebClient .

public class WebClientWithTimeout : WebClient
{
  private readonly int timeoutMilliseconds;
  public WebClientWithTimeout(int timeoutMilliseconds)
  {
    this.timeoutMilliseconds = timeoutMilliseconds;
  }

  protected override WebRequest GetWebRequest(Uri address)
  {
    var result = base.GetWebRequest(address);
    result.Timeout = timeoutMilliseconds;
    return result;
  }
}

Uso de muestra:

public string GetRequest(Uri uri, int timeoutMilliseconds)
{
  using (var client = new WebClientWithTimeout(timeoutMilliseconds))
  {
    return client.DownloadString();
  }
}