True asynchronous HttpWebRequest implementation with abort and timeout

D

Daniel

Hi,

I'm tired of seeing all these asynchronous HttpWebRequest
implementations that still tend to use a seperate thread or they just
block.

Two questions about the example below:

1) I wrapped the example below to a HttpGet class and fired Get (same
as Main() below). It would still just block, until the response would
be received. Commenting out the lines

//allDone.WaitOne();
//myRequestState.response.Close();

made it work asynchronously, without blocking and without throwing an
exception! hooray! But what am I giving away here? Is it ok to do that?

2) How do I implement an cancel method that aborts the request?
HttpWebRequest.Abort() method does just that, but I don't see how the
cancel method can get access to the RequestState, as it is passed
around in async object manner?

Found at MSDN under the HttpWebRequest.BeginGetResponse():


//////////////////////////////////////////////////////////
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");


/**
* If you are behind a firewall and you do not have your browser
proxy setup
* you need to use the following proxy creation code.

// Create a proxy object.
WebProxy myProxy = new WebProxy();

// Associate a new Uri object to the _wProxy object, using the
proxy address
// selected by the user.
myProxy.Address = new Uri("http://myproxy");


// Finally, initialize the Web request object proxy property with
the _wProxy
// object.
myHttpWebRequest.Proxy=myProxy;
***/

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


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

// this line impliments 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();

}
//////////////////////////////////////////////////////////

Thx and best regards,
Daniel
 
D

Daniel

And below the class implementation:

//////////////////////////////­////////////////////////////

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

namespace Http
{
class RequestState
{
const int BUFFER_SIZE = 1024;
public StringBuilder requestData;
public byte[] _readbuf;
public HttpWebRequest request;
public HttpWebResponse response;
public Stream streamResponse;

public RequestState()
{
_readbuf = new byte[BUFFER_SIZE];
requestData = new StringBuilder("");
request = null;
streamResponse = null;
}
}

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

private void TimeoutCallback(object state, bool timedOut)
{
if (timedOut)
{
HttpWebRequest request = state as HttpWebRequest;
if (request != null)
{
request.Abort();
Console.WriteLine("Timeout!");
}
}
}

private 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._readbuf, 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 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.GetEncoding(1252).GetString(myRequestState._readbuf,
0, read));
IAsyncResult asynchronousResult = responseStream.BeginRead(
myRequestState._readbuf, 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();
}

/* Needs to be implemented! Problem: how to access the httpwebrequest
to call Abort()*/
public void Cancel()
{

}

public void Get(string url)
{
try
{
// Create a HttpWebrequest object to the desired URL.
HttpWebRequest myHttpWebRequest=
(HttpWebRequest)WebRequest.Create(url);


/**
* If you are behind a firewall and you do not have your browser
proxy setup
* you need to use the following proxy creation code.

// Create a proxy object.
WebProxy myProxy = new WebProxy();

// Associate a new Uri object to the _wProxy object, using the
proxy address
// selected by the user.
myProxy.Address = new Uri("http://myproxy");


// Finally, initialize the Web request object proxy property with
the _wProxy
// object.
myHttpWebRequest.Proxy=myProxy;
***/

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


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

// this line impliments 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.
// Commented out//allDone.WaitOne();

// Release the HttpWebResponse resource.
// Commented out//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();
}
}
}
}
//////////////////////////////­////////////////////////////
 

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