Why is this HttpWebRequest class unreliable?

[sfoxover]

Hi,

Could someone please give me some suggestions on how to make this class
robust. I need to be able to handle around 20 similtanious requests to
this class which causes a web browser to display a waiting message
while it requests XML data from a third party server. Some requests can
take around 30 seconds.

Usually the first time I do the request it always works. If I try again
without closing the web browser it will fail sometimes. And if I try
from more than 1 web browser at the same time it will fail a lot.

bool CheckAvailable( ) is used for the requests.

Thanks
using System;
using System.Xml;
using System.Net;
using System.IO;
using System.Text;
using System.Threadin g;

namespace TestPost
{
/// <summary>
/// Summary description for SamplePost.
/// </summary>
public class SamplePost
{
public static AutoResetEvent m_allDone = null;

public SamplePost()
{
}

private bool CheckAvailable( string strURL, string strXMLPost,stri ng
strUser, string strPassword)
{
// send POST request
m_strURL = strURL;
m_strXMLPost = strXMLPost;
m_strUser = strUser;
m_strPassword = strPassword;

RequestState myRequestState = null;
// send POST request
try
{
// Create a new 'HttpWebRequest ' object to the mentioned URL.
HttpWebRequest myHttpWebReques t1 =
(HttpWebRequest )WebRequest.Cre ate(m_strURL);
myRequestState = new RequestState();
myRequestState. request = myHttpWebReques t1;
myRequestState. m_strPostData = m_strXMLPost;
myHttpWebReques t1.ContentType =
"applicatio n/x-www-form-urlencoded";
myHttpWebReques t1.Method = "POST";
myHttpWebReques t1.Headers.Add( "Cache-Control","no-cache");
myHttpWebReques t1.ContentLengt h = m_strXMLPost.Le ngth;
myHttpWebReques t1.KeepAlive = true;
myHttpWebReques t1.Credentials = new
NetworkCredenti al(m_strUser,m_ strPassword);

m_allDone = new AutoResetEvent( false);
IAsyncResult result = (IAsyncResult)
myHttpWebReques t1.BeginGetRequ estStream(new
AsyncCallback(P ostCallback),my RequestState);
// using result.AsyncWai tHandle slips past WaitOne, so trying
threadpool
// result.AsyncWai tHandle.WaitOne (20000,true);
ThreadPool.Regi sterWaitForSing leObject (result.AsyncWa itHandle, new
WaitOrTimerCall back(TimeoutSoc ketCallback), myHttpWebReques t1,
DefaultTimeout, true);
m_allDone.WaitO ne();

if(!myRequestSt ate.m_bResultOK )
return false;

// Start the asynchronous BeginGetRespons e request.
m_allDone = new AutoResetEvent( false);
IAsyncResult result2 = (IAsyncResult)
myHttpWebReques t1.BeginGetResp onse(new
AsyncCallback(R espCallback),my RequestState);
ThreadPool.Regi sterWaitForSing leObject (result2.AsyncW aitHandle,
new WaitOrTimerCall back(TimeoutSoc ketCallback), myHttpWebReques t1,
Defines.N_HTTP_ REQUEST_TIMEOUT , true);
m_allDone.WaitO ne();
myRequestState. response.Close( );
}
catch(WebExcept ion)
{
return false;
}
catch(Exception )
{
return false;
}
// check reply OK
bool bOK = false;
if(myRequestSta te != null)
{
string strReply = myRequestState. m_strReply;
bOK = VerifyXMLReply( strReply);
}
return bOK;
}

// send post data
private void PostCallback(IA syncResult asynchronousRes ult)
{
RequestState myRequestState = null;
try
{
// Set the State of request to asynchronous.
myRequestState = (RequestState)a synchronousResu lt.AsyncState;
HttpWebRequest myHttpWebReques t2 =
(HttpWebRequest )myRequestState .request;
// End of the Asynchronus writing .
Stream postStream =
myHttpWebReques t2.EndGetReques tStream(asynchr onousResult);
// send any post data
if(!Helpers.IsE mpty(myRequestS tate.m_strPostD ata))
{
ASCIIEncoding encoder = new ASCIIEncoding() ;
// Convert the string into byte array.
byte[] ByteArray = encoder.GetByte s(myRequestStat e.m_strPostData );
// Write to the stream.
postStream.Writ e(ByteArray,0,m yRequestState.m _strPostData.Le ngth);
}
postStream.Clos e();
myRequestState. m_bResultOK = true;
m_allDone.Set() ;
}
catch(WebExcept ion e)
{
if(myRequestSta te != null)
{
myRequestState. m_strErrorText = e.Message;
myRequestState. m_bResultOK = false;
}
}
catch(Exception e)
{
if(myRequestSta te != null)
{
myRequestState. m_strErrorText = e.Message;
myRequestState. m_bResultOK = false;
}
}
m_allDone.Set() ;
}

// read response
private void RespCallback(IA syncResult asynchronousRes ult)
{
RequestState myRequestState = null;
try
{
// State of request is asynchronous.
myRequestState = (RequestState) asynchronousRes ult.AsyncState;
HttpWebRequest myHttpWebReques t = myRequestState. request;
myRequestState. response = (HttpWebRespons e)
myHttpWebReques t.EndGetRespons e(asynchronousR esult);
// Read the response into a Stream object.
Stream responseStream =
myRequestState. response.GetRes ponseStream();
myRequestState. streamResponse = responseStream;
// Begin the Reading of the contents of the HTML page and print it
to the console.
IAsyncResult asynchronousInp utRead =
responseStream. BeginRead(myReq uestState.Buffe rRead, 0, BUFFER_SIZE, new
AsyncCallback(R eadCallBack), myRequestState) ;
return;
}
catch(WebExcept ion e)
{
if(myRequestSta te != null)
{
myRequestState. m_bResultOK = false;
myRequestState. m_strErrorText = e.Message;
}
}
m_allDone.Set() ;
}

// read callback
private void ReadCallBack(IA syncResult asyncResult)
{
RequestState myRequestState = null;
try
{
myRequestState = (RequestState)a syncResult.Asyn cState;
Stream responseStream = myRequestState. streamResponse;
int read = responseStream. EndRead(asyncRe sult);
// Read the HTML page and then print it to the console.
if (read > 0)
{
myRequestState. m_strReply +=
Encoding.ASCII. GetString(myReq uestState.Buffe rRead, 0, read);
IAsyncResult asynchronousRes ult = responseStream. BeginRead(
myRequestState. BufferRead, 0, BUFFER_SIZE, new
AsyncCallback(R eadCallBack), myRequestState) ;
return;
}
else
{
myRequestState. m_bResultOK = true;
responseStream. Close();
}
}
catch(WebExcept ion e)
{
if(myRequestSta te != null)
{
myRequestState. m_bResultOK = false;
myRequestState. m_strErrorText = e.Message;
}
}
m_allDone.Set() ;
}

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

// used for asyncronous requests
public class RequestState
{
// This class stores the State of the request.
const int BUFFER_SIZE = 1024;
public string m_strPostData;
public string m_strReply;
public string m_strErrorText;
public bool m_bResultOK;
public byte[] BufferRead;
public HttpWebRequest request;
public HttpWebResponse response;
public Stream streamResponse;
// constructor
public RequestState()
{
BufferRead = new byte[BUFFER_SIZE];
request = null;
streamResponse = null;
m_bResultOK = false;
m_strPostData = "";
m_strErrorText = "";
m_strReply = "";
}
}
}

[Scott Allen]

Hi sfoxover:

You have several threading issues in this code. For example,
declaring AutoResetEvent as a static member is begging for your
threads to miss the signal entirely.

My suggestion would be to get rid of all the asynch activity - it's
not buying you anything in this code. The original thread is doing
nothing but waiting for the second thread to finish - so why not skip
the 2nd thread and do all the work with 1?

Try to get it working first, and then see if you need to make some
optimizations.

You'll also want to bump up the number of HTTP connections you can
make to an external machine:
http://odetocode.com/Blogs/scott/arc...06/08/272.aspx

--
Scott
http://www.OdeToCode.com/blogs/scott/

On 11 Jul 2005 23:27:55 -0700, sf******@gmail. com wrote:

Hi,

Could someone please give me some suggestions on how to make this class
robust. I need to be able to handle around 20 similtanious requests to
this class which causes a web browser to display a waiting message
while it requests XML data from a third party server. Some requests can
take around 30 seconds.

Usually the first time I do the request it always works. If I try again
without closing the web browser it will fail sometimes. And if I try
from more than 1 web browser at the same time it will fail a lot.

bool CheckAvailable( ) is used for the requests.

Thanks
using System;
using System.Xml;
using System.Net;
using System.IO;
using System.Text;
using System.Threadin g;

namespace TestPost
{
/// <summary>
/// Summary description for SamplePost.
/// </summary>
public class SamplePost
{
public static AutoResetEvent m_allDone = null;

public SamplePost()
{
}

private bool CheckAvailable( string strURL, string strXMLPost,stri ng
strUser, string strPassword)
{
// send POST request
m_strURL = strURL;
m_strXMLPost = strXMLPost;
m_strUser = strUser;
m_strPassword = strPassword;

RequestState myRequestState = null;
// send POST request
try
{
// Create a new 'HttpWebRequest ' object to the mentioned URL.
HttpWebRequest myHttpWebReques t1 =
(HttpWebReques t)WebRequest.Cr eate(m_strURL);
myRequestState = new RequestState();
myRequestState. request = myHttpWebReques t1;
myRequestState. m_strPostData = m_strXMLPost;
myHttpWebReques t1.ContentType =
"applicatio n/x-www-form-urlencoded";
myHttpWebReques t1.Method = "POST";
myHttpWebReques t1.Headers.Add( "Cache-Control","no-cache");
myHttpWebReques t1.ContentLengt h = m_strXMLPost.Le ngth;
myHttpWebReques t1.KeepAlive = true;
myHttpWebReques t1.Credentials = new
NetworkCredent ial(m_strUser,m _strPassword);

m_allDone = new AutoResetEvent( false);
IAsyncResult result = (IAsyncResult)
myHttpWebReque st1.BeginGetReq uestStream(new
AsyncCallback( PostCallback),m yRequestState);
// using result.AsyncWai tHandle slips past WaitOne, so trying
threadpool
// result.AsyncWai tHandle.WaitOne (20000,true);
ThreadPool.Regi sterWaitForSing leObject (result.AsyncWa itHandle, new
WaitOrTimerCal lback(TimeoutSo cketCallback), myHttpWebReques t1,
DefaultTimeout , true);
m_allDone.WaitO ne();

if(!myRequestSt ate.m_bResultOK )
return false;

// Start the asynchronous BeginGetRespons e request.
m_allDone = new AutoResetEvent( false);
IAsyncResult result2 = (IAsyncResult)
myHttpWebReque st1.BeginGetRes ponse(new
AsyncCallback( RespCallback),m yRequestState);
ThreadPool.Regi sterWaitForSing leObject (result2.AsyncW aitHandle,
new WaitOrTimerCall back(TimeoutSoc ketCallback), myHttpWebReques t1,
Defines.N_HTTP _REQUEST_TIMEOU T, true);
m_allDone.WaitO ne();
myRequestState. response.Close( );
}
catch(WebExcept ion)
{
return false;
}
catch(Exception )
{
return false;
}
// check reply OK
bool bOK = false;
if(myRequestSta te != null)
{
string strReply = myRequestState. m_strReply;
bOK = VerifyXMLReply( strReply);
}
return bOK;
}

// send post data
private void PostCallback(IA syncResult asynchronousRes ult)
{
RequestState myRequestState = null;
try
{
// Set the State of request to asynchronous.
myRequestState = (RequestState)a synchronousResu lt.AsyncState;
HttpWebRequest myHttpWebReques t2 =
(HttpWebReques t)myRequestStat e.request;
// End of the Asynchronus writing .
Stream postStream =
myHttpWebReque st2.EndGetReque stStream(asynch ronousResult);
// send any post data
if(!Helpers.IsE mpty(myRequestS tate.m_strPostD ata))
{
ASCIIEncoding encoder = new ASCIIEncoding() ;
// Convert the string into byte array.
byte[] ByteArray = encoder.GetByte s(myRequestStat e.m_strPostData );
// Write to the stream.
postStream.Writ e(ByteArray,0,m yRequestState.m _strPostData.Le ngth);
}
postStream.Clos e();
myRequestState. m_bResultOK = true;
m_allDone.Set() ;
}
catch(WebExcept ion e)
{
if(myRequestSta te != null)
{
myRequestState. m_strErrorText = e.Message;
myRequestState. m_bResultOK = false;
}
}
catch(Exception e)
{
if(myRequestSta te != null)
{
myRequestState. m_strErrorText = e.Message;
myRequestState. m_bResultOK = false;
}
}
m_allDone.Set() ;
}

// read response
private void RespCallback(IA syncResult asynchronousRes ult)
{
RequestState myRequestState = null;
try
{
// State of request is asynchronous.
myRequestState = (RequestState) asynchronousRes ult.AsyncState;
HttpWebRequest myHttpWebReques t = myRequestState. request;
myRequestState. response = (HttpWebRespons e)
myHttpWebReque st.EndGetRespon se(asynchronous Result);
// Read the response into a Stream object.
Stream responseStream =
myRequestState .response.GetRe sponseStream();
myRequestState. streamResponse = responseStream;
// Begin the Reading of the contents of the HTML page and print it
to the console.
IAsyncResult asynchronousInp utRead =
responseStream .BeginRead(myRe questState.Buff erRead, 0, BUFFER_SIZE, new
AsyncCallback( ReadCallBack), myRequestState) ;
return;
}
catch(WebExcept ion e)
{
if(myRequestSta te != null)
{
myRequestState. m_bResultOK = false;
myRequestState. m_strErrorText = e.Message;
}
}
m_allDone.Set() ;
}

// read callback
private void ReadCallBack(IA syncResult asyncResult)
{
RequestState myRequestState = null;
try
{
myRequestState = (RequestState)a syncResult.Asyn cState;
Stream responseStream = myRequestState. streamResponse;
int read = responseStream. EndRead(asyncRe sult);
// Read the HTML page and then print it to the console.
if (read > 0)
{
myRequestState. m_strReply +=
Encoding.ASCII .GetString(myRe questState.Buff erRead, 0, read);
IAsyncResult asynchronousRes ult = responseStream. BeginRead(
myRequestState .BufferRead, 0, BUFFER_SIZE, new
AsyncCallback( ReadCallBack), myRequestState) ;
return;
}
else
{
myRequestState. m_bResultOK = true;
responseStream. Close();
}
}
catch(WebExcept ion e)
{
if(myRequestSta te != null)
{
myRequestState. m_bResultOK = false;
myRequestState. m_strErrorText = e.Message;
}
}
m_allDone.Set() ;
}

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

// used for asyncronous requests
public class RequestState
{
// This class stores the State of the request.
const int BUFFER_SIZE = 1024;
public string m_strPostData;
public string m_strReply;
public string m_strErrorText;
public bool m_bResultOK;
public byte[] BufferRead;
public HttpWebRequest request;
public HttpWebResponse response;
public Stream streamResponse;
// constructor
public RequestState()
{
BufferRead = new byte[BUFFER_SIZE];
request = null;
streamResponse = null;
m_bResultOK = false;
m_strPostData = "";
m_strErrorText = "";
m_strReply = "";
}
}
}