Develop Reference

FTP error: 530 Sorry, Only 5 connections per host are allowed

I have a FTP solution that works great. However after a while, perheps 20-30 minutes, I can get this error:
530 Sorry, Only 5 connections per host are allowed
I have googled on this problem but not really finding any solution to it.
I have different threads calling the function but only allow the function to be called maximum each 2 seconds.
I am make use of: using statements but I think I don't want to use:
request.KeepAlive = false;
to be sure that the connection will be closed. As I before was told to have it open in "ServicePoint" as I use "ConnectionGroupName" because open up a new connection is resource expensive and it is smoother to keep it open.
I think but are not sure. Please tell me if that is a bad approach. But when this error occurs. I like to close all connections, in this case 5 connections so it starts over from Zero connections. Is this possible to do and how would I go about to do that in code since I am not sure how to call those connections in the code?
public async Task<List<String>> FtpGetFiles(String host, String folderpath, String user_name, String password)
{
List<String> serverfileLIST = new List<String>(); String error = "";
try
{
var request = (FtpWebRequest)WebRequest.Create(host + "/" + folderpath + "/");
request.Credentials = new NetworkCredential(user_name, password);
request.Method = WebRequestMethods.Ftp.ListDirectory;
request.ConnectionGroupName = host.Replace(".", "").Replace(":", "").Replace("/", "").Replace("-", "").Replace("_", "") + user_name;
request.ServicePoint.ConnectionLimit = 4;
request.Timeout = 20000;
using (var responseWeb = await request.GetResponseAsync())
{
var response = (FtpWebResponse)responseWeb;
if (response.StatusDescription.Contains("150") || //150 opening binary mode data connection for file list
response.StatusDescription.Contains("226"))
{
using (StreamReader streamReader = new StreamReader(response.GetResponseStream()))
{
while (streamReader.Peek() >= 0)
{
serverfileLIST.Add(streamReader.ReadLine());
}
}
return serverfileLIST;
}
else { error = response.StatusDescription; }
}
}
catch (WebException ex) { String status = ((FtpWebResponse)ex.Response).StatusDescription; error = status; }
return serverfileLIST;
}
EDIT:
I have attached a network.txtfile. I can see in my own logfile that at this time GMT, I got the below error:
09 Dec 2019 16:09:40 530 Sorry, Only 5 connections per host are allowed
09 Dec 2019 16:09:42 530 Sorry, Only 5 connections per host are allowed
The network.txtfile is attached which is GMT also in the link below and I wonder if it is possible to trace what the problem is and how it could be solved?
network.txt
I could find those lines in the txt file where it occurs:
System.Net Information: 0 : [14868] FtpControlStream#13919402 - Sending command [PASS ********]
System.Net Information: 0 : [14868] FtpControlStream#13919402 - Received response [530 Sorry, Only 5 connections per host are allowed]
System.Net Information: 0 : [14868] FtpWebRequest#45677341::(Releasing FTP connection#13919402.)
System.Net Error: 0 : [14868] Exception in FtpWebRequest#45677341::EndGetResponse - The remote server returned an error: (530) Not logged in..
at System.Net.FtpWebRequest.EndGetResponse(IAsyncResult asyncResult)

Just the maximum throughput of one call per every 2 seconds does not prevent the external threads from invoking more than 5 connections. Just imagine you will temporarily have a very slow connection to the server or the list you request will be very long. It could take more time to download than usual (let's say it will take 15 seconds for some reason). Because it will take more time to finish, you will eventually reach the cap of 5 concurrent connections and get the error, because you will be initiating new calls before the previous downloads finished.
You could use SemaphoreSlim to "queue" all the calls to your method FtpGetFiles. This would make sure your threads are not executing more than 5 concurrent calls. When one call finishes, semaphore would release a spot and another call would start.
It would look something like this:
public class TaskQueue
{
private readonly SemaphoreSlim semaphore;
private int pendingTasks;
private int runningTasks;
public TaskQueue(int maxConcurrencyLevel = 5)
{
semaphore = new SemaphoreSlim(maxConcurrencyLevel);
}
private async Task AddTask(Func<Task> task)
{
Interlocked.Increment(ref pendingTasks);
await semaphore.WaitAsync();
Interlocked.Decrement(ref pendingTasks);
Interlocked.Increment(ref runningTasks);
try
{
await task();
}
finally
{
Interlocked.Decrement(ref runningTasks);
semaphore.Release();
}
}
}
Every thread calling your method would call this:
TaskQueue.AddTask(async () => await FtpGetFiles(host, folderpath, username, password));

Multithread HttpWebRequest hangs randomly on responseStream

I'm coding a multithreaded web-crawler that performs a lot of concurrent httpwebrequests every second using hundreds of threads, the application works great but sometimes(randomly) one of the webrequests hangs on the getResponseStream() completely ignoring the timeout(this happen when I perform hundreds of requests concurrently) making the crawling process never end, the strange thing is that with fiddler this never happen and the application never hang, it is really hard to debug because it happens randomly.
I've tried to set
Keep-Alive = false
ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;
but I still get the strange behavior, any ideas?
Thanks
HttpWebRequest code:
public static string RequestHttp(string url, string referer, ref CookieContainer cookieContainer_0, IWebProxy proxy)
{
string str = string.Empty;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip;
request.UserAgent = randomuseragent();
request.ContentType = "application/x-www-form-urlencoded";
request.Accept = "*/*";
request.CookieContainer = cookieContainer_0;
request.Proxy = proxy;
request.Timeout = 15000;
request.Referer = referer;
//request.ServicePoint.MaxIdleTime = 15000;
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
using (Stream responseStream = response.GetResponseStream())
{
List<byte> list = new List<byte>();
byte[] buffer = new byte[0x400];
int count = responseStream.Read(buffer, 0, buffer.Length);
while (count != 0)
{
list.AddRange(buffer.ToList<byte>().GetRange(0, count));
if (list.Count >= 0x100000)
{
break;
}
count = 0;
try
{
HERE IT HANGS SOMETIMES ---> count = responseStream.Read(buffer, 0, buffer.Length);
continue;
}
catch
{
continue;
}
}
//responseStream.Close();
int num2 = 0x200 * 0x400;
if (list.Count >= num2)
{
list.RemoveRange((num2 * 3) / 10, list.Count - num2);
}
byte[] bytes = list.ToArray();
str = Encoding.Default.GetString(bytes);
Encoding encoding = Encoding.Default;
if (str.ToLower().IndexOf("charset=") > 0)
{
encoding = GetEncoding(str);
}
else
{
try
{
encoding = Encoding.GetEncoding(response.CharacterSet);
}
catch
{
}
}
str = encoding.GetString(bytes);
// response.Close();
}
}
return str.Trim();
}

The Timeout property "Gets or sets the time-out value in milliseconds for the GetResponse and GetRequestStream methods." The default value is 100,000 milliseonds (100 seconds).
The ReadWriteTimeout property, "Gets or sets a time-out in milliseconds when writing to or reading from a stream." The default is 300,000 milliseconds (5 minutes).
You're setting Timeout, but leaving ReadWriteTimeout at the default, so your reads can take up to five minutes before timing out. You probably want to set ReadWriteTimeout to a lower value. You might also consider limiting the size of data that you download. With my crawler, I'd sometimes stumble upon an unending stream that would eventually result in an out of memory exception.
Something else I noticed when crawling is that sometimes closing the response stream will hang. I found that I had to call request.Abort to reliably terminate a request if I wanted to quit before reading the entire stream.

There is nothing apparent in the code you provided.
Why did you comment response.Close() out?
Documentation hints that connections may run out if not explicitly closed. The response getting disposed may close the connection but just releasing all the resources is not optimal I think. Closing the response will also close the stream so that is covered.
The system hanging without timeout can be just a network issue making the response object a dead duck or the problem is due the high number of threads resulting in memory fragmentation.
Looking at anything that may produce a pattern may help find the source:
How many threads are typically running (can you bundle request sets in less threads)
How is the network performance at the time the thread stopped
Is there a specific count or range when it happens
What data was processed last when it happened (are there any specific control characters or sequences of data that can upset the stream)
Want to ask more questions but not enough reputation so can only reply.
Good luck!

Below is some code that does something similar, it's also used to access multiple web sites, each call is in a different task. The difference is that I only read the stream once and then parse the results. That might be a way to get around the stream reader locking up randomly or at least make it easier to debug.
try
{
_webResponse = (HttpWebResponse)_request.GetResponse();
if(_request.HaveResponse)
{
if (_webResponse.StatusCode == HttpStatusCode.OK)
{
var _stream = _webResponse.GetResponseStream();
using (var _streamReader = new StreamReader(_stream))
{
string str = _streamReader.ReadToEnd();

How To Make Parallel HTTP Requests

I have a console app that makes a single request to a web page and returns its server status eg. 200, 404, etc..
I'd like to apply following changes:
List of User Inputs:
Url to request
How many parallel connections to use(concurrent users)
How long(seconds) to submit as many requests as it can
List of Outputs:
Show Total Fetches
Show Fetches per Second
Show Average Response Time (ms)
I imagine the best way to do it is to run multiple http fetches in parallel and run in a single process, so it doesn't bog down the client machine.
I really like C# but I'm still new to it. I've researched other articles about this but I don't fully understand them so any help would be greatly appreciated.
My Code:
static void Main(string[] args)
{
try
{
HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create("http://10.10.1.6/64k.html");
webRequest.AllowAutoRedirect = false;
HttpWebResponse response = (HttpWebResponse)webRequest.GetResponse();
//Returns "MovedPermanently", not 301 which is what I want.
int i_goodResponse = (int)response.StatusCode;
string s_goodResponse = response.StatusCode.ToString();
Console.WriteLine("Normal Response: " + i_goodResponse + " " + s_goodResponse);
Console.ReadLine();
}
catch (WebException we)
{
int i_badResponse = (int)((HttpWebResponse)we.Response).StatusCode;
string s_badResponse = ((HttpWebResponse)we.Response).StatusCode.ToString();
Console.WriteLine("Error Response: " + i_badResponse + " " + s_badResponse);
Console.ReadLine();
}
}
Some possible code that I found:
void StartWebRequest()
{
HttpWebRequest webRequest = ...;
webRequest.BeginGetResponse(new AsyncCallback(FinishWebRequest), webRequest);
}
void FinishWebRequest(IAsyncResult result)
{
HttpWebResponse response = (result.AsyncState as HttpWebRequest).EndGetResponse(result) as HttpWebResponse;
}

This is actually a good place to make use of the Task Parallel Library in .NET 4.0. I have wrapped your code in a Parallel.For block which will execute a number of sets of requests in parallel, collate the total times in each parallel branch, and then calculate the overall result afterwards.
int n = 16;
int reqs = 10;
var totalTimes = new long[n];
Parallel.For(0, n, i =>
{
for (int req = 0; req < reqs; req++)
{
Stopwatch w = new Stopwatch();
try
{
w.Start();
HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create("http://localhost:42838/Default.aspx");
webRequest.AllowAutoRedirect = false;
HttpWebResponse response = (HttpWebResponse)webRequest.GetResponse();
w.Stop();
totalTimes[i] += w.ElapsedMilliseconds;
//Returns "MovedPermanently", not 301 which is what I want.
int i_goodResponse = (int)response.StatusCode;
string s_goodResponse = response.StatusCode.ToString();
Console.WriteLine("Normal Response: " + i_goodResponse + " " + s_goodResponse);
}
catch (WebException we)
{
w.Stop();
totalTimes[i] += w.ElapsedMilliseconds;
int i_badResponse = (int)((HttpWebResponse)we.Response).StatusCode;
string s_badResponse = ((HttpWebResponse)we.Response).StatusCode.ToString();
Console.WriteLine("Error Response: " + i_badResponse + " " + s_badResponse);
}
}
});
var grandTotalTime = totalTimes.Sum();
var reqsPerSec = (double)(n * reqs * 1000) / (double)grandTotalTime;
Console.WriteLine("Requests per second: {0}", reqsPerSec);
The TPL is very useful here, as it abstracts away the detail of creating multiple threads of exececution within your process, and running each parallel branch on these threads.
Note that you still have to be careful here - we cannot share state which is updated during the tasks between threads, hence the array for totalTimes which collates the totals for each parallel branch, and only summed up at the very end, once the parallel execution is complete. If we didn't do this, we are open to the possibility of a race condition - where two seperate threads attempt to update the total count simultaneously, potentially corrupting the result.
I hope this makes sense and is useful as a start for you (I only calculate requests per second here, the other stats should be relatively easy to add). Add comments if you need further clarifications.

You have already answered your own question, you can use BeginGetResponse to start async request.
Another, and more convenient method might be using WebClient class, if you are more familiar with events then with AsyncResult.
DownloadDataCompletedEventHandlerd

Timer in C# windows service not restarting

I have a windows service that runs four timers for a monitoring application. The timer in question opens a web request, polls a rest web service, and saves the results in a database.
Please see the elapsed method below:
void iSMSPollTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
iSMSPollTimer.Stop();
try
{
Logger.Log("iSMSPollTimer elapsed - polling iSMS modem for new messages");
string url = "http://...:../recvmsg?user=" + iSMSUser + "&passwd=" + iSMSPassword;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream resStream = response.GetResponseStream();
XmlSerializer serializer = new XmlSerializer(typeof(Response));
using (XmlReader reader = XmlReader.Create(resStream))
{
Response responseXml = (Response)serializer.Deserialize(reader);
if (responseXml.MessageNotification != null)
{
foreach (var messageWrapper in responseXml.MessageNotification)
{
DataContext dc = new DataContext();
DateTime monitorTimestamp = DateTime.Now;
if (messageWrapper.Message.ToUpper().EndsWith("..."))
{
//Saved to DB
}
else if (messageWrapper.Message.ToUpper().EndsWith("..."))
{
//Saved to DB
}
dc.SubmitChanges();
}
}
else
{
Logger.Log("No messages waiting in the iSMS Modem");
}
}
Logger.Log("iSMSPollTimer processing completed");
}
catch (Exception ex)
{
Logger.Log(GetExceptionLogMessage("iSMSPollTimer_Elapsed", ex));
Logger.Debug(GetExceptionLogMessage("iSMSPollTimer_Elapsed", ex));
}
finally
{
iSMSPollTimer.Start();
}
}
When I look at the log messages, I do get "iSMSPollTimer processing completed" and randomly afterwards the timer does not restart.
Any thoughts?

I'm thinking there's a potential reentrancy problem here, but I can't put my finger on it exactly.
I would suggest that, rather than calling Timer.Stop and then Timer.Start, set the timer's AutoReset property to false when you create it. That will prevent any reentrancy problems because the timer is automatically stopped the first time the interval elapses.
Your handler code remains the same except that you remove the code that calls iSMSPollTimer.Stop.
I'm not saying that this will solve your problem for sure, but it will remove the lingering doubt about a reentrancy problem.

This is a pretty well known issue with using timers in .NET service. People will tell you to use a different type of timer (Threading vs System), but in the end they will also fail you. How long before they stop triggering? The shorter your interval, the faster it will fail. If you set it to 1 second, you'll see it happen every couple hours.
The only workaround that I found working for me, is not depending on timers altogether and use a while loop with a Sleep function inside.

"Unable to connect to remote server fail" in HttpWebRequest

I am using VSTS 2008 + C# + .Net 3.5 to develop a console application and I send request to another server (IIS 7.0 on Windows Server 2008). I find when the # of request threads are big (e.g. 2000 threads), the client will receive error "Unable to connect to remote server fail" when invoking response = (HttpWebResponse)request.GetResponse().My confusion is -- I have set timeout to be a large value, but I got such fail message within a minute. I think even if the connection are really larger than what IIS could serve, client should not get such fail message so soon, it should get such message after timeout period. Any comments? Any ideas what is wrong? Any ideas to make more number of concurrent connection being served by IIS 7.0?
Here is my code,
class Program
{
private static int ClientCount = 2000;
private static string TargetURL = "http://labtest/abc.wmv";
private static int Timeout = 3600;
static void PerformanceWorker()
{
Stream dataStream = null;
HttpWebRequest request = null;
HttpWebResponse response = null;
StreamReader reader = null;
try
{
request = (HttpWebRequest)WebRequest.Create(TargetURL);
request.Timeout = Timeout * 1000;
request.Proxy = null;
response = (HttpWebResponse)request.GetResponse();
dataStream = response.GetResponseStream();
reader = new StreamReader(dataStream);
// 1 M at one time
char[] c = new char[1000 * 10];
while (reader.Read(c, 0, c.Length) > 0)
{
Console.WriteLine(Thread.CurrentThread.ManagedThreadId);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message + "\n" + ex.StackTrace);
}
finally
{
if (null != reader)
{
reader.Close();
}
if (null != dataStream)
{
dataStream.Close();
}
if (null != response)
{
response.Close();
}
}
}
static void Main(string[] args)
{
Thread[] workers = new Thread[ClientCount];
for (int i = 0; i < ClientCount; i++)
{
workers[i] = new Thread((new ThreadStart(PerformanceWorker)));
}
for (int i = 0; i < ClientCount; i++)
{
workers[i].Start();
}
for (int i = 0; i < ClientCount; i++)
{
workers[i].Join();
}
return;
}
}

Kev answered you question already, I just want to add that creating so many threads is not really good design solution (just context switching overhead is a big minus) plus it won't scale good.
The quick answer would be: use asynchronous operations to read data instead of creating a bunch of threads. Or at least use thread pool (and lower worker thread count). Remember that more connections to one source will only speed things up till some degree. Try benchmarking it and you will see that probably 3-5 connections will work faster that 2000 you are using now.
You can read more about asynchronous client/server architecture (IOCP - input/output completion ports) and its advantages here. You can start from here:
MSDN - Using an Asynchronous Server Socket
MSDN - Asynchronous Server Socket Example
CodeProject - Multi-threaded .NET TCP Server Examples
All of these examples uses lower level TCP object, but it can be applied to WebRequest/WebResponse as well.
UPDATE
To try thread pool version, you can do something like this:
ManualResetEvent[] events = new ManualResetEvent[ClientCount];
for (uint cnt = 0; cnt < events.Length; cnt++)
{
events[cnt] = new ManualResetEvent(false);
ThreadPool.QueueUserWorkItem(obj => PerformanceWorker());
}
WaitHandle.WaitAll(events);
Not tested, may need some adjustment.

I reckon you've maxed out the web site's application pool queue. The default is 1000 requests, you're flooding the server with 2000 requests more or less all at once. Increasing the timeout isn't going to solve this.
Try increasing the Queue Length for the application pool the site resides in.
You should try and capture the underlying HTTP status, that'll give you a clue as to what is really going on.
Update:
When I run your code and try and download a sizeable file (200MB) I get (503) Server Unavailable.. Increasing the size of the Application Pool's request queue solves this (I set mine to 10000).
Only once did I see Unable to connect to remote server and sadly have been unable to replicate. This error sounds like there's something broken at the TCP/IP layer. Can you post the full exception?

Go to Smart Thread Pool and downlod the code. It is an instance thread pool that constrains the number of threads. The .Net Thread pool can be problematic in applications that connect to web servers and SQL servers.
Change the loop to this
static void Main(string[] args)
{
var stp = new SmartThreadPool((int) TimeSpan.FromMinutes(5).TotalMilliseconds,
Environment.ProcessorCount - 1, Environment.ProcessorCount - 1);
stp.Start();
for (var i = 0; i < ClientCount; i++)
{
stp.QueueWorkItem(PerformanceWorker);
}
stp.WaitForIdle();
stp.Shutdown();
return;
}
This constrains the thread pool to use 1 thread per proc. Adjust this up until performance starts to degrade. Too many threads are worse than too few. you many find that this is optimal.
Also add this to you config. The value of 100 is a default I use. There is a way to do this in code but the syntax escapes me now.
<system.net>
<connectionManagement>
<add address=“*“ maxconnection=“100“ />
</connectionManagement>
</system.net>

I am using Visual Studio 2005. How to send an SMS, here is my code:
IPHostEntry host;
host = Dns.GetHostEntry(Dns.GetHostName());
UriBuilder urlbuilder = new UriBuilder();
urlbuilder.Host = host.HostName;
urlbuilder.Port = 4719;
string PhoneNumber = "9655336272";
string message = "Just a simple text";
string subject = "MMS subject";
string YourChoiceofName = "victoria";
urlbuilder.Query = string.Format("PhoneNumber=%2B" + PhoneNumber + "&MMSFrom=" + YourChoiceofName + "&MMSSubject=" + subject + "&MMSText=" + message);//+ "&MMSFile=http://127.0.0.1/" + fileName
HttpWebRequest httpReq = (HttpWebRequest)WebRequest.Create(new Uri(urlbuilder.ToString(), false));
HttpWebResponse httpResponse = (HttpWebResponse)(httpReq.GetResponse());