I'm here because I have a problem while downloading some files through ftp protocol. It's weird because it occurs occasionally and even for the same single file.
Just a precision: I'm downloading very large files (from 500 Mo to 30Go)
Here are the kind of Exceptions returned by my function : (sorry it's in french)
System.Net.WebException: La connexion sous-jacente a été fermée : Une erreur inattendue s'est produite lors de la réception.
à System.Net.FtpWebRequest.CheckError()
à System.Net.FtpWebRequest.SyncRequestCallback(Object obj)
à System.IO.Stream.Close()
à System.Net.ConnectionPool.Destroy(PooledStream pooledStream)
à System.Net.ConnectionPool.PutConnection(PooledStream pooledStream, Object owningObject, Int32 creationTimeout, Boolean canReuse)
à System.Net.FtpWebRequest.FinishRequestStage(RequestStage stage)
à System.Net.FtpWebRequest.SyncRequestCallback(Object obj)
à System.Net.CommandStream.Abort(Exception e)
à System.Net.CommandStream.CheckContinuePipeline()
à System.Net.FtpDataStream.System.Net.ICloseEx.CloseEx(CloseExState closeState)
à System.Net.FtpDataStream.Dispose(Boolean disposing)
à System.IO.Stream.Close()
à UtilityClasses.FTP.Download(String srcDirectoryPath, String file, String destDirectoryPath)
Here is the code used to download :
the download methods :
public Dictionary<string, object> Download(string srcDirectoryPath, string file, string destDirectoryPath, int attemptLimitNb, int delay)
{
int attemptNb = 0;
bool downloadFailed;
Dictionary<string, object> result = new Dictionary<string,object>();
do
{
attemptNb++;
result = Download(srcDirectoryPath, file, destDirectoryPath);
downloadFailed = result["downloadfailed"] != null;
if (downloadFailed) Thread.Sleep((int)(1000 * delay));
}
while (downloadFailed && attemptNb < attemptLimitNb);
return result;
}
public Dictionary<string, object> Download(string srcDirectoryPath, string file, string destDirectoryPath)
{
Exception downloadFailed = null;
Dictionary<string, object> result = new Dictionary<string, object>();
bool fileFound = false;
try
{
if (destDirectoryPath == null || !Directory.Exists(destDirectoryPath)) throw new Exception("Download destination path does not exist");
if (file != null && file != "")
{
if (file.Contains("/"))
{
throw new Exception("Invalid file name. Impossible to download");
}
Uri serverUri;
if (srcDirectoryPath == null || srcDirectoryPath == "")
{
serverUri = new Uri("ftp://" + this.Server + "/" + file);
}
else if (Regex.IsMatch(srcDirectoryPath, "^/.*$") || Regex.IsMatch(srcDirectoryPath, "^.*/$"))
{
throw new Exception("Path must not start and end with '/'");
}
else
{
serverUri = new Uri("ftp://" + this.Server + "/" + srcDirectoryPath + "/" + file);
}
if (serverUri.Scheme != Uri.UriSchemeFtp) throw new Exception("server URI Scheme does not match FTP URI Scheme");
if (Exists(srcDirectoryPath, file))
{
fileFound = true;
FtpWebRequest downloadRequest = (FtpWebRequest)FtpWebRequest.Create(serverUri);
downloadRequest.Credentials = new NetworkCredential(UserName, Password);
downloadRequest.KeepAlive = false;
downloadRequest.Method = WebRequestMethods.Ftp.DownloadFile;
FtpWebResponse response = (FtpWebResponse)downloadRequest.GetResponse();
Stream responseStream = response.GetResponseStream();
FileStream fileStream = new FileStream(Path.Combine(destDirectoryPath, file), FileMode.Create);
byte[] buffer = new byte[2000];
int read = 0;
try
{
do
{
read = responseStream.Read(buffer, 0, buffer.Length);
fileStream.Write(buffer, 0, read);
fileStream.Flush();
}
while (read != 0);
}
catch (Exception e)
{
fileStream.Close();
responseStream.Close();
response.Close();
throw e;
}
fileStream.Close();
responseStream.Close();
response.Close();
}
}
}
catch (WebException webExcptn)
{
downloadFailed = webExcptn;
}
finally
{
result.Add("filefound", fileFound);
result.Add("downloadfailed", downloadFailed);
}
return result;
}
the Exists method :
public bool Exists(string srcPath, string elementName)
{
if (elementName == null || elementName == "")
{
return false;
}
Uri serverUri;
bool res = false;
if (srcPath == null || srcPath == "")
{
serverUri = new Uri("ftp://" + this.Server);
}
else if (Regex.IsMatch(srcPath, "^/.*$") || Regex.IsMatch(srcPath, "^.*/$"))
{
throw new Exception("Path must not start and end with '/'");
}
else
{
serverUri = new Uri("ftp://" + this.Server + "/" + srcPath);
}
if (serverUri.Scheme != Uri.UriSchemeFtp) throw new Exception("server URI Scheme does not match FTP URI Scheme");
FtpWebRequest listingRequest = (FtpWebRequest)FtpWebRequest.Create(serverUri);
listingRequest.Credentials = new NetworkCredential(UserName, Password);
listingRequest.KeepAlive = false;
listingRequest.Method = WebRequestMethods.Ftp.ListDirectory;
FtpWebResponse response = (FtpWebResponse)listingRequest.GetResponse();
Stream responseStream = response.GetResponseStream();
StreamReader streamReader = new StreamReader(responseStream);
string ftpElementName;
do
{
ftpElementName = Path.GetFileName(streamReader.ReadLine());
if (ftpElementName == null) break;
else
{
string pattern = "^" + elementName.Replace("[", "\\[").Replace("]", "\\]").Replace("+", "[+]").Replace(".", "[.]") + "$";
if (Regex.IsMatch(ftpElementName, pattern, RegexOptions.IgnoreCase))
{
res = true;
}
}
}
while (ftpElementName != null && !res);
streamReader.Close();
responseStream.Close();
response.Close();
return res;
}
Maybe it's a timeout problem, but i don't really know. I searched for a long time for an answer but without success. Maybe some of you will have a solution.
///
EDIT : Some progress :
I have tested my code in debug mode with VS and in fact the Exception above is the consequence of a previous one. (I Couldn't know that because I only wrote the last Exception returned in a log file)
Here is the original exception :
Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
The second exception is caused by this part of the Download method code :
catch (Exception e)
{
fileStream.Close();
responseStream.Close(); // <<<<<<<<<<<<<<
response.Close();
throw e;
}
I keep on my investigations but it seems that the "timeout pb" hypothesis is the most consistent. I will try with a large timeout value tonight.
Just want to strengthen ScottE's diagnosis, and be more specific. Timeout is most likely the issue.
Either .Net implementation of FtpWebRequest is erroneous or the MSDN document has a typo, the default value of FtpWebRequest.Timeout is not -1 (Infinite). It is 100000 (100 seconds).
In addition there is another timeout issue. A few tests have shown that responseStream always has a timeout value of 300000 (300 seconds). I do not know how this value is assigned. Anyways, this value needs to be modified to accommodate large files.
In summary, the solution is to set FtpWebRequest.Timeout and Stream.Timeout to a sufficiently large value.
Here's a good thread of things to try:
http://social.msdn.microsoft.com/Forums/en/ncl/thread/47634ec2-4d40-4d3f-b075-8cc92bfa2b24
Increasing the timeout is probably a good idea in the least.
This could be a symptom of an issue with the settings of your Windows Firewall. Disabling the "Application Layer Gateway Service" in the "services" interface fixed it for me.
This thread has a lot of information:
Try setting:
request.EnableSsl = true
来源：https://stackoverflow.com/questions/6304689/the-underlying-connection-was-closed-an-unexpected-error-occurred-on-a-receive