FTP problems

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kpg - 28 May 2008 21:18 GMT

(Multi-post from microsoft.public.dotnet.framework.aspnet.webservices,
Please apply all applicable pardons.)

Hi all,

I have a web service that FTPs data it receives to a third party
FTP site.

The web service will upload to the FTP site 12 times. The 13th
time it will timeout. Once the web service is reset - that is
modified in some way that IIS is forced to unload and JIT, then
it will upload an additional 12 times. This behavior is
remarkably consistent.

Note it does not matter what FTP site I upload to. I tested
against a server on my local LAN and it fails the same way.

This behavior leads me to believe that some session limit is being
reached, however the FTP site will allow 100,000 connections, and
in the test I uploaded once each second, but in production the files
come in hours apart. Plenty of time for the FTP server to dump any
possible open sessions.

The Web service will function normally for many hours until 12
upload are done, then I get FTP server timeouts.

Just as remarkable however, after about 6 hours, the FTP site will
again be accessible and an additional 12 uploads can be processed.

Actually the number of uploads is 24, since each post to the web
service results in 2 uploads to the FTP site.

Note that the FTP server is up and running with no problems while
the web service is failing and reporting a timeout, and the FTP
logs show no activity at all.

All this on a server that has many other functioning web services,
although none dealing with FTP transfers.

Any ideas? This is driving me nuts.

Thanks,
kpg

Here is the FTP upload code:

Private Function Upload(ByVal FTPPath As String, ByVal Data As
String, Optional ByVal UserName As String = "", Optional ByVal Password
As String = "") As Boolean

Try

Dim buffer As Byte() = Encoding.UTF8.GetBytes(Data)

Dim ftp As FtpWebRequest = CType(FtpWebRequest.Create
(FTPPath), FtpWebRequest)
If UserName.Length <> 0 Then
ftp.Credentials = New NetworkCredential(UserName,
Password)
End If

ftp.KeepAlive = False
ftp.UseBinary = True
ftp.Method = WebRequestMethods.Ftp.UploadFile
ftp.GetRequestStream().Write(buffer, 0, buffer.Length)

Upload = True

Catch ex As Exception

WriteToLog("Upload Error: " & ex.Message)

End Try

End Function

Reply to this Message

Joy - 29 May 2008 11:30 GMT

Hi,
While going thru your code it appears to me that once you are done with
writing the file you dont close the stream.

can you do a ".close()" on your stream and then try the code?

Let me know if the problem still persists.

regards,
Joy

> (Multi-post from microsoft.public.dotnet.framework.aspnet.webservices,
> Please apply all applicable pardons.)
[quoted text clipped - 71 lines]
>
> End Function

Reply to this Message

kpg - 29 May 2008 19:16 GMT

> Hi,
> While going thru your code it appears to me that once you are done with
[quoted text clipped - 6 lines]
> regards,
> Joy

I see your point. There are code examples out there
that create a stream variable and assign it the value
of ftp.GetRequestStream, then when complete they
close the stream. I perhaps incorrectly assumed that
the inplace GetRequestStream used below closed the stream
itself once completed.

Incidentally, as the code below does not use an explicit
stream object, how would it be closed in this case?

ftp.GetRequestStream().close ?

I would try it but I found a different solution that
works.

I replaced this:

Dim ftp As FtpWebRequest = _
CType(FtpWebRequest.Create(FTPPath),FtpWebRequest)
ftp.Credentials = New NetworkCredential(UserName,
ftp.KeepAlive = False
ftp.UseBinary = True
ftp.Method = WebRequestMethods.Ftp.UploadFile
ftp.GetRequestStream().Write(buffer, 0, buffer.Length)

with this:

Dim ftp As New WebClient
ftp.Credentials = New NetworkCredential(UserName, Password)
ftp.UploadData(FTPPath, buffer)

and that corrected the problem.

I have little doubt that either the stream (seems likely)
or something else was not being cleaned up properly, but
calling the higher level WebClient object's UploadData
method does any needed closing and cleanup for me.

When I searched for an ASP.NET 2.0 FTP examples I found
many using the ftpWebRequest object, but it took some
looking to discover the WebClient technique, which in
my mind is better because it works (!) and does so in
fewer lines of code.

I'm sure it uses the ftpWebRequest underneath, however.

Also in defense of the ftpWebRequest technique, most
examples used an explicit stream object that was then
closed in code, so that may well be the problem. I don't
noramlly like condensing the code down to one-liners
but in this case I did use that particular example.

Go Figure.

Thanks,
kpg

Reply to this Message

Joy - 30 May 2008 06:46 GMT

Hi,
I am glad to know that finally you could get it working.

As far as calling the ".close()" function goes, for that you would need to
first make a stream object and close it as is given below

Using requestStream As System.IO.Stream = ftp.GetRequestStream()
'The rest of the code goes here
requestStream.Close()
End Using

And you got it right, the most of the problem was attributed to the fact
that the clean up was not being done properly.

regards,
Joy

> > Hi,
> > While going thru your code it appears to me that once you are done
[quoted text clipped - 64 lines]
> Thanks,
> kpg

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