'Connection closed by server' message partway through FTP, but session continues

[Brennig]

Hi,

About 52% of the way through FTP of a 35Mb audio file, FileZilla returns a 'connection closed by server' message and yet the FTP session continues. The moment the FTP is completed though, the session is dropped. You can see the message about 12 lines from the end of the attached file:

Session log:
Status: Resolving address of incorrectlypolitical.co.uk
Status: Connecting to 72.167.232.52:21...
Status: Connection established, waiting for welcome message...
Response: 220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
Response: 220-You are user number 4 of 50 allowed.
Response: 220-Local time is now 02:20. Server port: 21.
Response: 220-This is a private system - No anonymous login
Response: 220 You will be disconnected after 3 minutes of inactivity.
Command: USER brennigjones
Response: 331 User brennigjones OK. Password required
Command: PASS
Response: 230-User brennigjones has group access to: 450
Response: 230 OK. Current directory is /
Command: SYST
Response: 215 UNIX Type: L8
Command: FEAT
Response: 211-Extensions supported:
Response: EPRT
Response: IDLE
Response: MDTM
Response: SIZE
Response: REST STREAM
Response: MLST type*;size*;sizd*;modify*;UNIX.mode*;UNIX.uid*;UNIX.gid*;unique*;
Response: MLSD
Response: ESTP
Response: PASV
Response: EPSV
Response: SPSV
Response: ESTA
Response: AUTH TLS
Response: PBSZ
Response: PROT
Response: 211 End.
Status: Connected
Status: Retrieving directory listing...
Command: PWD
Response: 257 "/" is your current location
Command: TYPE I
Response: 200 TYPE is now 8-bit binary
Command: PASV
Response: 227 Entering Passive Mode (72,167,232,52,196,124)
Command: LIST
Response: 150 Accepted data connection
Response: 226-ASCII
Response: 226-Options: -a -l
Response: 226 45 matches total
Command: PASV
Response: 227 Entering Passive Mode (72,167,232,52,198,40)
Command: LIST -a
Response: 150 Accepted data connection
Response: 226-ASCII
Response: 226-Options: -a -l
Response: 226 45 matches total
Status: Calculating timezone offset of server...
Command: MDTM favicon.ico
Response: 213 20081118122530
Status: Timezone offsets: Server: -25200 seconds. Local: 0 seconds. Difference: 25200 seconds.
Status: Directory listing successful
Status: Retrieving directory listing...
Command: CWD thisrealitypodcast
Response: 250 OK. Current directory is /thisrealitypodcast
Command: PWD
Response: 257 "/thisrealitypodcast" is your current location
Command: PASV
Response: 227 Entering Passive Mode (72,167,232,52,196,229)
Command: LIST -a
Response: 150 Accepted data connection
Response: 226-ASCII
Response: 226-Options: -a -l
Response: 226 33 matches total
Status: Directory listing successful
Status: Retrieving directory listing...
Command: CWD audio
Response: 250 OK. Current directory is /thisrealitypodcast/audio
Command: PWD
Response: 257 "/thisrealitypodcast/audio" is your current location
Command: PASV
Response: 227 Entering Passive Mode (72,167,232,52,195,119)
Command: LIST -a
Response: 150 Accepted data connection
Response: 226-ASCII
Response: 226-Options: -a -l
Response: 226 30 matches total
Status: Directory listing successful
Status: Resolving address of incorrectlypolitical.co.uk
Status: Connecting to 72.167.232.52:21...
Status: Connection established, waiting for welcome message...
Response: 220---------- Welcome to Pure-FTPd [privsep] [TLS] ----------
Response: 220-You are user number 4 of 50 allowed.
Response: 220-Local time is now 02:21. Server port: 21.
Response: 220-This is a private system - No anonymous login
Response: 220 You will be disconnected after 3 minutes of inactivity.
Command: USER brennigjones
Response: 331 User brennigjones OK. Password required
Command: PASS
Response: 230-User brennigjones has group access to: 450
Response: 230 OK. Current directory is /
Status: Connected
Status: Starting upload of C:\Documents and Settings\Brennig Jones\My Documents\My Music\Podcast Files\Source Files\2009-01-03.mp3
Command: CWD /thisrealitypodcast/audio
Response: 250 OK. Current directory is /thisrealitypodcast/audio
Command: PWD

Response: 257 "/thisrealitypodcast/audio" is your current location
Command: TYPE I
Response: 200 TYPE is now 8-bit binary
Command: PASV
Response: 227 Entering Passive Mode (72,167,232,52,196,188)
Command: STOR 2009-01-03.mp3
Response: 150 Accepted data connection
Error: Connection closed by server
Response: 226-File successfully transferred
Response: 226 653.861 seconds (measured here), 45.49 Kbytes per second
Status: File transfer successful
Status: Retrieving directory listing...
Command: PASV
Response: 227 Entering Passive Mode (72,167,232,52,199,28)
Command: LIST -a
Response: 150 Accepted data connection
Response: 226-ASCII
Response: 226-Options: -a -l
Response: 226 31 matches total
Status: Directory listing successful

[Brennig]

Session log from FileZilla client

[Tim Kosse]

Many servers close idle connections (with a far too short timeout, should be hours to days). Note that FileZilla uses multiple connections so that you can browse the server during transfers.

[Brennig]

Hey, I think you're missing the point here!

The connection was not closed. The connection was not idle. FileZilla incorrectly reported that the connection was closed but the FTP session continued.

Can we have this looked at again because you've got hold of the wrong end of the stick completely codesquid!

[Tim Kosse]

Actually the connection has been closed. But in order to not interrupt the user's workflow, the session (i.e what the user sees in FileZilla other than the log) remains unchanged.

[Brennig]

So what you seem to be saying here (just to make sure I'm understandingly you correctly, is that the session was closed at the point indicated, but FileZilla continued with the session under the file had been completely transferred? Is that correct?

[Tim Kosse]

Can you please rephrase your question? I have problems understanding it.

[Brennig]

Sorry, I'll try again. I just need to understand what you're telling me:

You seem to be saying that the connection had been closed. And yet the file continued to transfer - and the transfer was concluded after the passage of a further 15Mb of data *after* the connection had been dropped.

So what you're saying is that even though the connection had been dropped FileZilla still somehow completed the transfer, is that right?

[Tim Kosse]

FileZilla uses more than one connection so that you are able to browse the server during transfers. In your case, just the browsing connection got closed.
Even if the transfer connection were to close, it would resume automatically without you ever noticing if the log would not be.