C# - Ftp protocol implementation

Question

in Compact Framework, the Ftp Protocol is not implemented so I developed it myself.

I've a question about the passive mode and commands that need to have a data channel to read the response.

In my case, I'm trying to retrieve (RETR) a file on my FTP Server, So I do :

Part that works well :

OpenControlChannel
ReadControl (Banner Message)
SendUser
ReadControl (Awaiting pass?)
SendPass
ReadControl (Welcome Message)
SendPassive
ReadControl (Extract IP for the DataChannel)

Parts that doesn't work very well (but work too, see explanation below)

RETR myFile
OpenDataChannel
ReadControl (Here I become the message "Begin Transfert" AND "Transfert complete", before reading any data !)
ReadData
CloseDataChannel
CloseControlChannel

Problem is, I need just to open data channel to have the message "Transfert complete" even if I haven't read any data on the stream, is this behavior normal?

For me, when I open the data channel I should just receive

"150 Opening ASCII mode data connection for a.she (0 bytes).\r\n"

Then once the read operation done :

"226 Transfer complete.\r\n"

When I look to the classic Ftp protocol used in the .NET Framework, it is the case :

FtpWebResponse ftpres = (FtpWebResponse)ftp.GetResponse();
// ftpres.StatusDescription = "150 Opening ASCII mode data connection for a.she (0 bytes).\r\n" 
string res = new StreamReader(ftpres.GetResponseStream()).ReadToEnd();
// ftpres.StatusDescription = "226 Transfer complete.\r\n"

Hope I'm clear enough... Thanks !

Just a note - handling data connection properly requires a bunch of tricks, so in general using some existing FTP component for .NET CF makes more sense then trying to write your own. — Eugene Mayevski 'Callback, Feb 16 '11 at 10:19
@Eugene Except it doesn't handle some of the special command needed for servers like MVS. — C. Ross, Mar 31 '11 at 14:34

score 0 · Accepted Answer · answered Feb 17 '11 at 21:24

I think this behavior is normal, it pre-load data in a cache on server side and send the message in order to say data are available and loaded.

This because when data channel is between 2 servers (and not client/server mode), the user should now when transfer is done, so it only take a look on this cache...

(EDIT : In some case it appears that I got messages in the good order (only once data read), strange...)

C# - Ftp protocol implementation

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