FTP upload error

Question

Hello, I've a couple of Android apps that worked well for years.
One of these apps has been recently restyled, and recompiled under VS2017. My big problem is that I can regularly download files from our external FTP server (Cerberus, no SSL), but I cannot anymore upload anything. There was no change in the FTP code, so I cannot wonder what it could be.
I've tested it on three different devices (Samsung SM-T550, V4.4.2, Asus Nexus 7 with 6.0.1 and a brand new Samsung Tab A6 with V7.0); if I install a simple app, like AndFTP, all the operations (download/upload) are carried out without errors.
I cannot paste an excerpt of the upload process taken from the Android Monitor, it exceedes the caracter's limit; the file I'm trying to upload is about 2MB in size.

Any suggestion is obviously welcome; if you need furter details please let me know.
Thanks.
Rodolfo.

Answer 1

This is very strange - in FTP (at the low level), uploads, downloads and directory listings are almost identical; only the direction of the data transfer differs. Has anything changed at the server? This look like a server-side issue, although it's too early to tell.

In any case, could you please create a communication log using Ftp object's LogWriter property showing a successful download and a failed upload? This should make it possible to tell what is actually going on. Either post the log here or mail it to support@rebex.net for analysis.

Comments

Hi, Lukas, I've had to email the logs, as they are beyond the characters limit for the forum's messages.

Rodolfo

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Forgot to mention that (for what I know) nothing has changed on the server, as it is heavily used by our customers for data transfer.
At this moment my colleague is RDP connected to the server for a demo, so I cannot retrieve Cerberus version number. If this version can be of any interest, I'll post it when the RDP will be available.

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Thanks! According to the log, this looks like some kind of connectivity issue. The client and server were able to successfully establish the FTP data connection and start uploading data, but later the data connection failed. From the client side, this manifested as a SocketException(0x80004005 / Connection timed out). From the server side, this almost certainly manifested in a similar way. However, the FTP control connection survived this - the server was able to respond with an error code (426 File transfer failed). This means that the issue might be caused by something along the way, and it's quite possible that neither the client nor the server are the real cause. We would like to look into this - I'll send you a list of possible next steps via email.