But in a system we worked on for years we dealt with intermittent connections by building a queue of what needed to be sent in.
This queue tested some programmer limits. That is, we lost a few programmers that could not wrap their head around failed sends and putting the item into a queue for retries later.
But that's how our system works. You can never be sure of the connections (we are in a mobile situation so cellular access is spotty.) so we rewrote the code and made a system that worked around the iffy nature of mobile use.
Now you should use this to make your code handle failures.
FTP connections are intermittent, one minute I can connect, the next I can't.
I have a webcam that takes a picture every minute and FTPs it to my weather website. www.bobhatcher.info. It's a good test because if the FTP doesn't connect one minute, it will over the next hour or so. If you look at my site you will see that the "current" picture will be ten minutes to two hours old. I know it's not a problem with the software because I have the same issues with FileZilla and other FTP software products.
Here's my configuration.
- Time Warner internet service
- Surfboard Motorola/Arris SBG6580-G228 Cable Modem Router
- 1and1 webhosting
The TWC people tell me it's the fault of the router and to call Arris. The Arris folks tell me it's TWCs fault and there are signal problems. The 1and1 people have no clue.
So, what do the esteemed members of this community think? Can you help me?

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