B4J Question Pass large file from one NAT network to another

[wl]

Hi,

I would need a way to pass large files from one network to another (over the internet) and with both networks having a NAT connection to the internet (no incomming ports open).
Certainly this requires an intermediate server on the internet with open incomming ports.

Just using B4J (and thus no VPN, IP tunnel etc, ...) what would be the best approach, taking into accoutnt the intermediate server has lots of bandwidth bu no diskspace so storing the files (for a while) on the internet sevrer is not an option.

Thanks

 

[Erel]

MQTT can be a good option here. You just need an online broker.

 

[wl]

But as I read there is a limitation on the size of a message in MQTT and thus it might not be the best solution to send large files ?
I guess I will be able to set up my own broker and play with the message size limits ?

But still: if we talk about large videofiles to be passed, MQTT will porbbaly not be the best choice ?

 

[Erel]

Split the file and send it in chunks. If I remember correctly the maximum packet size is ~250mb which is very large. You should use smaller chunks.

 

[wl]

Would it be necessary to split the file in chunks myself and do the administration, or is this just a setting I need to provide and will MQTT will do it automatically ?

Thanks !

 

[DonManfred]

Would it be necessary to split the file in chunks myself and do the administration

Yes, you need to implement it by yourself.
MQTT is just the Transportpart in this Solution.

 

[Erel]

It is quite simple to do with InputStream and a large buffer.

 

[wl]

I should not be worried that the chunks will arrive in a reverse order at the subscriber, or that other chunks/packages arrive in the middle of packages of another file etc ? Just so I know before deliving in the details if it would not work out... thanks !

 

[Erel]

A robust solution is to add a "header" to each chunk. Maybe just to verify the data integrity and reject it if there are problems.

 

[wl]

I just tried it and it works, BUT:
the maximum size of each packet seems to be < 8 Kb which makes it extremely slow to pass anything but the smallest files
see my question at: https://www.b4x.com/android/forum/threads/mqtt-unknow-packet-limitation-on-messagesize.133081/

 

[Erel]

Why make duplicate posts???