[FIX] smaller chunked upload size for slow connections

[chfsx]

This is concerning #88:
Defining the right chunk size is difficult. A larger chunk size leads to faster uploads, but in the case of slow connections, the upload is aborted because, for example, the connection time is exceeded. Therefore, we would probably have to change to a very small chunk size if very slow connections are also to be supported.
Suggestion here:

• Half upload limit or
• 2MB
  what is smaller will be used...

[dagraf]

I do not fully understand what chunk size you defined. @chfsx Could you please explain shortly what solution you chose for this PR? As a reminder: In the 'old' plugin, the default chunk size was set to 20MB, and we never heard complaints about uploads getting stuck.

[chfsx]

@dagraf with this PR the chunk size is either 2MB or (if the PHP upload-limit is < 4MB) half this upload-limit (since chunkes should be smaller that the php upload-limit. Smaller upload-limits lead to longer upload times but better support for slow connections. It's always a tradeof and there isn't a perfect value IMO.

[chfsx]

But we can go with 20MB since you mentioned there haven't been problems with this value in the past

[DZenker]

But,
min($upload_limit / 2, 2000000)
means that the chunk size will ALWAYS be 2 MB only. I think that nobody is using an ILIAS server with an upload limit <= 4 MB (at least in production).
That means 20 MB would be a good compromize.

Currently, we are using a chunk size of 50 MB in our production system with the Fluxlabs version of the plugin (and before 100 MB for some time), and I've never realized issues described in #88.

[chfsx]

@DZenker not ALWAYS but nearly ;-) Absolutely, nobobdy will run ILAIS with an upload-limit of just 3MB, but we must catch the case. I think 20 MB would be a good compromise, too and I'll update the PR accordingly.

[DZenker]

I implemented this fix in our test installation - but I've increased the chunk size to 20 MB instead of 2 MB - and can confirm that upload is working now even with slower internet connection. For details, see comment in #88.

[chfsx]

Thanks a lot for your feedbacks! I updated the PR to use 20MB as a default which seems to be a good compromize.

[okaufman]

Thank you very much for this fix. It looks very good.