Add total disk space to free-space RPC request

[johman10]

Hi! I'm the creator of Flood for Transmission and I was working on a little detail panel that shows the available space. In that panel I was hoping to show user configured paths and how much space is available with a progress bar kind of representation.

However as of today Transmission doesn't let me know how much space is available in total. For this purpose I made this PR. It basically also returns the amount of bytes that the disk has in total (along side the untouched free space).

To do this I had to dig through some layers all the way to the deepest native call and pass it back up, which I used a struct for. Please review carefully as this is my first ever work in any form of C so I may have done somethings a bit different than conventional. But if so, please do let me know and I can look at it, or feel free to update the PR yourself if you feel like it.

I tested this on Linux (via Windows subsystem) with a Postman request see below:

I don't know how else to test this so let me know if something is off.

[lgtm-com]

This pull request introduces 1 alert when merging d34ec4a into faafc9e - view on LGTM.com

new alerts:

• 1 for Comparison result is always the same

[johman10]

So I have been trying a bunch of things but fail to get a passing windows build. Problem is the following:
C:\BuildAgent2\work\1f3bff43dd55cfe9\libtransmission\utils.h(87,22): error C2526: 'tr_getDirSpace': C linkage function cannot return C++ class 'tr_disk_space'

I have no idea what's going on here. @ckerr do you have any idea how to resolve this? Feel free to change the PR to what's needed or let me know how to resolve it.

As I mentioned before this is one of the first times looking at C so this is not clear to me at all.

[ckerr]

Hmm I see I left this PR in limbo. Sorry about that @johman10. Is this feature something your'e still interested in, and would you be willing to update the PR to sync with all the recent changes in master? It doesn't look like the conflicts would be too extreme and will likely fix the C linkage cannot return C++ class 'disk space' error as a happy side-effect 🙂

[johman10]

@ckerr I'm still interested in this and wouldn't mind updating this PR.

I can have a look at it soon-ish. Can't promise any timeframe right now but I will aim to find some time this week. :)

[ckerr]

ftbfs on lgtm:

2021-10-12 17:38:38] [build-stderr] /opt/src/libtransmission/platform-quota.cc: In function ‘tr_disk_space getquota(const char*)’:
[2021-10-12 17:38:38] [build-stderr] /opt/src/libtransmission/platform-quota.cc:363:17: error: could not convert ‘-1’ from ‘int’ to ‘tr_disk_space’
[2021-10-12 17:38:38] [build-stderr]   363 |         return -1;
[2021-10-12 17:38:38] [build-stderr]       |                 ^
[2021-10-12 17:38:38] [build-stderr]       |                 |
[2021-10-12 17:38:38] [build-stderr]       |                 int

[johman10]

@ckerr I updated the branch and it seems like the builds will pass now, as you predicted.

Please give it another review when you have time! :)