MTP transport missing for windows runtimes.

Start with the dctool Windows device-detection and dump path, then trace how existing USB and MTP transports are selected. Review the related issues and determine how a Windows Portable Devices transport could fit the library. Done means dctool can dump FIT files from Garmin Mk2i+ and similar MTP devices on Windows without requiring a local file copy.

I recently started using Subsurface and found that my Garmin mk3i does not automatically import dives. I believe this is because this library does not include an MTP driver for Windows. I did a bit of digging and found that there really isn't a compelling way to get libmtp to work on a Windows installation.

It is unclear to me why Garmin stopped supporting USB, but based on the minimal posts I found, they seem to be trying to protect the device's memory. I am guessing it has something to do with controlling what files are visible or something. I dunno TBH.

I am interested in fixing this issue. I am posting this to facilitate discussion.

I believe the solution could be to use Windows Portable Devices (WPD) API. I know this is primarily a Linux project, but I think as long as I define the transport correctly, we can support Windows.

I am pretty sure no MTP implementation works on Windows for this reason. I have not combed through the code base to find them all yet (if they exist at all), though. Ideally, the solution would be included for them, too.

I am posting this message here, not in subsurface, because I believe the fix is here. Happy to move the issue if that is not what is preferred.

Expected behavior

dctool (examples) should be able to dump from a Garmin MK2i+ without issue.

Current behavior

I got a build working and debugged dctool to try to dump data.

dctool attempts to read from the Garmin device as a USB device (because no MTP library is available). This fails because mk2i devices do not mount as USB devices; they mount as MTP devices.

So I can't actually work around this by specifying the path either; there is no valid path on Windows for the device.

This can be worked around by just copying out the FIT files locally but that is not quite the experiance I would like 😄

My setup

Windows 11 Pro (Version 24H2)
Garmin Descent Mk3i 51mm
Subsurface 6.0.5576-CICD-release
Intel(R) Core(TM) i7-14700K (3.40 GHz)

Related issues

https://github.com/subsurface/subsurface/issues/3204
https://github.com/subsurface/subsurface/issues/4661 (I think there may be something similar here in the root cause but I have not tested this on a mac and it might be seperate)
https://groups.google.com/g/subsurface-divelog/c/EOL7GhHqE6I/m/AzzxwocQAQAJ (Maybe related?)