Web workflow: use absolute paths to avoid paths being adjusted by current directory

[dhalbert]

• Fixes Web Workflow uploads file to wrong folder if default folder has been changed using os.chdir() #9053 (opened by @RetiredWizard).

The web workflow was using relative paths internally when adjusting paths at the root /. This made them subject to whatever os.chdir() had been set to. Instead, use absolute paths to avoid any influence by the current directory.

I tested by doing os.chdir("/lib") in the REPL while using the web workflow. Previously this messed up being able to descend into directories or fetch files. Now it seems to work fine.

[dhalbert]

@tannewt One confusion I had when tracking this down was what MP_VFS_ROOT meant, as returned by mp_vfs_lookup_path() in extmod/vfs.c. It seems to mean only /, and not the whole default filesystem. I'm thinking that even CIRCUITPY is a VFS that is mounted on MP_VFS_ROOT. So it seems MP_VFS_ROOT is only the / mount point, and not the filesystem itself. Do you remember the details here?

[RetiredWizard]

I only looked at the changes so I don't have the context for what the variables are, but the comments are talking about mount points and the issue seems to be more general as simple sub-directories exhibited the issue.

I did test the artifact and it resolved the problem demonstrated by the test code.py in the original issue, however now I don't think a file can be deleted using web workflow if the folder has been changed from the root folder using os.chdir.

[dhalbert]

Internally, the code is now using an absolute path instead of a relative path. That eliminates the current directory as something that influences path lookup. I'll look at the "delete" case: it may be taking a different path.

[RetiredWizard]

Ah, I guess I didn't check the delete before this update, it probably never worked. Rename isn't working either but Edit does....

[tannewt]

Thanks for the fix!

[tannewt]

@tannewt One confusion I had when tracking this down was what MP_VFS_ROOT meant, as returned by mp_vfs_lookup_path() in extmod/vfs.c. It seems to mean only /, and not the whole default filesystem. I'm thinking that even CIRCUITPY is a VFS that is mounted on MP_VFS_ROOT. So it seems MP_VFS_ROOT is only the / mount point, and not the filesystem itself. Do you remember the details here?

I don't remember. Sorry!