I'm desperately trying to find where the google drive and google docs urls scheme and query parameters are documented. For example what is the usp= parameter which seems to have several possible values ? Also, why a link like this https://drive.google.com/drive/u/2/#folders/ will open a folder in Safari and Chrome without new authentication while a link like https://drive.google.com/drive/#folders/ will only work correctly in chrome. What is the meaning of u/2/ ? etc. Anyone knows how to find a complete documentation of these url schemes ?
As the part about /u/2/ has already been satisfactorily explained, I'll try to explain the part about usp from my best understanding.
It seems to just be providing data on from where you got access to the document.
usp=docs_home
is when you create a new document from Google Docs itself
usp=drivesdk
is given when you get a link using the Drive SDK
usp=sharing
is when you get a link from the sharing dialogue
usp=drive_web
is what you get when you click on a document in the Docs homepage or in Drive
usp=direct_url
is seen on the Docs homepage when you directly go to sheets.google.com
or slides.google.com
There are probably more to be found, but it doesn't seem to be doing anything other than likely providing referrer information. Replacing usp=sharing
with anything else still doesn't seem to stop you from retrieving a document, and it seems unlikely that this would be a document-specific property as it is also seen on other Google URLs, like the slides/sheets homepage.