Unify File Locking Across Domains

[emmacasolin]

Specification

Previously we were using the proper-lockfile library to lock and unlock the session file during CLI calls, however, we have recently switched over to using the much simpler (and newer) fd-lock for this purpose. However, proper-lockfile is still being used for the agent lockfile, so we should change this to use fd-lock instead in order to unify our file locking across all domains.

Since fd-lock currently only has a lock() and unlock() command (and no way of checking if a file is locked without attempting to lock it or blocking access to a locked file) we will most likely need to look into the Node C++ bindings and the POSIX manual in order to adapt the library to our needs.

Additional context

See #236, where fd-lock was incorporated into the sessions domain.

Tasks

• Look into the Node C++ bindings and POSIX manual
• Make changes to the fd-lock library to meet our requirements
• Replace proper-lockfile usage with fd-lock in the agent lockfile
• Test that these changes have not affected functionality in any way

[CMCDragonkai]

Instead of C++, one can also use Rust: https://github.com/napi-rs/napi-rs

Can be useful if you want to gain experience in this new language.

[CMCDragonkai]

Locking at https://github.com/mafintosh/fd-lock/blob/master/binding.cc C++ code I see it using flock on linux/posix systems. The flock call actually supports read write locks, which means during reads of the session token file we should be using a shared lock, however this is not currently exposed in JS. The C++ code requires some changes to enable this and exposing shared vs exclusive locks. https://man7.org/linux/man-pages/man2/flock.2.html this shows that there's LOCK_SH flag capable of being used.

On win32 however, it should be swapped to using this call instead: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-lockfileex

Also important would be to apply promise-based API, so one can wait or block on the locks as well. Promise based system would require the C++ to notify the events. It appears the Node API can be called from C++ to create a promise: https://github.com/nodejs/node-addon-api/blob/main/doc/promises.md

[CMCDragonkai]

Testing should make use of a Windows CI/CD environment, just do manual test for now as it seems integrating Windows in our current CI/CD setup might be a bit difficult.

[CMCDragonkai]

No longer necessary because both Status and Session can just use fd-lock for now.

The Session is implemented in https://gitlab.com/MatrixAI/Engineering/Polykey/js-polykey/-/merge_requests/213

And Status is in #283.

This means lockfile domain and also the dependency proper-lockfile can be removed from js-polykey.

In the future we can improve lock performance and lock portability by following the above instructions/notes, but for now it's a wontfix.

@tegefaulkes @emmacasolin @joshuakarp

Note that this only applies to "file locking". Which is only used by Status and Session. Currently all other uses of locking uses async-mutex which is for in-process locking, not inter-process locking. And we already have a RWLock implementation on top of async-mutex.