Use Kakoune's socket to send commands instead of kak -p.

[tadeokondrak]

There is a noticeable lag when using #545 on a project with a few hundred crate dependencies just to show the progress bar when rust-analyzer is sending updates very fast. I'm not sure where it comes from.

It occurred to me that this might come from this code:
https://github.com/kak-lsp/kak-lsp/blob/23c5f3c450c1e42856c7ff15af4234d566ee5b11/src/editor_transport.rs#L57-L62

Instead of using kak -p, we can use the remote socket at $XDG_RUNTIME_DIR/kakoune/$pid. This allows us to have a persistent connection up, so we don't need to make a new process every time we send a command.

I believe the protocol is just a 0x02 byte, followed by a 32-bit size, followed by the string. Because there's probably no stability guarantee, this could be an optional setting - if it ends up speeding anything up at all.

I will probably try this out soon and see if there's any performance improvement.

[caksoylar]

I use this approach in kakoune-smooth-scroll (relevant code here to discover the socket path and construct the message). Like you also noted, my understanding is that this is an internal API so it is subject to change, but in practice I only had to update it once so far due to a socket location tweak in Kakoune.

This approach indeed buys a decent amount of time on systems where process invocation is slow, like Cygwin/MSYS or when network filesystems are involved.

[krobelus]

an option sounds reasonable but we should confirm that it makes a difference.
Maybe we can also add some profiling tool to find performance problems.
On my system echo nop | kak -p somesession takes 4-8 milliseconds.

[krobelus]

There is a noticeable lag when using #545 on a project with a few hundred crate dependencies just to show the progress bar when rust-analyzer is sending updates very fast. I'm not sure where it comes from.

I think this has been fixed by c32aa61 (lsp-handle-progress: forward at most one progress update per second, 2022-10-18).

Regardless, I think it'd be a good idea to use the socket, shouldn't be too much work.
The other direction is trickier: when sending from editor to kak-lsp, we can't really avoid a shell + kak-lsp process unless we cut down on usability (automatic restarts).