fix: close HTTP sockets after responding

[alswl]

What

Every HTTP request leaks a file descriptor.

handler.client calls read_stop() as soon as a request is buffered, so the EOF branch that would close the socket never runs.

send_http_response only writes, and never closes either. The sockets sit in CLOSE_WAIT until the process dies.

Why it matters

A markdown page load is about 10 requests: the file itself, plus the katex, mermaid, highlight and markdown-it assets.

macOS defaults to 256 descriptors, so a normal editing session reaches the limit in an afternoon.

Past that point the server stops accepting connections, and processes_listening_on_port throws EMFILE out of vim.system.

It also snowballs. ws-client.js reloads the page whenever its socket drops, and retries every second. Each reload is another 10 requests.

How

HTTP. Close the socket in send_http_response once the write drains. shutdown() rather than close(), otherwise large responses get truncated.

WebSocket. Same cause: reads stop after the upgrade, so a closed tab is never noticed. Re-arm reads purely to watch for EOF.

Two related fixes while in here:

• connecting_clients now only holds WebSocket clients. It exists to broadcast WebSocket frames, but every accepted socket was added to it, so send_json was writing frames into plain HTTP connections.

• Server:stop closes the remaining clients, instead of leaving their descriptors open until Neovim exits.

Evidence

Load only this plugin, start a server on 5701, then:

for i in $(seq 1 60); do
  curl -s -o /dev/null http://127.0.0.1:5701/index.md
done
lsof -p $PID | grep IPv4 | awk '{print $NF}' | sort | uniq -c

	sockets after 60 requests
without the fix	60 CLOSE_WAIT + 1 LISTEN

No regressions found: a 892KB markdown file still comes back whole (914542 bytes, closing </html> intact), and four WebSockets stay open while connected, then get reaped once the peers disconnect.

[github-actions]

Thank you for your pull request! We appreciate your contribution. Please ensure that your changes are well documented and tested, and are formatted as noexpandtab.

[alswl]

@brianhuster Hi, could you take a moment to look at it, thanks?

[brianhuster]

Thank u, lgtm