gridcraft/apps/sheetcraft/src/control_server.rs

//! Localhost JSON-lines control server. Each connection may send many requests; each line
//! `{"id":…, "method":…, "params":…}` gets one reply line `{"id":…, "ok":…, …}`.

use std::io::{BufRead, BufReader, Write};
use std::net::{TcpListener, TcpStream};
use std::sync::mpsc::{Receiver, Sender, channel};
use std::time::Duration;

use serde_json::{Value as Json, json};
use sheetcraft_ui_egui::ControlRequest;

const MAX_LINE: usize = 64 * 1024 * 1024;

pub fn start(port: u16, ctx: egui::Context) -> std::io::Result<Receiver<ControlRequest>> {
    let listener = TcpListener::bind(("127.0.0.1", port))?;
    let (tx, rx) = channel();
    std::thread::Builder::new().name("control".into()).spawn(move || {
        for stream in listener.incoming().flatten() {
            let tx = tx.clone();
            let ctx = ctx.clone();
            let _ = std::thread::Builder::new().name("control-conn".into()).spawn(move || serve(stream, tx, ctx));
        }
    })?;
    eprintln!("SheetCraft control channel listening on 127.0.0.1:{port}");
    Ok(rx)
}

fn serve(stream: TcpStream, tx: Sender<ControlRequest>, ctx: egui::Context) {
    let Ok(read) = stream.try_clone() else { return };
    let mut out = stream;
    let reader = BufReader::new(read);
    for line in reader.lines() {
        let Ok(line) = line else { break };
        if line.trim().is_empty() {
            continue;
        }
        if line.len() > MAX_LINE {
            let _ = writeln!(out, "{}", json!({"ok": false, "error": "request too large"}));
            continue;
        }
        let msg: Json = match serde_json::from_str(&line) {
            Ok(v) => v,
            Err(e) => {
                let _ = writeln!(out, "{}", json!({"ok": false, "error": format!("invalid JSON: {e}")}));
                continue;
            }
        };
        let id = msg.get("id").cloned().unwrap_or(Json::Null);
        let method = msg.get("method").and_then(Json::as_str).unwrap_or("").to_string();
        let params = msg.get("params").cloned().unwrap_or(json!({}));
        let (req, rx) = ControlRequest::new(method, params);
        if tx.send(req).is_err() {
            break;
        }
        // Wake the UI thread: egui only runs frames when something happens.
        ctx.request_repaint();
        let mut reply = rx
            .recv_timeout(Duration::from_secs(60))
            .unwrap_or_else(|_| json!({"ok": false, "error": "timed out waiting for the UI (is the window minimised?)"}));
        if let Some(o) = reply.as_object_mut() {
            o.insert("id".into(), id);
        }
        if writeln!(out, "{reply}").is_err() {
            break;
        }
    }
}