settled-reach/server/src/bridge/local.rs

// LocalBridge - Unix socket IPC implementation
// Implements D-020 subprocess/IPC architecture
// Deterministic client-server communication via Unix domain sockets

use super::{BridgeError, ObserverSnapshot, PlayerInput, SimBridge};
use crate::bridge::framing::{read_framed, write_framed};
use std::fs;
use std::io::{BufReader, BufWriter};
use std::os::unix::net::{UnixListener, UnixStream};
use std::path::{Path, PathBuf};
use std::sync::Mutex;

/// LocalBridge: Unix socket transport for client-server IPC
pub struct LocalBridge {
    reader: Mutex<BufReader<UnixStream>>,
    writer: Mutex<BufWriter<UnixStream>>,
    socket_path: PathBuf,
}

impl LocalBridge {
    /// Server-side: create a Unix socket listener and accept one connection.
    /// Removes any stale socket file before binding.
    pub fn accept(path: &Path) -> Result<Self, BridgeError> {
        // Remove stale socket if it exists
        if path.exists() {
            fs::remove_file(path).map_err(|e| {
                BridgeError::Transport(format!("failed to remove stale socket: {}", e))
            })?;
        }

        tracing::info!("LocalBridge listening on {:?}", path);

        let listener = UnixListener::bind(path)
            .map_err(|e| BridgeError::Transport(format!("failed to bind Unix socket: {}", e)))?;

        // Accept one connection
        let (stream, _addr) = listener
            .accept()
            .map_err(|e| BridgeError::Transport(format!("failed to accept connection: {}", e)))?;

        tracing::info!("LocalBridge accepted connection on {:?}", path);

        // Clone stream for reader and writer
        let reader_stream = stream.try_clone().map_err(|e| {
            BridgeError::Transport(format!("failed to clone stream for reader: {}", e))
        })?;

        Ok(Self {
            reader: Mutex::new(BufReader::new(reader_stream)),
            writer: Mutex::new(BufWriter::new(stream)),
            socket_path: path.to_path_buf(),
        })
    }

    /// Client-side: connect to an existing Unix socket.
    pub fn connect(path: &Path) -> Result<Self, BridgeError> {
        tracing::info!("LocalBridge connecting to {:?}", path);

        let stream = UnixStream::connect(path).map_err(|e| {
            BridgeError::Transport(format!("failed to connect to Unix socket: {}", e))
        })?;

        tracing::trace!("LocalBridge connected to {:?}", path);

        // Clone stream for reader and writer
        let reader_stream = stream.try_clone().map_err(|e| {
            BridgeError::Transport(format!("failed to clone stream for reader: {}", e))
        })?;

        Ok(Self {
            reader: Mutex::new(BufReader::new(reader_stream)),
            writer: Mutex::new(BufWriter::new(stream)),
            socket_path: path.to_path_buf(),
        })
    }

    pub fn socket_path(&self) -> &Path {
        &self.socket_path
    }
}

impl SimBridge for LocalBridge {
    fn send_snapshot(&self, snapshot: &ObserverSnapshot) -> Result<(), BridgeError> {
        let payload = rmp_serde::to_vec_named(snapshot)?;

        let mut writer = self.writer.lock().expect("writer mutex poisoned");
        write_framed(writer.get_mut(), &payload)?;

        tracing::trace!("sent snapshot: tick={}", snapshot.tick);
        Ok(())
    }

    fn receive_inputs(&self) -> Result<Vec<PlayerInput>, BridgeError> {
        let mut reader = self.reader.lock().expect("reader mutex poisoned");

        match read_framed(reader.get_mut())? {
            Some(payload) => {
                let inputs: Vec<PlayerInput> = rmp_serde::from_slice(&payload)?;
                tracing::trace!("received {} inputs", inputs.len());
                Ok(inputs)
            }
            None => Err(BridgeError::Disconnected),
        }
    }
}

impl Drop for LocalBridge {
    fn drop(&mut self) {
        // Best-effort socket cleanup
        if self.socket_path.exists() {
            let _ = fs::remove_file(&self.socket_path);
            tracing::trace!("removed socket file {:?}", self.socket_path);
        }
    }
}