Add multi-window support

Previously Alacritty would always initialize only a single terminal
emulator window feeding into the winit event loop, however some
platforms like macOS expect all windows to be spawned by the same
process and this "daemon-mode" can also come with the advantage of
increased memory efficiency.

The event loop has been restructured to handle all window-specific
events only by the event processing context with the associated window
id. This makes it possible to add new terminal windows at any time using
the WindowContext::new function call.

Some preliminary tests have shown that for empty terminals, this reduces
the cost of additional terminal emulators from ~100M to ~6M. However at
this point the robustness of the daemon against issues with individual
terminals has not been refined, making the reliability of this system
questionable.

New windows can be created either by using the new `CreateNewWindow`
action, or with the `alacritty msg create-window` subcommand. The
subcommand sends a message to an IPC socket which Alacritty listens on,
its location can be found in the `ALACRITTY_SOCKET` environment
variable.

Fixes #607.

1 files changed, 145 insertions, 0 deletions

diff --git a/alacritty/src/ipc.rs b/alacritty/src/ipc.rs
new file mode 100644
index 00000000..02aaf85f
--- /dev/null
+++ b/alacritty/src/ipc.rs
@@ -0,0 +1,145 @@
+//! Alacritty socket IPC.
+
+use std::ffi::OsStr;
+use std::io::{Error as IoError, ErrorKind, Result as IoResult};
+use std::os::unix::net::UnixDatagram;
+use std::path::PathBuf;
+use std::{env, fs, process};
+
+use glutin::event_loop::EventLoopProxy;
+use log::warn;
+
+use alacritty_terminal::thread;
+
+use crate::cli::Options;
+use crate::event::{Event, EventType};
+
+/// IPC socket message for creating a new window.
+pub const SOCKET_MESSAGE_CREATE_WINDOW: [u8; 1] = [1];
+
+/// Environment variable name for the IPC socket path.
+const ALACRITTY_SOCKET_ENV: &str = "ALACRITTY_SOCKET";
+
+/// Create an IPC socket.
+pub fn spawn_ipc_socket(options: &Options, event_proxy: EventLoopProxy<Event>) -> Option<PathBuf> {
+    // Create the IPC socket and export its path as env variable if necessary.
+    let socket_path = options.socket.clone().unwrap_or_else(|| {
+        let mut path = socket_dir();
+        path.push(format!("{}-{}.sock", socket_prefix(), process::id()));
+        path
+    });
+    env::set_var(ALACRITTY_SOCKET_ENV, socket_path.as_os_str());
+
+    let socket = match UnixDatagram::bind(&socket_path) {
+        Ok(socket) => socket,
+        Err(err) => {
+            warn!("Unable to create socket: {:?}", err);
+            return None;
+        },
+    };
+
+    // Spawn a thread to listen on the IPC socket.
+    thread::spawn_named("socket listener", move || {
+        // Accept up to 2 bytes to ensure only one byte is received.
+        // This ensures forward-compatibility.
+        let mut buf = [0; 2];
+
+        while let Ok(received) = socket.recv(&mut buf) {
+            if buf[..received] == SOCKET_MESSAGE_CREATE_WINDOW {
+                let _ = event_proxy.send_event(Event::new(EventType::CreateWindow, None));
+            }
+        }
+    });
+
+    Some(socket_path)
+}
+
+/// Send a message to the active Alacritty socket.
+pub fn send_message(socket: Option<PathBuf>, message: &[u8]) -> IoResult<()> {
+    let socket = find_socket(socket)?;
+    socket.send(message)?;
+    Ok(())
+}
+
+/// Directory for the IPC socket file.
+#[cfg(not(target_os = "macos"))]
+fn socket_dir() -> PathBuf {
+    xdg::BaseDirectories::with_prefix("alacritty")
+        .ok()
+        .and_then(|xdg| xdg.get_runtime_directory().map(ToOwned::to_owned).ok())
+        .and_then(|path| fs::create_dir_all(&path).map(|_| path).ok())
+        .unwrap_or_else(env::temp_dir)
+}
+
+/// Directory for the IPC socket file.
+#[cfg(target_os = "macos")]
+fn socket_dir() -> PathBuf {
+    env::temp_dir()
+}
+
+/// Find the IPC socket path.
+fn find_socket(socket_path: Option<PathBuf>) -> IoResult<UnixDatagram> {
+    let socket = UnixDatagram::unbound()?;
+
+    // Handle --socket CLI override.
+    if let Some(socket_path) = socket_path {
+        // Ensure we inform the user about an invalid path.
+        socket.connect(&socket_path).map_err(|err| {
+            let message = format!("invalid socket path {:?}", socket_path);
+            IoError::new(err.kind(), message)
+        })?;
+    }
+
+    // Handle environment variable.
+    if let Ok(path) = env::var(ALACRITTY_SOCKET_ENV) {
+        let socket_path = PathBuf::from(path);
+        if socket.connect(&socket_path).is_ok() {
+            return Ok(socket);
+        }
+    }
+
+    // Search for sockets files.
+    for entry in fs::read_dir(socket_dir())?.filter_map(|entry| entry.ok()) {
+        let path = entry.path();
+
+        // Skip files that aren't Alacritty sockets.
+        let socket_prefix = socket_prefix();
+        if path
+            .file_name()
+            .and_then(OsStr::to_str)
+            .filter(|file| file.starts_with(&socket_prefix) && file.ends_with(".sock"))
+            .is_none()
+        {
+            continue;
+        }
+
+        // Attempt to connect to the socket.
+        match socket.connect(&path) {
+            Ok(_) => return Ok(socket),
+            // Delete orphan sockets.
+            Err(error) if error.kind() == ErrorKind::ConnectionRefused => {
+                let _ = fs::remove_file(&path);
+            },
+            // Ignore other errors like permission issues.
+            Err(_) => (),
+        }
+    }
+
+    Err(IoError::new(ErrorKind::NotFound, "no socket found"))
+}
+
+/// File prefix matching all available sockets.
+///
+/// This prefix will include display server information to allow for environments with multiple
+/// display servers running for the same user.
+#[cfg(not(target_os = "macos"))]
+fn socket_prefix() -> String {
+    let display = env::var("WAYLAND_DISPLAY").or_else(|_| env::var("DISPLAY")).unwrap_or_default();
+    format!("Alacritty-{}", display)
+}
+
+/// File prefix matching all available sockets.
+#[cfg(target_os = "macos")]
+fn socket_prefix() -> String {
+    String::from("Alacritty")
+}