Automatically detect TTY (closes #795)

Signed-off-by: AnErrupTion <anerruption@disroot.org>

res/config.ini

@@ -272,9 +272,6 @@ sleep_key = F3
 # Center the session name.
 text_in_center = false
 
-# TTY in use
-tty = $DEFAULT_TTY
-
 # Default vi mode
 # normal   -> normal mode
 # insert   -> insert mode

src/config/Config.zig

@@ -72,7 +72,6 @@ shutdown_key: []const u8 = "F1",
 sleep_cmd: ?[]const u8 = null,
 sleep_key: []const u8 = "F3",
 text_in_center: bool = false,
-tty: u8 = build_options.tty,
 vi_default_mode: ViMode = .normal,
 vi_mode: bool = false,
 waylandsessions: []const u8 = build_options.prefix_directory ++ "/share/wayland-sessions",

src/interop.zig

@@ -84,6 +84,73 @@ fn PlatformStruct() type {
                 std.posix.setgid(@intCast(entry.gid)) catch return error.SetUserGidFailed;
                 std.posix.setuid(@intCast(entry.uid)) catch return error.SetUserUidFailed;
             }
+
+            // Procedure:
+            // 1. Open /proc/self/stat to retrieve the tty_nr field
+            // 2. Parse the tty_nr field to extract the major and minor device
+            //    numbers
+            // 3. Then, read every /sys/class/tty/[dir]/dev, where [dir] is every
+            //    sub-directory
+            // 4. Finally, compare the major and minor device numbers with the
+            //    extracted values. If they correspond, parse [dir] to get the
+            //    TTY ID
+            pub fn getActiveTtyImpl(allocator: std.mem.Allocator) !u8 {
+                var file_buffer: [256]u8 = undefined;
+                var tty_major: u16 = undefined;
+                var tty_minor: u16 = undefined;
+
+                {
+                    var file = try std.fs.openFileAbsolute("/proc/self/stat", .{});
+                    defer file.close();
+
+                    var reader = file.reader(&file_buffer);
+                    var buffer: [1024]u8 = undefined;
+                    const read = try reader.read(&buffer);
+
+                    var iterator = std.mem.splitScalar(u8, buffer[0..read], ' ');
+                    var fields: [52][]const u8 = undefined;
+                    var index: usize = 0;
+
+                    while (iterator.next()) |field| {
+                        fields[index] = field;
+                        index += 1;
+                    }
+
+                    const tty_nr = try std.fmt.parseInt(u16, fields[6], 10);
+                    tty_major = tty_nr / 256;
+                    tty_minor = tty_nr % 256;
+                }
+
+                var directory = try std.fs.openDirAbsolute("/sys/class/tty", .{ .iterate = true });
+                defer directory.close();
+
+                var iterator = directory.iterate();
+                while (try iterator.next()) |entry| {
+                    const path = try std.fmt.allocPrint(allocator, "/sys/class/tty/{s}/dev", .{entry.name});
+                    defer allocator.free(path);
+
+                    var file = try std.fs.openFileAbsolute(path, .{});
+                    defer file.close();
+
+                    var reader = file.reader(&file_buffer);
+                    var buffer: [16]u8 = undefined;
+                    const read = try reader.read(&buffer);
+
+                    var device_iterator = std.mem.splitScalar(u8, buffer[0..(read - 1)], ':');
+                    const device_major_str = device_iterator.next() orelse continue;
+                    const device_minor_str = device_iterator.next() orelse continue;
+
+                    const device_major = try std.fmt.parseInt(u8, device_major_str, 10);
+                    const device_minor = try std.fmt.parseInt(u8, device_minor_str, 10);
+
+                    if (device_major == tty_major and device_minor == tty_minor) {
+                        const tty_id_str = entry.name["tty".len..];
+                        return try std.fmt.parseInt(u8, tty_id_str, 10);
+                    }
+                }
+
+                return error.NoTtyFound;
+            }
         },
         .freebsd => struct {
             pub const kbio = @cImport({
@@ -142,6 +209,10 @@ pub fn getTimeOfDay() !TimeOfDay {
     };
 }
 
+pub fn getActiveTty(allocator: std.mem.Allocator) !u8 {
+    return platform_struct.getActiveTtyImpl(allocator);
+}
+
 pub fn switchTty(tty: u8) !void {
     var status = std.c.ioctl(std.posix.STDIN_FILENO, platform_struct.vt_activate, tty);
     if (status != 0) return error.FailedToActivateTty;

src/main.zig

@@ -58,6 +58,7 @@ pub fn main() !void {
     var restart = false;
     var shutdown_cmd: []const u8 = undefined;
     var restart_cmd: []const u8 = undefined;
+    var commands_allocated = false;
 
     var stderr_buffer: [128]u8 = undefined;
     var stderr_writer = std.fs.File.stderr().writer(&stderr_buffer);
@@ -75,10 +76,13 @@ pub fn main() !void {
             stderr.flush() catch std.process.exit(1);
         } else {
             // The user has quit Ly using Ctrl+C
+            if (commands_allocated) {
+                // Necessary if we error out before allocating
                 temporary_allocator.free(shutdown_cmd);
                 temporary_allocator.free(restart_cmd);
             }
         }
+    }
 
     var gpa = std.heap.DebugAllocator(.{}).init;
     defer _ = gpa.deinit();
@@ -242,6 +246,7 @@ pub fn main() !void {
     // we end up shutting down or restarting the system
     shutdown_cmd = try temporary_allocator.dupe(u8, config.shutdown_cmd);
     restart_cmd = try temporary_allocator.dupe(u8, config.restart_cmd);
+    commands_allocated = true;
 
     // Initialize termbox
     try log_writer.writeAll("initializing termbox2\n");
@@ -478,7 +483,8 @@ pub fn main() !void {
     var auth_fails: u64 = 0;
 
     // Switch to selected TTY
-    interop.switchTty(config.tty) catch |err| {
+    const active_tty = try interop.getActiveTty(allocator);
+    interop.switchTty(active_tty) catch |err| {
         try info_line.addMessage(lang.err_switch_tty, config.error_bg, config.error_fg);
         try log_writer.print("failed to switch tty: {s}\n", .{@errorName(err)});
     };
@@ -843,7 +849,7 @@ pub fn main() !void {
                     if (session_pid == 0) {
                         const current_environment = session.label.list.items[session.label.current];
                         const auth_options = auth.AuthOptions{
-                            .tty = config.tty,
+                            .tty = active_tty,
                             .service_name = config.service_name,
                             .path = config.path,
                             .session_log = config.session_log,