tauri-plugins-workspace/plugins/single-instance/src/platform_impl/windows.rs

// Copyright 2019-2023 Tauri Programme within The Commons Conservancy
// SPDX-License-Identifier: Apache-2.0
// SPDX-License-Identifier: MIT

#[cfg(feature = "semver")]
use crate::semver_compat::semver_compat_string;

use crate::SingleInstanceCallback;
use tauri::{
    AppHandle, Manager, RunEvent, Runtime,
    plugin::{self, TauriPlugin},
};
use windows_sys::Win32::{
    Foundation::{CloseHandle, ERROR_ALREADY_EXISTS, GetLastError, HWND, LPARAM, LRESULT, WPARAM},
    System::{
        DataExchange::COPYDATASTRUCT,
        LibraryLoader::GetModuleHandleW,
        Threading::{CreateMutexW, ReleaseMutex},
    },
    UI::WindowsAndMessaging::{
        self as w32wm, AllowSetForegroundWindow, CREATESTRUCTW, CreateWindowExW, DefWindowProcW,
        DestroyWindow, FindWindowW, GWL_STYLE, GWLP_USERDATA, GetWindowThreadProcessId,
        RegisterClassExW, SMTO_NORMAL, SendMessageTimeoutW, WINDOW_LONG_PTR_INDEX, WM_COPYDATA,
        WM_CREATE, WM_DESTROY, WNDCLASSEXW, WS_EX_LAYERED, WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW,
        WS_EX_TRANSPARENT, WS_OVERLAPPED, WS_POPUP, WS_VISIBLE,
    },
};

// TODO(v3): remove this
/// Legacy payload: cwd and arguments joined by `|`, which splits any argument containing a `|`.
/// Still accepted from second instances running an older version of the plugin.
const WMCOPYDATA_SINGLE_INSTANCE_DATA: usize = 1542;
/// Cwd and arguments separated by NUL, without a terminator.
const WMCOPYDATA_SINGLE_INSTANCE_DATA_NUL: usize = 1543;

/// How long the second instance waits for the first instance to take its arguments.
const FORWARD_TIMEOUT_MS: u32 = 10_000;

struct MutexHandle(isize);

struct TargetWindowHandle(isize);

struct UserData<R: Runtime> {
    app: AppHandle<R>,
    callback: Box<SingleInstanceCallback<R>>,
}

impl<R: Runtime> UserData<R> {
    unsafe fn from_hwnd_raw(hwnd: HWND) -> *mut Self {
        unsafe { GetWindowLongPtrW(hwnd, GWLP_USERDATA) as *mut Self }
    }

    unsafe fn from_hwnd<'a>(hwnd: HWND) -> &'a mut Self {
        unsafe { &mut *Self::from_hwnd_raw(hwnd) }
    }

    fn run_callback(&mut self, args: Vec<String>, cwd: String) {
        (self.callback)(&self.app, args, cwd)
    }
}

pub fn init<R: Runtime>(callback: Box<SingleInstanceCallback<R>>) -> TauriPlugin<R> {
    plugin::Builder::new("single-instance")
        .setup(|app, _api| {
            #[allow(unused_mut)]
            let mut id = app.config().identifier.clone();
            #[cfg(feature = "semver")]
            {
                id.push('_');
                id.push_str(semver_compat_string(&app.package_info().version).as_str());
            }

            let class_name = encode_wide(format!("{id}-sic"));
            let window_name = encode_wide(format!("{id}-siw"));
            let mutex_name = encode_wide(format!("{id}-sim"));

            let hmutex =
                unsafe { CreateMutexW(std::ptr::null(), true.into(), mutex_name.as_ptr()) };

            if unsafe { GetLastError() } == ERROR_ALREADY_EXISTS {
                unsafe {
                    let hwnd = FindWindowW(class_name.as_ptr(), window_name.as_ptr());

                    if !hwnd.is_null() {
                        // Windows lets us bring a window to the front, but not the first
                        // instance. Hand that right over before we exit, so focusing a window
                        // from the callback works. Windows takes it back if the user switches
                        // to another app in the meantime.
                        let mut pid = 0;
                        GetWindowThreadProcessId(hwnd, &mut pid);
                        if pid != 0 {
                            AllowSetForegroundWindow(pid);
                        }

                        // Neither the cwd nor an argument can contain a NUL on Windows, so it
                        // separates them unambiguously.
                        let mut data = std::env::current_dir()
                            .unwrap_or_default()
                            .to_string_lossy()
                            .into_owned();
                        for arg in std::env::args_os() {
                            data.push('\0');
                            data.push_str(&arg.to_string_lossy());
                        }

                        let bytes = data.as_bytes();
                        let cds = COPYDATASTRUCT {
                            dwData: WMCOPYDATA_SINGLE_INSTANCE_DATA_NUL,
                            cbData: bytes.len() as _,
                            lpData: bytes.as_ptr() as _,
                        };

                        let sent = SendMessageTimeoutW(
                            hwnd,
                            WM_COPYDATA,
                            0,
                            &cds as *const _ as _,
                            SMTO_NORMAL,
                            FORWARD_TIMEOUT_MS,
                            std::ptr::null_mut(),
                        );
                        if sent == 0 {
                            tracing::warn!(
                                "single_instance failed to forward arguments to the running instance within {FORWARD_TIMEOUT_MS}ms (error {})",
                                GetLastError()
                            );
                        }

                        app.cleanup_before_exit();
                        std::process::exit(0);
                    }
                }
            } else {
                app.manage(MutexHandle(hmutex as _));

                let userdata = UserData {
                    app: app.clone(),
                    callback,
                };
                let userdata = Box::into_raw(Box::new(userdata));
                let hwnd = create_event_target_window::<R>(&class_name, &window_name, userdata);
                app.manage(TargetWindowHandle(hwnd as _));
            }

            Ok(())
        })
        .on_event(|app, event| {
            if let RunEvent::Exit = event {
                destroy(app);
            }
        })
        .build()
}

pub fn destroy<R: Runtime, M: Manager<R>>(manager: &M) {
    if let Some(hmutex) = manager.try_state::<MutexHandle>() {
        unsafe {
            ReleaseMutex(hmutex.0 as _);
            CloseHandle(hmutex.0 as _);
        }
    }
    if let Some(hwnd) = manager.try_state::<TargetWindowHandle>() {
        unsafe { DestroyWindow(hwnd.0 as _) };
    }
}

unsafe extern "system" fn single_instance_window_proc<R: Runtime>(
    hwnd: HWND,
    msg: u32,
    wparam: WPARAM,
    lparam: LPARAM,
) -> LRESULT {
    match msg {
        WM_CREATE => {
            let create_struct = unsafe { &*(lparam as *const CREATESTRUCTW) };
            let userdata = create_struct.lpCreateParams as *const UserData<R>;
            unsafe { SetWindowLongPtrW(hwnd, GWLP_USERDATA, userdata as _) };
            0
        }

        WM_COPYDATA => {
            let cds = unsafe { &*(lparam as *const COPYDATASTRUCT) };
            let separator = match cds.dwData {
                WMCOPYDATA_SINGLE_INSTANCE_DATA_NUL => '\0',
                WMCOPYDATA_SINGLE_INSTANCE_DATA => '|',
                _ => return 1,
            };

            let bytes = if cds.lpData.is_null() {
                &[][..]
            } else {
                unsafe { std::slice::from_raw_parts(cds.lpData as *const u8, cds.cbData as _) }
            };
            // The legacy format ends with a NUL terminator. The new one doesn't: a trailing NUL
            // there precedes an empty last argument.
            let bytes = if separator == '|' {
                bytes.split(|b| *b == 0).next().unwrap_or_default()
            } else {
                bytes
            };
            let data = String::from_utf8_lossy(bytes);

            let mut s = data.split(separator);
            let cwd = s.next().unwrap_or_default().to_string();
            let args = s.map(|s| s.to_string()).collect();

            let userdata = unsafe { UserData::<R>::from_hwnd(hwnd) };
            userdata.run_callback(args, cwd);
            1
        }

        WM_DESTROY => {
            let userdata = unsafe { UserData::<R>::from_hwnd_raw(hwnd) };
            drop(unsafe { Box::from_raw(userdata) });
            0
        }
        _ => unsafe { DefWindowProcW(hwnd, msg, wparam, lparam) },
    }
}

fn create_event_target_window<R: Runtime>(
    class_name: &[u16],
    window_name: &[u16],
    userdata: *const UserData<R>,
) -> HWND {
    unsafe {
        let class = WNDCLASSEXW {
            cbSize: std::mem::size_of::<WNDCLASSEXW>() as u32,
            style: 0,
            lpfnWndProc: Some(single_instance_window_proc::<R>),
            cbClsExtra: 0,
            cbWndExtra: 0,
            hInstance: GetModuleHandleW(std::ptr::null()),
            hIcon: std::ptr::null_mut(),
            hCursor: std::ptr::null_mut(),
            hbrBackground: std::ptr::null_mut(),
            lpszMenuName: std::ptr::null(),
            lpszClassName: class_name.as_ptr(),
            hIconSm: std::ptr::null_mut(),
        };

        RegisterClassExW(&class);

        let hwnd = CreateWindowExW(
            WS_EX_NOACTIVATE
            | WS_EX_TRANSPARENT
            | WS_EX_LAYERED
            // WS_EX_TOOLWINDOW prevents this window from ever showing up in the taskbar, which
            // we want to avoid. If you remove this style, this window won't show up in the
            // taskbar *initially*, but it can show up at some later point. This can sometimes
            // happen on its own after several hours have passed, although this has proven
            // difficult to reproduce. Alternatively, it can be manually triggered by killing
            // `explorer.exe` and then starting the process back up.
            // It is unclear why the bug is triggered by waiting for several hours.
            | WS_EX_TOOLWINDOW,
            class_name.as_ptr(),
            window_name.as_ptr(),
            WS_OVERLAPPED,
            0,
            0,
            0,
            0,
            std::ptr::null_mut(),
            std::ptr::null_mut(),
            GetModuleHandleW(std::ptr::null()),
            userdata as _,
        );
        SetWindowLongPtrW(
            hwnd,
            GWL_STYLE,
            // The window technically has to be visible to receive WM_PAINT messages (which are used
            // for delivering events during resizes), but it isn't displayed to the user because of
            // the LAYERED style.
            (WS_VISIBLE | WS_POPUP) as isize,
        );
        hwnd
    }
}

pub fn encode_wide(string: impl AsRef<std::ffi::OsStr>) -> Vec<u16> {
    std::os::windows::prelude::OsStrExt::encode_wide(string.as_ref())
        .chain(std::iter::once(0))
        .collect()
}

#[cfg(target_pointer_width = "32")]
#[allow(non_snake_case)]
unsafe fn SetWindowLongPtrW(hwnd: HWND, index: WINDOW_LONG_PTR_INDEX, value: isize) -> isize {
    unsafe { w32wm::SetWindowLongW(hwnd, index, value as _) as _ }
}

#[cfg(target_pointer_width = "64")]
#[allow(non_snake_case)]
unsafe fn SetWindowLongPtrW(hwnd: HWND, index: WINDOW_LONG_PTR_INDEX, value: isize) -> isize {
    unsafe { w32wm::SetWindowLongPtrW(hwnd, index, value) }
}

#[cfg(target_pointer_width = "32")]
#[allow(non_snake_case)]
unsafe fn GetWindowLongPtrW(hwnd: HWND, index: WINDOW_LONG_PTR_INDEX) -> isize {
    unsafe { w32wm::GetWindowLongW(hwnd, index) as _ }
}

#[cfg(target_pointer_width = "64")]
#[allow(non_snake_case)]
unsafe fn GetWindowLongPtrW(hwnd: HWND, index: WINDOW_LONG_PTR_INDEX) -> isize {
    unsafe { w32wm::GetWindowLongPtrW(hwnd, index) }
}