tauri/
state.rs

// Copyright 2019-2024 Tauri Programme within The Commons Conservancy
// SPDX-License-Identifier: Apache-2.0
// SPDX-License-Identifier: MIT

use std::{
  any::{Any, TypeId},
  cell::UnsafeCell,
  collections::HashMap,
  hash::BuildHasherDefault,
  sync::Mutex,
};

use crate::{
  ipc::{CommandArg, CommandItem, InvokeError},
  Runtime,
};

/// A guard for a state value.
///
/// See [`Manager::manage`](`crate::Manager::manage`) for usage examples.
pub struct State<'r, T: Send + Sync + 'static>(&'r T);

impl<'r, T: Send + Sync + 'static> State<'r, T> {
  /// Retrieve a borrow to the underlying value with a lifetime of `'r`.
  /// Using this method is typically unnecessary as `State` implements
  /// [`std::ops::Deref`] with a [`std::ops::Deref::Target`] of `T`.
  #[inline(always)]
  pub fn inner(&self) -> &'r T {
    self.0
  }
}

impl<T: Send + Sync + 'static> std::ops::Deref for State<'_, T> {
  type Target = T;

  #[inline(always)]
  fn deref(&self) -> &T {
    self.0
  }
}

impl<T: Send + Sync + 'static> Clone for State<'_, T> {
  fn clone(&self) -> Self {
    State(self.0)
  }
}

impl<T: Send + Sync + 'static + PartialEq> PartialEq for State<'_, T> {
  fn eq(&self, other: &Self) -> bool {
    self.0 == other.0
  }
}

impl<'r, T: Send + Sync + std::fmt::Debug> std::fmt::Debug for State<'r, T> {
  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
    f.debug_tuple("State").field(&self.0).finish()
  }
}

impl<'r, 'de: 'r, T: Send + Sync + 'static, R: Runtime> CommandArg<'de, R> for State<'r, T> {
  /// Grabs the [`State`] from the [`CommandItem`]. This will never fail.
  fn from_command(command: CommandItem<'de, R>) -> Result<Self, InvokeError> {
    Ok(command.message.state_ref().try_get().unwrap_or_else(|| {
      panic!(
        "state not managed for field `{}` on command `{}`. You must call `.manage()` before using this command",
        command.key, command.name
      )
    }))
  }
}

// Taken from: https://github.com/SergioBenitez/state/blob/556c1b94db8ce8427a0e72de7983ab5a9af4cc41/src/ident_hash.rs
// This is a _super_ stupid hash. It just uses its input as the hash value. This
// hash is meant to be used _only_ for "prehashed" values. In particular, we use
// this so that hashing a TypeId is essentially a noop. This is because TypeIds
// are already unique integers.
#[derive(Default)]
struct IdentHash(u64);

impl std::hash::Hasher for IdentHash {
  fn finish(&self) -> u64 {
    self.0
  }

  fn write(&mut self, bytes: &[u8]) {
    for byte in bytes {
      self.write_u8(*byte);
    }
  }

  fn write_u8(&mut self, i: u8) {
    self.0 = (self.0 << 8) | (i as u64);
  }

  fn write_u64(&mut self, i: u64) {
    self.0 = i;
  }
}

type TypeIdMap = HashMap<TypeId, Box<dyn Any>, BuildHasherDefault<IdentHash>>;

/// The Tauri state manager.
#[derive(Debug)]
pub struct StateManager {
  map: Mutex<UnsafeCell<TypeIdMap>>,
}

// SAFETY: data is accessed behind a lock
unsafe impl Sync for StateManager {}
unsafe impl Send for StateManager {}

impl StateManager {
  pub(crate) fn new() -> Self {
    Self {
      map: Default::default(),
    }
  }

  fn with_map_ref<'a, F: FnOnce(&'a TypeIdMap) -> R, R>(&'a self, f: F) -> R {
    let map = self.map.lock().unwrap();
    let map = map.get();
    // SAFETY: safe to access since we are holding a lock
    f(unsafe { &*map })
  }

  fn with_map_mut<F: FnOnce(&mut TypeIdMap) -> R, R>(&self, f: F) -> R {
    let mut map = self.map.lock().unwrap();
    let map = map.get_mut();
    f(map)
  }

  pub(crate) fn set<T: Send + Sync + 'static>(&self, state: T) -> bool {
    self.with_map_mut(|map| {
      let type_id = TypeId::of::<T>();
      let already_set = map.contains_key(&type_id);
      if !already_set {
        map.insert(type_id, Box::new(state) as Box<dyn Any>);
      }
      !already_set
    })
  }

  pub(crate) fn unmanage<T: Send + Sync + 'static>(&self) -> Option<T> {
    self.with_map_mut(|map| {
      let type_id = TypeId::of::<T>();
      map
        .remove(&type_id)
        .and_then(|ptr| ptr.downcast().ok().map(|b| *b))
    })
  }

  /// Gets the state associated with the specified type.
  pub fn get<T: Send + Sync + 'static>(&self) -> State<'_, T> {
    self
      .try_get()
      .expect("state: get() when given type is not managed")
  }

  /// Gets the state associated with the specified type.
  pub fn try_get<T: Send + Sync + 'static>(&self) -> Option<State<'_, T>> {
    self.with_map_ref(|map| {
      map
        .get(&TypeId::of::<T>())
        .and_then(|ptr| ptr.downcast_ref::<T>())
        .map(State)
    })
  }
}

// Ported from https://github.com/SergioBenitez/state/blob/556c1b94db8ce8427a0e72de7983ab5a9af4cc41/tests/main.rs
#[cfg(test)]
mod tests {
  use super::StateManager;

  use std::sync::{Arc, RwLock};
  use std::thread;

  // Tiny structures to test that dropping works as expected.
  struct DroppingStruct(Arc<RwLock<bool>>);
  struct DroppingStructWrap(#[allow(dead_code)] DroppingStruct);

  impl Drop for DroppingStruct {
    fn drop(&mut self) {
      *self.0.write().unwrap() = true;
    }
  }

  #[test]
  fn simple_set_get() {
    let state = StateManager::new();
    assert!(state.set(1u32));
    assert_eq!(*state.get::<u32>(), 1);
  }

  #[test]
  fn simple_set_get_unmanage() {
    let state = StateManager::new();
    assert!(state.set(1u32));
    assert_eq!(*state.get::<u32>(), 1);
    assert!(state.unmanage::<u32>().is_some());
    assert!(state.unmanage::<u32>().is_none());
    assert_eq!(state.try_get::<u32>(), None);
    assert!(state.set(2u32));
    assert_eq!(*state.get::<u32>(), 2);
  }

  #[test]
  fn dst_set_get() {
    let state = StateManager::new();
    assert!(state.set::<[u32; 4]>([1, 2, 3, 4u32]));
    assert_eq!(*state.get::<[u32; 4]>(), [1, 2, 3, 4]);
  }

  #[test]
  fn set_get_remote() {
    let state = Arc::new(StateManager::new());
    let sate_ = Arc::clone(&state);
    thread::spawn(move || {
      sate_.set(10isize);
    })
    .join()
    .unwrap();

    assert_eq!(*state.get::<isize>(), 10);
  }

  #[test]
  fn two_put_get() {
    let state = StateManager::new();
    assert!(state.set("Hello, world!".to_string()));

    let s_old = state.get::<String>();
    assert_eq!(*s_old, "Hello, world!");

    assert!(!state.set::<String>("Bye bye!".into()));
    assert_eq!(*state.get::<String>(), "Hello, world!");
    assert_eq!(state.get::<String>(), s_old);
  }

  #[test]
  fn many_puts_only_one_succeeds() {
    let state = Arc::new(StateManager::new());
    let mut threads = vec![];
    for _ in 0..1000 {
      let state_ = Arc::clone(&state);
      threads.push(thread::spawn(move || state_.set(10i64)))
    }

    let results: Vec<bool> = threads.into_iter().map(|t| t.join().unwrap()).collect();
    assert_eq!(results.into_iter().filter(|&b| b).count(), 1);
    assert_eq!(*state.get::<i64>(), 10);
  }

  // Ensure setting when already set doesn't cause a drop.
  #[test]
  fn test_no_drop_on_set() {
    let state = StateManager::new();
    let drop_flag = Arc::new(RwLock::new(false));
    let dropping_struct = DroppingStruct(drop_flag.clone());

    let _drop_flag_ignore = Arc::new(RwLock::new(false));
    let _dropping_struct_ignore = DroppingStruct(_drop_flag_ignore.clone());

    state.set::<DroppingStruct>(dropping_struct);
    assert!(!state.set::<DroppingStruct>(_dropping_struct_ignore));
    assert!(!*drop_flag.read().unwrap());
  }

  // Ensure dropping a type_map drops its contents.
  #[test]
  fn drop_inners_on_drop() {
    let drop_flag_a = Arc::new(RwLock::new(false));
    let dropping_struct_a = DroppingStruct(drop_flag_a.clone());

    let drop_flag_b = Arc::new(RwLock::new(false));
    let dropping_struct_b = DroppingStructWrap(DroppingStruct(drop_flag_b.clone()));

    {
      let state = StateManager::new();
      state.set(dropping_struct_a);
      assert!(!*drop_flag_a.read().unwrap());

      state.set(dropping_struct_b);
      assert!(!*drop_flag_a.read().unwrap());
      assert!(!*drop_flag_b.read().unwrap());
    }

    assert!(*drop_flag_a.read().unwrap());
    assert!(*drop_flag_b.read().unwrap());
  }
}
tauri/state.rs

tauri/
state.rs
