store.rs

use crate::{wasm_engine_t, wasmi_error_t, ForeignData};
use alloc::{boxed::Box, sync::Arc};
use core::{cell::UnsafeCell, ffi};
use wasmi::{AsContext, AsContextMut, Store, StoreContext, StoreContextMut};

/// This representation of a `Store` is used to implement the `wasm.h` API (and
/// *not* the `wasmi.h` API!)
///
/// This is stored alongside `Func` and such for `wasm.h` so each object is
/// independently owned. The usage of `Arc` here is mostly to just get it to be
/// safe to drop across multiple threads, but otherwise acquiring the `context`
/// values from this struct is considered unsafe due to it being unknown how the
/// aliasing is working on the C side of things.
///
/// The aliasing requirements are documented in the C API `wasm.h` itself (at
/// least Wasmi's implementation).
#[derive(Clone)]
pub struct WasmStoreRef {
    inner: Arc<UnsafeCell<Store<()>>>,
}

impl WasmStoreRef {
    /// Returns shared access to the store context of the [`WasmStoreRef`].
    ///
    /// Wraps [`wasmi::AsContext`].
    ///
    /// # Safety
    ///
    /// It is the callers responsibility to provide a valid `self`.
    pub unsafe fn context(&self) -> StoreContext<'_, ()> {
        (*self.inner.get()).as_context()
    }

    /// Returns mutable access to the store context of the [`WasmStoreRef`].
    ///
    /// Wraps [`wasmi::AsContextMut`].
    ///
    /// # Safety
    ///
    /// It is the callers responsibility to provide a valid `self`.
    pub unsafe fn context_mut(&mut self) -> StoreContextMut<'_, ()> {
        (*self.inner.get()).as_context_mut()
    }
}

/// The Wasm store.
///
/// The returned [`wasm_engine_t`] must be freed using [`wasm_store_delete`].
///
/// Wraps [`wasmi::Store<()>`](wasmi::Store).
#[repr(C)]
#[derive(Clone)]
pub struct wasm_store_t {
    pub(crate) inner: WasmStoreRef,
}

wasmi_c_api_macros::declare_own!(wasm_store_t);

/// Creates a new [`Store<()>`](wasmi::Store) for the given `engine`.
///
/// The returned [`wasm_store_t`] must be freed using [`wasm_store_delete`].
///
/// Wraps [`<wasmi::Store<()>>::new`](wasmi::Store::new).
#[cfg_attr(not(feature = "prefix-symbols"), no_mangle)]
#[allow(clippy::arc_with_non_send_sync)]
#[cfg_attr(feature = "prefix-symbols", wasmi_c_api_macros::prefix_symbol)]
pub extern "C" fn wasm_store_new(engine: &wasm_engine_t) -> Box<wasm_store_t> {
    let engine = &engine.inner;
    let store = Store::new(engine, ());
    Box::new(wasm_store_t {
        inner: WasmStoreRef {
            inner: Arc::new(UnsafeCell::new(store)),
        },
    })
}

/// The Wasm store with foreign data and optional WASI support.
///
/// The returned [`wasm_engine_t`] must be freed using [`wasm_store_delete`].
///
/// Wraps [`wasmi::Store<WasmiStoreData>`](wasmi::Store).
#[repr(C)]
pub struct wasmi_store_t {
    pub(crate) store: Store<WasmiStoreData>,
}

wasmi_c_api_macros::declare_own!(wasmi_store_t);

/// Extensional data stored by [`wasmi_store_t`] to handle foreign data and optional WASI support.
pub struct WasmiStoreData {
    foreign: ForeignData,
}

/// Creates a new [`Store<()>`](wasmi::Store) for the given `engine`.
///
/// - This takes a foreign `data` with an associated `finalizer`.
/// - The returned [`wasm_store_t`] must be freed using [`wasm_store_delete`].
///
/// Wraps [`<wasmi::Store<()>>::new`](wasmi::Store::new).
#[no_mangle]
pub extern "C" fn wasmi_store_new(
    engine: &wasm_engine_t,
    data: *mut ffi::c_void,
    finalizer: Option<extern "C" fn(*mut ffi::c_void)>,
) -> Box<wasmi_store_t> {
    Box::new(wasmi_store_t {
        store: Store::new(
            &engine.inner,
            WasmiStoreData {
                foreign: ForeignData { data, finalizer },
            },
        ),
    })
}

/// Returns mutable access to the store context of the [`wasmi_store_t`].
///
/// Wraps [`wasmi::AsContext`].
///
/// # Safety
///
/// It is the callers responsibility to provide a valid `self`.
#[no_mangle]
pub extern "C" fn wasmi_store_context(
    store: &mut wasmi_store_t,
) -> StoreContextMut<'_, WasmiStoreData> {
    store.store.as_context_mut()
}

/// Returns a pointer to the foreign data of the Wasmi store context.
#[no_mangle]
pub extern "C" fn wasmi_context_get_data(
    store: StoreContext<'_, WasmiStoreData>,
) -> *mut ffi::c_void {
    store.data().foreign.data
}

/// Sets the foreign data of the Wasmi store context.
#[no_mangle]
pub extern "C" fn wasmi_context_set_data(
    mut store: StoreContextMut<'_, WasmiStoreData>,
    data: *mut ffi::c_void,
) {
    store.data_mut().foreign.data = data;
}

/// Returns the current fuel of the Wasmi store context in `fuel`.
///
/// Wraps [`Store::get_fuel`].
///
/// # Errors
///
/// If [`Store::get_fuel`] errors.
#[no_mangle]
pub extern "C" fn wasmi_context_get_fuel(
    store: StoreContext<'_, WasmiStoreData>,
    fuel: &mut u64,
) -> Option<Box<wasmi_error_t>> {
    crate::handle_result(store.get_fuel(), |amt| {
        *fuel = amt;
    })
}

/// Sets the current fuel of the Wasmi store context to `fuel`.
///
/// Wraps [`Store::set_fuel`].
///
/// # Errors
///
/// If [`Store::set_fuel`] errors.
#[no_mangle]
pub extern "C" fn wasmi_context_set_fuel(
    mut store: StoreContextMut<'_, WasmiStoreData>,
    fuel: u64,
) -> Option<Box<wasmi_error_t>> {
    crate::handle_result(store.set_fuel(fuel), |()| {})
}