gp_wasm_interface/

lib.rs

// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Types and traits for interfacing between the host and the wasm runtime.

#![cfg_attr(not(feature = "std"), no_std)]

use sp_std::{iter::Iterator, marker::PhantomData, result, vec, vec::Vec};
pub use sp_wasm_interface_common::{self as common, Value, ValueType, Pointer, PointerType, IntoValue, TryFromValue, ReturnValue, WordSize, MemoryId, HostPointer, Signature};

if_wasmtime_is_enabled! {
    mod host_state;
    pub use host_state::HostState;

    mod store_data;
    pub use store_data::StoreData;

    mod memory_wrapper;
    pub use memory_wrapper::MemoryWrapper;

    pub mod util;
}

#[cfg(not(all(feature = "std", feature = "wasmtime")))]
pub struct StoreData;

#[cfg(not(all(feature = "std", feature = "wasmtime")))]
#[macro_export]
macro_rules! if_wasmtime_is_enabled {
	($($token:tt)*) => {};
}

#[cfg(all(feature = "std", feature = "wasmtime"))]
#[macro_export]
macro_rules! if_wasmtime_is_enabled {
    ($($token:tt)*) => {
        $($token)*
    }
}

if_wasmtime_is_enabled! {
	// Reexport wasmtime so that its types are accessible from the procedural macro.
	pub use wasmtime;

	// Wasmtime uses anyhow types but doesn't reexport them.
	pub use anyhow;
}

/// Result type used by traits in this crate.
#[cfg(feature = "std")]
pub type Result<T> = result::Result<T, String>;
#[cfg(not(feature = "std"))]
pub type Result<T> = result::Result<T, &'static str>;

/// Provides `Sealed` trait to prevent implementing trait `PointerType` and `WasmTy` outside of this
/// crate.
mod private {
	pub trait Sealed {}

	impl Sealed for u8 {}
	impl Sealed for u16 {}
	impl Sealed for u32 {}
	impl Sealed for u64 {}

	impl Sealed for i32 {}
	impl Sealed for i64 {}

    pub(super) struct Token;
}

/// A trait that requires `RefUnwindSafe` when `feature = std`.
#[cfg(feature = "std")]
pub trait MaybeRefUnwindSafe: std::panic::RefUnwindSafe {}
#[cfg(feature = "std")]
impl<T: std::panic::RefUnwindSafe> MaybeRefUnwindSafe for T {}

/// A trait that requires `RefUnwindSafe` when `feature = std`.
#[cfg(not(feature = "std"))]
pub trait MaybeRefUnwindSafe {}
#[cfg(not(feature = "std"))]
impl<T> MaybeRefUnwindSafe for T {}

/// Something that provides a function implementation on the host for a wasm function.
pub trait Function: MaybeRefUnwindSafe + Send + Sync {
	/// Returns the name of this function.
	fn name(&self) -> &str;
	/// Returns the signature of this function.
	fn signature(&self) -> Signature;
	/// Execute this function with the given arguments.
	fn execute(
		&self,
		context: &mut dyn FunctionContext,
		args: &mut dyn Iterator<Item = Value>,
	) -> Result<Option<Value>>;
}

impl PartialEq for dyn Function {
	fn eq(&self, other: &Self) -> bool {
		other.name() == self.name() && other.signature() == self.signature()
	}
}

#[cfg(not(all(feature = "std", feature = "wasmtime")))]
pub struct Caller<'a, T>(PhantomData<&'a T>);

#[cfg(all(feature = "std", feature = "wasmtime"))]
pub use wasmtime::Caller;

pub struct FunctionContextToken(private::Token);

impl FunctionContextToken {
    fn new() -> Self {
        Self(private::Token)
    }
}

/// Context used by `Function` to interact with the allocator and the memory of the wasm instance.
pub trait FunctionContext {
	/// Read memory from `address` into a vector.
	fn read_memory(&self, address: Pointer<u8>, size: WordSize) -> Result<Vec<u8>> {
		let mut vec = vec![0; size as usize];
		self.read_memory_into(address, &mut vec)?;
		Ok(vec)
	}
	/// Read memory into the given `dest` buffer from `address`.
	fn read_memory_into(&self, address: Pointer<u8>, dest: &mut [u8]) -> Result<()>;
	/// Write the given data at `address` into the memory.
	fn write_memory(&mut self, address: Pointer<u8>, data: &[u8]) -> Result<()>;
	/// Allocate a memory instance of `size` bytes.
	fn allocate_memory(&mut self, size: WordSize) -> Result<Pointer<u8>>;
	/// Deallocate a given memory instance.
	fn deallocate_memory(&mut self, ptr: Pointer<u8>) -> Result<()>;
	/// Registers a panic error message within the executor.
	///
	/// This is meant to be used in situations where the runtime
	/// encounters an unrecoverable error and intends to panic.
	///
	/// Panicking in WASM is done through the [`unreachable`](https://webassembly.github.io/spec/core/syntax/instructions.html#syntax-instr-control)
	/// instruction which causes an unconditional trap and immediately aborts
	/// the execution. It does not however allow for any diagnostics to be
	/// passed through to the host, so while we do know that *something* went
	/// wrong we don't have any direct indication of what *exactly* went wrong.
	///
	/// As a workaround we use this method right before the execution is
	/// actually aborted to pass an error message to the host so that it
	/// can associate it with the next trap, and return that to the caller.
	///
	/// A WASM trap should be triggered immediately after calling this method;
	/// otherwise the error message might be associated with a completely
	/// unrelated trap.
	///
	/// It should only be called once, however calling it more than once
	/// is harmless and will overwrite the previously set error message.
	fn register_panic_error_message(&mut self, message: &str);

    fn with_caller_mut_impl(&mut self, _: FunctionContextToken, context: *mut (), callback: fn(*mut (), &mut Caller<StoreData>));

}

pub fn with_caller_mut<T: FnMut(&mut Caller<StoreData>)>(context: &mut dyn FunctionContext, mut callback: T) {
    let callback: *mut T = &mut callback;
    context.with_caller_mut_impl(FunctionContextToken::new(), callback.cast(), |callback, caller| {
        let callback: *mut T = callback.cast();
        let callback: &mut T = unsafe { callback.as_mut().expect("we own the value, obtain mutable reference to it and cast to pointer (correct (not null) and aligned properly); qed") };

        callback(caller);
    })
}

if_wasmtime_is_enabled! {
	/// A trait used to statically register host callbacks with the WASM executor,
	/// so that they call be called from within the runtime with minimal overhead.
	///
	/// This is used internally to interface the wasmtime-based executor with the
	/// host functions' definitions generated through the runtime interface macro,
	/// and is not meant to be used directly.
	pub trait HostFunctionRegistry {
		type State;
		type Error;
		type FunctionContext: FunctionContext;

		/// Wraps the given `caller` in a type which implements `FunctionContext`
		/// and calls the given `callback`.
		fn with_function_context<R>(
			caller: wasmtime::Caller<Self::State>,
			callback: impl FnOnce(&mut dyn FunctionContext) -> R,
		) -> R;

		/// Registers a given host function with the WASM executor.
		///
		/// The function has to be statically callable, and all of its arguments
		/// and its return value have to be compatible with WASM FFI.
		fn register_static<Params, Results>(
			&mut self,
			fn_name: &str,
			func: impl wasmtime::IntoFunc<Self::State, Params, Results> + 'static,
		) -> core::result::Result<(), Self::Error>;
	}
}

/// Something that provides implementations for host functions.
pub trait HostFunctions: 'static + Send + Sync {
	/// Returns the host functions `Self` provides.
	fn host_functions() -> Vec<&'static dyn Function>;

	if_wasmtime_is_enabled! {
		/// Statically registers the host functions.
		fn register_static<T>(registry: &mut T) -> core::result::Result<(), T::Error>
		where
			T: HostFunctionRegistry;
	}
}

#[impl_trait_for_tuples::impl_for_tuples(30)]
impl HostFunctions for Tuple {
	fn host_functions() -> Vec<&'static dyn Function> {
		let mut host_functions = Vec::new();

		for_tuples!( #( host_functions.extend(Tuple::host_functions()); )* );

		host_functions
	}

	#[cfg(all(feature = "std", feature = "wasmtime"))]
	fn register_static<T>(registry: &mut T) -> core::result::Result<(), T::Error>
	where
		T: HostFunctionRegistry,
	{
		for_tuples!(
			#( Tuple::register_static(registry)?; )*
		);

		Ok(())
	}
}

/// A wrapper which merges two sets of host functions, and allows the second set to override
/// the host functions from the first set.
pub struct ExtendedHostFunctions<Base, Overlay> {
	phantom: PhantomData<(Base, Overlay)>,
}

impl<Base, Overlay> HostFunctions for ExtendedHostFunctions<Base, Overlay>
where
	Base: HostFunctions,
	Overlay: HostFunctions,
{
	fn host_functions() -> Vec<&'static dyn Function> {
		let mut base = Base::host_functions();
		let overlay = Overlay::host_functions();
		base.retain(|host_fn| {
			!overlay.iter().any(|ext_host_fn| host_fn.name() == ext_host_fn.name())
		});
		base.extend(overlay);
		base
	}

	if_wasmtime_is_enabled! {
		fn register_static<T>(registry: &mut T) -> core::result::Result<(), T::Error>
		where
			T: HostFunctionRegistry,
		{
			struct Proxy<'a, T> {
				registry: &'a mut T,
				seen_overlay: std::collections::HashSet<String>,
				seen_base: std::collections::HashSet<String>,
				overlay_registered: bool,
			}

			impl<'a, T> HostFunctionRegistry for Proxy<'a, T>
			where
				T: HostFunctionRegistry,
			{
				type State = T::State;
				type Error = T::Error;
				type FunctionContext = T::FunctionContext;

				fn with_function_context<R>(
					caller: wasmtime::Caller<Self::State>,
					callback: impl FnOnce(&mut dyn FunctionContext) -> R,
				) -> R {
					T::with_function_context(caller, callback)
				}

				fn register_static<Params, Results>(
					&mut self,
					fn_name: &str,
					func: impl wasmtime::IntoFunc<Self::State, Params, Results> + 'static,
				) -> core::result::Result<(), Self::Error> {
					if self.overlay_registered {
						if !self.seen_base.insert(fn_name.to_owned()) {
							log::warn!(
								target: "extended_host_functions",
								"Duplicate base host function: '{}'",
								fn_name,
							);

							// TODO: Return an error here?
							return Ok(())
						}

						if self.seen_overlay.contains(fn_name) {
							// Was already registered when we went through the overlay, so just ignore it.
							log::debug!(
								target: "extended_host_functions",
								"Overriding base host function: '{}'",
								fn_name,
							);

							return Ok(())
						}
					} else if !self.seen_overlay.insert(fn_name.to_owned()) {
						log::warn!(
							target: "extended_host_functions",
							"Duplicate overlay host function: '{}'",
							fn_name,
						);

						// TODO: Return an error here?
						return Ok(())
					}

					self.registry.register_static(fn_name, func)
				}
			}

			let mut proxy = Proxy {
				registry,
				seen_overlay: Default::default(),
				seen_base: Default::default(),
				overlay_registered: false,
			};

			// The functions from the `Overlay` can override those from the `Base`,
			// so `Overlay` is registered first, and then we skip those functions
			// in `Base` if they were already registered from the `Overlay`.
			Overlay::register_static(&mut proxy)?;
			proxy.overlay_registered = true;
			Base::register_static(&mut proxy)?;

			Ok(())
		}
	}
}

/// A trait for types directly usable at the WASM FFI boundary without any conversion at all.
///
/// This trait is sealed and should not be implemented downstream.
#[cfg(all(feature = "std", feature = "wasmtime"))]
pub trait WasmTy: wasmtime::WasmTy + private::Sealed {}

/// A trait for types directly usable at the WASM FFI boundary without any conversion at all.
///
/// This trait is sealed and should not be implemented downstream.
#[cfg(not(all(feature = "std", feature = "wasmtime")))]
pub trait WasmTy: private::Sealed {}

impl WasmTy for i32 {}
impl WasmTy for u32 {}
impl WasmTy for i64 {}
impl WasmTy for u64 {}