sp_runtime_interface/

host.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.

//! Traits required by the runtime interface from the host side.

use crate::RIType;

use sp_wasm_interface::{FunctionContext, Result};

/// A type used as a return value in a host function. Can be turned into an FFI value.
pub trait IntoFFIValue: RIType {
	/// Convert `Self::Inner` into an FFI value.
	fn into_ffi_value(
		value: Self::Inner,
		context: &mut dyn FunctionContext,
	) -> Result<Self::FFIType>;
}

/// A type used as a parameter in a host function. Can be created from an FFI value.
///
/// Implementations are safe to assume that the `arg` given to `from_ffi_value`
/// is only generated by the corresponding [`wasm::IntoFFIValue`](crate::wasm::IntoFFIValue)
/// implementation.
pub trait FromFFIValue<'a>: RIType {
	/// The owned inner type.
	type Owned;

	/// Creates `Self::Owned` from the given `arg` received through the FFI boundary from the
	/// runtime.
	fn from_ffi_value(context: &mut dyn FunctionContext, arg: Self::FFIType)
		-> Result<Self::Owned>;

	/// Creates `Self::Inner` from an owned value.
	fn take_from_owned(owned: &'a mut Self::Owned) -> Self::Inner;

	/// Write back a modified `value` back into the runtime's memory.
	///
	/// Only makes sense for parameters like e.g. `&mut [u8]`.
	#[inline]
	fn write_back_into_runtime(
		_value: Self::Owned,
		_context: &mut dyn FunctionContext,
		_arg: Self::FFIType,
	) -> Result<()> {
		// Default dummy implementation, because the vast majority of impls won't need this.
		Ok(())
	}
}