Function sp_runtime_interface::unpack_ptr_and_len

pub fn unpack_ptr_and_len(val: u64) -> (u32, u32)

Unpacks an u64 into the pointer and length.

Runtime API functions return a 64-bit value which encodes a pointer in the least-significant 32-bits and a length in the most-significant 32 bits. This interprets the returned value as a pointer, length tuple.

Examples found in repository

src/pass_by.rs (line 230)

	fn from_ffi_value(context: &mut dyn FunctionContext, arg: Self::FFIType) -> Result<T> {
		let (ptr, len) = unpack_ptr_and_len(arg);
		let vec = context.read_memory(Pointer::new(ptr), len)?;
		T::decode(&mut &vec[..]).map_err(|e| format!("Could not decode value from wasm: {}", e))
	}

src/impls.rs (line 227)

	fn from_ffi_value(context: &mut dyn FunctionContext, arg: u64) -> Result<Vec<T>> {
		let (ptr, len) = unpack_ptr_and_len(arg);

		let vec = context.read_memory(Pointer::new(ptr), len)?;

		if TypeId::of::<T>() == TypeId::of::<u8>() {
			Ok(unsafe { mem::transmute(vec) })
		} else {
			Ok(Vec::<T>::decode(&mut &vec[..])
				.expect("Wasm to host values are encoded correctly; qed"))
		}
	}
}

#[cfg(feature = "std")]
impl IntoPreallocatedFFIValue for [u8] {
	type SelfInstance = Vec<u8>;

	fn into_preallocated_ffi_value(
		self_instance: Self::SelfInstance,
		context: &mut dyn FunctionContext,
		allocated: u64,
	) -> Result<()> {
		let (ptr, len) = unpack_ptr_and_len(allocated);

		if (len as usize) < self_instance.len() {
			Err(format!(
				"Preallocated buffer is not big enough (given {} vs needed {})!",
				len,
				self_instance.len()
			))
		} else {
			context.write_memory(Pointer::new(ptr), &self_instance)
		}
	}
}

#[cfg(not(feature = "std"))]
impl<T: 'static + Encode> IntoFFIValue for [T] {
	type Owned = Vec<u8>;

	fn into_ffi_value(&self) -> WrappedFFIValue<u64, Vec<u8>> {
		if TypeId::of::<T>() == TypeId::of::<u8>() {
			let slice = unsafe { mem::transmute::<&[T], &[u8]>(self) };
			pack_ptr_and_len(slice.as_ptr() as u32, slice.len() as u32).into()
		} else {
			let data = self.encode();
			let ffi_value = pack_ptr_and_len(data.as_ptr() as u32, data.len() as u32);
			(ffi_value, data).into()
		}
	}
}

/// Implement the traits for the `[u8; N]` arrays, where `N` is the input to this macro.
macro_rules! impl_traits_for_arrays {
	(
		$(
			$n:expr
		),*
		$(,)?
	) => {
		$(
			/// The type is passed as `u32`.
			///
			/// The `u32` is the pointer to the array.
			impl RIType for [u8; $n] {
				type FFIType = u32;
			}

			#[cfg(not(feature = "std"))]
			impl IntoFFIValue for [u8; $n] {
				type Owned = ();

				fn into_ffi_value(&self) -> WrappedFFIValue<u32> {
					(self.as_ptr() as u32).into()
				}
			}

			#[cfg(not(feature = "std"))]
			impl FromFFIValue for [u8; $n] {
				fn from_ffi_value(arg: u32) -> [u8; $n] {
					let mut res = [0u8; $n];
					let data = unsafe { Vec::from_raw_parts(arg as *mut u8, $n, $n) };

					res.copy_from_slice(&data);

					res
				}
			}

			#[cfg(feature = "std")]
			impl FromFFIValue for [u8; $n] {
				type SelfInstance = [u8; $n];

				fn from_ffi_value(context: &mut dyn FunctionContext, arg: u32) -> Result<[u8; $n]> {
					let mut res = [0u8; $n];
					context.read_memory_into(Pointer::new(arg), &mut res)?;
					Ok(res)
				}
			}

			#[cfg(feature = "std")]
			impl IntoFFIValue for [u8; $n] {
				fn into_ffi_value(self, context: &mut dyn FunctionContext) -> Result<u32> {
					let addr = context.allocate_memory($n)?;
					context.write_memory(addr, &self)?;
					Ok(addr.into())
				}
			}

			#[cfg(feature = "std")]
			impl IntoPreallocatedFFIValue for [u8; $n] {
				type SelfInstance = [u8; $n];

				fn into_preallocated_ffi_value(
					self_instance: Self::SelfInstance,
					context: &mut dyn FunctionContext,
					allocated: u32,
				) -> Result<()> {
					context.write_memory(Pointer::new(allocated), &self_instance)
				}
			}
		)*
	}
}

impl_traits_for_arrays! {
	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26,
	27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
	51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74,
	75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96,
}

impl<T: codec::Codec, E: codec::Codec> PassBy for sp_std::result::Result<T, E> {
	type PassBy = Codec<Self>;
}

impl<T: codec::Codec> PassBy for Option<T> {
	type PassBy = Codec<Self>;
}

#[impl_trait_for_tuples::impl_for_tuples(30)]
#[tuple_types_no_default_trait_bound]
impl PassBy for Tuple
where
	Self: codec::Codec,
{
	type PassBy = Codec<Self>;
}

/// Implement `PassBy` with `Inner` for the given fixed sized hash types.
macro_rules! for_primitive_types {
	{ $( $hash:ident $n:expr ),* $(,)? } => {
		$(
			impl PassBy for primitive_types::$hash {
				type PassBy = Inner<Self, [u8; $n]>;
			}

			impl PassByInner for primitive_types::$hash {
				type Inner = [u8; $n];

				fn inner(&self) -> &Self::Inner {
					&self.0
				}

				fn into_inner(self) -> Self::Inner {
					self.0
				}

				fn from_inner(inner: Self::Inner) -> Self {
					Self(inner)
				}
			}
		)*
	}
}

for_primitive_types! {
	H160 20,
	H256 32,
	H512 64,
}

/// The type is passed as `u64`.
///
/// The `u64` value is build by `length 32bit << 32 | pointer 32bit`
///
/// The length and the pointer are taken directly from `Self`.
impl RIType for str {
	type FFIType = u64;
}

#[cfg(feature = "std")]
impl FromFFIValue for str {
	type SelfInstance = String;

	fn from_ffi_value(context: &mut dyn FunctionContext, arg: u64) -> Result<String> {
		let (ptr, len) = unpack_ptr_and_len(arg);

		let vec = context.read_memory(Pointer::new(ptr), len)?;

		// The data is valid utf8, as it is stored as `&str` in wasm.
		String::from_utf8(vec).map_err(|_| "Invalid utf8 data provided".into())
	}