Big refactor.

substrate/wasm-runtime/polkadot/src/slicable.rs

@@ -0,0 +1,69 @@
+use runtime_support::{Vec, size_of, transmute, uninitialized, slice};
+use streamreader::Joiner;
+use endiansensitive::EndianSensitive;
+
+/// Trait that allows zero-copy read/write of value-references to/from slices in LE format.
+pub trait Slicable: Sized {
+	fn from_slice(value: &[u8]) -> Option<Self> {
+		Self::set_as_slice(|out| if value.len() == out.len() {
+			out.copy_from_slice(&value);
+			true
+		} else {
+			false
+		})
+	}
+	fn to_vec(&self) -> Vec<u8> {
+		self.as_slice_then(|s| s.to_vec())
+	}
+	fn set_as_slice<F: FnOnce(&mut[u8]) -> bool>(set_slice: F) -> Option<Self>;
+	fn as_slice_then<R, F: FnOnce(&[u8]) -> R>(&self, f: F) -> R {
+		f(&self.to_vec())
+	}
+	fn size_of(_value: &[u8]) -> Option<usize>;
+}
+
+pub trait NonTrivialSlicable: Slicable {}
+
+impl<T: EndianSensitive> Slicable for T {
+	fn set_as_slice<F: FnOnce(&mut[u8]) -> bool>(fill_slice: F) -> Option<Self> {
+		let size = size_of::<T>();
+		let mut result: T = unsafe { uninitialized() };
+		let result_slice = unsafe {
+			slice::from_raw_parts_mut(transmute::<*mut T, *mut u8>(&mut result), size)
+		};
+		if fill_slice(result_slice) {
+			Some(result.from_le())
+		} else {
+			None
+		}
+	}
+	fn as_slice_then<R, F: FnOnce(&[u8]) -> R>(&self, f: F) -> R {
+		let size = size_of::<Self>();
+		self.as_le_then(|le| {
+			let value_slice = unsafe {
+				slice::from_raw_parts(transmute::<*const Self, *const u8>(le), size)
+			};
+			f(value_slice)
+		})
+	}
+	fn size_of(_value: &[u8]) -> Option<usize> {
+		Some(size_of::<Self>())
+	}
+}
+
+impl Slicable for Vec<u8> {
+	fn from_slice(value: &[u8]) -> Option<Self> {
+		Some(value[4..].to_vec())
+	}
+	fn set_as_slice<F: FnOnce(&mut[u8]) -> bool>(_fill_slice: F) -> Option<Self> {
+		unimplemented!();
+	}
+	fn to_vec(&self) -> Vec<u8> {
+		let mut r: Vec<u8> = vec![].join(&(self.len() as u32));
+		r.extend_from_slice(&self);
+		r
+	}
+	fn size_of(data: &[u8]) -> Option<usize> {
+		u32::from_slice(&data[0..4]).map(|i| (i + 4) as usize)
+	}
+}