openethereum/src/bytes.rs

//! Unified interfaces for bytes operations on basic types
//! 
//! # Examples
//! ```rust
//! extern crate ethcore_util as util;
//! 
//! fn bytes_convertable() {
//! 	use util::bytes::BytesConvertable;
//!
//! 	let arr = [0; 5];
//! 	let slice: &[u8] = arr.bytes();
//! }
//! 
//! fn to_bytes() {
//! 	use util::bytes::ToBytes;
//! 	
//! 	let a: Vec<u8> = "hello_world".to_bytes();
//! 	let b: Vec<u8> = 400u32.to_bytes();
//! 	let c: Vec<u8> = 0xffffffffffffffffu64.to_bytes();
//! }
//! 
//! fn from_bytes() {
//! 	use util::bytes::FromBytes;
//! 	
//! 	let a = String::from_bytes(&[b'd', b'o', b'g']);
//! 	let b = u8::from_bytes(&[0xfa]);
//! 	let c = u64::from_bytes(&[0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff]);
//! }
//!
//! fn main() {
//! 	bytes_convertable();
//! 	to_bytes();
//! 	from_bytes();
//! }
//! ```

use std::fmt;
use std::cmp::Ordering;
use std::error::Error as StdError;
use uint::{U128, U256};
use hash::FixedHash;

/// Vector of bytes
pub type Bytes = Vec<u8>;

/// Slice of bytes to underlying memory
pub trait BytesConvertable {
	fn bytes(&self) -> &[u8];
}

impl<'a> BytesConvertable for &'a [u8] {
	fn bytes(&self) -> &[u8] { self }
}

impl BytesConvertable for Vec<u8> {
	fn bytes(&self) -> &[u8] { self }
}

macro_rules! impl_bytes_convertable_for_array {
    ($zero: expr) => ();
    ($len: expr, $($idx: expr),*) => {
        impl BytesConvertable for [u8; $len] {
            fn bytes(&self) -> &[u8] { self }
        }
        impl_bytes_convertable_for_array! { $($idx),* }
    }
}

// -1 at the end is not expanded
impl_bytes_convertable_for_array! {
        32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,
        15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, -1
}

#[test]
fn bytes_convertable() {
	assert_eq!(vec![0x12u8, 0x34].bytes(), &[0x12u8, 0x34]);
    assert_eq!([0u8; 0].bytes(), &[]);
}

/// Converts given type to its shortest representation in bytes
///
/// TODO: optimise some conversations
pub trait ToBytes {
	fn to_bytes(&self) -> Vec<u8>;
	fn to_bytes_len(&self) -> usize { self.to_bytes().len() }
	fn first_byte(&self) -> Option<u8> { self.to_bytes().first().map(|&x| { x })}
}

impl <'a> ToBytes for &'a str {
	fn to_bytes(&self) -> Vec<u8> {
		From::from(*self)
	}
	
	fn to_bytes_len(&self) -> usize { self.len() }
}

impl ToBytes for String {
	fn to_bytes(&self) -> Vec<u8> {
		let s: &str = self.as_ref();
		From::from(s)
	}
	
	fn to_bytes_len(&self) -> usize { self.len() }
}

impl ToBytes for u8 {
	fn to_bytes(&self) -> Vec<u8> {
		match *self {
			0 => vec![],
			_ => vec![*self]
		}
	}

	fn to_bytes_len(&self) -> usize {
		match *self {
			0 => 0,
			_ => 1
		}
	}
	fn first_byte(&self) -> Option<u8> { 
		match *self {
			0 => None,
			_ => Some(*self) 
		}
	}
}

impl ToBytes for u64 {
	fn to_bytes(&self) -> Vec<u8> {
		let mut res= vec![];
		let count = self.to_bytes_len();
		res.reserve(count);
		for i in 0..count {
			let j = count - 1 - i;
			res.push((*self >> (j * 8)) as u8);
		}
		res
	}

	fn to_bytes_len(&self) -> usize { 8 - self.leading_zeros() as usize / 8 }
}

macro_rules! impl_map_to_bytes {
	($from: ident, $to: ty) => {
		impl ToBytes for $from {
			fn to_bytes(&self) -> Vec<u8> { (*self as $to).to_bytes() }
			fn to_bytes_len(&self) -> usize { (*self as $to).to_bytes_len() }
		}
	}
}

impl_map_to_bytes!(usize, u64);
impl_map_to_bytes!(u16, u64);
impl_map_to_bytes!(u32, u64);

macro_rules! impl_uint_to_bytes {
	($name: ident) => {
		impl ToBytes for $name {
			fn to_bytes(&self) -> Vec<u8> { 
				let mut res= vec![];
				let count = self.to_bytes_len();
				res.reserve(count);
				for i in 0..count {
					let j = count - 1 - i;
					res.push(self.byte(j));
				}
				res
			}
			fn to_bytes_len(&self) -> usize { (self.bits() + 7) / 8 }
		}
	}
}

impl_uint_to_bytes!(U256);
impl_uint_to_bytes!(U128);

impl <T>ToBytes for T where T: FixedHash {
	fn to_bytes(&self) -> Vec<u8> {
		let mut res: Vec<u8> = vec![];
		res.reserve(T::size());

		unsafe {
			use std::ptr;
			ptr::copy(self.bytes().as_ptr(), res.as_mut_ptr(), T::size());
			res.set_len(T::size());
		}
		
		res
	}
}

/// Error returned when FromBytes conversation goes wrong
#[derive(Debug, PartialEq, Eq)]
pub enum FromBytesError {
	DataIsTooShort,
	DataIsTooLong
}

impl StdError for FromBytesError {
	fn description(&self) -> &str { "from_bytes error" }
}

impl fmt::Display for FromBytesError {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		fmt::Debug::fmt(&self, f)
	}
}

/// Alias for the result of FromBytes trait
pub type FromBytesResult<T> = Result<T, FromBytesError>;

/// Converts to given type from its bytes representation
///
/// TODO: check size of bytes before conversation and return appropriate error
pub trait FromBytes: Sized {
	fn from_bytes(bytes: &[u8]) -> FromBytesResult<Self>;
}

impl FromBytes for String {
	fn from_bytes(bytes: &[u8]) -> FromBytesResult<String> {
		Ok(::std::str::from_utf8(bytes).unwrap().to_string())
	}
}

impl FromBytes for u8 {
	fn from_bytes(bytes: &[u8]) -> FromBytesResult<u8> {
		match bytes.len() {
			0 => Ok(0),
			_ => Ok(bytes[0])
		}
	}
}

impl FromBytes for u64 {
	fn from_bytes(bytes: &[u8]) -> FromBytesResult<u64> {
		match bytes.len() {
			0 => Ok(0),
			l => {
				let mut res = 0u64;
				for i in 0..l {
					let shift = (l - 1 - i) * 8;
					res = res + ((bytes[i] as u64) << shift);
				}
				Ok(res)
			}
		}
	}
}

macro_rules! impl_map_from_bytes {
	($from: ident, $to: ident) => {
		impl FromBytes for $from {
			fn from_bytes(bytes: &[u8]) -> FromBytesResult<$from> {
				$to::from_bytes(bytes).map(| x | { x as $from })
			}
		}
	}
}

impl_map_from_bytes!(usize, u64);
impl_map_from_bytes!(u16, u64);
impl_map_from_bytes!(u32, u64);

macro_rules! impl_uint_from_bytes {
	($name: ident) => {
		impl FromBytes for $name {
			fn from_bytes(bytes: &[u8]) -> FromBytesResult<$name> {
				Ok($name::from(bytes))
			}
		}
	}
}

impl_uint_from_bytes!(U256);
impl_uint_from_bytes!(U128);

impl <T>FromBytes for T where T: FixedHash {
	fn from_bytes(bytes: &[u8]) -> FromBytesResult<T> {
		match bytes.len().cmp(&T::size()) {
			Ordering::Less => return Err(FromBytesError::DataIsTooShort),
			Ordering::Greater => return Err(FromBytesError::DataIsTooLong),
			Ordering::Equal => ()
		};

		unsafe {
			use std::{mem, ptr};

			let mut res: T = mem::uninitialized();
			ptr::copy(bytes.as_ptr(), res.mut_bytes().as_mut_ptr(), T::size());

			Ok(res)
		}
	}
}