flat-bytes 0.1.1

#![deny(clippy::pedantic)]

pub use flat_bytes_derive::flat_enum;
pub use flat_bytes_derive::Flat;

pub trait Flat: Sized {
    fn serialize(&self) -> Vec<u8>;
    fn deserialize_with_size(data: &[u8]) -> Option<(Self, usize)>;
    #[must_use]
    fn deserialize(data: &[u8]) -> Option<Self> {
        Self::deserialize_with_size(data).map(|(r, _)| r)
    }
}

macro_rules! impl_primitive {
    ($t:ident) => {
        impl Flat for $t {
            fn serialize(&self) -> Vec<u8> {
                self.to_le_bytes().to_vec()
            }

            fn deserialize_with_size(data: &[u8]) -> Option<(Self, usize)> {
                if data.len() < std::mem::size_of::<Self>() {
                    return None;
                }
                let mut tmp = [0u8; std::mem::size_of::<Self>()];
                tmp.copy_from_slice(&data[..::std::mem::size_of::<Self>()]);
                Some((Self::from_le_bytes(tmp), ::std::mem::size_of::<Self>()))
            }
        }
    };
}

impl_primitive!(u8);
impl_primitive!(u16);
impl_primitive!(u32);
impl_primitive!(u64);
impl_primitive!(i8);
impl_primitive!(i16);
impl_primitive!(i32);
impl_primitive!(i64);

impl Flat for bool {
    fn serialize(&self) -> Vec<u8> {
        Flat::serialize(&(u8::from(*self)))
    }

    fn deserialize_with_size(data: &[u8]) -> Option<(Self, usize)> {
        <u8 as Flat>::deserialize_with_size(data).map(|(v, s)| (v != 0, s))
    }
}

macro_rules! impl_array {
    (@step ($d: ident, $idx:expr,) -> ($($body:tt)*)) => {
        impl_array!(@as_expr [$($body)*])
    };
    (@step ($d: ident, $idx:expr, $t:ident, $($ts:ident,)*) -> ($($body:tt)*)) => {
        impl_array!(@step ($d, $idx+1, $($ts,)*) -> ($($body)* $t::deserialize(&$d[::std::mem::size_of::<$t>()*($idx)..])?,))
    };
    (@as_expr $e:expr) => {$e};
    {$n:expr, $t:ident $($ts:ident)*}=> {
        impl<T: Flat> Flat for [T; $n] {
            fn serialize(&self) -> Vec<u8> {
                self.iter().map(Flat::serialize).flatten().collect()
            }

            fn deserialize_with_size(data: &[u8]) -> Option<(Self, usize)> {
                let res =
                    impl_array!(@step (data, 0, $t, $($ts,)*) -> ());
                Some((res, ::std::mem::size_of::<Self>()))
            }
        }
        impl_array!{($n - 1), $($ts)*}
    };
    {$n:expr,} => {
        impl<T: Flat> Flat for [T; $n] {
            fn serialize(&self) -> Vec<u8> {
                vec![]
            }

            fn deserialize_with_size(_data: &[u8]) -> Option<(Self, usize)> {
                Some(([], 0))
            }
        }
    };
}
impl_array! {32, T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T}

#[cfg(test)]
mod tests {
    use super::*;
    use crate as flat_bytes;

    flat_enum! {
        #[repr(u8)]
        pub enum Foo {
            Bar = 1,
            Baz(bool) = 3,
            Blubb{a: bool, b: u8},
        }
    }

    static FOO: [u16; 4] = [1, 2, 3, 4];

    #[derive(Flat)]
    struct Header {
        magic: [u8; 2],
        size: u16,
        admin: bool,
    }

    #[derive(Flat)]
    struct Wrapper(Foo);

    #[test]
    fn serialize() {
        #![allow(clippy::many_single_char_names)]

        let a = Foo::Bar;
        assert_eq!(a.serialize(), vec![1]);
        let b = Foo::Baz(true);
        assert_eq!(b.serialize(), vec![3, 1]);
        let b = Foo::Baz(false);
        assert_eq!(b.serialize(), vec![3, 0]);
        let c = Foo::Blubb { a: true, b: 1 };
        assert_eq!(c.serialize(), vec![4, 1, 1]);
        let c = Foo::Blubb { a: false, b: 2 };
        assert_eq!(c.serialize(), vec![4, 0, 2]);

        assert_eq!(FOO.serialize(), vec![1, 0, 2, 0, 3, 0, 4, 0]);

        let h = Header {
            magic: *b"AB",
            size: 123,
            admin: true,
        };
        assert_eq!(h.serialize(), vec![0x41, 0x42, 123, 0, 1]);

        let w = Wrapper(Foo::Bar);
        assert_eq!(w.serialize(), vec![1]);
    }

    #[test]
    fn deserialize() {
        assert!(Foo::deserialize(&[]).is_none());
        assert!(Foo::deserialize(&[5]).is_none());
        assert!(Foo::deserialize(&[0]).is_none());
        let a = Foo::deserialize(&[1]).unwrap();
        assert!(matches!(a, Foo::Bar));
        let b = Foo::deserialize(&[3, 0]).unwrap();
        assert!(matches!(b, Foo::Baz(false)));
        let b = Foo::deserialize(&[3, 1]).unwrap();
        assert!(matches!(b, Foo::Baz(true)));
        let c = Foo::deserialize(&[4, 1, 1]).unwrap();
        assert!(matches!(c, Foo::Blubb { a: true, b: 1 }));
        let c = Foo::deserialize(&[4, 0, 2]).unwrap();
        assert!(matches!(c, Foo::Blubb { a: false, b: 2 }));

        assert_eq!(
            <[u16; 4]>::deserialize(&[1, 0, 2, 0, 3, 0, 4, 0]).unwrap(),
            FOO
        );

        let w = Wrapper::deserialize(&[1]).unwrap();
        assert!(matches!(w.0, Foo::Bar));
    }
}