# BitWrap
[](https://docs.rs/bitwrap)
BitWrap is a derive macro and trait to declare a struct data member
with explicit size, in bits.
---
## BitWrap Trait
BitWrap trait declares 2 methods:
```rust
fn pack(&self, dst: &mut [u8]) -> Result<usize, BitWrapError>
```
`pack` method serialize struct fields into dst array
```rust
fn unpack(&mut self, src: &[u8]) -> Result<usize, BitWrapError>
```
`unpack` method deserialize struct fields from src array
## BitWrap Macro
```rust
use bitwrap::BitWrap;
#[derive(BitWrap)]
struct Packet {
// Get/Set bit
#[bits(1)]
flag_1: u8,
// Get/Set bit and convert into bool:
// - 0 - false
// - 1 - true
#[bits(1)]
flag_2: bool,
// Fixed 6 bits
// on 'pack()' set 6 bits with defined value
// on 'unpack()' skip 6 bits
#[bits(6, skip = 0b111111)]
// Get 8 bits and convert them to Enum
// on 'pack()' call 'into(Enum) -> T'
// on 'unpack()' call 'from(T) -> Enum'
// T is a unsigned depends of the bit field size
#[bits(8, from = Enum::from, into = Enum::into)]
variant: Enum,
// call BitWrap methods for Ipv4Addr
#[bits]
ip: std::net::Ipv4Addr
// byte array
#[bytes]
mac: [u8; 6],
// virtual field for the bytes option
// unpacked value should be greater or equal to 1
// and less or equal to 10
#[bits(8,
name = data_len,
value = self.data.len(),
min = 1,
max = 10)]
// call BitWrap method for Vec<T> with defined
// buffer length where T is u8 or with implemented
// BitWrap + Default traits
#[bytes(data_len)]
data: Vec<u8>,
}
```