use std::{io::Error, mem::size_of};
use integer_encoding::VarInt;
pub const MSB: u8 = 0b1000_0000;
pub trait VarIntExt {
fn varint_max_size() -> usize;
}
impl<VI: VarInt> VarIntExt for VI {
fn varint_max_size() -> usize {
(size_of::<VI>() * 8 + 7) / 7
}
}
#[derive(Default)]
pub struct VarIntProcessor {
buf: [u8; 10],
maxsize: usize,
pub i: usize,
}
impl VarIntProcessor {
pub fn new<VI: VarIntExt>() -> VarIntProcessor {
VarIntProcessor {
maxsize: VI::varint_max_size(),
..VarIntProcessor::default()
}
}
pub fn push(&mut self, b: u8) -> Result<(), Error> {
if self.i >= self.maxsize {
return Err(Error::new(
std::io::ErrorKind::InvalidData,
"Unterminated varint",
));
}
self.buf[self.i] = b;
self.i += 1;
Ok(())
}
pub fn finished(&self) -> bool {
self.i > 0 && (self.buf[self.i - 1] & MSB == 0)
}
pub fn decode<VI: VarInt>(&self) -> Option<VI> {
Some(VI::decode_var(&self.buf[0..self.i])?.0)
}
}