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use std::io;
#[derive(Debug)]
pub struct HexReader<R> {
reader: R,
}
impl<R> HexReader<R> {
pub fn new(reader: R) -> Self {
HexReader { reader }
}
}
#[derive(Debug, Copy, Clone)]
enum HexState {
Comment(Nibble),
Data(Nibble),
}
#[derive(Debug, Copy, Clone)]
enum Nibble {
Low,
High,
}
fn as_nibble(octet: u8) -> Option<u8> {
match octet {
b'0'..=b'9' => Some(octet - b'0'),
b'a'..=b'f' => Some(10 + (octet - b'a')),
b'A'..=b'F' => Some(10 + (octet - b'A')),
_ => None,
}
}
impl<R: io::Read> io::Read for HexReader<R> {
fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
let mut n_decoded = 0;
for loc in buf.iter_mut() {
use HexState::*;
use Nibble::*;
let mut state = Data(High);
let mut acc = 0;
loop {
let mut b = [0u8; 1];
let n_read = self.reader.read(&mut b)?;
if n_read == 0 {
match state {
Data(High) | Comment(High) => {
return Ok(n_decoded);
}
_ => {
return Err(io::Error::new(
io::ErrorKind::InvalidData,
"end of input when expecting low nibble",
));
}
}
}
let octet = b[0];
match state {
Comment(n) => {
if octet == b'\n' {
state = Data(n);
}
}
Data(n) => match as_nibble(octet) {
Some(nibble) => match n {
High => {
acc = nibble << 4;
state = Data(Low);
}
Low => {
*loc = acc | nibble;
n_decoded += 1;
break;
}
},
None => match octet {
b'#' => {
state = Comment(n);
}
b'\n' | b' ' | b'\t' | 12 => {}
_ => {
return Err(io::Error::new(
io::ErrorKind::InvalidData,
"octet not hexidecimal ASCII",
));
}
},
},
}
}
}
Ok(n_decoded)
}
}