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#[derive(Clone, Copy, Eq, PartialEq)]
enum State {
/// The state after seeing a `\`.
Escape,
/// The state after seeing a `\x`.
HexFirst,
/// The state after seeing a `\x[0-9A-Fa-f]`.
HexSecond(char),
/// Default state.
Literal,
}
pub fn unescape(s: &str) -> Vec<u8> {
use self::State::*;
let mut bytes = vec![];
let mut state = Literal;
for c in s.chars() {
match state {
Escape => match c {
'\\' => {
bytes.push(b'\\');
state = Literal;
}
'n' => {
bytes.push(b'\n');
state = Literal;
}
'r' => {
bytes.push(b'\r');
state = Literal;
}
't' => {
bytes.push(b'\t');
state = Literal;
}
'x' => {
state = HexFirst;
}
c => {
bytes.extend(format!(r"\{}", c).into_bytes());
state = Literal;
}
},
HexFirst => match c {
'0'..='9' | 'A'..='F' | 'a'..='f' => {
state = HexSecond(c);
}
c => {
bytes.extend(format!(r"\x{}", c).into_bytes());
state = Literal;
}
},
HexSecond(first) => match c {
'0'..='9' | 'A'..='F' | 'a'..='f' => {
let ordinal = format!("{}{}", first, c);
let byte = u8::from_str_radix(&ordinal, 16).unwrap();
bytes.push(byte);
state = Literal;
}
c => {
let original = format!(r"\x{}{}", first, c);
bytes.extend(original.into_bytes());
state = Literal;
}
},
Literal => match c {
'\\' => {
state = Escape;
}
c => {
bytes.extend(c.to_string().as_bytes());
}
},
}
}
match state {
Escape => bytes.push(b'\\'),
HexFirst => bytes.extend(b"\\x"),
HexSecond(c) => bytes.extend(format!("\\x{}", c).into_bytes()),
Literal => {}
}
bytes
}
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