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/// A single state in the state machine used by `unescape`.
#[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,
}
/// Escapes an arbitrary byte slice such that it can be presented as a human
/// readable string.
pub fn escape(bytes: &[u8]) -> String {
use std::ascii::escape_default;
let escaped = bytes.iter().flat_map(|&b| escape_default(b)).collect();
String::from_utf8(escaped).unwrap()
}
/// Unescapes a string given on the command line. It supports a limited set of
/// escape sequences:
///
/// * `\t`, `\r` and `\n` are mapped to their corresponding ASCII bytes.
/// * `\xZZ` hexadecimal escapes are mapped to their byte.
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 {
'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
}
#[cfg(test)]
mod tests {
use super::unescape;
fn b(bytes: &'static [u8]) -> Vec<u8> {
bytes.to_vec()
}
#[test]
fn unescape_nul() {
assert_eq!(b(b"\x00"), unescape(r"\x00"));
}
#[test]
fn unescape_nl() {
assert_eq!(b(b"\n"), unescape(r"\n"));
}
#[test]
fn unescape_tab() {
assert_eq!(b(b"\t"), unescape(r"\t"));
}
#[test]
fn unescape_carriage() {
assert_eq!(b(b"\r"), unescape(r"\r"));
}
#[test]
fn unescape_nothing_simple() {
assert_eq!(b(b"\\a"), unescape(r"\a"));
}
#[test]
fn unescape_nothing_hex0() {
assert_eq!(b(b"\\x"), unescape(r"\x"));
}
#[test]
fn unescape_nothing_hex1() {
assert_eq!(b(b"\\xz"), unescape(r"\xz"));
}
#[test]
fn unescape_nothing_hex2() {
assert_eq!(b(b"\\xzz"), unescape(r"\xzz"));
}
}
|
