1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316
//! `escape8259` performs RFC8259-compliant string escaping and un-escaping.
//!
//! [RFC8259] is a JSON encoding standard. Many JSON encoders exist, but other
//! RFCs use the same string escaping mechanism, so it's useful to be able to
//! access the string escaping functions by themselves.
//!
//! # Examples
//!
//! ```
//! use escape8259::{escape, unescape};
//!
//! let s = "A null (\0) and a double-quote (\")";
//! assert_eq!(escape(s), r#"A null (\u0000) and a double-quote (\")"#);
//!
//! let crab = r#"This is a crab: \ud83e\udd80"#;
//! assert_eq!(unescape(crab).unwrap(), "This is a crab: 🦀");
//!
//! // We accept encodings that weren't really necessary.
//! assert_eq!(unescape(r#"\u0041\n"#).unwrap(), "A\n");
//!
//! let multiline = r#"hello
//! world"#;
//! assert_eq!(escape(multiline), r#"hello\n world"#);
//! ```
//!
//! [RFC8259]: https://tools.ietf.org/html/rfc8259
#![warn(missing_docs)]
#![forbid(unsafe_code)]
#![warn(clippy::cast_possible_truncation)]
use std::char::decode_utf16;
use std::fmt::{Display, Write};
/// An error occurred while unescaping.
#[allow(clippy::empty_structs_with_brackets)] // FIXME: correct this if releasing a new major version.
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct UnescapeError {}
impl Display for UnescapeError {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.write_str("failed rfc8259 unescape")
}
}
impl std::error::Error for UnescapeError {}
type UnescapeResult<T> = Result<T, UnescapeError>;
// Used to collect output characters and queue u16 values for translation.
struct UnescapeState {
// The accumulated characters
out: String,
// Store a fragment of a large character for later decoding
stash: u16,
}
impl UnescapeState {
fn new() -> UnescapeState {
UnescapeState {
out: String::new(),
stash: 0,
}
}
// Collect a new character
fn push_char(&mut self, c: char) -> UnescapeResult<()> {
if self.stash != 0 {
return Err(UnescapeError {});
}
self.out.push(c);
Ok(())
}
// Collect a new UTF16 word. This can either be one whole character,
// or part of a larger character.
fn push_u16(&mut self, x: u16) -> UnescapeResult<()> {
let surrogate = (0xD800..=0xDFFF).contains(&x);
match (self.stash, surrogate) {
(0, false) => {
// The std library only provides utf16 decode of an iterator,
// so to decode a single character we wrap it in an array.
// Hopefully the compiler will elide most of this extra work.
let words = [x];
match decode_utf16(words.iter().copied()).next() {
Some(Ok(c)) => {
self.out.push(c);
}
_ => return Err(UnescapeError {}),
}
}
(0, true) => self.stash = x,
(_, false) => {
return Err(UnescapeError {});
}
(w, true) => {
let words = [w, x];
match decode_utf16(words.iter().copied()).next() {
Some(Ok(c)) => {
self.out.push(c);
self.stash = 0;
}
_ => return Err(UnescapeError {}),
}
}
}
Ok(())
}
// If we queued up part of a UTF-16 encoded word but didn't
// finish it, return an error. Otherwise, consume self and
// return the accumulated String.
fn finalize(self) -> UnescapeResult<String> {
if self.stash != 0 {
return Err(UnescapeError {});
}
Ok(self.out)
}
}
fn parse_u16<S>(s: &mut S) -> UnescapeResult<u16>
where
S: Iterator<Item = char>,
{
// Placeholder character in case the input doesn't have the 4 chars we want.
let placeholders = std::iter::repeat('\0');
let hexnum: String = s.chain(placeholders).take(4).collect();
u16::from_str_radix(&hexnum, 16).map_err(|_| UnescapeError {})
}
// RFC8259 says non-escaped characters must be in one of the following ranges:
// %x20-21 / %x23-5B / %x5D-10FFFF
fn is_safe_char(c: char) -> bool {
let safe_ranges = [(0x20..=0x21), (0x23..=0x5B), (0x5D..=0x10FFFF)];
let cv = c as u32;
safe_ranges.iter().any(|range| range.contains(&cv))
}
/// Un-escape a string, following RFC8259 rules.
///
/// The only allowed single-character escapes are:
/// `\" \\ \/ /b /f /n /r /t`
///
/// Any other character may be escaped in UTF-16 form:
/// `\uXXXX` or `\uXXXX\uXXXX`
///
/// Characters in the ranges `0x20-21`, `0x23-5B`, `0x5D-10FFFF`
/// may appear un-escaped in the input.
#[inline]
pub fn unescape<S>(s: S) -> UnescapeResult<String>
where
S: AsRef<str>,
{
unescape_inner(s.as_ref())
}
fn unescape_inner(s: &str) -> UnescapeResult<String> {
let mut state = UnescapeState::new();
let mut ins = s.chars();
while let Some(c) = ins.next() {
if c == '\\' {
match ins.next() {
None => {
return Err(UnescapeError {});
}
Some(d) => {
match d {
'"' | '\\' | '/' => state.push_char(d)?,
'b' => state.push_char('\x08')?, // backspace
'f' => state.push_char('\x0C')?, // formfeed
'n' => state.push_char('\n')?, // linefeed
'r' => state.push_char('\r')?, // carriage return
't' => state.push_char('\t')?, // tab
'u' => {
let val = parse_u16(&mut ins)?;
state.push_u16(val)?;
}
_ => {
return Err(UnescapeError {});
}
}
}
}
} else if is_safe_char(c) {
state.push_char(c)?;
} else {
return Err(UnescapeError {});
}
}
state.finalize()
}
// %x22 / ; " quotation mark U+0022
// %x5C / ; \ reverse solidus U+005C
// %x2F / ; / solidus U+002F
// %x62 / ; b backspace U+0008
// %x66 / ; f form feed U+000C
// %x6E / ; n line feed U+000A
// %x72 / ; r carriage return U+000D
// %x74 / ; t tab U+0009
// %x75 4HEXDIG ) ; uXXXX U+XXXX
fn force_escape(c: char, out: &mut String) {
let c = c as u32;
match c {
0x08 => out.push_str("\\b"),
0x09 => out.push_str("\\t"),
0x0A => out.push_str("\\n"),
0x0C => out.push_str("\\f"),
0x0D => out.push_str("\\r"),
0x22 => out.push_str("\\\""),
0x5C => out.push_str("\\\\"),
_ => {
// RFC8259 allows unicode characters natively, so there is no need
// to convert everything into \uXXXX form. The only thing that's
// required to use that form are the ASCII control characters,
// which will never require more than one \uXXXX value.
if c >= 0x20 {
panic!("force_escape unnecessary encoding requested");
}
write!(out, "\\u{:04x}", c).unwrap();
}
}
}
/// Escape a string, following RFC8259 rules.
///
/// Only characters that require escaping will be escaped:
/// quotation mark `?`,
/// reverse solidus `\` (backslash),
/// and the control characters (`0x00-1F`).
#[inline]
pub fn escape<S>(s: S) -> String
where
S: AsRef<str>,
{
escape_inner(s.as_ref())
}
fn escape_inner(s: &str) -> String {
let mut out = String::new();
for c in s.chars() {
if is_safe_char(c) {
out.push(c);
} else {
force_escape(c, &mut out);
}
}
out
}
#[cfg(test)]
mod tests {
use super::*;
#[rustversion::attr(since(1.46), track_caller)]
fn assert_round_trip(s: &str) {
assert_eq!(s, unescape(&escape(s)).unwrap());
}
#[test]
fn test_round_trip() {
assert_round_trip("abc");
assert_round_trip("\n\r\t\x08\x0C\x00");
assert_round_trip(r#"\"#);
assert_round_trip(r#"""#);
assert_round_trip("Σ𝄞");
assert_round_trip(r#"\𝄞"#);
assert_round_trip(r#"(╯°□°)╯︵ ┻━┻"#);
}
#[test]
fn test_escape() {
assert_eq!(escape("\0"), r#"\u0000"#);
assert_eq!(escape("\n"), r#"\n"#);
assert_eq!(escape(r#"\"#), r#"\\"#);
assert_eq!(escape(r#"""#), r#"\""#);
assert_eq!(escape("Σ"), "Σ"); // U+03A3
assert_eq!(escape("𝄞"), "𝄞"); // U+1D11E
}
#[test]
fn test_unescape() {
assert_eq!(unescape(&r#"abc"#), Ok("abc".into()));
assert_eq!(unescape(&r#"ab\nc"#), Ok("ab\nc".into()));
assert_eq!(unescape(r#"ab\zc"#), Err(UnescapeError {}));
assert_eq!(unescape(r#" \"abc\" "#), Ok(" \"abc\" ".into()));
assert_eq!(unescape(r#"𝄞"#), Ok("𝄞".into()));
assert_eq!(unescape(r#"\𝄞"#), Err(UnescapeError {}));
assert_eq!(unescape(r#"\uD834\uDD1E"#), Ok("𝄞".into()));
assert_eq!(unescape(r#"\uD834"#), Err(UnescapeError {}));
assert_eq!(unescape(r#"\uDD1E"#), Err(UnescapeError {}));
assert_eq!(unescape("\t"), Err(UnescapeError {}));
}
#[test]
fn test_generic_asref() {
assert_eq!(escape("\n"), r#"\n"#);
assert_eq!(escape(String::from("\n")), r#"\n"#);
assert_eq!(escape(&String::from("\n")), r#"\n"#);
assert_eq!(unescape("abc"), Ok("abc".into()));
assert_eq!(unescape(String::from("abc")), Ok("abc".into()));
assert_eq!(unescape(&String::from("abc")), Ok("abc".into()));
}
#[test]
fn test_error_impl() {
// This won't compile if UnescapeError doesn't impl Display + Error.
let e = UnescapeError {};
let _x: Box<dyn std::error::Error> = e.into();
}
}