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// Copyright 2013 The rust-url developers.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//!
//! Since Punycode fundamentally works on unicode code points,
//! `encode` and `decode` take and return slices and vectors of `char`.
//! `encode_str` and `decode_to_string` provide convenience wrappers
//! that convert from and to Rust’s UTF-8 based `str` and `String` types.
use alloc::{string::String, vec::Vec};
use core::char;
use core::u32;
// Bootstring parameters for Punycode
static BASE: u32 = 36;
static T_MIN: u32 = 1;
static T_MAX: u32 = 26;
static SKEW: u32 = 38;
static DAMP: u32 = 700;
static INITIAL_BIAS: u32 = 72;
static INITIAL_N: u32 = 0x80;
static DELIMITER: char = '-';
#[inline]
fn adapt(mut delta: u32, num_points: u32, first_time: bool) -> u32 {
delta /= if first_time { DAMP } else { 2 };
delta += delta / num_points;
let mut k = 0;
while delta > ((BASE - T_MIN) * T_MAX) / 2 {
delta /= BASE - T_MIN;
k += BASE;
}
k + (((BASE - T_MIN + 1) * delta) / (delta + SKEW))
}
/// Convert Punycode to an Unicode `String`.
///
/// This is a convenience wrapper around `decode`.
#[inline]
pub fn decode_to_string(input: &str) -> Option<String> {
decode(input).map(|chars| chars.into_iter().collect())
}
/// Convert Punycode to Unicode.
///
/// Return None on malformed input or overflow.
/// Overflow can only happen on inputs that take more than
/// 63 encoded bytes, the DNS limit on domain name labels.
pub fn decode(input: &str) -> Option<Vec<char>> {
Some(Decoder::default().decode(input).ok()?.collect())
}
#[derive(Default)]
pub(crate) struct Decoder {
insertions: Vec<(usize, char)>,
}
impl Decoder {
/// Split the input iterator and return a Vec with insertions of encoded characters
pub(crate) fn decode<'a>(&'a mut self, input: &'a str) -> Result<Decode<'a>, ()> {
self.insertions.clear();
// Handle "basic" (ASCII) code points.
// They are encoded as-is before the last delimiter, if any.
let (base, input) = match input.rfind(DELIMITER) {
None => ("", input),
Some(position) => (
&input[..position],
if position > 0 {
&input[position + 1..]
} else {
input
},
),
};
if !base.is_ascii() {
return Err(());
}
let base_len = base.len();
let mut length = base_len as u32;
let mut code_point = INITIAL_N;
let mut bias = INITIAL_BIAS;
let mut i = 0;
let mut iter = input.bytes();
loop {
let previous_i = i;
let mut weight = 1;
let mut k = BASE;
let mut byte = match iter.next() {
None => break,
Some(byte) => byte,
};
// Decode a generalized variable-length integer into delta,
// which gets added to i.
loop {
let digit = match byte {
byte @ b'0'..=b'9' => byte - b'0' + 26,
byte @ b'A'..=b'Z' => byte - b'A',
byte @ b'a'..=b'z' => byte - b'a',
_ => return Err(()),
} as u32;
if digit > (u32::MAX - i) / weight {
return Err(()); // Overflow
}
i += digit * weight;
let t = if k <= bias {
T_MIN
} else if k >= bias + T_MAX {
T_MAX
} else {
k - bias
};
if digit < t {
break;
}
if weight > u32::MAX / (BASE - t) {
return Err(()); // Overflow
}
weight *= BASE - t;
k += BASE;
byte = match iter.next() {
None => return Err(()), // End of input before the end of this delta
Some(byte) => byte,
};
}
bias = adapt(i - previous_i, length + 1, previous_i == 0);
if i / (length + 1) > u32::MAX - code_point {
return Err(()); // Overflow
}
// i was supposed to wrap around from length+1 to 0,
// incrementing code_point each time.
code_point += i / (length + 1);
i %= length + 1;
let c = match char::from_u32(code_point) {
Some(c) => c,
None => return Err(()),
};
// Move earlier insertions farther out in the string
for (idx, _) in &mut self.insertions {
if *idx >= i as usize {
*idx += 1;
}
}
self.insertions.push((i as usize, c));
length += 1;
i += 1;
}
self.insertions.sort_by_key(|(i, _)| *i);
Ok(Decode {
base: base.chars(),
insertions: &self.insertions,
inserted: 0,
position: 0,
len: base_len + self.insertions.len(),
})
}
}
pub(crate) struct Decode<'a> {
base: core::str::Chars<'a>,
pub(crate) insertions: &'a [(usize, char)],
inserted: usize,
position: usize,
len: usize,
}
impl<'a> Iterator for Decode<'a> {
type Item = char;
fn next(&mut self) -> Option<Self::Item> {
loop {
match self.insertions.get(self.inserted) {
Some((pos, c)) if *pos == self.position => {
self.inserted += 1;
self.position += 1;
return Some(*c);
}
_ => {}
}
if let Some(c) = self.base.next() {
self.position += 1;
return Some(c);
} else if self.inserted >= self.insertions.len() {
return None;
}
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
let len = self.len - self.position;
(len, Some(len))
}
}
impl<'a> ExactSizeIterator for Decode<'a> {
fn len(&self) -> usize {
self.len - self.position
}
}
/// Convert an Unicode `str` to Punycode.
///
/// This is a convenience wrapper around `encode`.
#[inline]
pub fn encode_str(input: &str) -> Option<String> {
if input.len() > u32::MAX as usize {
return None;
}
let mut buf = String::with_capacity(input.len());
encode_into(input.chars(), &mut buf).ok().map(|()| buf)
}
/// Convert Unicode to Punycode.
///
/// Return None on overflow, which can only happen on inputs that would take more than
/// 63 encoded bytes, the DNS limit on domain name labels.
pub fn encode(input: &[char]) -> Option<String> {
if input.len() > u32::MAX as usize {
return None;
}
let mut buf = String::with_capacity(input.len());
encode_into(input.iter().copied(), &mut buf)
.ok()
.map(|()| buf)
}
pub(crate) fn encode_into<I>(input: I, output: &mut String) -> Result<(), ()>
where
I: Iterator<Item = char> + Clone,
{
// Handle "basic" (ASCII) code points. They are encoded as-is.
let (mut input_length, mut basic_length) = (0u32, 0);
for c in input.clone() {
input_length = input_length.checked_add(1).ok_or(())?;
if c.is_ascii() {
output.push(c);
basic_length += 1;
}
}
if basic_length > 0 {
output.push('-')
}
let mut code_point = INITIAL_N;
let mut delta = 0;
let mut bias = INITIAL_BIAS;
let mut processed = basic_length;
while processed < input_length {
// All code points < code_point have been handled already.
// Find the next larger one.
let min_code_point = input
.clone()
.map(|c| c as u32)
.filter(|&c| c >= code_point)
.min()
.unwrap();
if min_code_point - code_point > (u32::MAX - delta) / (processed + 1) {
return Err(()); // Overflow
}
// Increase delta to advance the decoder’s <code_point,i> state to <min_code_point,0>
delta += (min_code_point - code_point) * (processed + 1);
code_point = min_code_point;
for c in input.clone() {
let c = c as u32;
if c < code_point {
delta = delta.checked_add(1).ok_or(())?;
}
if c == code_point {
// Represent delta as a generalized variable-length integer:
let mut q = delta;
let mut k = BASE;
loop {
let t = if k <= bias {
T_MIN
} else if k >= bias + T_MAX {
T_MAX
} else {
k - bias
};
if q < t {
break;
}
let value = t + ((q - t) % (BASE - t));
output.push(value_to_digit(value));
q = (q - t) / (BASE - t);
k += BASE;
}
output.push(value_to_digit(q));
bias = adapt(delta, processed + 1, processed == basic_length);
delta = 0;
processed += 1;
}
}
delta += 1;
code_point += 1;
}
Ok(())
}
#[inline]
fn value_to_digit(value: u32) -> char {
match value {
0..=25 => (value as u8 + b'a') as char, // a..z
26..=35 => (value as u8 - 26 + b'0') as char, // 0..9
_ => panic!(),
}
}
#[test]
#[ignore = "slow"]
#[cfg(target_pointer_width = "64")]
fn huge_encode() {
let mut buf = String::new();
assert!(encode_into(std::iter::repeat('ß').take(u32::MAX as usize + 1), &mut buf).is_err());
assert_eq!(buf.len(), 0);
}