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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::fmt::Write;
use core::marker::PhantomData;
// Bootstring parameters for Punycode
const BASE: u32 = 36;
const T_MIN: u32 = 1;
const T_MAX: u32 = 26;
const SKEW: u32 = 38;
const DAMP: u32 = 700;
const INITIAL_BIAS: u32 = 72;
const INITIAL_N: u32 = 0x80;
#[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`.
///
/// 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.
#[inline]
pub fn decode_to_string(input: &str) -> Option<String> {
Some(
Decoder::default()
.decode::<u8, ExternalCaller>(input.as_bytes())
.ok()?
.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::<u8, ExternalCaller>(input.as_bytes())
.ok()?
.collect(),
)
}
/// Marker for internal vs. external caller to retain old API behavior
/// while tweaking behavior for internal callers.
///
/// External callers need overflow checks when encoding, but internal
/// callers don't, because `PUNYCODE_ENCODE_MAX_INPUT_LENGTH` is set
/// to 1000, and per RFC 3492 section 6.4, the integer variable does
/// not need to be able to represent values larger than
/// (char::MAX - INITIAL_N) * (PUNYCODE_ENCODE_MAX_INPUT_LENGTH + 1),
/// which is less than u32::MAX.
///
/// External callers need to handle upper-case ASCII when decoding,
/// but internal callers don't, because the internal code calls the
/// decoder only with lower-case inputs.
pub(crate) trait PunycodeCaller {
const EXTERNAL_CALLER: bool;
}
pub(crate) struct InternalCaller;
impl PunycodeCaller for InternalCaller {
const EXTERNAL_CALLER: bool = false;
}
struct ExternalCaller;
impl PunycodeCaller for ExternalCaller {
const EXTERNAL_CALLER: bool = true;
}
pub(crate) trait PunycodeCodeUnit {
fn is_delimiter(&self) -> bool;
fn is_ascii(&self) -> bool;
fn digit(&self) -> Option<u32>;
fn char(&self) -> char;
fn char_ascii_lower_case(&self) -> char;
}
impl PunycodeCodeUnit for u8 {
fn is_delimiter(&self) -> bool {
*self == b'-'
}
fn is_ascii(&self) -> bool {
*self < 0x80
}
fn digit(&self) -> Option<u32> {
let byte = *self;
Some(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 None,
} as u32)
}
fn char(&self) -> char {
char::from(*self)
}
fn char_ascii_lower_case(&self) -> char {
char::from(self.to_ascii_lowercase())
}
}
impl PunycodeCodeUnit for char {
fn is_delimiter(&self) -> bool {
*self == '-'
}
fn is_ascii(&self) -> bool {
debug_assert!(false); // Unused
true
}
fn digit(&self) -> Option<u32> {
let byte = *self;
Some(match byte {
byte @ '0'..='9' => u32::from(byte) - u32::from('0') + 26,
// byte @ 'A'..='Z' => u32::from(byte) - u32::from('A'), // XXX not needed if no public input
byte @ 'a'..='z' => u32::from(byte) - u32::from('a'),
_ => return None,
})
}
fn char(&self) -> char {
debug_assert!(false); // Unused
*self
}
fn char_ascii_lower_case(&self) -> char {
// No need to actually lower-case!
*self
}
}
#[derive(Default)]
pub(crate) struct Decoder {
insertions: smallvec::SmallVec<[(usize, char); 59]>,
}
impl Decoder {
/// Split the input iterator and return a Vec with insertions of encoded characters
pub(crate) fn decode<'a, T: PunycodeCodeUnit + Copy, C: PunycodeCaller>(
&'a mut self,
input: &'a [T],
) -> Result<Decode<'a, T, C>, ()> {
self.insertions.clear();
// Handle "basic" (ASCII) code points.
// They are encoded as-is before the last delimiter, if any.
let (base, input) = if let Some(position) = input.iter().rposition(|c| c.is_delimiter()) {
(
&input[..position],
if position > 0 {
&input[position + 1..]
} else {
input
},
)
} else {
(&input[..0], input)
};
if C::EXTERNAL_CALLER && !base.iter().all(|c| c.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 = 0u32;
let mut iter = input.iter();
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 = if let Some(digit) = byte.digit() {
digit
} else {
return Err(());
};
let product = digit.checked_mul(weight).ok_or(())?;
i = i.checked_add(product).ok_or(())?;
let t = if k <= bias {
T_MIN
} else if k >= bias + T_MAX {
T_MAX
} else {
k - bias
};
if digit < t {
break;
}
weight = weight.checked_mul(BASE - t).ok_or(())?;
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);
// i was supposed to wrap around from length+1 to 0,
// incrementing code_point each time.
code_point = code_point.checked_add(i / (length + 1)).ok_or(())?;
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.iter(),
insertions: &self.insertions,
inserted: 0,
position: 0,
len: base_len + self.insertions.len(),
phantom: PhantomData::<C>,
})
}
}
pub(crate) struct Decode<'a, T, C>
where
T: PunycodeCodeUnit + Copy,
C: PunycodeCaller,
{
base: core::slice::Iter<'a, T>,
pub(crate) insertions: &'a [(usize, char)],
inserted: usize,
position: usize,
len: usize,
phantom: PhantomData<C>,
}
impl<'a, T: PunycodeCodeUnit + Copy, C: PunycodeCaller> Iterator for Decode<'a, T, C> {
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(if C::EXTERNAL_CALLER {
c.char()
} else {
c.char_ascii_lower_case()
});
} 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, T: PunycodeCodeUnit + Copy, C: PunycodeCaller> ExactSizeIterator for Decode<'a, T, C> {
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::<_, _, ExternalCaller>(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::<_, _, ExternalCaller>(input.iter().copied(), &mut buf)
.ok()
.map(|()| buf)
}
pub(crate) enum PunycodeEncodeError {
Overflow,
Sink,
}
impl From<core::fmt::Error> for PunycodeEncodeError {
fn from(_: core::fmt::Error) -> Self {
PunycodeEncodeError::Sink
}
}
pub(crate) fn encode_into<I, W, C>(input: I, output: &mut W) -> Result<(), PunycodeEncodeError>
where
I: Iterator<Item = char> + Clone,
W: Write + ?Sized,
C: PunycodeCaller,
{
// 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(PunycodeEncodeError::Overflow)?;
if c.is_ascii() {
output.write_char(c)?;
basic_length += 1;
}
}
if !C::EXTERNAL_CALLER {
// We should never get an overflow here with the internal caller being
// length-limited, but let's check anyway once here trusting the math
// from RFC 3492 section 6.4 and then omit the overflow checks in the
// loop below.
let len_plus_one = input_length
.checked_add(1)
.ok_or(PunycodeEncodeError::Overflow)?;
len_plus_one
.checked_mul(u32::from(char::MAX) - INITIAL_N)
.ok_or(PunycodeEncodeError::Overflow)?;
}
if basic_length > 0 {
output.write_char('-')?;
}
let mut code_point = INITIAL_N;
let mut delta = 0u32;
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();
// Increase delta to advance the decoder’s <code_point,i> state to <min_code_point,0>
if C::EXTERNAL_CALLER {
let product = (min_code_point - code_point)
.checked_mul(processed + 1)
.ok_or(PunycodeEncodeError::Overflow)?;
delta = delta
.checked_add(product)
.ok_or(PunycodeEncodeError::Overflow)?;
} else {
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 {
if C::EXTERNAL_CALLER {
delta = delta.checked_add(1).ok_or(PunycodeEncodeError::Overflow)?;
} else {
delta += 1;
}
}
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.write_char(value_to_digit(value))?;
q = (q - t) / (BASE - t);
k += BASE;
}
output.write_char(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::<_, _, ExternalCaller>(
core::iter::repeat('ß').take(u32::MAX as usize + 1),
&mut buf
)
.is_err());
assert_eq!(buf.len(), 0);
}