// Copyright Mozilla Foundation
//
// Licensed under the Apache License (Version 2.0), or the MIT license,
// (the "Licenses") at your option. You may not use this file except in
// compliance with one of the Licenses. You may obtain copies of the
// Licenses at:
//
//
https://www.apache.org/licenses/LICENSE-2.0
//
https://opensource.org/licenses/MIT
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Licenses is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the Licenses for the specific language governing permissions and
// limitations under the Licenses.
use crate::in_inclusive_range8;
use crate::UTF8_DATA;
use core::fmt::Formatter;
use core::iter::FusedIterator;
/// A type for signaling UTF-8 errors.
///
/// Note: `core::error::Error` is not implemented due to implementing it
/// being an [unstable feature][1] at the time of writing.
///
/// [1]:
https://github.com/rust-lang/rust/issues/103765
#[derive(Debug, PartialEq)]
#[non_exhaustive]
pub struct Utf8CharsError;
impl core::fmt::Display for Utf8CharsError {
fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), core::fmt::Error> {
write!(f, "byte sequence not well-formed UTF-8")
}
}
/// Iterator by `Result<char,Utf8CharsError>` over `&[u8]` that contains
/// potentially-invalid UTF-8. There is exactly one `Utf8CharsError` per
/// each error as defined by the WHATWG Encoding Standard.
///
/// ```
/// let s = b"a\xFFb\xFF\x80c\xF0\x9F\xA4\xA6\xF0\x9F\xA4\xF0\x9F\xF0d";
/// let plain = utf8_iter::Utf8Chars::new(s);
/// let reporting = utf8_iter::ErrorReportingUtf8Chars::new(s);
/// assert!(plain.eq(reporting.map(|r| r.unwrap_or('\u{FFFD}'))));
/// ```
#[derive(Debug, Clone)]
pub struct ErrorReportingUtf8Chars<'a> {
remaining: &'a [u8],
}
impl<'a> ErrorReportingUtf8Chars<'a> {
#[inline(always)]
/// Creates the iterator from a byte slice.
pub fn new(bytes: &'a [u8]) -> Self {
ErrorReportingUtf8Chars::<'a> { remaining: bytes }
}
/// Views the current remaining data in the iterator as a subslice
/// of the original slice.
#[inline(always)]
pub fn as_slice(&self) -> &'a [u8] {
self.remaining
}
#[inline(never)]
fn next_fallback(&mut self) -> Option<Result<char, Utf8CharsError>> {
if self.remaining.is_empty() {
return None;
}
let first = self.remaining[0];
if first < 0x80 {
self.remaining = &self.remaining[1..];
return Some(Ok(char::from(first)));
}
if !in_inclusive_range8(first, 0xC2, 0xF4) || self.remaining.len() == 1 {
self.remaining = &self.remaining[1..];
return Some(Err(Utf8CharsError));
}
let second = self.remaining[1];
let (lower_bound, upper_bound) = match first {
0xE0 => (0xA0, 0xBF),
0xED => (0x80, 0x9F),
0xF0 => (0x90, 0xBF),
0xF4 => (0x80, 0x8F),
_ => (0x80, 0xBF),
};
if !in_inclusive_range8(second, lower_bound, upper_bound) {
self.remaining = &self.remaining[1..];
return Some(Err(Utf8CharsError));
}
if first < 0xE0 {
self.remaining = &self.remaining[2..];
let point = ((u32::from(first) & 0x1F) << 6) | (u32::from(second) & 0x3F);
return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
}
if self.remaining.len() == 2 {
self.remaining = &self.remaining[2..];
return Some(Err(Utf8CharsError));
}
let third = self.remaining[2];
if !in_inclusive_range8(third, 0x80, 0xBF) {
self.remaining = &self.remaining[2..];
return Some(Err(Utf8CharsError));
}
if first < 0xF0 {
self.remaining = &self.remaining[3..];
let point = ((u32::from(first) & 0xF) << 12)
| ((u32::from(second) & 0x3F) << 6)
| (u32::from(third) & 0x3F);
return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
}
// At this point, we have a valid 3-byte prefix of a
// four-byte sequence that has to be incomplete, because
// otherwise `next()` would have succeeded.
self.remaining = &self.remaining[3..];
Some(Err(Utf8CharsError))
}
}
impl<'a> Iterator for ErrorReportingUtf8Chars<'a> {
type Item = Result<char, Utf8CharsError>;
#[inline]
fn next(&mut self) -> Option<Result<char, Utf8CharsError>> {
// This loop is only broken out of as goto forward
#[allow(clippy::never_loop)]
loop {
if self.remaining.len() < 4 {
break;
}
let first = self.remaining[0];
if first < 0x80 {
self.remaining = &self.remaining[1..];
return Some(Ok(char::from(first)));
}
let second = self.remaining[1];
if in_inclusive_range8(first, 0xC2, 0xDF) {
if !in_inclusive_range8(second, 0x80, 0xBF) {
break;
}
let point = ((u32::from(first) & 0x1F) << 6) | (u32::from(second) & 0x3F);
self.remaining = &self.remaining[2..];
return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
}
// This table-based formulation was benchmark-based in encoding_rs,
// but it hasn't been re-benchmarked in this iterator context.
let third = self.remaining[2];
if first < 0xF0 {
if ((UTF8_DATA.table[usize::from(second)]
& UTF8_DATA.table[usize::from(first) + 0x80])
| (third >> 6))
!= 2
{
break;
}
let point = ((u32::from(first) & 0xF) << 12)
| ((u32::from(second) & 0x3F) << 6)
| (u32::from(third) & 0x3F);
self.remaining = &self.remaining[3..];
return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
}
let fourth = self.remaining[3];
if (u16::from(
UTF8_DATA.table[usize::from(second)] & UTF8_DATA.table[usize::from(first) + 0x80
],
) | u16::from(third >> 6)
| (u16::from(fourth & 0xC0) << 2))
!= 0x202
{
break;
}
let point = ((u32::from(first) & 0x7) << 18)
| ((u32::from(second) & 0x3F) << 12)
| ((u32::from(third) & 0x3F) << 6)
| (u32::from(fourth) & 0x3F);
self.remaining = &self.remaining[4..];
return Some(Ok(unsafe { char::from_u32_unchecked(point) }));
}
self.next_fallback()
}
}
impl<'a> DoubleEndedIterator for ErrorReportingUtf8Chars<'a> {
#[inline]
fn next_back(&mut self) -> Option<Result<char, Utf8CharsError>> {
if self.remaining.is_empty() {
return None;
}
let mut attempt = 1;
for b in self.remaining.iter().rev() {
if b & 0xC0 != 0x80 {
let (head, tail) = self.remaining.split_at(self.remaining.len() - attempt);
let mut inner = ErrorReportingUtf8Chars::new(tail);
let candidate = inner.next();
if inner.as_slice().is_empty() {
self.remaining = head;
return candidate;
}
break;
}
if attempt == 4 {
break;
}
attempt += 1;
}
self.remaining = &self.remaining[..self.remaining.len() - 1];
Some(Err(Utf8CharsError))
}
}
impl FusedIterator for ErrorReportingUtf8Chars<'_> {}
#[cfg(test)]
mod tests {
use crate::ErrorReportingUtf8Chars;
// Should be a static assert, but not taking a dependency for this.
#[test]
fn test_size() {
assert_eq!(
core::mem::size_of::<Option<<ErrorReportingUtf8Chars<'_> as Iterator>::Item>>(),
core::mem::size_of::<Option<char>>()
);
}
#[test]
fn test_eq() {
let a: <ErrorReportingUtf8Chars<'_> as Iterator>::Item = Ok('a');
let a_again: <ErrorReportingUtf8Chars<'_> as Iterator>::Item = Ok('a');
assert_eq!(a, a_again);
}
}
