| // Protocol Buffers - Google's data interchange format |
| // Copyright 2023 Google LLC. All rights reserved. |
| // |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file or at |
| // https://developers.google.com/open-source/licenses/bsd |
| |
| //! Lossy UTF-8 processing utilities. |
| #![deny(unsafe_op_in_unsafe_fn)] |
| |
| // TODO: Replace this with the `std` versions once stable. |
| // This is adapted from https://github.com/rust-lang/rust/blob/e8ee0b7/library/core/src/str/lossy.rs |
| // The adaptations: |
| // - remove `#[unstable]` attributes. |
| // - replace `crate`/`super` paths with their `std` equivalents in code and |
| // examples. |
| // - include `UTF8_CHAR_WIDTH`/`utf8_char_width` from `core::str::validations`. |
| // - use a custom `split_at_unchecked` instead of the nightly one |
| |
| use std::fmt; |
| use std::fmt::Formatter; |
| use std::fmt::Write; |
| use std::iter::FusedIterator; |
| use std::str::from_utf8_unchecked; |
| |
| /// An item returned by the [`Utf8Chunks`] iterator. |
| /// |
| /// A `Utf8Chunk` stores a sequence of [`u8`] up to the first broken character |
| /// when decoding a UTF-8 string. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use googletest::prelude::*; |
| /// use utf8::Utf8Chunks; |
| /// |
| /// // An invalid UTF-8 string |
| /// let bytes = b"foo\xF1\x80bar"; |
| /// |
| /// // Decode the first `Utf8Chunk` |
| /// let chunk = Utf8Chunks::new(bytes).next().unwrap(); |
| /// |
| /// // The first three characters are valid UTF-8 |
| /// assert_that!("foo", eq(chunk.valid())); |
| /// |
| /// // The fourth character is broken |
| /// assert_that!(b"\xF1\x80", eq(chunk.invalid())); |
| /// ``` |
| #[derive(Clone, Debug, PartialEq, Eq)] |
| pub struct Utf8Chunk<'a> { |
| valid: &'a str, |
| invalid: &'a [u8], |
| } |
| |
| impl<'a> Utf8Chunk<'a> { |
| /// Returns the next validated UTF-8 substring. |
| /// |
| /// This substring can be empty at the start of the string or between |
| /// broken UTF-8 characters. |
| #[must_use] |
| pub fn valid(&self) -> &'a str { |
| self.valid |
| } |
| |
| /// Returns the invalid sequence that caused a failure. |
| /// |
| /// The returned slice will have a maximum length of 3 and starts after the |
| /// substring given by [`valid`]. Decoding will resume after this sequence. |
| /// |
| /// If empty, this is the last chunk in the string. If non-empty, an |
| /// unexpected byte was encountered or the end of the input was reached |
| /// unexpectedly. |
| /// |
| /// Lossy decoding would replace this sequence with [`U+FFFD REPLACEMENT |
| /// CHARACTER`]. |
| /// |
| /// [`valid`]: Self::valid |
| /// [`U+FFFD REPLACEMENT CHARACTER`]: std::char::REPLACEMENT_CHARACTER |
| #[must_use] |
| pub fn invalid(&self) -> &'a [u8] { |
| self.invalid |
| } |
| } |
| |
| #[must_use] |
| pub struct Debug<'a>(&'a [u8]); |
| |
| impl fmt::Debug for Debug<'_> { |
| fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result { |
| f.write_char('"')?; |
| |
| for chunk in Utf8Chunks::new(self.0) { |
| // Valid part. |
| // Here we partially parse UTF-8 again which is suboptimal. |
| { |
| let valid = chunk.valid(); |
| let mut from = 0; |
| for (i, c) in valid.char_indices() { |
| let esc = c.escape_debug(); |
| // If char needs escaping, flush backlog so far and write, else skip |
| if esc.len() != 1 { |
| f.write_str(&valid[from..i])?; |
| for c in esc { |
| f.write_char(c)?; |
| } |
| from = i + c.len_utf8(); |
| } |
| } |
| f.write_str(&valid[from..])?; |
| } |
| |
| // Broken parts of string as hex escape. |
| for &b in chunk.invalid() { |
| write!(f, "\\x{:02X}", b)?; |
| } |
| } |
| |
| f.write_char('"') |
| } |
| } |
| |
| /// An iterator used to decode a slice of mostly UTF-8 bytes to string slices |
| /// ([`&str`]) and byte slices ([`&[u8]`][byteslice]). |
| /// |
| /// If you want a simple conversion from UTF-8 byte slices to string slices, |
| /// [`from_utf8`] is easier to use. |
| /// |
| /// [byteslice]: slice |
| /// [`from_utf8`]: std::str::from_utf8 |
| /// |
| /// # Examples |
| /// |
| /// This can be used to create functionality similar to |
| /// [`String::from_utf8_lossy`] without allocating heap memory: |
| /// |
| /// ``` |
| /// use utf8::Utf8Chunks; |
| /// |
| /// fn from_utf8_lossy<F>(input: &[u8], mut push: F) where F: FnMut(&str) { |
| /// for chunk in Utf8Chunks::new(input) { |
| /// push(chunk.valid()); |
| /// |
| /// if !chunk.invalid().is_empty() { |
| /// push("\u{FFFD}"); |
| /// } |
| /// } |
| /// } |
| /// ``` |
| #[must_use = "iterators are lazy and do nothing unless consumed"] |
| #[derive(Clone)] |
| pub struct Utf8Chunks<'a> { |
| source: &'a [u8], |
| } |
| |
| impl<'a> Utf8Chunks<'a> { |
| /// Creates a new iterator to decode the bytes. |
| pub fn new(bytes: &'a [u8]) -> Self { |
| Self { source: bytes } |
| } |
| |
| #[doc(hidden)] |
| pub fn debug(&self) -> Debug<'_> { |
| Debug(self.source) |
| } |
| } |
| |
| impl<'a> Iterator for Utf8Chunks<'a> { |
| type Item = Utf8Chunk<'a>; |
| |
| fn next(&mut self) -> Option<Utf8Chunk<'a>> { |
| if self.source.is_empty() { |
| return None; |
| } |
| |
| const TAG_CONT_U8: u8 = 128; |
| fn safe_get(xs: &[u8], i: usize) -> u8 { |
| *xs.get(i).unwrap_or(&0) |
| } |
| |
| let mut i = 0; |
| let mut valid_up_to = 0; |
| while i < self.source.len() { |
| // SAFETY: `i < self.source.len()` per previous line. |
| // For some reason the following are both significantly slower: |
| // while let Some(&byte) = self.source.get(i) { |
| // while let Some(byte) = self.source.get(i).copied() { |
| let byte = unsafe { *self.source.get_unchecked(i) }; |
| i += 1; |
| |
| if byte < 128 { |
| // This could be a `1 => ...` case in the match below, but for |
| // the common case of all-ASCII inputs, we bypass loading the |
| // sizeable UTF8_CHAR_WIDTH table into cache. |
| } else { |
| let w = utf8_char_width(byte); |
| |
| match w { |
| 2 => { |
| if safe_get(self.source, i) & 192 != TAG_CONT_U8 { |
| break; |
| } |
| i += 1; |
| } |
| 3 => { |
| match (byte, safe_get(self.source, i)) { |
| (0xE0, 0xA0..=0xBF) => (), |
| (0xE1..=0xEC, 0x80..=0xBF) => (), |
| (0xED, 0x80..=0x9F) => (), |
| (0xEE..=0xEF, 0x80..=0xBF) => (), |
| _ => break, |
| } |
| i += 1; |
| if safe_get(self.source, i) & 192 != TAG_CONT_U8 { |
| break; |
| } |
| i += 1; |
| } |
| 4 => { |
| match (byte, safe_get(self.source, i)) { |
| (0xF0, 0x90..=0xBF) => (), |
| (0xF1..=0xF3, 0x80..=0xBF) => (), |
| (0xF4, 0x80..=0x8F) => (), |
| _ => break, |
| } |
| i += 1; |
| if safe_get(self.source, i) & 192 != TAG_CONT_U8 { |
| break; |
| } |
| i += 1; |
| if safe_get(self.source, i) & 192 != TAG_CONT_U8 { |
| break; |
| } |
| i += 1; |
| } |
| _ => break, |
| } |
| } |
| |
| valid_up_to = i; |
| } |
| |
| /// # Safety |
| /// `index` must be in-bounds for `x` |
| unsafe fn split_at_unchecked(x: &[u8], index: usize) -> (&[u8], &[u8]) { |
| // SAFETY: in-bounds as promised by the caller |
| unsafe { (x.get_unchecked(..index), x.get_unchecked(index..)) } |
| } |
| |
| // SAFETY: `i <= self.source.len()` because it is only ever incremented |
| // via `i += 1` and in between every single one of those increments, `i` |
| // is compared against `self.source.len()`. That happens either |
| // literally by `i < self.source.len()` in the while-loop's condition, |
| // or indirectly by `safe_get(self.source, i) & 192 != TAG_CONT_U8`. The |
| // loop is terminated as soon as the latest `i += 1` has made `i` no |
| // longer less than `self.source.len()`, which means it'll be at most |
| // equal to `self.source.len()`. |
| let (inspected, remaining) = unsafe { split_at_unchecked(self.source, i) }; |
| self.source = remaining; |
| |
| // SAFETY: `valid_up_to <= i` because it is only ever assigned via |
| // `valid_up_to = i` and `i` only increases. |
| let (valid, invalid) = unsafe { split_at_unchecked(inspected, valid_up_to) }; |
| |
| Some(Utf8Chunk { |
| // SAFETY: All bytes up to `valid_up_to` are valid UTF-8. |
| valid: unsafe { from_utf8_unchecked(valid) }, |
| invalid, |
| }) |
| } |
| } |
| |
| impl FusedIterator for Utf8Chunks<'_> {} |
| |
| impl fmt::Debug for Utf8Chunks<'_> { |
| fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result { |
| f.debug_struct("Utf8Chunks").field("source", &self.debug()).finish() |
| } |
| } |
| |
| // https://tools.ietf.org/html/rfc3629 |
| const UTF8_CHAR_WIDTH: &[u8; 256] = &[ |
| // 1 2 3 4 5 6 7 8 9 A B C D E F |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0 |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 1 |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 2 |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 3 |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 4 |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 5 |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 6 |
| 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 7 |
| 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 8 |
| 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // 9 |
| 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // A |
| 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // B |
| 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // C |
| 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // D |
| 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, // E |
| 4, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // F |
| ]; |
| |
| /// Given a first byte, determines how many bytes are in this UTF-8 character. |
| #[must_use] |
| #[inline] |
| const fn utf8_char_width(b: u8) -> usize { |
| UTF8_CHAR_WIDTH[b as usize] as usize |
| } |
