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-rw-r--r--third_party/rust/regex/src/utf8.rs264
1 files changed, 264 insertions, 0 deletions
diff --git a/third_party/rust/regex/src/utf8.rs b/third_party/rust/regex/src/utf8.rs
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+/// A few elementary UTF-8 encoding and decoding functions used by the matching
+/// engines.
+///
+/// In an ideal world, the matching engines operate on `&str` and we can just
+/// lean on the standard library for all our UTF-8 needs. However, to support
+/// byte based regexes (that can match on arbitrary bytes which may contain
+/// UTF-8), we need to be capable of searching and decoding UTF-8 on a `&[u8]`.
+/// The standard library doesn't really recognize this use case, so we have
+/// to build it out ourselves.
+///
+/// Should this be factored out into a separate crate? It seems independently
+/// useful. There are other crates that already exist (e.g., `utf-8`) that have
+/// overlapping use cases. Not sure what to do.
+use std::char;
+
+const TAG_CONT: u8 = 0b1000_0000;
+const TAG_TWO: u8 = 0b1100_0000;
+const TAG_THREE: u8 = 0b1110_0000;
+const TAG_FOUR: u8 = 0b1111_0000;
+
+/// Returns the smallest possible index of the next valid UTF-8 sequence
+/// starting after `i`.
+pub fn next_utf8(text: &[u8], i: usize) -> usize {
+ let b = match text.get(i) {
+ None => return i + 1,
+ Some(&b) => b,
+ };
+ let inc = if b <= 0x7F {
+ 1
+ } else if b <= 0b110_11111 {
+ 2
+ } else if b <= 0b1110_1111 {
+ 3
+ } else {
+ 4
+ };
+ i + inc
+}
+
+/// Decode a single UTF-8 sequence into a single Unicode codepoint from `src`.
+///
+/// If no valid UTF-8 sequence could be found, then `None` is returned.
+/// Otherwise, the decoded codepoint and the number of bytes read is returned.
+/// The number of bytes read (for a valid UTF-8 sequence) is guaranteed to be
+/// 1, 2, 3 or 4.
+///
+/// Note that a UTF-8 sequence is invalid if it is incorrect UTF-8, encodes a
+/// codepoint that is out of range (surrogate codepoints are out of range) or
+/// is not the shortest possible UTF-8 sequence for that codepoint.
+#[inline]
+pub fn decode_utf8(src: &[u8]) -> Option<(char, usize)> {
+ let b0 = match src.get(0) {
+ None => return None,
+ Some(&b) if b <= 0x7F => return Some((b as char, 1)),
+ Some(&b) => b,
+ };
+ match b0 {
+ 0b110_00000..=0b110_11111 => {
+ if src.len() < 2 {
+ return None;
+ }
+ let b1 = src[1];
+ if 0b11_000000 & b1 != TAG_CONT {
+ return None;
+ }
+ let cp = ((b0 & !TAG_TWO) as u32) << 6 | ((b1 & !TAG_CONT) as u32);
+ match cp {
+ 0x80..=0x7FF => char::from_u32(cp).map(|cp| (cp, 2)),
+ _ => None,
+ }
+ }
+ 0b1110_0000..=0b1110_1111 => {
+ if src.len() < 3 {
+ return None;
+ }
+ let (b1, b2) = (src[1], src[2]);
+ if 0b11_000000 & b1 != TAG_CONT {
+ return None;
+ }
+ if 0b11_000000 & b2 != TAG_CONT {
+ return None;
+ }
+ let cp = ((b0 & !TAG_THREE) as u32) << 12
+ | ((b1 & !TAG_CONT) as u32) << 6
+ | ((b2 & !TAG_CONT) as u32);
+ match cp {
+ // char::from_u32 will disallow surrogate codepoints.
+ 0x800..=0xFFFF => char::from_u32(cp).map(|cp| (cp, 3)),
+ _ => None,
+ }
+ }
+ 0b11110_000..=0b11110_111 => {
+ if src.len() < 4 {
+ return None;
+ }
+ let (b1, b2, b3) = (src[1], src[2], src[3]);
+ if 0b11_000000 & b1 != TAG_CONT {
+ return None;
+ }
+ if 0b11_000000 & b2 != TAG_CONT {
+ return None;
+ }
+ if 0b11_000000 & b3 != TAG_CONT {
+ return None;
+ }
+ let cp = ((b0 & !TAG_FOUR) as u32) << 18
+ | ((b1 & !TAG_CONT) as u32) << 12
+ | ((b2 & !TAG_CONT) as u32) << 6
+ | ((b3 & !TAG_CONT) as u32);
+ match cp {
+ 0x10000..=0x0010_FFFF => char::from_u32(cp).map(|cp| (cp, 4)),
+ _ => None,
+ }
+ }
+ _ => None,
+ }
+}
+
+/// Like `decode_utf8`, but decodes the last UTF-8 sequence in `src` instead
+/// of the first.
+pub fn decode_last_utf8(src: &[u8]) -> Option<(char, usize)> {
+ if src.is_empty() {
+ return None;
+ }
+ let mut start = src.len() - 1;
+ if src[start] <= 0x7F {
+ return Some((src[start] as char, 1));
+ }
+ while start > src.len().saturating_sub(4) {
+ start -= 1;
+ if is_start_byte(src[start]) {
+ break;
+ }
+ }
+ match decode_utf8(&src[start..]) {
+ None => None,
+ Some((_, n)) if n < src.len() - start => None,
+ Some((cp, n)) => Some((cp, n)),
+ }
+}
+
+fn is_start_byte(b: u8) -> bool {
+ b & 0b11_000000 != 0b1_0000000
+}
+
+#[cfg(test)]
+mod tests {
+ use std::str;
+
+ use quickcheck::quickcheck;
+
+ use super::{
+ decode_last_utf8, decode_utf8, TAG_CONT, TAG_FOUR, TAG_THREE, TAG_TWO,
+ };
+
+ #[test]
+ fn prop_roundtrip() {
+ fn p(given_cp: char) -> bool {
+ let mut tmp = [0; 4];
+ let encoded_len = given_cp.encode_utf8(&mut tmp).len();
+ let (got_cp, got_len) = decode_utf8(&tmp[..encoded_len]).unwrap();
+ encoded_len == got_len && given_cp == got_cp
+ }
+ quickcheck(p as fn(char) -> bool)
+ }
+
+ #[test]
+ fn prop_roundtrip_last() {
+ fn p(given_cp: char) -> bool {
+ let mut tmp = [0; 4];
+ let encoded_len = given_cp.encode_utf8(&mut tmp).len();
+ let (got_cp, got_len) =
+ decode_last_utf8(&tmp[..encoded_len]).unwrap();
+ encoded_len == got_len && given_cp == got_cp
+ }
+ quickcheck(p as fn(char) -> bool)
+ }
+
+ #[test]
+ fn prop_encode_matches_std() {
+ fn p(cp: char) -> bool {
+ let mut got = [0; 4];
+ let n = cp.encode_utf8(&mut got).len();
+ let expected = cp.to_string();
+ &got[..n] == expected.as_bytes()
+ }
+ quickcheck(p as fn(char) -> bool)
+ }
+
+ #[test]
+ fn prop_decode_matches_std() {
+ fn p(given_cp: char) -> bool {
+ let mut tmp = [0; 4];
+ let n = given_cp.encode_utf8(&mut tmp).len();
+ let (got_cp, _) = decode_utf8(&tmp[..n]).unwrap();
+ let expected_cp =
+ str::from_utf8(&tmp[..n]).unwrap().chars().next().unwrap();
+ got_cp == expected_cp
+ }
+ quickcheck(p as fn(char) -> bool)
+ }
+
+ #[test]
+ fn prop_decode_last_matches_std() {
+ fn p(given_cp: char) -> bool {
+ let mut tmp = [0; 4];
+ let n = given_cp.encode_utf8(&mut tmp).len();
+ let (got_cp, _) = decode_last_utf8(&tmp[..n]).unwrap();
+ let expected_cp = str::from_utf8(&tmp[..n])
+ .unwrap()
+ .chars()
+ .rev()
+ .next()
+ .unwrap();
+ got_cp == expected_cp
+ }
+ quickcheck(p as fn(char) -> bool)
+ }
+
+ #[test]
+ fn reject_invalid() {
+ // Invalid start byte
+ assert_eq!(decode_utf8(&[0xFF]), None);
+ // Surrogate pair
+ assert_eq!(decode_utf8(&[0xED, 0xA0, 0x81]), None);
+ // Invalid continuation byte.
+ assert_eq!(decode_utf8(&[0xD4, 0xC2]), None);
+ // Bad lengths
+ assert_eq!(decode_utf8(&[0xC3]), None); // 2 bytes
+ assert_eq!(decode_utf8(&[0xEF, 0xBF]), None); // 3 bytes
+ assert_eq!(decode_utf8(&[0xF4, 0x8F, 0xBF]), None); // 4 bytes
+ // Not a minimal UTF-8 sequence
+ assert_eq!(decode_utf8(&[TAG_TWO, TAG_CONT | b'a']), None);
+ assert_eq!(decode_utf8(&[TAG_THREE, TAG_CONT, TAG_CONT | b'a']), None);
+ assert_eq!(
+ decode_utf8(&[TAG_FOUR, TAG_CONT, TAG_CONT, TAG_CONT | b'a',]),
+ None
+ );
+ }
+
+ #[test]
+ fn reject_invalid_last() {
+ // Invalid start byte
+ assert_eq!(decode_last_utf8(&[0xFF]), None);
+ // Surrogate pair
+ assert_eq!(decode_last_utf8(&[0xED, 0xA0, 0x81]), None);
+ // Bad lengths
+ assert_eq!(decode_last_utf8(&[0xC3]), None); // 2 bytes
+ assert_eq!(decode_last_utf8(&[0xEF, 0xBF]), None); // 3 bytes
+ assert_eq!(decode_last_utf8(&[0xF4, 0x8F, 0xBF]), None); // 4 bytes
+ // Not a minimal UTF-8 sequence
+ assert_eq!(decode_last_utf8(&[TAG_TWO, TAG_CONT | b'a']), None);
+ assert_eq!(
+ decode_last_utf8(&[TAG_THREE, TAG_CONT, TAG_CONT | b'a',]),
+ None
+ );
+ assert_eq!(
+ decode_last_utf8(
+ &[TAG_FOUR, TAG_CONT, TAG_CONT, TAG_CONT | b'a',]
+ ),
+ None
+ );
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-03 00:11:42 +0000