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/// A type that provides a human readable debug impl for arbitrary bytes.
///
/// This generally works best when the bytes are presumed to be mostly UTF-8,
/// but will work for anything.
///
/// N.B. This is copied nearly verbatim from regex-automata. Sigh.
pub(crate) struct Bytes<'a>(pub(crate) &'a [u8]);
impl<'a> core::fmt::Debug for Bytes<'a> {
fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
write!(f, "\"")?;
// This is a sad re-implementation of a similar impl found in bstr.
let mut bytes = self.0;
while let Some(result) = utf8_decode(bytes) {
let ch = match result {
Ok(ch) => ch,
Err(byte) => {
write!(f, r"\x{:02x}", byte)?;
bytes = &bytes[1..];
continue;
}
};
bytes = &bytes[ch.len_utf8()..];
match ch {
'\0' => write!(f, "\\0")?,
// ASCII control characters except \0, \n, \r, \t
'\x01'..='\x08'
| '\x0b'
| '\x0c'
| '\x0e'..='\x19'
| '\x7f' => {
write!(f, "\\x{:02x}", u32::from(ch))?;
}
'\n' | '\r' | '\t' | _ => {
write!(f, "{}", ch.escape_debug())?;
}
}
}
write!(f, "\"")?;
Ok(())
}
}
/// Decodes the next UTF-8 encoded codepoint from the given byte slice.
///
/// If no valid encoding of a codepoint exists at the beginning of the given
/// byte slice, then the first byte is returned instead.
///
/// This returns `None` if and only if `bytes` is empty.
pub(crate) fn utf8_decode(bytes: &[u8]) -> Option<Result<char, u8>> {
fn len(byte: u8) -> Option<usize> {
if byte <= 0x7F {
return Some(1);
} else if byte & 0b1100_0000 == 0b1000_0000 {
return None;
} else if byte <= 0b1101_1111 {
Some(2)
} else if byte <= 0b1110_1111 {
Some(3)
} else if byte <= 0b1111_0111 {
Some(4)
} else {
None
}
}
if bytes.is_empty() {
return None;
}
let len = match len(bytes[0]) {
None => return Some(Err(bytes[0])),
Some(len) if len > bytes.len() => return Some(Err(bytes[0])),
Some(1) => return Some(Ok(char::from(bytes[0]))),
Some(len) => len,
};
match core::str::from_utf8(&bytes[..len]) {
Ok(s) => Some(Ok(s.chars().next().unwrap())),
Err(_) => Some(Err(bytes[0])),
}
}
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