Function utf8_prefix_at_or_before

src/text.rs:9–19

Small text-handling utilities shared across crates. Returns the longest prefix of `s` whose byte length does not exceed `max_bytes`, snapping back to the nearest preceding UTF-8 char boundary when the budget lands inside a multi-byte character. This is the safe replacement for `&s[..max_bytes]` when `s` may contain non-ASCII text and the caller has a byte budget rather than a char budget.

(s: &str, max_bytes: usize)

/// This is the safe replacement for `&s[..max_bytes]` when `s` may contain
/// non-ASCII text and the caller has a byte budget rather than a char budget.
pub fn utf8_prefix_at_or_before(s: &str, max_bytes: usize) -> &str {
    if s.len() <= max_bytes {
        return s;
    }

    let mut end = max_bytes;
    while !s.is_char_boundary(end) && end > 0 {
        end -= 1;
    }
    &s[..end]
}

#[cfg(test)]
mod tests {