ic-host-text 0.19.0

//! Escape untrusted scalar text without selecting terminal or colour policy.
use std::fmt::Write as _;

/// Escape terminal controls, Unicode line separators and bidirectional controls.
///
/// LF, CR and tab become visible `\n`, `\r` and `\t`; other unsafe characters
/// become `\u{hex}`. Printable Unicode and literal backslashes remain unchanged.
/// This is a presentation, not an identity-preserving or reversible encoding.
/// It performs no terminal detection, output, truncation or size admission.
#[must_use]
pub fn terminal_text(value: &str) -> String {
    let mut escaped = String::with_capacity(value.len());
    for character in value.chars() {
        match character {
            '\n' => escaped.push_str("\\n"),
            '\r' => escaped.push_str("\\r"),
            '\t' => escaped.push_str("\\t"),
            character
                if character.is_control()
                    || matches!(character, '\u{061c}' | '\u{200e}' | '\u{200f}'
                    | '\u{2028}'..='\u{202e}' | '\u{2066}'..='\u{2069}') =>
            {
                write!(escaped, "\\u{{{:x}}}", u32::from(character))
                    .expect("String writes cannot fail");
            }
            character => escaped.push(character),
        }
    }
    escaped
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn controls_cannot_create_terminal_commands_or_report_lines() {
        assert_eq!(
            terminal_text("a\n\r\t\0\x1b[31m\u{009b}\u{2028}\u{202e}\u{2069}"),
            "a\\n\\r\\t\\u{0}\\u{1b}[31m\\u{9b}\\u{2028}\\u{202e}\\u{2069}"
        );
    }

    #[test]
    fn printable_unicode_spaces_and_literal_backslashes_are_preserved() {
        let text = "  界 e\u{301} 👩‍💻 \\n  ";
        assert_eq!(terminal_text(text), text);
        assert_eq!(terminal_text(""), "");
    }
}