ai-usagebar 1.0.3

//! Sanitization for text that crosses an untrusted data boundary into a UI.
//!
//! Vendor responses and cached diagnostics are data, not terminal programs.
//! Keep ordinary Unicode and line breaks, but remove terminal control bytes
//! before the text is persisted or handed to Pango/ratatui/ANSI renderers.

/// Generous bound for one remote label or diagnostic field. Legitimate values
/// are normally a few dozen characters; the cap prevents a valid-but-hostile
/// JSON response from turning one UI cell or cache sidecar into megabytes.
pub const MAX_UNTRUSTED_FIELD_CHARS: usize = 4 * 1024;

/// Strip terminal control characters while preserving readable line layout.
///
/// Newlines are safe and useful in diagnostics. Tabs and carriage returns are
/// normalized to spaces; every other Unicode control character (including ESC,
/// BEL, DEL, and C1 controls) is removed. Invisible bidirectional markers and
/// overrides are also removed so an untrusted label cannot visually reorder
/// neighboring UI text. The result is capped by character, not byte, so UTF-8
/// is never split.
pub fn sanitize_untrusted_field(value: &str) -> String {
    value
        .chars()
        .filter_map(|ch| match ch {
            '\n' => Some('\n'),
            '\t' | '\r' => Some(' '),
            _ if ch.is_control() || is_bidi_control(ch) => None,
            _ => Some(ch),
        })
        .take(MAX_UNTRUSTED_FIELD_CHARS)
        .collect()
}

fn is_bidi_control(ch: char) -> bool {
    matches!(
        ch,
        '\u{200e}' | '\u{200f}' | '\u{202a}'..='\u{202e}' | '\u{2066}'..='\u{2069}'
    )
}

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

    #[test]
    fn strips_terminal_sequences_but_keeps_text_and_newlines() {
        let input = "before\x1b]52;c;Y2xpcGJvYXJk\x07after\nnext\tcolumn\rreturn\u{202e}spoof";
        assert_eq!(
            sanitize_untrusted_field(input),
            "before]52;c;Y2xpcGJvYXJkafter\nnext column returnspoof"
        );
    }

    #[test]
    fn caps_untrusted_fields_without_splitting_unicode() {
        let input = "é".repeat(MAX_UNTRUSTED_FIELD_CHARS + 10);
        let output = sanitize_untrusted_field(&input);
        assert_eq!(output.chars().count(), MAX_UNTRUSTED_FIELD_CHARS);
        assert!(output.chars().all(|ch| ch == 'é'));
    }
}