magi/

scrub.rs

//! Last-line scrub for text that lands on GitHub.
//!
//! The prompts tell agents not to put machine- or operator-identifying data
//! (hostnames, account names, IPs, home paths, emails, tokens) into pull
//! requests and issues, but a prompt is advisory. [`scrub`] is the enforced
//! half: shared rules used by the GitHub text posting gate.
//!
//! It scans the input left to right exactly once and pushes into a *separate*
//! output string, so a replacement is never scanned again (compare the
//! `blind::redact` loop, whose `[REDACTED]` contains the letters of the words it
//! hunted). It prefers missing something to mangling ordinary prose: repo-
//! relative paths, URLs, `std::io::Error`, `v1.2.3` and `@handle` all pass.

/// The local facts worth hiding. `Default` is "nothing known", which leaves only
/// the pattern-based rules.
#[derive(Debug, Clone, Default)]
pub struct Identity {
    /// Local account name.
    pub user: String,
    /// Machine hostname.
    pub host: String,
    /// Home directory path.
    pub home: String,
}

impl Identity {
    /// Read the current account, host and home directory. The only I/O here.
    pub fn current() -> Self {
        let env = |k: &str| std::env::var(k).ok().filter(|v| !v.trim().is_empty());
        let host = env("HOSTNAME")
            .or_else(|| env("COMPUTERNAME"))
            .or_else(|| {
                std::fs::read_to_string("/etc/hostname")
                    .ok()
                    .map(|s| s.trim().to_owned())
                    .filter(|s| !s.is_empty())
            })
            .unwrap_or_default();
        Self {
            user: env("USER").or_else(|| env("USERNAME")).unwrap_or_default(),
            host,
            home: dirs::home_dir()
                .map(|p| p.to_string_lossy().into_owned())
                .unwrap_or_default(),
        }
    }
}

const TOKEN_PREFIXES: [&str; 9] = [
    "AKIA",
    "github_pat_",
    "ghp_",
    "gho_",
    "ghs_",
    "ghu_",
    "sk-",
    "xoxb-",
    "xoxp-",
];
const TOKEN_MIN_TAIL: usize = 16;
/// Identity words shorter than this are too likely to be ordinary prose.
const MIN_IDENTITY_WORD: usize = 3;

fn is_word(c: char) -> bool {
    c.is_ascii_alphanumeric() || c == '_' || c == '-'
}

fn is_name(c: char) -> bool {
    c.is_alphanumeric() || matches!(c, '_' | '-' | '.')
}

fn is_email_local(c: char) -> bool {
    c.is_ascii_alphanumeric() || matches!(c, '.' | '_' | '%' | '+' | '-')
}

/// A path component: the name run minus trailing dots, which are punctuation.
fn name_len(s: &str) -> usize {
    s[..run(s, is_name)].trim_end_matches('.').len()
}

/// Length in bytes of the leading run of `s` whose chars satisfy `f`.
fn run(s: &str, f: impl Fn(char) -> bool) -> usize {
    s.char_indices()
        .find(|&(_, c)| !f(c))
        .map_or(s.len(), |(i, _)| i)
}

/// Replace machine- and operator-identifying data in `text`. Pure.
pub fn scrub(text: &str, id: &Identity) -> String {
    let mut out = String::with_capacity(text.len());
    let mut i = 0;
    while i < text.len() {
        let prev = text[..i].chars().next_back();
        if let Some((len, rep)) = match_at(&text[i..], prev, id) {
            out.push_str(rep);
            i += len;
        } else {
            let c = text[i..].chars().next().expect("i is on a char boundary");
            out.push(c);
            i += c.len_utf8();
        }
    }
    out
}

fn match_at(rest: &str, prev: Option<char>, id: &Identity) -> Option<(usize, &'static str)> {
    let starts_word = prev.is_none_or(|p| !is_word(p));
    home_path(rest, prev, id)
        .or_else(|| {
            starts_word
                .then(|| {
                    token(rest).or_else(|| credential(rest)).or_else(|| {
                        prev.is_none_or(|c| !is_name(c))
                            .then(|| named_identity(rest))
                            .flatten()
                    })
                })
                .flatten()
        })
        .or_else(|| absolute_path(rest, prev))
        .or_else(|| {
            prev.is_none_or(|p| !is_email_local(p))
                .then(|| email(rest))
                .flatten()
        })
        .or_else(|| {
            prev.is_none_or(|p| !p.is_ascii_alphanumeric() && p != '.' && p != ':')
                .then(|| ipv4(rest).or_else(|| ipv6(rest)))
                .flatten()
        })
        .or_else(|| starts_word.then(|| identity_word(rest, id)).flatten())
}

/// `/Users/x`, `/home/x`, `/root`, `C:\Users\x`, `C:/Users/x` and the literal
/// home directory, each collapsed to `~` so the repo-relative tail survives.
fn home_path(rest: &str, prev: Option<char>, id: &Identity) -> Option<(usize, &'static str)> {
    if prev.is_some_and(|p| p.is_ascii_alphanumeric() || matches!(p, '.' | '_' | '-' | '~')) {
        return None;
    }
    if id.home.len() > 1 && rest.starts_with(id.home.as_str()) {
        let tail = &rest[id.home.len()..];
        if tail.chars().next().is_none_or(|c| !is_name(c)) {
            return Some((id.home.len(), "~"));
        }
    }
    for base in ["/Users/", "/home/"] {
        if let Some(tail) = rest.strip_prefix(base) {
            let n = name_len(tail);
            if n > 0 {
                return Some((base.len() + n, "~"));
            }
        }
    }
    if let Some(tail) = rest.strip_prefix("/root")
        && tail.chars().next().is_none_or(|c| !is_word(c))
    {
        return Some(("/root".len(), "~"));
    }
    let b = rest.as_bytes();
    if b.len() > 9
        && b[0].is_ascii_alphabetic()
        && b[1] == b':'
        && matches!(b[2], b'\\' | b'/')
        && b[3..8].eq_ignore_ascii_case(b"users")
        && matches!(b[8], b'\\' | b'/')
    {
        let n = name_len(&rest[9..]);
        if n > 0 {
            return Some((9 + n, "~"));
        }
    }
    None
}

fn token(rest: &str) -> Option<(usize, &'static str)> {
    let prefix = TOKEN_PREFIXES.iter().find(|p| rest.starts_with(**p))?;
    let tail = run(&rest[prefix.len()..], is_word);
    (tail >= TOKEN_MIN_TAIL).then_some((prefix.len() + tail, "[redacted-token]"))
}

/// Explicit assignments avoid guessing whether an ordinary word is an account.
fn named_identity(rest: &str) -> Option<(usize, &'static str)> {
    for key in [
        "hostname=",
        "hostname: ",
        "username=",
        "username: ",
        "user=",
        "host=",
    ] {
        if rest
            .get(..key.len())
            .is_some_and(|prefix| prefix.eq_ignore_ascii_case(key))
        {
            let n = run(&rest[key.len()..], is_name);
            if n > 0 {
                return Some((key.len() + n, "[redacted-identity]"));
            }
        }
    }
    let n = name_len(rest);
    if n > 0
        && [".local", ".internal", ".lan"].iter().any(|suffix| {
            n.checked_sub(suffix.len())
                .and_then(|start| rest.get(start..n))
                .is_some_and(|tail| tail.eq_ignore_ascii_case(suffix))
        })
    {
        return Some((n, "[redacted-host]"));
    }
    None
}

/// `"password": "value"` and `'token':'value'`: the key is quoted, so the
/// unquoted `key=` / `key: ` forms below never match.
fn quoted_credential(rest: &str) -> Option<(usize, &'static str)> {
    for key in [
        "password", "token", "api_key", "api-key", "apikey", "secret",
    ] {
        let Some(after) = rest
            .get(..key.len())
            .filter(|p| p.eq_ignore_ascii_case(key))
            .map(|_| &rest[key.len()..])
        else {
            continue;
        };
        let Some(after_quote) = after.strip_prefix(['"', '\'']) else {
            continue;
        };
        let t = after_quote.trim_start();
        let Some(t) = t.strip_prefix([':', '=']) else {
            continue;
        };
        let t = t.trim_start();
        // A quoted value runs to its closing quote and may hold spaces or commas.
        let n = match t.chars().next() {
            Some(q @ ('"' | '\'')) => {
                let inner = &t[1..];
                let end = quoted_end(inner, q).unwrap_or(inner.len());
                1 + end + usize::from(end < inner.len())
            }
            _ => run(t, |c| {
                !c.is_whitespace() && !matches!(c, '`' | '<' | '>' | ',' | '}')
            }),
        };
        let value = t;
        if n > 0 {
            return Some((rest.len() - value.len() + n, "[redacted-token]"));
        }
    }
    None
}

/// Byte offset of the first `q` in `inner` that no backslash escapes.
fn quoted_end(inner: &str, q: char) -> Option<usize> {
    let mut chars = inner.char_indices();
    while let Some((i, c)) = chars.next() {
        if c == '\\' {
            chars.next();
        } else if c == q {
            return Some(i);
        }
    }
    None
}

fn credential(rest: &str) -> Option<(usize, &'static str)> {
    if let Some(hit) = quoted_credential(rest) {
        return Some(hit);
    }
    for key in [
        "password=",
        "token=",
        "api_key=",
        "api-key=",
        "password: ",
        "token: ",
        "api_key: ",
        "bearer ",
        "password ",
        "token ",
        "api key ",
    ] {
        if rest
            .get(..key.len())
            .is_some_and(|prefix| prefix.eq_ignore_ascii_case(key))
        {
            let tail = &rest[key.len()..];
            let padding = tail.len() - tail.trim_start_matches([' ', '\'', '"']).len();
            let value = &tail[padding..];
            let n = run(value, |c| {
                !c.is_whitespace() && !matches!(c, '`' | '<' | '>' | '"' | '\'')
            });
            let contextual = matches!(key, "password " | "token " | "api key ");
            let entropy = n >= 20
                && value[..n].bytes().any(|b| b.is_ascii_digit())
                && value[..n].bytes().any(|b| b.is_ascii_alphabetic());
            if n > 0 && (!contextual || entropy) {
                return Some((key.len() + padding + n, "[redacted-token]"));
            }
        }
    }
    None
}

fn absolute_path(rest: &str, prev: Option<char>) -> Option<(usize, &'static str)> {
    if prev.is_some_and(|c| c.is_alphanumeric() || matches!(c, '/' | ':' | '.' | '~')) {
        return None;
    }
    let b = rest.as_bytes();
    let windows =
        b.len() > 3 && b[0].is_ascii_alphabetic() && b[1] == b':' && matches!(b[2], b'/' | b'\\');
    // Known filesystem roots, rather than arbitrary slash-prefixed API routes.
    let unix = [
        "/tmp/",
        "/private/",
        "/var/",
        "/etc/",
        "/opt/",
        "/srv/",
        "/usr/",
        "/mnt/",
        "/Volumes/",
    ]
    .iter()
    .any(|root| rest.starts_with(root));
    if windows || unix {
        let n = run(rest, |c| {
            !c.is_whitespace() && !matches!(c, '`' | '"' | '\'' | '<' | '>')
        });
        return Some((n, "[redacted-path]"));
    }
    None
}

fn email(rest: &str) -> Option<(usize, &'static str)> {
    let local = run(rest, is_email_local);
    if local == 0 || !rest[local..].starts_with('@') {
        return None;
    }
    let domain = &rest[local + 1..];
    let mut end = 0;
    let mut labels = 0;
    loop {
        let n = run(&domain[end..], |c| c.is_ascii_alphanumeric() || c == '-');
        if n == 0 {
            break;
        }
        end += n;
        labels += 1;
        if domain[end..].starts_with('.')
            && run(&domain[end + 1..], |c| c.is_ascii_alphanumeric()) > 0
        {
            end += 1;
        } else {
            break;
        }
    }
    (labels >= 2).then_some((local + 1 + end, "[redacted-email]"))
}

fn ipv4(rest: &str) -> Option<(usize, &'static str)> {
    let mut len = 0;
    for part in 0..4 {
        let s = &rest[len..];
        let n = run(s, |c| c.is_ascii_digit());
        if n == 0 || n > 3 || s[..n].parse::<u16>().ok()? > 255 {
            return None;
        }
        len += n;
        if part < 3 {
            if !rest[len..].starts_with('.') {
                return None;
            }
            len += 1;
        }
    }
    let after = &rest[len..];
    let mut chars = after.chars();
    match chars.next() {
        Some(c) if c.is_ascii_alphanumeric() => return None,
        Some('.') if chars.next().is_some_and(|c| c.is_ascii_digit()) => return None,
        _ => {}
    }
    Some((len, "[redacted-ip]"))
}

fn ipv6(rest: &str) -> Option<(usize, &'static str)> {
    let mut n = run(rest, |c| c.is_ascii_hexdigit() || c == ':');
    // A trailing single colon is punctuation, not part of the address.
    while n > 0 && rest[..n].ends_with(':') && !rest[..n].ends_with("::") {
        n -= 1;
    }
    let cand = &rest[..n];
    let colons = cand.matches(':').count();
    let shaped = (cand.contains("::") && colons >= 2) || colons == 7;
    if !shaped
        || !cand.bytes().any(|b| b.is_ascii_digit())
        || cand.split(':').any(|g| g.len() > 4)
        || rest[n..]
            .chars()
            .next()
            .is_some_and(|c| c.is_ascii_alphanumeric())
    {
        return None;
    }
    Some((n, "[redacted-ip]"))
}

fn identity_word(rest: &str, id: &Identity) -> Option<(usize, &'static str)> {
    for (word, rep) in [(&id.user, "[redacted-user]"), (&id.host, "[redacted-host]")] {
        let w = word.trim();
        if w.len() < MIN_IDENTITY_WORD || rest.len() < w.len() || !rest.is_char_boundary(w.len()) {
            continue;
        }
        if rest[..w.len()].eq_ignore_ascii_case(w)
            && rest[w.len()..].chars().next().is_none_or(|c| !is_word(c))
        {
            return Some((w.len(), rep));
        }
    }
    None
}

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

    fn id() -> Identity {
        Identity {
            user: "alice".into(),
            host: "buildbox".into(),
            home: "/srv/people/alice".into(),
        }
    }

    fn s(t: &str) -> String {
        scrub(t, &id())
    }

    #[test]
    fn quoted_credentials_honor_escaped_quotes() {
        let out = s(r#"{"password":"prefix\"hunter2"} tail"#);
        assert!(!out.contains("hunter2") && !out.contains("prefix"), "{out}");
        assert!(out.ends_with("} tail"), "{out}");
        // An even run of backslashes leaves the quote as the closer.
        let out = s(r#"{"password":"a\\\\"} tail"#);
        assert!(out.ends_with("} tail") && !out.contains("a\\"), "{out}");
        // An odd run escapes it.
        let out = s(r#"{"password":"a\\\"hunter2"} tail"#);
        assert!(!out.contains("hunter2"), "{out}");
        let out = s(r#"{'token':'x\'hunter2'} tail"#);
        assert!(!out.contains("hunter2"), "{out}");
        let out = s(r#"{"password":"日本\"語hunter2"} tail"#);
        assert!(!out.contains("hunter2") && !out.contains('語'), "{out}");
        // No closing quote: everything after is removed.
        let out = s(r#"{"password":"abc\"hunter2"#);
        assert!(!out.contains("hunter2"), "{out}");
    }

    #[test]
    fn home_paths_collapse_and_keep_the_tail() {
        assert_eq!(s("see /Users/bob/src/x.rs now"), "see ~/src/x.rs now");
        assert_eq!(s("in /home/bob-1/.config"), "in ~/.config");
        assert_eq!(s("at C:\\Users\\Bob\\proj\\a.rs"), "at ~\\proj\\a.rs");
        assert_eq!(s("at C:/Users/Bob/proj"), "at ~/proj");
        assert_eq!(s("/root/x and /root."), "~/x and ~.");
        assert_eq!(s("/srv/people/alice/wt/a"), "~/wt/a");
    }

    #[test]
    fn emails_ips_and_tokens() {
        assert_eq!(s("mail dev.x+y@example.co.uk!"), "mail [redacted-email]!");
        assert_eq!(s("host 192.168.0.12:8080"), "host [redacted-ip]:8080");
        assert_eq!(
            s("v6 fe80::1 and ::1"),
            "v6 [redacted-ip] and [redacted-ip]"
        );
        assert_eq!(s("full 2001:db8:0:0:0:0:0:1."), "full [redacted-ip].");
        assert_eq!(
            s("tok ghp_abcdefghijklmnopqrstuv end"),
            "tok [redacted-token] end"
        );
    }

    #[test]
    fn identity_words_match_whole_words_only() {
        assert_eq!(
            s("by Alice on buildbox"),
            "by [redacted-user] on [redacted-host]"
        );
        assert_eq!(
            s("alicein wonderland, xbuildbox"),
            "alicein wonderland, xbuildbox"
        );
    }

    #[test]
    fn ordinary_text_is_untouched() {
        for t in [
            "Change src/graph.rs and tests/common/mod.rs.",
            "See https://github.com/o/r/pull/12 for #12",
            "returns std::io::Error, or a::b, Vec::new()",
            "released v1.2.3, version 0.41.1, 300.1.1.1",
            "thanks @coderabbitai; at 12:34:56 it ran",
            "/api/v1/runs; docs/home/x and ./Users/y",
            "A plain sentence about background and motivation.",
            "日本語のテキスト 🎉 with émoji",
        ] {
            assert_eq!(s(t), t);
        }
    }

    #[test]
    fn multibyte_input_does_not_panic_and_replacement_is_not_rescanned() {
        assert_eq!(
            s("C:\\日本語 and C:/日本"),
            "[redacted-path] and [redacted-path]"
        );
        assert_eq!(s("é/Users/bob/é 日本 alice"), "é~/é 日本 [redacted-user]");
        let once = s("/Users/bob 10.0.0.1 a@b.io alice");
        assert_eq!(scrub(&once, &Identity::default()), once);
        // A user named like the replacement text cannot loop or re-match.
        let odd = Identity {
            user: "redacted".into(),
            ..Identity::default()
        };
        assert_eq!(scrub("redacted x", &odd), "[redacted-user] x");
    }
}