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inbuxa-server/crates/features/src/mailflow/engine.rs
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jcoffey-dev c8280de9c3 DLP and mail flow rules: the rule model, the engine and the node cache
Phase 2e of the DLP and mail flow rules spec, in the features crate.

- rules.rs: a rule (§2.2) with its conditions (§2.3) and actions (§2.4),
  as JSON under R/r in the fork's subspace. validate() enforces the
  spec's shape: DLP rules check outgoing mail and have exactly one of
  block, warn or hold; transport rules have neither those nor
  detectors; lists, header names, header values (one line), addresses,
  texts, word lists, patterns and detector ids are checked.
- engine.rs: rules compiled once (word lists to automata, patterns to
  size-limited regexes) and run in priority order with exceptions and
  stop processing. Each detector runs at most once per message and
  only when a rule asks for it. The outcome lists what matched with
  each detector's count, and decides DLP strictest first: block, hold,
  warn; an override answers warnings only (§2.5).
- cache.rs: each node's compiled copy, refreshed after 30 seconds or at
  once when this node changes a rule.

Nothing calls this yet: the JMAP object and the check at DATA follow.
55 unit tests in mailflow.
2026-09-28 17:29:35 -07:00

696 lines
23 KiB
Rust

/*
* SPDX-FileCopyrightText: 2026 Coffey Labs
*
* SPDX-License-Identifier: AGPL-3.0-only
*/
//! Evaluating rules against a message (§2.1–§2.4). Rules are compiled once,
//! when they change: word lists become automata, patterns regexes. A message
//! is then checked against every enabled rule in order; each detector runs
//! at most once per message, and only when some rule asks for it.
//!
//! Pure: the caller parses the message, extracts attachment text
//! ([`super::extract`]) and knows the sender's groups and tenant. What comes
//! back is which rules matched, with each detector's count, and what DLP
//! decided; the matched text itself never leaves here (§2.7).
use super::{
detectors::{self, Findings},
extract::Extracted,
rules::{Action, Condition, Direction, Kind, Rule},
words::{Pattern, WordList},
};
use ahash::AHashMap;
use std::borrow::Cow;
/// Who sent a message, and to whom.
#[derive(Debug, Clone, Default)]
pub struct Envelope<'a> {
/// Outgoing (an authenticated sender) or incoming.
pub outgoing: bool,
pub sender: &'a str,
pub sender_groups: &'a [u32],
pub sender_tenant: Option<u32>,
pub recipients: Vec<Recipient<'a>>,
}
#[derive(Debug, Clone, Default)]
pub struct Recipient<'a> {
pub address: &'a str,
/// At a domain this server hosts.
pub local: bool,
pub groups: &'a [u32],
}
#[derive(Debug, Clone)]
pub struct Attachment<'a> {
pub name: Option<&'a str>,
/// Declared type, or detected where the caller knows better.
pub content_type: &'a str,
pub size: u64,
pub extracted: Extracted,
}
/// What rules look at.
#[derive(Debug, Clone, Default)]
pub struct Content<'a> {
pub subject: &'a str,
/// Each text and HTML part, as text.
pub bodies: Vec<Cow<'a, str>>,
pub headers: Vec<(&'a str, &'a str)>,
pub attachments: Vec<Attachment<'a>>,
pub size: u64,
/// Text past the inspection limit wasn't read.
pub truncated: bool,
}
impl Content<'_> {
fn texts(&self) -> impl Iterator<Item = &str> {
std::iter::once(self.subject)
.chain(self.bodies.iter().map(|b| b.as_ref()))
.chain(self.attachments.iter().filter_map(|a| match &a.extracted {
Extracted::Text(text) => Some(text.as_str()),
_ => None,
}))
}
fn cant_be_inspected(&self) -> bool {
self.truncated
|| self
.attachments
.iter()
.any(|a| matches!(a.extracted, Extracted::NotInspectable(_)))
}
}
enum Check {
Plain(Condition),
Words(WordList, u32),
Pattern(Pattern, u32),
Header {
name: String,
contains: Option<String>,
matches: Option<Pattern>,
},
AttachmentName(Pattern),
}
struct CompiledRule {
rule: Rule,
conditions: Vec<Check>,
exceptions: Vec<Check>,
}
/// The enabled rules, ready to run.
pub struct Compiled {
rules: Vec<CompiledRule>,
}
/// A rule reference, for notices and the audit record.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct RuleRef {
pub id: u32,
pub name: String,
pub notice: String,
}
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Match {
pub rule_id: u32,
pub name: String,
pub kind: Kind,
pub actions: Vec<Action>,
/// Each detector (or `words`, `pattern`) that counted, and its count.
pub counts: Vec<(String, usize)>,
}
#[derive(Debug, Default)]
pub struct Outcome {
pub matched: Vec<Match>,
pub blocks: Vec<RuleRef>,
pub holds: Vec<(RuleRef, bool)>,
pub warns: Vec<RuleRef>,
}
/// What DLP decided, strictest first (§2.4).
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Decision {
Pass,
Block(Vec<RuleRef>),
Hold {
rules: Vec<RuleRef>,
notify_sender: bool,
},
Warn(Vec<RuleRef>),
}
impl Outcome {
/// Block beats hold beats warn. An override (§2.5) answers the warnings
/// only: a block or hold still applies.
pub fn decision(&self, overridden: bool) -> Decision {
if !self.blocks.is_empty() {
Decision::Block(self.blocks.clone())
} else if !self.holds.is_empty() {
Decision::Hold {
rules: self.holds.iter().map(|(r, _)| r.clone()).collect(),
notify_sender: self.holds.iter().any(|(_, notify)| *notify),
}
} else if !self.warns.is_empty() && !overridden {
Decision::Warn(self.warns.clone())
} else {
Decision::Pass
}
}
}
fn compile_check(condition: &Condition) -> Result<Check, String> {
Ok(match condition {
Condition::Words { words, at_least } => Check::Words(WordList::new(words)?, *at_least),
Condition::Pattern { pattern, at_least } => {
Check::Pattern(Pattern::new(pattern)?, *at_least)
}
Condition::Header {
name,
contains,
matches,
} => Check::Header {
name: name.to_ascii_lowercase(),
contains: contains.as_ref().map(|c| c.to_lowercase()),
matches: matches.as_deref().map(Pattern::new).transpose()?,
},
Condition::AttachmentName { pattern } => Check::AttachmentName(Pattern::new(pattern)?),
other => Check::Plain(other.clone()),
})
}
impl Compiled {
/// Compiles the enabled rules; one that no longer compiles (a detector
/// renamed since it was saved) is skipped and named in the second list.
pub fn new(rules: &[Rule]) -> (Self, Vec<(u32, String)>) {
let mut compiled = Vec::new();
let mut skipped = Vec::new();
for rule in rules.iter().filter(|r| r.enabled) {
let result = rule.validate().map_err(|e| e.reason).and_then(|_| {
Ok(CompiledRule {
rule: rule.clone(),
conditions: rule
.conditions
.iter()
.map(compile_check)
.collect::<Result<_, _>>()?,
exceptions: rule
.exceptions
.iter()
.map(compile_check)
.collect::<Result<_, _>>()?,
})
});
match result {
Ok(c) => compiled.push(c),
Err(reason) => skipped.push((rule.id, reason)),
}
}
compiled.sort_by_key(|c| (c.rule.priority, c.rule.id));
(Self { rules: compiled }, skipped)
}
pub fn is_empty(&self) -> bool {
self.rules.is_empty()
}
/// Whether any rule could apply to mail going this way, so a caller can
/// skip parsing when none can.
pub fn applies_to(&self, outgoing: bool) -> bool {
self.rules
.iter()
.any(|c| direction_matches(c.rule.direction, outgoing))
}
pub fn evaluate(&self, envelope: &Envelope<'_>, content: &Content<'_>) -> Outcome {
let mut state = State {
content,
detected: AHashMap::new(),
};
let mut outcome = Outcome::default();
for compiled in &self.rules {
let rule = &compiled.rule;
if !direction_matches(rule.direction, envelope.outgoing) {
continue;
}
let mut counts = Vec::new();
let all_match = compiled
.conditions
.iter()
.all(|check| state.check(check, envelope, &mut counts));
if !all_match {
continue;
}
let mut ignored = Vec::new();
if compiled
.exceptions
.iter()
.any(|check| state.check(check, envelope, &mut ignored))
{
continue;
}
for action in &rule.actions {
let reference = |notice: &str| RuleRef {
id: rule.id,
name: rule.name.clone(),
notice: notice.to_string(),
};
match action {
Action::Block { notice } => outcome.blocks.push(reference(notice)),
Action::Hold {
notice,
notify_sender,
} => outcome.holds.push((reference(notice), *notify_sender)),
Action::Warn { notice } => outcome.warns.push(reference(notice)),
_ => {}
}
}
outcome.matched.push(Match {
rule_id: rule.id,
name: rule.name.clone(),
kind: rule.kind,
actions: rule.actions.clone(),
counts,
});
if rule.stop_processing {
break;
}
}
outcome
}
}
fn direction_matches(direction: Direction, outgoing: bool) -> bool {
match direction {
Direction::Any => true,
Direction::Outgoing => outgoing,
Direction::Incoming => !outgoing,
}
}
fn domain_of(address: &str) -> &str {
address.rsplit_once('@').map_or("", |(_, d)| d)
}
fn in_list(value: &str, list: &[String]) -> bool {
list.iter().any(|v| v.eq_ignore_ascii_case(value))
}
struct State<'c, 'a> {
content: &'c Content<'a>,
/// Each detector's count, run once per message.
detected: AHashMap<&'static str, usize>,
}
impl State<'_, '_> {
fn detector_count(&mut self, id: &str) -> usize {
let Some(detector) = detectors::by_id(id) else {
return 0;
};
if let Some(count) = self.detected.get(detector.id) {
return *count;
}
let mut findings = Findings::default();
for text in self.content.texts() {
detector.find(text, &mut findings);
}
self.detected.insert(detector.id, findings.len());
findings.len()
}
fn check(
&mut self,
check: &Check,
envelope: &Envelope<'_>,
counts: &mut Vec<(String, usize)>,
) -> bool {
let content = self.content;
match check {
Check::Words(list, at_least) => {
let n: usize = content.texts().map(|t| list.count(t)).sum();
counts.push(("words".into(), n));
n >= *at_least as usize
}
Check::Pattern(pattern, at_least) => {
let n: usize = content.texts().map(|t| pattern.count(t)).sum();
counts.push(("pattern".into(), n));
n >= *at_least as usize
}
Check::Header {
name,
contains,
matches,
} => content
.headers
.iter()
.filter(|(n, _)| n.eq_ignore_ascii_case(name))
.any(|(_, value)| match (contains, matches) {
(Some(needle), _) => value.to_lowercase().contains(needle.as_str()),
(_, Some(pattern)) => pattern.count(value) > 0,
_ => true,
}),
Check::AttachmentName(pattern) => content
.attachments
.iter()
.any(|a| a.name.is_some_and(|n| pattern.count(n) > 0)),
Check::Plain(condition) => match condition {
Condition::SenderAddress { addresses } => in_list(envelope.sender, addresses),
Condition::SenderDomain { domains } => in_list(domain_of(envelope.sender), domains),
Condition::SenderGroup { groups } => {
envelope.sender_groups.iter().any(|g| groups.contains(g))
}
Condition::SenderTenant { tenants } => {
envelope.sender_tenant.is_some_and(|t| tenants.contains(&t))
}
Condition::RecipientAddress { addresses } => envelope
.recipients
.iter()
.any(|r| in_list(r.address, addresses)),
Condition::RecipientDomain { domains } => envelope
.recipients
.iter()
.any(|r| in_list(domain_of(r.address), domains)),
Condition::RecipientGroup { groups } => envelope
.recipients
.iter()
.any(|r| r.groups.iter().any(|g| groups.contains(g))),
Condition::RecipientOutside => envelope.recipients.iter().any(|r| !r.local),
Condition::AttachmentType { types } => content.attachments.iter().any(|a| {
let ct = a.content_type.to_ascii_lowercase();
types
.iter()
.any(|t| ct.starts_with(&t.to_ascii_lowercase()))
}),
Condition::AttachmentExtension { extensions } => {
content.attachments.iter().any(|a| {
a.name
.and_then(|n| n.rsplit_once('.'))
.is_some_and(|(_, ext)| {
extensions
.iter()
.any(|e| e.trim_start_matches('.').eq_ignore_ascii_case(ext))
})
})
}
Condition::AttachmentSizeOver { bytes } => {
content.attachments.iter().any(|a| a.size > *bytes)
}
Condition::AttachmentCountOver { count } => {
content.attachments.len() > *count as usize
}
Condition::CantBeInspected => content.cant_be_inspected(),
Condition::MessageSizeOver { bytes } => content.size > *bytes,
Condition::Detected { detectors } => {
let mut any = false;
for d in detectors {
let n = self.detector_count(&d.id);
counts.push((d.id.clone(), n));
any |= n >= d.at_least as usize;
}
any
}
// Compiled into their own checks
Condition::Words { .. }
| Condition::Pattern { .. }
| Condition::Header { .. }
| Condition::AttachmentName { .. } => false,
},
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::mailflow::{
extract::Why,
rules::{DetectorMin, Position},
};
fn rule(id: u32, kind: Kind, conditions: Vec<Condition>, action: Action) -> Rule {
Rule {
id,
name: format!("rule {id}"),
description: String::new(),
kind,
enabled: true,
priority: id as i32,
direction: if kind == Kind::Dlp {
Direction::Outgoing
} else {
Direction::Any
},
conditions,
exceptions: vec![],
actions: vec![action],
stop_processing: false,
created_by: String::new(),
created_at: 0,
updated_at: 0,
}
}
fn envelope(outside: bool) -> Envelope<'static> {
Envelope {
outgoing: true,
sender: "[email protected]",
sender_groups: &[7],
sender_tenant: None,
recipients: vec![Recipient {
address: if outside {
"[email protected]"
} else {
"[email protected]"
},
local: !outside,
groups: &[],
}],
}
}
fn cards(n: usize) -> Content<'static> {
let body: String = [
"4242 4242 4242 4242",
"5555-5555-5555-4444",
"378282246310005",
"6011111111111117",
"3566002020360505",
]
.iter()
.take(n)
.map(|c| format!("card {c}\n"))
.collect();
Content {
subject: "Numbers",
bodies: vec![body.into()],
..Default::default()
}
}
fn five_cards_outside(action: Action) -> Rule {
rule(
1,
Kind::Dlp,
vec![
Condition::RecipientOutside,
Condition::Detected {
detectors: vec![DetectorMin {
id: "payment-card".into(),
at_least: 5,
}],
},
],
action,
)
}
#[test]
fn detector_threshold_and_recipients() {
let (rules, skipped) = Compiled::new(&[five_cards_outside(Action::Hold {
notice: "Held".into(),
notify_sender: true,
})]);
assert!(skipped.is_empty());
let outcome = rules.evaluate(&envelope(true), &cards(5));
assert_eq!(
outcome.matched[0].counts,
vec![("payment-card".to_string(), 5)]
);
assert!(matches!(
outcome.decision(false),
Decision::Hold {
notify_sender: true,
..
}
));
// Four cards, or everyone inside: nothing
assert_eq!(
rules.evaluate(&envelope(true), &cards(4)).decision(false),
Decision::Pass
);
assert_eq!(
rules.evaluate(&envelope(false), &cards(5)).decision(false),
Decision::Pass
);
}
#[test]
fn strictest_wins_and_override_answers_warnings_only() {
let warn = five_cards_outside(Action::Warn {
notice: "Sure?".into(),
});
let mut block = five_cards_outside(Action::Block {
notice: "No".into(),
});
block.id = 2;
let (rules, _) = Compiled::new(&[warn.clone(), block]);
let outcome = rules.evaluate(&envelope(true), &cards(5));
assert!(matches!(outcome.decision(true), Decision::Block(_)));
let (rules, _) = Compiled::new(&[warn]);
let outcome = rules.evaluate(&envelope(true), &cards(5));
assert!(matches!(outcome.decision(false), Decision::Warn(ref w) if w[0].notice == "Sure?"));
assert_eq!(outcome.decision(true), Decision::Pass);
}
#[test]
fn exceptions_order_and_stop_processing() {
let disclaimer = |id| {
rule(
id,
Kind::Transport,
vec![Condition::RecipientOutside],
Action::AddDisclaimer {
text: "t".into(),
html: None,
position: Position::Bottom,
},
)
};
let mut first = disclaimer(1);
first.stop_processing = true;
let (rules, _) = Compiled::new(&[disclaimer(2), first.clone()]);
let outcome = rules.evaluate(&envelope(true), &cards(0));
assert_eq!(
outcome
.matched
.iter()
.map(|m| m.rule_id)
.collect::<Vec<_>>(),
vec![1]
);
first.stop_processing = false;
first.exceptions = vec![Condition::SenderGroup { groups: vec![7] }];
let (rules, _) = Compiled::new(&[disclaimer(2), first]);
let outcome = rules.evaluate(&envelope(true), &cards(0));
assert_eq!(
outcome
.matched
.iter()
.map(|m| m.rule_id)
.collect::<Vec<_>>(),
vec![2]
);
}
#[test]
fn content_conditions() {
let content = Content {
subject: "Project Falcon",
bodies: vec!["see attached".into()],
headers: vec![("X-Class", "Internal only")],
attachments: vec![
Attachment {
name: Some("plan.docx"),
content_type: "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
size: 40_000,
extracted: Extracted::Text("IBAN GB29 NWBK 6016 1331 9268 19".into()),
},
Attachment {
name: Some("scan.pdf"),
content_type: "application/pdf",
size: 900_000,
extracted: Extracted::NotInspectable(Why::Pdf),
},
],
size: 1_000_000,
truncated: false,
};
let block = || Action::Block { notice: "n".into() };
let checks = [
(
Condition::Words {
words: vec!["project falcon".into()],
at_least: 1,
},
true,
),
(
Condition::Header {
name: "x-class".into(),
contains: Some("internal".into()),
matches: None,
},
true,
),
(
Condition::AttachmentExtension {
extensions: vec![".PDF".into()],
},
true,
),
(
Condition::AttachmentType {
types: vec!["image/".into()],
},
false,
),
(Condition::AttachmentSizeOver { bytes: 500_000 }, true),
(Condition::AttachmentCountOver { count: 2 }, false),
(Condition::CantBeInspected, true),
(Condition::MessageSizeOver { bytes: 2_000_000 }, false),
(
Condition::Detected {
detectors: vec![DetectorMin {
id: "iban".into(),
at_least: 1,
}],
},
true,
),
(
Condition::SenderDomain {
domains: vec!["EXAMPLE.com".into()],
},
true,
),
];
for (condition, expected) in checks {
let (rules, skipped) =
Compiled::new(&[rule(1, Kind::Dlp, vec![condition.clone()], block())]);
assert!(skipped.is_empty(), "{condition:?}");
let matched = !rules.evaluate(&envelope(true), &content).matched.is_empty();
assert_eq!(matched, expected, "{condition:?}");
}
}
#[test]
fn direction_and_disabled_rules() {
let mut r = five_cards_outside(Action::Block { notice: "n".into() });
let (rules, _) = Compiled::new(std::slice::from_ref(&r));
assert!(rules.applies_to(true) && !rules.applies_to(false));
let mut incoming = envelope(true);
incoming.outgoing = false;
assert_eq!(
rules.evaluate(&incoming, &cards(5)).decision(false),
Decision::Pass
);
r.enabled = false;
assert!(Compiled::new(&[r]).0.is_empty());
}
}