tor_circmgr/
isolation.rs

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1//! Types related to stream isolation
2use downcast_rs::{impl_downcast, Downcast};
3use dyn_clone::{clone_trait_object, DynClone};
4use std::sync::atomic::{AtomicU64, Ordering};
5
6/// A type that can make isolation decisions about streams it is attached to.
7///
8/// Types that implement `Isolation` contain properties about a stream that are
9/// used to make decisions about whether that stream can share the same circuit
10/// as other streams. You may pass in any type implementing `Isolation` when
11/// creating a stream via `TorClient::connect_with_prefs`, or constructing a
12/// circuit with [`CircMgr::get_or_launch_exit()`](crate::CircMgr::get_or_launch_exit).
13///
14/// You typically do not want to implement this trait directly.  Instead, most
15/// users should implement [`IsolationHelper`].
16pub trait Isolation:
17    seal::Sealed + Downcast + DynClone + std::fmt::Debug + Send + Sync + 'static
18{
19    /// Return true if this Isolation is compatible with another.
20    ///
21    /// Two streams may share a circuit if and only if they have compatible
22    /// `Isolation`s.
23    ///
24    /// # Requirements
25    ///
26    /// For correctness, this relation must be symmetrical and reflexive:
27    /// `self.compatible(other)` must equal `other.compatible(self)`, and
28    /// `self.compatible(self)` must be true.
29    ///
30    /// For correctness, this function must always give the same result as
31    /// `self.join(other).is_some()`.
32    ///
33    /// This relationship does **not** have to be transitive: it's possible that
34    /// stream A can share a circuit with either stream B or stream C, but not
35    /// with both.
36    fn compatible(&self, other: &dyn Isolation) -> bool;
37
38    /// Join two [`Isolation`] into the intersection of what each allows.
39    ///
40    /// A circuit's isolation is the `join` of the isolation values of all of
41    /// the streams that have _ever_ used that circuit.  A circuit's isolation
42    /// can never be `None`: streams that would cause it to be `None` can't be
43    /// attached to the circuit.
44    ///
45    /// When a stream is added to a circuit, `join` is used to calculate the
46    /// circuit's new isolation.
47    ///
48    /// # Requirements
49    ///
50    /// For correctness, this function must be commutative: `self.join(other)`
51    /// must equal `other.join(self)`.  Also, it must be idempotent:
52    /// `self.join(self)` must equal self.
53    //
54    // TODO: (This function probably should be associative too, but we haven't done
55    // all the math.)
56    fn join(&self, other: &dyn Isolation) -> Option<Box<dyn Isolation>>;
57}
58
59/// Seal preventing implementation of Isolation not relying on IsolationHelper
60mod seal {
61    /// Seal preventing implementation of Isolation not relying on IsolationHelper
62    pub trait Sealed {}
63    impl<T: super::IsolationHelper> Sealed for T {}
64}
65
66impl_downcast!(Isolation);
67clone_trait_object!(Isolation);
68impl<T: Isolation> From<T> for Box<dyn Isolation> {
69    fn from(isolation: T) -> Self {
70        Box::new(isolation)
71    }
72}
73
74impl<T: IsolationHelper + Clone + std::fmt::Debug + Send + Sync + 'static> Isolation for T {
75    fn compatible(&self, other: &dyn Isolation) -> bool {
76        if let Some(other) = other.as_any().downcast_ref() {
77            self.compatible_same_type(other)
78        } else {
79            false
80        }
81    }
82
83    fn join(&self, other: &dyn Isolation) -> Option<Box<dyn Isolation>> {
84        if let Some(other) = other.as_any().downcast_ref() {
85            self.join_same_type(other)
86                .map(|res| Box::new(res) as Box<dyn Isolation>)
87        } else {
88            None
89        }
90    }
91}
92
93/// Trait to help implement [`Isolation`].
94///
95/// You should generally implement this trait whenever you need to implement a
96/// new set of stream isolation rules: it takes care of down-casting and type
97/// checking for you.
98///
99/// When you implement this trait for some type T, isolation objects of that
100/// type will be incompatible (unable to share circuits) with objects of _any
101/// other type_.  (That's usually what you want; if you're defining a new type
102/// of Isolation rules, then you probably don't want streams using different
103/// rules to share circuits with yours.)
104pub trait IsolationHelper: Sized {
105    /// Returns whether self and other are compatible.
106    ///
107    /// Two streams may share a circuit if and only if they have compatible
108    /// `Isolation`s.
109    ///
110    /// (See [`Isolation::compatible`] for more information and requirements.)
111    fn compatible_same_type(&self, other: &Self) -> bool;
112
113    /// Join self and other into the intersection of what they allows.
114    ///
115    /// (See [`Isolation::join`] for more information and requirements.)
116    fn join_same_type(&self, other: &Self) -> Option<Self>;
117}
118
119/// A token used to isolate unrelated streams on different circuits.
120///
121/// When two streams are associated with different isolation tokens, they
122/// can never share the same circuit.
123///
124/// Tokens created with [`IsolationToken::new`] are all different from
125/// one another, and different from tokens created with
126/// [`IsolationToken::no_isolation`]. However, tokens created with
127/// [`IsolationToken::no_isolation`] are all equal to one another.
128///
129/// # Examples
130///
131/// Creating distinct isolation tokens:
132///
133/// ```rust
134/// # use tor_circmgr::IsolationToken;
135/// let token_1 = IsolationToken::new();
136/// let token_2 = IsolationToken::new();
137///
138/// assert_ne!(token_1, token_2);
139///
140/// // Demonstrating the behaviour of no_isolation() tokens:
141/// assert_ne!(token_1, IsolationToken::no_isolation());
142/// assert_eq!(IsolationToken::no_isolation(), IsolationToken::no_isolation());
143/// ```
144///
145/// Using an isolation token to route streams differently over the Tor network:
146///
147/// ```ignore
148/// use arti_client::StreamPrefs;
149///
150/// let token_1 = IsolationToken::new();
151/// let token_2 = IsolationToken::new();
152///
153/// let mut prefs_1 = StreamPrefs::new();
154/// prefs_1.set_isolation(token_1);
155///
156/// let mut prefs_2 = StreamPrefs::new();
157/// prefs_2.set_isolation(token_2);
158///
159/// // These two connections will come from different source IP addresses.
160/// tor_client.connect(("example.com", 80), Some(prefs_1)).await?;
161/// tor_client.connect(("example.com", 80), Some(prefs_2)).await?;
162/// ```
163// # Semver note
164//
165// This type is re-exported by `arti-client`: any changes to it must be
166// reflected in `arti-client`'s version.
167#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
168pub struct IsolationToken(u64);
169
170#[allow(clippy::new_without_default)]
171impl IsolationToken {
172    /// Create a new IsolationToken, unequal to any other token this function
173    /// has created.
174    ///
175    /// # Panics
176    ///
177    /// Panics if we have already allocated 2^64 isolation tokens: in that
178    /// case, we have exhausted the space of possible tokens, and it is
179    /// no longer possible to ensure isolation.
180    pub fn new() -> Self {
181        /// Internal counter used to generate different tokens each time
182        static COUNTER: AtomicU64 = AtomicU64::new(1);
183        // Ordering::Relaxed is fine because we don't care about causality, we just want a
184        // different number each time
185        let token = COUNTER.fetch_add(1, Ordering::Relaxed);
186        assert!(token < u64::MAX);
187        IsolationToken(token)
188    }
189
190    /// Create a new IsolationToken equal to every other token created
191    /// with this function, but different from all tokens created with
192    /// `new`.
193    ///
194    /// This can be used when no isolation is wanted for some streams.
195    pub fn no_isolation() -> Self {
196        IsolationToken(0)
197    }
198}
199
200impl IsolationHelper for IsolationToken {
201    fn compatible_same_type(&self, other: &Self) -> bool {
202        self == other
203    }
204    fn join_same_type(&self, other: &Self) -> Option<Self> {
205        if self.compatible_same_type(other) {
206            Some(*self)
207        } else {
208            None
209        }
210    }
211}
212
213/// Helper macro to implement IsolationHelper for tuple of IsolationHelper
214macro_rules! tuple_impls {
215    ($(
216        $Tuple:ident {
217            $(($idx:tt) -> $T:ident)+
218        }
219    )+) => {
220        $(
221            impl<$($T:IsolationHelper),+> IsolationHelper for ($($T,)+) {
222                fn compatible_same_type(&self, other: &Self) -> bool {
223                    $(self.$idx.compatible_same_type(&other.$idx))&&+
224                }
225
226                fn join_same_type(&self, other: &Self) -> Option<Self> {
227                    Some((
228                    $(self.$idx.join_same_type(&other.$idx)?,)+
229                    ))
230                }
231            }
232        )+
233    }
234}
235
236tuple_impls! {
237    Tuple1 {
238        (0) -> A
239    }
240    Tuple2 {
241        (0) -> A
242        (1) -> B
243    }
244    Tuple3 {
245        (0) -> A
246        (1) -> B
247        (2) -> C
248    }
249    Tuple4 {
250        (0) -> A
251        (1) -> B
252        (2) -> C
253        (3) -> D
254    }
255    Tuple5 {
256        (0) -> A
257        (1) -> B
258        (2) -> C
259        (3) -> D
260        (4) -> E
261    }
262    Tuple6 {
263        (0) -> A
264        (1) -> B
265        (2) -> C
266        (3) -> D
267        (4) -> E
268        (5) -> F
269    }
270    Tuple7 {
271        (0) -> A
272        (1) -> B
273        (2) -> C
274        (3) -> D
275        (4) -> E
276        (5) -> F
277        (6) -> G
278    }
279    Tuple8 {
280        (0) -> A
281        (1) -> B
282        (2) -> C
283        (3) -> D
284        (4) -> E
285        (5) -> F
286        (6) -> G
287        (7) -> H
288    }
289    Tuple9 {
290        (0) -> A
291        (1) -> B
292        (2) -> C
293        (3) -> D
294        (4) -> E
295        (5) -> F
296        (6) -> G
297        (7) -> H
298        (8) -> I
299    }
300    Tuple10 {
301        (0) -> A
302        (1) -> B
303        (2) -> C
304        (3) -> D
305        (4) -> E
306        (5) -> F
307        (6) -> G
308        (7) -> H
309        (8) -> I
310        (9) -> J
311    }
312    Tuple11 {
313        (0) -> A
314        (1) -> B
315        (2) -> C
316        (3) -> D
317        (4) -> E
318        (5) -> F
319        (6) -> G
320        (7) -> H
321        (8) -> I
322        (9) -> J
323        (10) -> K
324    }
325    Tuple12 {
326        (0) -> A
327        (1) -> B
328        (2) -> C
329        (3) -> D
330        (4) -> E
331        (5) -> F
332        (6) -> G
333        (7) -> H
334        (8) -> I
335        (9) -> J
336        (10) -> K
337        (11) -> L
338    }
339}
340
341/// A set of information about how a stream should be isolated.
342///
343/// If two streams are isolated from one another, they may not share
344/// a circuit.
345#[derive(Clone, Debug, derive_builder::Builder)]
346pub struct StreamIsolation {
347    /// Any isolation set on the stream.
348    #[builder(default = "Box::new(IsolationToken::no_isolation())")]
349    stream_isolation: Box<dyn Isolation>,
350    /// Any additional isolation token set on an object that "owns" this
351    /// stream.  This is typically owned by a `TorClient`.
352    #[builder(default = "IsolationToken::no_isolation()")]
353    owner_token: IsolationToken,
354}
355
356impl StreamIsolation {
357    /// Construct a new StreamIsolation with no isolation enabled.
358    pub fn no_isolation() -> Self {
359        StreamIsolationBuilder::new()
360            .build()
361            .expect("Bug constructing StreamIsolation")
362    }
363
364    /// Return a new StreamIsolationBuilder for constructing
365    /// StreamIsolation objects.
366    pub fn builder() -> StreamIsolationBuilder {
367        StreamIsolationBuilder::new()
368    }
369}
370
371impl IsolationHelper for StreamIsolation {
372    fn compatible_same_type(&self, other: &StreamIsolation) -> bool {
373        self.owner_token == other.owner_token
374            && self
375                .stream_isolation
376                .compatible(other.stream_isolation.as_ref())
377    }
378
379    fn join_same_type(&self, other: &StreamIsolation) -> Option<StreamIsolation> {
380        if self.owner_token != other.owner_token {
381            return None;
382        }
383        self.stream_isolation
384            .join(other.stream_isolation.as_ref())
385            .map(|stream_isolation| StreamIsolation {
386                stream_isolation,
387                owner_token: self.owner_token,
388            })
389    }
390}
391
392impl StreamIsolationBuilder {
393    /// Construct a builder with no items set.
394    pub fn new() -> Self {
395        StreamIsolationBuilder::default()
396    }
397}
398
399#[cfg(test)]
400pub(crate) mod test {
401    #![allow(clippy::unwrap_used)]
402    use super::*;
403
404    /// Trait for testing use only. Much like PartialEq, but for type containing an dyn Isolation
405    /// which is known to be an IsolationToken.
406    pub(crate) trait IsolationTokenEq {
407        /// Compare two values, returning true if they are equals and all dyn Isolation they contain
408        /// are IsolationToken (which are equal too).
409        fn isol_eq(&self, other: &Self) -> bool;
410    }
411
412    macro_rules! assert_isoleq {
413        { $arg1:expr, $arg2:expr } => {
414            assert!($arg1.isol_eq(&$arg2))
415        }
416    }
417    pub(crate) use assert_isoleq;
418
419    impl IsolationTokenEq for IsolationToken {
420        fn isol_eq(&self, other: &Self) -> bool {
421            self == other
422        }
423    }
424
425    impl<T: IsolationTokenEq> IsolationTokenEq for Option<T> {
426        fn isol_eq(&self, other: &Self) -> bool {
427            match (self, other) {
428                (Some(this), Some(other)) => this.isol_eq(other),
429                (None, None) => true,
430                _ => false,
431            }
432        }
433    }
434
435    impl<T: IsolationTokenEq + std::fmt::Debug> IsolationTokenEq for Vec<T> {
436        fn isol_eq(&self, other: &Self) -> bool {
437            if self.len() != other.len() {
438                return false;
439            }
440            self.iter()
441                .zip(other.iter())
442                .all(|(this, other)| this.isol_eq(other))
443        }
444    }
445
446    impl IsolationTokenEq for dyn Isolation {
447        fn isol_eq(&self, other: &Self) -> bool {
448            let this = self.as_any().downcast_ref::<IsolationToken>();
449            let other = other.as_any().downcast_ref::<IsolationToken>();
450            match (this, other) {
451                (Some(this), Some(other)) => this == other,
452                _ => false,
453            }
454        }
455    }
456
457    impl IsolationTokenEq for StreamIsolation {
458        fn isol_eq(&self, other: &Self) -> bool {
459            self.stream_isolation
460                .isol_eq(other.stream_isolation.as_ref())
461                && self.owner_token == other.owner_token
462        }
463    }
464
465    #[derive(PartialEq, Clone, Copy, Debug, Eq)]
466    struct OtherIsolation(usize);
467
468    impl IsolationHelper for OtherIsolation {
469        fn compatible_same_type(&self, other: &Self) -> bool {
470            self == other
471        }
472        fn join_same_type(&self, other: &Self) -> Option<Self> {
473            if self.compatible_same_type(other) {
474                Some(*self)
475            } else {
476                None
477            }
478        }
479    }
480
481    #[test]
482    fn isolation_token() {
483        let token_1 = IsolationToken::new();
484        let token_2 = IsolationToken::new();
485
486        assert!(token_1.compatible_same_type(&token_1));
487        assert!(token_2.compatible_same_type(&token_2));
488        assert!(!token_1.compatible_same_type(&token_2));
489
490        assert_eq!(token_1.join_same_type(&token_1), Some(token_1));
491        assert_eq!(token_2.join_same_type(&token_2), Some(token_2));
492        assert_eq!(token_1.join_same_type(&token_2), None);
493    }
494
495    #[test]
496    fn isolation_trait() {
497        let token_1: Box<dyn Isolation> = Box::new(IsolationToken::new());
498        let token_2: Box<dyn Isolation> = Box::new(IsolationToken::new());
499        let other_1: Box<dyn Isolation> = Box::new(OtherIsolation(0));
500        let other_2: Box<dyn Isolation> = Box::new(OtherIsolation(1));
501
502        assert!(token_1.compatible(token_1.as_ref()));
503        assert!(token_2.compatible(token_2.as_ref()));
504        assert!(!token_1.compatible(token_2.as_ref()));
505
506        assert!(other_1.compatible(other_1.as_ref()));
507        assert!(other_2.compatible(other_2.as_ref()));
508        assert!(!other_1.compatible(other_2.as_ref()));
509
510        assert!(!token_1.compatible(other_1.as_ref()));
511        assert!(!other_1.compatible(token_1.as_ref()));
512
513        assert!(token_1.join(token_1.as_ref()).is_some());
514        assert!(token_1.join(token_2.as_ref()).is_none());
515
516        assert!(other_1.join(other_1.as_ref()).is_some());
517        assert!(other_1.join(other_2.as_ref()).is_none());
518
519        assert!(token_1.join(other_1.as_ref()).is_none());
520        assert!(other_1.join(token_1.as_ref()).is_none());
521    }
522
523    #[test]
524    fn isolation_tuple() {
525        let token_1 = IsolationToken::new();
526        let token_2 = IsolationToken::new();
527        let other_1 = OtherIsolation(0);
528        let other_2 = OtherIsolation(1);
529
530        let token_12: Box<dyn Isolation> = Box::new((token_1, token_2));
531        let token_21: Box<dyn Isolation> = Box::new((token_2, token_1));
532        let mix_11: Box<dyn Isolation> = Box::new((token_1, other_1));
533        let mix_12: Box<dyn Isolation> = Box::new((token_1, other_2));
534        let revmix_11: Box<dyn Isolation> = Box::new((other_1, token_1));
535
536        let join_token = token_12.join(token_12.as_ref()).unwrap();
537        assert!(join_token.compatible(token_12.as_ref()));
538        let join_mix = mix_12.join(mix_12.as_ref()).unwrap();
539        assert!(join_mix.compatible(mix_12.as_ref()));
540
541        let isol_list = [token_12, token_21, mix_11, mix_12, revmix_11];
542
543        for (i, isol1) in isol_list.iter().enumerate() {
544            for (j, isol2) in isol_list.iter().enumerate() {
545                assert_eq!(isol1.compatible(isol2.as_ref()), i == j);
546            }
547        }
548    }
549
550    #[test]
551    fn build_isolation() {
552        let no_isolation = StreamIsolation::no_isolation();
553        let no_isolation2 = StreamIsolation::builder()
554            .owner_token(IsolationToken::no_isolation())
555            .stream_isolation(Box::new(IsolationToken::no_isolation()))
556            .build()
557            .unwrap();
558        assert_eq!(no_isolation.owner_token, no_isolation2.owner_token);
559        assert_eq!(
560            no_isolation
561                .stream_isolation
562                .as_ref()
563                .as_any()
564                .downcast_ref::<IsolationToken>(),
565            no_isolation2
566                .stream_isolation
567                .as_ref()
568                .as_any()
569                .downcast_ref::<IsolationToken>()
570        );
571        assert!(no_isolation.compatible(&no_isolation2));
572
573        let tok = IsolationToken::new();
574        let some_isolation = StreamIsolation::builder().owner_token(tok).build().unwrap();
575        let some_isolation2 = StreamIsolation::builder()
576            .stream_isolation(Box::new(tok))
577            .build()
578            .unwrap();
579        assert!(!no_isolation.compatible(&some_isolation));
580        assert!(!no_isolation.compatible(&some_isolation2));
581        assert!(!some_isolation.compatible(&some_isolation2));
582        assert!(some_isolation.compatible(&some_isolation));
583    }
584}
tor_circmgr/isolation.rs

tor_circmgr/
isolation.rs
