libp2p_kad/kbucket/
key.rs

1// Copyright 2018 Parity Technologies (UK) Ltd.
2//
3// Permission is hereby granted, free of charge, to any person obtaining a
4// copy of this software and associated documentation files (the "Software"),
5// to deal in the Software without restriction, including without limitation
6// the rights to use, copy, modify, merge, publish, distribute, sublicense,
7// and/or sell copies of the Software, and to permit persons to whom the
8// Software is furnished to do so, subject to the following conditions:
9//
10// The above copyright notice and this permission notice shall be included in
11// all copies or substantial portions of the Software.
12//
13// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
14// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
15// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
16// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
17// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
18// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
19// DEALINGS IN THE SOFTWARE.
20
21use crate::record;
22use libp2p_core::multihash::Multihash;
23use libp2p_identity::PeerId;
24use sha2::digest::generic_array::{typenum::U32, GenericArray};
25use sha2::{Digest, Sha256};
26use std::borrow::Borrow;
27use std::hash::{Hash, Hasher};
28use uint::*;
29
30construct_uint! {
31    /// 256-bit unsigned integer.
32    pub(super) struct U256(4);
33}
34
35/// A `Key` in the DHT keyspace with preserved preimage.
36///
37/// Keys in the DHT keyspace identify both the participating nodes, as well as
38/// the records stored in the DHT.
39///
40/// `Key`s have an XOR metric as defined in the Kademlia paper, i.e. the bitwise XOR of
41/// the hash digests, interpreted as an integer. See [`Key::distance`].
42#[derive(Clone, Copy, Debug)]
43pub struct Key<T> {
44    preimage: T,
45    bytes: KeyBytes,
46}
47
48impl<T> Key<T> {
49    /// Constructs a new `Key` by running the given value through a random
50    /// oracle.
51    ///
52    /// The preimage of type `T` is preserved. See [`Key::preimage`] and
53    /// [`Key::into_preimage`].
54    pub fn new(preimage: T) -> Key<T>
55    where
56        T: Borrow<[u8]>,
57    {
58        let bytes = KeyBytes::new(preimage.borrow());
59        Key { preimage, bytes }
60    }
61
62    /// Borrows the preimage of the key.
63    pub fn preimage(&self) -> &T {
64        &self.preimage
65    }
66
67    /// Converts the key into its preimage.
68    pub fn into_preimage(self) -> T {
69        self.preimage
70    }
71
72    /// Computes the distance of the keys according to the XOR metric.
73    pub fn distance<U>(&self, other: &U) -> Distance
74    where
75        U: AsRef<KeyBytes>,
76    {
77        self.bytes.distance(other)
78    }
79
80    /// Exposing the hashed bytes.
81    pub fn hashed_bytes(&self) -> &[u8] {
82        &self.bytes.0
83    }
84
85    /// Returns the uniquely determined key with the given distance to `self`.
86    ///
87    /// This implements the following equivalence:
88    ///
89    /// `self xor other = distance <==> other = self xor distance`
90    pub fn for_distance(&self, d: Distance) -> KeyBytes {
91        self.bytes.for_distance(d)
92    }
93}
94
95impl<T> From<Key<T>> for KeyBytes {
96    fn from(key: Key<T>) -> KeyBytes {
97        key.bytes
98    }
99}
100
101impl<const S: usize> From<Multihash<S>> for Key<Multihash<S>> {
102    fn from(m: Multihash<S>) -> Self {
103        let bytes = KeyBytes(Sha256::digest(m.to_bytes()));
104        Key { preimage: m, bytes }
105    }
106}
107
108impl From<PeerId> for Key<PeerId> {
109    fn from(p: PeerId) -> Self {
110        let bytes = KeyBytes(Sha256::digest(p.to_bytes()));
111        Key { preimage: p, bytes }
112    }
113}
114
115impl From<Vec<u8>> for Key<Vec<u8>> {
116    fn from(b: Vec<u8>) -> Self {
117        Key::new(b)
118    }
119}
120
121impl From<record::Key> for Key<record::Key> {
122    fn from(k: record::Key) -> Self {
123        Key::new(k)
124    }
125}
126
127impl<T> AsRef<KeyBytes> for Key<T> {
128    fn as_ref(&self) -> &KeyBytes {
129        &self.bytes
130    }
131}
132
133impl<T, U> PartialEq<Key<U>> for Key<T> {
134    fn eq(&self, other: &Key<U>) -> bool {
135        self.bytes == other.bytes
136    }
137}
138
139impl<T> Eq for Key<T> {}
140
141impl<T> Hash for Key<T> {
142    fn hash<H: Hasher>(&self, state: &mut H) {
143        self.bytes.0.hash(state);
144    }
145}
146
147/// The raw bytes of a key in the DHT keyspace.
148#[derive(PartialEq, Eq, Clone, Copy, Debug)]
149pub struct KeyBytes(GenericArray<u8, U32>);
150
151impl KeyBytes {
152    /// Creates a new key in the DHT keyspace by running the given
153    /// value through a random oracle.
154    pub fn new<T>(value: T) -> Self
155    where
156        T: Borrow<[u8]>,
157    {
158        KeyBytes(Sha256::digest(value.borrow()))
159    }
160
161    /// Computes the distance of the keys according to the XOR metric.
162    pub fn distance<U>(&self, other: &U) -> Distance
163    where
164        U: AsRef<KeyBytes>,
165    {
166        let a = U256::from(self.0.as_slice());
167        let b = U256::from(other.as_ref().0.as_slice());
168        Distance(a ^ b)
169    }
170
171    /// Returns the uniquely determined key with the given distance to `self`.
172    ///
173    /// This implements the following equivalence:
174    ///
175    /// `self xor other = distance <==> other = self xor distance`
176    pub fn for_distance(&self, d: Distance) -> KeyBytes {
177        let key_int = U256::from(self.0.as_slice()) ^ d.0;
178        KeyBytes(GenericArray::from(<[u8; 32]>::from(key_int)))
179    }
180}
181
182impl AsRef<KeyBytes> for KeyBytes {
183    fn as_ref(&self) -> &KeyBytes {
184        self
185    }
186}
187
188/// A distance between two keys in the DHT keyspace.
189#[derive(Copy, Clone, PartialEq, Eq, Default, PartialOrd, Ord, Debug)]
190pub struct Distance(pub(super) U256);
191
192impl Distance {
193    /// Returns the integer part of the base 2 logarithm of the [`Distance`].
194    ///
195    /// Returns `None` if the distance is zero.
196    pub fn ilog2(&self) -> Option<u32> {
197        (256 - self.0.leading_zeros()).checked_sub(1)
198    }
199}
200
201#[cfg(test)]
202mod tests {
203    use super::*;
204    use crate::SHA_256_MH;
205    use quickcheck::*;
206
207    impl Arbitrary for Key<PeerId> {
208        fn arbitrary(_: &mut Gen) -> Key<PeerId> {
209            Key::from(PeerId::random())
210        }
211    }
212
213    impl Arbitrary for Key<Multihash<64>> {
214        fn arbitrary(g: &mut Gen) -> Key<Multihash<64>> {
215            let hash: [u8; 32] = core::array::from_fn(|_| u8::arbitrary(g));
216            Key::from(Multihash::wrap(SHA_256_MH, &hash).unwrap())
217        }
218    }
219
220    #[test]
221    fn identity() {
222        fn prop(a: Key<PeerId>) -> bool {
223            a.distance(&a) == Distance::default()
224        }
225        quickcheck(prop as fn(_) -> _)
226    }
227
228    #[test]
229    fn symmetry() {
230        fn prop(a: Key<PeerId>, b: Key<PeerId>) -> bool {
231            a.distance(&b) == b.distance(&a)
232        }
233        quickcheck(prop as fn(_, _) -> _)
234    }
235
236    #[test]
237    fn triangle_inequality() {
238        fn prop(a: Key<PeerId>, b: Key<PeerId>, c: Key<PeerId>) -> TestResult {
239            let ab = a.distance(&b);
240            let bc = b.distance(&c);
241            let (ab_plus_bc, overflow) = ab.0.overflowing_add(bc.0);
242            if overflow {
243                TestResult::discard()
244            } else {
245                TestResult::from_bool(a.distance(&c) <= Distance(ab_plus_bc))
246            }
247        }
248        quickcheck(prop as fn(_, _, _) -> _)
249    }
250
251    #[test]
252    fn unidirectionality() {
253        fn prop(a: Key<PeerId>, b: Key<PeerId>) -> bool {
254            let d = a.distance(&b);
255            (0..100).all(|_| {
256                let c = Key::from(PeerId::random());
257                a.distance(&c) != d || b == c
258            })
259        }
260        quickcheck(prop as fn(_, _) -> _)
261    }
262}
libp2p_kad/kbucket/key.rs

libp2p_kad/kbucket/
key.rs
