aranya_runtime/storage/
mod.rs

1//! Interfaces for graph storage.
2//!
3//! The [`StorageProvider`] and [`Storage`] interfaces enable high-level
4//! actions on the graph. Traversing the graph is made simpler by splitting
5//! its [`Command`]s into [`Segment`]s. Updating the graph is possible using
6//! [`Perspective`]s, which represent a slice of state.
7
8use alloc::{boxed::Box, string::String, vec::Vec};
9use core::{fmt, ops::Deref};
10
11use buggy::{Bug, BugExt};
12use serde::{Deserialize, Serialize};
13
14use crate::{Address, Command, CommandId, PolicyId, Prior};
15
16pub mod linear;
17pub mod memory;
18
19/// The maximum size of a serialized message
20pub const MAX_COMMAND_LENGTH: usize = 2048;
21
22aranya_crypto::custom_id! {
23    /// The ID of the graph, taken from initialization.
24    pub struct GraphId;
25}
26
27#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
28pub struct Location {
29    pub segment: usize,
30    pub command: usize,
31}
32
33impl From<(usize, usize)> for Location {
34    fn from((segment, command): (usize, usize)) -> Self {
35        Self::new(segment, command)
36    }
37}
38
39impl AsRef<Location> for Location {
40    fn as_ref(&self) -> &Location {
41        self
42    }
43}
44
45impl Location {
46    pub fn new(segment: usize, command: usize) -> Location {
47        Location { segment, command }
48    }
49
50    /// If this is not the first command in a segment, return a location
51    /// pointing to the previous command.
52    #[must_use]
53    pub fn previous(mut self) -> Option<Self> {
54        if let Some(n) = usize::checked_sub(self.command, 1) {
55            self.command = n;
56            Some(self)
57        } else {
58            None
59        }
60    }
61
62    /// Returns true if other location is in the same segment.
63    pub fn same_segment(self, other: Location) -> bool {
64        self.segment == other.segment
65    }
66}
67
68impl fmt::Display for Location {
69    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
70        write!(f, "{}:{}", self.segment, self.command)
71    }
72}
73
74/// An error returned by [`Storage`] or [`StorageProvider`].
75#[derive(Debug, PartialEq, Eq, thiserror::Error)]
76pub enum StorageError {
77    #[error("storage already exists")]
78    StorageExists,
79    #[error("no such storage")]
80    NoSuchStorage,
81    #[error("segment index {} is out of bounds", .0.segment)]
82    SegmentOutOfBounds(Location),
83    #[error("command index {} is out of bounds in segment {}", .0.command, .0.segment)]
84    CommandOutOfBounds(Location),
85    #[error("IO error")]
86    IoError,
87    #[error("not a merge command")]
88    NotMerge,
89    #[error("command with id {0} not found")]
90    NoSuchId(CommandId),
91    #[error("policy mismatch")]
92    PolicyMismatch,
93    #[error("cannot write an empty perspective")]
94    EmptyPerspective,
95    #[error("segment must be a descendant of the head for commit")]
96    HeadNotAncestor,
97    #[error("command's parents do not match the perspective head")]
98    PerspectiveHeadMismatch,
99    #[error(transparent)]
100    Bug(#[from] Bug),
101}
102
103/// Handle to storage implementations used by the runtime.
104pub trait StorageProvider {
105    type Perspective: Perspective + Revertable;
106    type Segment: Segment;
107    type Storage: Storage<
108        Segment = Self::Segment,
109        Perspective = Self::Perspective,
110        FactIndex = <Self::Segment as Segment>::FactIndex,
111    >;
112
113    /// Create an unrooted perspective, intended for creating a new graph.
114    ///
115    /// # Arguments
116    ///
117    /// * `policy_id` - The policy to associate with the graph.
118    fn new_perspective(&mut self, policy_id: PolicyId) -> Self::Perspective;
119
120    /// Create a new graph.
121    ///
122    /// # Arguments
123    ///
124    /// * `graph` - ID of the graph, taken from the initialization command.
125    /// * `init` - Contains the data necessary to initialize the new graph.
126    fn new_storage(
127        &mut self,
128        init: Self::Perspective,
129    ) -> Result<(GraphId, &mut Self::Storage), StorageError>;
130
131    /// Get an existing graph.
132    ///
133    /// # Arguments
134    ///
135    /// * `graph` - ID of the graph, taken from the initialization command.
136    fn get_storage(&mut self, graph: GraphId) -> Result<&mut Self::Storage, StorageError>;
137}
138
139/// Represents the runtime's graph; [`Command`]s in storage have been validated
140/// by an associated policy and committed to state.
141pub trait Storage {
142    type Perspective: Perspective + Revertable;
143    type FactPerspective: FactPerspective;
144    type Segment: Segment<FactIndex = Self::FactIndex>;
145    type FactIndex: FactIndex;
146
147    /// Returns the location of Command with id if it has been stored by
148    /// searching from the head.
149    fn get_location(&self, address: Address) -> Result<Option<Location>, StorageError> {
150        self.get_location_from(self.get_head()?, address)
151    }
152
153    /// Returns the location of Command with id by searching from the given location.
154    fn get_location_from(
155        &self,
156        start: Location,
157        address: Address,
158    ) -> Result<Option<Location>, StorageError> {
159        let mut queue = Vec::new();
160        queue.push(start);
161        'outer: while let Some(loc) = queue.pop() {
162            let head = self.get_segment(loc)?;
163            if address.max_cut > head.longest_max_cut()? {
164                continue;
165            }
166            if let Some(loc) = head.get_from_max_cut(address.max_cut)? {
167                let command = head.get_command(loc).assume("command must exist")?;
168                if command.id() == address.id {
169                    return Ok(Some(loc));
170                }
171            }
172            // Assumes skip list is sorted in ascending order.
173            // We always want to skip as close to the root as possible.
174            for (skip, max_cut) in head.skip_list() {
175                if max_cut >= &address.max_cut {
176                    queue.push(*skip);
177                    continue 'outer;
178                }
179            }
180            queue.extend(head.prior());
181        }
182        Ok(None)
183    }
184
185    /// Returns the CommandId of the command at the location.
186    fn get_command_id(&self, location: Location) -> Result<CommandId, StorageError>;
187
188    /// Returns a linear perspective at the given location.
189    fn get_linear_perspective(
190        &self,
191        parent: Location,
192    ) -> Result<Option<Self::Perspective>, StorageError>;
193
194    /// Returns a fact perspective at the given location, intended for evaluating braids.
195    /// The fact perspective will include the facts of the command at the given location.
196    fn get_fact_perspective(&self, first: Location) -> Result<Self::FactPerspective, StorageError>;
197
198    /// Returns a merge perspective based on the given locations with the braid as prior facts.
199    fn new_merge_perspective(
200        &self,
201        left: Location,
202        right: Location,
203        last_common_ancestor: (Location, usize),
204        policy_id: PolicyId,
205        braid: Self::FactIndex,
206    ) -> Result<Option<Self::Perspective>, StorageError>;
207
208    /// Returns the segment at the given location.
209    fn get_segment(&self, location: Location) -> Result<Self::Segment, StorageError>;
210
211    /// Returns the head of the graph.
212    fn get_head(&self) -> Result<Location, StorageError>;
213
214    /// Sets the given segment as the head of the graph.  Returns an error if
215    /// the current head is not an ancestor of the provided segment.
216    fn commit(&mut self, segment: Self::Segment) -> Result<(), StorageError>;
217
218    /// Writes the given perspective to a segment.
219    fn write(&mut self, perspective: Self::Perspective) -> Result<Self::Segment, StorageError>;
220
221    /// Writes the given fact perspective to a fact index.
222    fn write_facts(
223        &mut self,
224        fact_perspective: Self::FactPerspective,
225    ) -> Result<Self::FactIndex, StorageError>;
226
227    /// Determine whether the given location is an ancestor of the given segment.
228    fn is_ancestor(
229        &self,
230        search_location: Location,
231        segment: &Self::Segment,
232    ) -> Result<bool, StorageError> {
233        let mut queue = Vec::new();
234        queue.extend(segment.prior());
235        let segment = self.get_segment(search_location)?;
236        let address = segment
237            .get_command(search_location)
238            .assume("location must exist")?
239            .address()?;
240        'outer: while let Some(location) = queue.pop() {
241            if location.segment == search_location.segment
242                && location.command >= search_location.command
243            {
244                return Ok(true);
245            }
246            let segment = self.get_segment(location)?;
247            if address.max_cut > segment.longest_max_cut()? {
248                continue;
249            }
250            for (skip, max_cut) in segment.skip_list() {
251                if max_cut >= &address.max_cut {
252                    queue.push(*skip);
253                    continue 'outer;
254                }
255            }
256            queue.extend(segment.prior());
257        }
258        Ok(false)
259    }
260}
261
262type MaxCut = usize;
263
264/// A segment is a nonempty sequence of commands persisted to storage.
265///
266/// A segment can be one of three types. This might be encoded in a future version of the API.
267/// * init   - This segment is the first segment of the graph and begins with an init command.
268/// * linear - This segment has a single prior command and is simply a sequence of linear commands.
269/// * merge  - This segment merges two other segments and thus begins with a merge command.
270///            A merge segment has a braid as it's prior facts.
271///
272/// Each command past the first must have the parent of the previous command in the segment.
273pub trait Segment {
274    type FactIndex: FactIndex;
275    type Command<'a>: Command
276    where
277        Self: 'a;
278
279    /// Returns the head of the segment.
280    fn head(&self) -> Result<Self::Command<'_>, StorageError>;
281
282    /// Returns the first Command in the segment.
283    fn first(&self) -> Self::Command<'_>;
284
285    /// Returns the location of the head of the segment.
286    fn head_location(&self) -> Location;
287
288    /// Returns the location of the first command.
289    fn first_location(&self) -> Location;
290
291    /// Returns true if the segment contains the location.
292    fn contains(&self, location: Location) -> bool;
293
294    /// Returns the id for the policy used for this segment.
295    fn policy(&self) -> PolicyId;
296
297    /// Returns the prior segments for this segment.
298    fn prior(&self) -> Prior<Location>;
299
300    /// Returns the command at the given location.
301    fn get_command(&self, location: Location) -> Option<Self::Command<'_>>;
302
303    /// Returns the command with the given max cut from within this segment.
304    fn get_from_max_cut(&self, max_cut: usize) -> Result<Option<Location>, StorageError>;
305
306    /// Returns an iterator of commands starting at the given location.
307    fn get_from(&self, location: Location) -> Vec<Self::Command<'_>>;
308
309    /// Get the fact index associated with this segment.
310    fn facts(&self) -> Result<Self::FactIndex, StorageError>;
311
312    fn contains_any<I>(&self, locations: I) -> bool
313    where
314        I: IntoIterator,
315        I::Item: AsRef<Location>,
316    {
317        locations
318            .into_iter()
319            .any(|loc| self.contains(*loc.as_ref()))
320    }
321
322    /// The shortest max cut for this segment.
323    ///
324    /// This will always the max cut of the first command in the segment.
325    fn shortest_max_cut(&self) -> MaxCut;
326
327    /// The longest max cut for this segment.
328    ///
329    /// This will always be the max cut of the last command in the segment.
330    fn longest_max_cut(&self) -> Result<MaxCut, StorageError>;
331
332    /// The skip list is a series of locations that can be safely jumped to
333    /// when searching for a location. As long as the max cut of the location
334    /// you're jumping to is greater than or equal to the location you're
335    /// searching for you can jump to it and be guaranteed not to miss
336    /// the location you're searching for.
337    ///
338    /// For merge commands the last location in the skip list is the least
339    /// common ancestor.
340    fn skip_list(&self) -> &[(Location, MaxCut)];
341}
342
343/// An index of facts in storage.
344pub trait FactIndex: Query {}
345
346/// A perspective is essentially a mutable, in-memory version of a [`Segment`],
347/// with the same three types.
348pub trait Perspective: FactPerspective {
349    /// Returns the id for the policy used for this perspective.
350    fn policy(&self) -> PolicyId;
351
352    /// Adds the given command to the head of the perspective. The command's
353    /// parent must be the head of the perspective.
354    fn add_command(&mut self, command: &impl Command) -> Result<usize, StorageError>;
355
356    /// Returns true if the perspective contains a command with the given ID.
357    fn includes(&self, id: CommandId) -> bool;
358
359    /// Returns the head address in the perspective, if it exists
360    fn head_address(&self) -> Result<Prior<Address>, Bug>;
361}
362
363/// A fact perspective is essentially a mutable, in-memory version of a [`FactIndex`].
364pub trait FactPerspective: QueryMut {}
365
366/// A revertable perspective can make checkpoints and be reverted such that the
367/// state of the perspective matches that when the checkpoint was created.
368pub trait Revertable {
369    /// Create a checkpoint which can be used to revert the perspective.
370    fn checkpoint(&self) -> Checkpoint;
371
372    /// Revert the perspective to the state it was at when the checkpoint was created.
373    fn revert(&mut self, checkpoint: Checkpoint) -> Result<(), Bug>;
374}
375
376/// A checkpoint used to revert perspectives.
377pub struct Checkpoint {
378    /// An index interpreted by a given `Revertable` implementation to revert to a prior point.
379    pub index: usize,
380}
381
382/// Can be queried to look up facts.
383///
384/// Facts are labeled by a name, which are generally a bounded set of human-readable strings determined in advance.
385///
386/// Within a name, facts are an association of compound keys to values. The facts are keyed by a compound key
387/// `(k_1, k_2, ..., k_n)`, where each `k` is a sequence of bytes. The fact value is also a sequence of bytes.
388pub trait Query {
389    /// Look up a named fact by an exact match of the compound key.
390    fn query(&self, name: &str, keys: &[Box<[u8]>]) -> Result<Option<Box<[u8]>>, StorageError>;
391
392    /// Iterator for [`Query::query_prefix`].
393    type QueryIterator: Iterator<Item = Result<Fact, StorageError>>;
394
395    /// Look up all named facts that begin with the prefix of keys, in sorted key order.
396    ///
397    /// The `prefix` is a partial compound key `(k_1, k_2, ..., k_n)`, where each `k` is a sequence of bytes.
398    /// This returns all facts under the name with keys such that `prefix` is equal to a prefix of the fact's keys.
399    fn query_prefix(
400        &self,
401        name: &str,
402        prefix: &[Box<[u8]>],
403    ) -> Result<Self::QueryIterator, StorageError>;
404}
405
406/// A fact with a key and value.
407#[derive(Debug, PartialEq, Eq)]
408pub struct Fact {
409    /// The sequence of keys.
410    pub key: Keys,
411    /// The bytes of the value.
412    pub value: Box<[u8]>,
413}
414
415/// Can mutate facts by inserting and deleting them.
416///
417/// See [`Query`] for details on the nature of facts.
418pub trait QueryMut: Query {
419    /// Insert a fact labeled by a name, with a given compound key and a value.
420    ///
421    /// This fact can later be looked up by [`Query`] methods, using the name and keys.
422    fn insert(&mut self, name: String, keys: Keys, value: Box<[u8]>);
423
424    /// Delete any fact associated to the compound key, under the given name.
425    fn delete(&mut self, name: String, keys: Keys);
426}
427
428/// A sequence of byte-based keys, used for facts.
429#[derive(Clone, Debug, Default, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
430pub struct Keys(Box<[Box<[u8]>]>);
431
432impl Deref for Keys {
433    type Target = [Box<[u8]>];
434    fn deref(&self) -> &[Box<[u8]>] {
435        self.0.as_ref()
436    }
437}
438
439impl AsRef<[Box<[u8]>]> for Keys {
440    fn as_ref(&self) -> &[Box<[u8]>] {
441        self.0.as_ref()
442    }
443}
444
445impl core::borrow::Borrow<[Box<[u8]>]> for Keys {
446    fn borrow(&self) -> &[Box<[u8]>] {
447        self.0.as_ref()
448    }
449}
450
451impl From<&[&[u8]]> for Keys {
452    fn from(value: &[&[u8]]) -> Self {
453        value.iter().copied().collect()
454    }
455}
456
457impl Keys {
458    fn starts_with(&self, prefix: &[Box<[u8]>]) -> bool {
459        self.as_ref().starts_with(prefix)
460    }
461}
462
463impl<B: Into<Box<[u8]>>> FromIterator<B> for Keys {
464    fn from_iter<T: IntoIterator<Item = B>>(iter: T) -> Self {
465        Self(iter.into_iter().map(Into::into).collect())
466    }
467}
468
469// TODO: Fix and enable
470// #[cfg(test)]
471// mod tests;
aranya_runtime/storage/mod.rs

aranya_runtime/storage/
mod.rs
