ic_storage/adapter/
tree.rs

1//! Owned degree-six B-tree. The multi-entry search, split/borrow/merge design and
2//! selective payload access follow the established B-tree techniques used by
3//! ic-stable-structures 0.7.2 (see docs/storage/upstreams.md). This is a new checked
4//! format, not an implementation of its durable layout or compatibility reader.
5//! Routing records contain small inline values; larger values have separate
6//! checksummed records. Mutations stage bytes and reserve before publication.
7use super::{
8    Memory, Storable,
9    error::{CollectionError as Error, Result, ensure},
10    record,
11};
12use serde::{Deserialize, Serialize};
13use std::{
14    borrow::Cow,
15    cell::{Cell, RefCell},
16    collections::BTreeMap,
17    marker::PhantomData,
18    ops::{Bound, RangeBounds},
19    rc::Rc,
20};
21mod read;
22use read::{NodeCache, ReadNode};
23
24pub const MAGIC: [u8; 8] = *b"ICMAP002";
25const NODE: [u8; 8] = *b"ICBTND01";
26const VALUE: [u8; 8] = *b"ICBTVAL1";
27const FREE: [u8; 8] = *b"ICFREE01";
28const BINS: usize = 32;
29const MAX_DEPTH: usize = 32;
30const DEGREE: usize = 6;
31const MAX_ENTRIES: usize = DEGREE * 2 - 1;
32const MIN_ENTRIES: usize = DEGREE - 1;
33const INLINE: usize = 32;
34
35#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
36struct Pointer {
37    offset: u64,
38    order: u8,
39}
40impl Pointer {
41    fn capacity(self) -> u64 {
42        1_u64 << self.order
43    }
44    fn check(self, cursor: u64) -> Result<()> {
45        ensure(
46            (8..32).contains(&self.order),
47            Error::Corrupt("tree block order"),
48        )?;
49        ensure(
50            self.offset >= record::HEADER_BYTES
51                && self
52                    .offset
53                    .checked_add(self.capacity())
54                    .is_some_and(|end| end <= cursor),
55            Error::Corrupt("tree block bounds"),
56        )
57    }
58    fn put(self, bytes: &mut Vec<u8>) {
59        bytes.extend_from_slice(&self.offset.to_le_bytes());
60        bytes.push(self.order);
61    }
62}
63#[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]
64struct Root {
65    top: Option<Pointer>,
66    length: u64,
67    cursor: u64,
68    free: Vec<Option<Pointer>>,
69    key_bound: Option<(u32, bool)>,
70    value_bound: Option<(u32, bool)>,
71}
72#[derive(Clone)]
73enum Value {
74    Inline(Vec<u8>),
75    External(Pointer),
76}
77#[derive(Clone)]
78struct Entry {
79    key: Vec<u8>,
80    value: Value,
81}
82#[derive(Clone, Default)]
83struct Node {
84    entries: Vec<Entry>,
85    children: Vec<Pointer>,
86}
87impl Node {
88    fn encode(&self) -> Result<Vec<u8>> {
89        ensure(
90            self.entries.len() <= MAX_ENTRIES,
91            Error::Corrupt("B-tree node capacity"),
92        )?;
93        ensure(
94            self.children.is_empty() || self.children.len() == self.entries.len() + 1,
95            Error::Corrupt("B-tree child count"),
96        )?;
97        let capacity =
98            self.entries
99                .iter()
100                .try_fold(2 + self.children.len() * 9, |size, entry| {
101                    let value_size = match &entry.value {
102                        Value::Inline(v) => v.len(),
103                        Value::External(_) => 9,
104                    };
105                    size.checked_add(5)
106                        .and_then(|n| n.checked_add(entry.key.len()))
107                        .and_then(|n| n.checked_add(value_size))
108                        .ok_or(Error::Budget)
109                })?;
110        ensure(capacity <= record::MAX_RECORD, Error::Budget)?;
111        let mut bytes = Vec::with_capacity(capacity);
112        bytes.extend_from_slice(&[
113            u8::try_from(self.entries.len()).unwrap(),
114            u8::from(!self.children.is_empty()),
115        ]);
116        for p in &self.children {
117            p.put(&mut bytes);
118        }
119        for entry in &self.entries {
120            bytes.extend_from_slice(
121                &u32::try_from(entry.key.len())
122                    .map_err(|_| Error::Budget)?
123                    .to_le_bytes(),
124            );
125            bytes.extend_from_slice(&entry.key);
126            match &entry.value {
127                Value::Inline(value) => {
128                    bytes.push(u8::try_from(value.len()).unwrap());
129                    bytes.extend_from_slice(value);
130                }
131                Value::External(p) => {
132                    bytes.push(255);
133                    p.put(&mut bytes);
134                }
135            }
136        }
137        record::encode_payload(NODE, &bytes)
138    }
139}
140struct Reader<'a>(&'a [u8]);
141impl<'a> Reader<'a> {
142    fn take(&mut self, n: usize) -> Result<&'a [u8]> {
143        ensure(n <= self.0.len(), Error::Corrupt("truncated B-tree node"))?;
144        let (a, b) = self.0.split_at(n);
145        self.0 = b;
146        Ok(a)
147    }
148    fn byte(&mut self) -> Result<u8> {
149        Ok(self.take(1)?[0])
150    }
151    fn pointer(&mut self, cursor: u64) -> Result<Pointer> {
152        let offset = u64::from_le_bytes(self.take(8)?.try_into().unwrap());
153        let p = Pointer {
154            offset,
155            order: self.byte()?,
156        };
157        p.check(cursor)?;
158        Ok(p)
159    }
160}
161
162pub struct Tree<K, V, M: Memory> {
163    pub memory: M,
164    root: RefCell<Root>,
165    poisoned: Cell<bool>,
166    cache: RefCell<NodeCache>,
167    types: PhantomData<(K, V)>,
168}
169impl<K: Storable + Ord + Clone, V: Storable, M: Memory> Tree<K, V, M> {
170    pub fn reset(memory: M) -> Result<Self> {
171        let root = Root {
172            top: None,
173            length: 0,
174            cursor: record::HEADER_BYTES,
175            free: vec![None; BINS],
176            key_bound: record::bound::<K>(),
177            value_bound: record::bound::<V>(),
178        };
179        let bytes = record::encode(MAGIC, &root)?;
180        ensure(bytes.len() as u64 <= record::HEADER_BYTES, Error::Budget)?;
181        record::reserve(&memory, record::HEADER_BYTES)?;
182        memory.write(0, &bytes);
183        Ok(Self {
184            memory,
185            root: RefCell::new(root),
186            poisoned: Cell::new(false),
187            cache: RefCell::default(),
188            types: PhantomData,
189        })
190    }
191    pub fn load(memory: M) -> Result<Self> {
192        let root: Root = record::read(&memory, 0, record::HEADER_BYTES, MAGIC)?;
193        ensure(
194            root.key_bound == record::bound::<K>() && root.value_bound == record::bound::<V>(),
195            Error::Corrupt("map codec bound changed"),
196        )?;
197        ensure(
198            root.free.len() == BINS
199                && root.cursor >= record::HEADER_BYTES
200                && root.cursor
201                    <= memory
202                        .size()
203                        .checked_mul(crate::WASM_PAGE_SIZE_BYTES)
204                        .ok_or(Error::Budget)?,
205            Error::Corrupt("map allocator bounds"),
206        )?;
207        ensure(
208            root.top.is_none() == (root.length == 0),
209            Error::Corrupt("map root/count disagree"),
210        )?;
211        if let Some(p) = root.top {
212            p.check(root.cursor)?;
213        }
214        for (order, p) in root.free.iter().enumerate() {
215            if let Some(p) = p {
216                p.check(root.cursor)?;
217                ensure(
218                    usize::from(p.order) == order,
219                    Error::Corrupt("free block order"),
220                )?;
221            }
222        }
223        Ok(Self {
224            memory,
225            root: RefCell::new(root),
226            poisoned: Cell::new(false),
227            cache: RefCell::default(),
228            types: PhantomData,
229        })
230    }
231    fn healthy(&self) -> Result<()> {
232        ensure(!self.poisoned.get(), Error::Poisoned)?;
233        // A different allocation can poison the shared governed backing. This
234        // also covers iterator entries already held in a routing frame.
235        let capacity = self
236            .memory
237            .size()
238            .checked_mul(crate::WASM_PAGE_SIZE_BYTES)
239            .ok_or(Error::Budget)?;
240        ensure(
241            self.root.borrow().cursor <= capacity,
242            Error::Corrupt("map allocator bounds"),
243        )
244    }
245    pub fn len(&self) -> u64 {
246        self.healthy().expect("map owner is poisoned");
247        self.root.borrow().length
248    }
249    #[cfg(test)]
250    fn node(&self, p: Pointer) -> Result<Node> {
251        Ok(self.read_node(p, MAX_DEPTH)?.owned())
252    }
253    pub fn set_cache_budget(&mut self, bytes: usize) {
254        self.cache.get_mut().configure(bytes);
255    }
256    fn read_node(&self, p: Pointer, depth: usize) -> Result<Rc<ReadNode>> {
257        let cursor = self.root.borrow().cursor;
258        p.check(cursor)?;
259        if let Some(node) = self.cache.borrow_mut().get(p, depth) {
260            return Ok(node);
261        }
262        let node = Rc::new(ReadNode::decode::<K, V>(
263            record::read_bytes(&self.memory, p.offset, p.capacity(), NODE)?,
264            cursor,
265        )?);
266        self.cache.borrow_mut().put(p, Rc::clone(&node), depth);
267        Ok(node)
268    }
269    fn value(&self, v: Value) -> Result<Vec<u8>> {
270        let bytes = match v {
271            Value::Inline(bytes) => bytes,
272            Value::External(p) => {
273                p.check(self.root.borrow().cursor)?;
274                record::read_payload(&self.memory, p.offset, p.capacity(), VALUE)?
275            }
276        };
277        V::check_bounds(&bytes)?;
278        Ok(bytes)
279    }
280    fn find(&self, key: &K) -> Result<Option<Value>> {
281        self.healthy()?;
282        let mut p = self.root.borrow().top;
283        for depth in 0..MAX_DEPTH {
284            let Some(current) = p else { return Ok(None) };
285            let node = self.read_node(current, depth)?;
286            match node.search(key)? {
287                Ok(i) => return Ok(Some(node.value(i))),
288                Err(i) => p = node.children.get(i).copied(),
289            }
290        }
291        Err(Error::Corrupt("map path exceeds height bound"))
292    }
293    pub fn get(&self, key: &K) -> Result<Option<V>> {
294        self.find(key)?.map(|v| decode(self.value(v)?)).transpose()
295    }
296    pub fn contains_key(&self, key: &K) -> Result<bool> {
297        Ok(self.find(key)?.is_some())
298    }
299    pub fn insert(&mut self, key: K, value: V) -> Result<Option<V>> {
300        self.healthy()?;
301        let key_bytes = key.to_bytes_checked()?.into_owned();
302        let bytes = value.into_bytes_checked()?;
303        let mut tx = Transaction::new(self);
304        let (top, split, old) = tx.insert(tx.root.top, &key, key_bytes, bytes, 0)?;
305        tx.root.top = Some(if let Some((entry, right)) = split {
306            tx.save(
307                None,
308                &Node {
309                    entries: vec![entry],
310                    children: vec![top, right],
311                },
312            )?
313        } else {
314            top
315        });
316        drop(key);
317        let old = old.map(decode).transpose()?;
318        tx.commit()?;
319        Ok(old)
320    }
321    pub fn remove(&mut self, key: &K) -> Result<Option<V>> {
322        self.healthy()?;
323        let mut tx = Transaction::new(self);
324        let Some(top) = tx.root.top else {
325            return Ok(None);
326        };
327        let (changed, old) = tx.remove(top, key, 0)?;
328        let Some(old) = old else { return Ok(None) };
329        let value = decode(old)?;
330        if let Some(node) = changed {
331            tx.root.top = if node.entries.is_empty() {
332                tx.free(top)?;
333                node.children.first().copied()
334            } else {
335                Some(tx.save(Some(top), &node)?)
336            };
337        }
338        tx.root.length -= 1;
339        tx.commit()?;
340        Ok(Some(value))
341    }
342    pub fn clear(&mut self) -> Result<()> {
343        self.healthy()?;
344        let mut tx = Transaction::new(self);
345        tx.root.top = None;
346        tx.root.length = 0;
347        tx.root.cursor = record::HEADER_BYTES;
348        tx.root.free.fill(None);
349        tx.commit()
350    }
351    fn seek_path(&self, bound: &Bound<K>, forward: bool) -> Result<Vec<Frame>> {
352        self.healthy()?;
353        let mut path = Vec::new();
354        let mut pointer = self.root.borrow().top;
355        while let Some(p) = pointer {
356            ensure(
357                path.len() < MAX_DEPTH,
358                Error::Corrupt("map cursor exceeds height bound"),
359            )?;
360            let node = self.read_node(p, path.len())?;
361            let index = match bound {
362                Bound::Unbounded => {
363                    if forward {
364                        0
365                    } else {
366                        node.len()
367                    }
368                }
369                Bound::Included(k) => match node.search(k)? {
370                    Ok(i) => {
371                        if forward {
372                            i
373                        } else {
374                            i + 1
375                        }
376                    }
377                    Err(i) => i,
378                },
379                Bound::Excluded(k) => match node.search(k)? {
380                    Ok(i) => {
381                        if forward {
382                            i + 1
383                        } else {
384                            i
385                        }
386                    }
387                    Err(i) => i,
388                },
389            };
390            pointer = node.children.get(index).copied();
391            path.push(Frame {
392                node,
393                index,
394                descend: false,
395            });
396        }
397        Ok(path)
398    }
399    fn advance_path(&self, path: &mut Vec<Frame>, forward: bool) -> Result<Option<Entry>> {
400        self.healthy()?;
401        while let Some(frame) = path.last_mut() {
402            if frame.descend {
403                frame.descend = false;
404                let mut child = frame.node.children.get(frame.index).copied();
405                while let Some(p) = child {
406                    ensure(
407                        path.len() < MAX_DEPTH,
408                        Error::Corrupt("map cursor exceeds height bound"),
409                    )?;
410                    let node = self.read_node(p, path.len())?;
411                    let index = if forward { 0 } else { node.len() };
412                    child = node.children.get(index).copied();
413                    path.push(Frame {
414                        node,
415                        index,
416                        descend: false,
417                    });
418                }
419                continue;
420            }
421            let index = if forward {
422                frame.index
423            } else {
424                if frame.index == 0 {
425                    path.pop();
426                    continue;
427                }
428                frame.index - 1
429            };
430            if index >= frame.node.len() {
431                path.pop();
432                continue;
433            }
434            let entry = frame.node.entry(index);
435            frame.index = if forward { index + 1 } else { index };
436            // A caller may stop at this entry. Read the following subtree only
437            // when another step in this direction is actually requested.
438            frame.descend = !frame.node.children.is_empty();
439            return Ok(Some(entry));
440        }
441        Ok(None)
442    }
443    pub fn range(&self, bounds: impl RangeBounds<K>) -> TreeIter<'_, K, V, M> {
444        let lower = bounds.start_bound().cloned();
445        let upper = bounds.end_bound().cloned();
446        let invalid = match (&lower, &upper) {
447            (Bound::Included(a) | Bound::Excluded(a), Bound::Included(b) | Bound::Excluded(b)) => {
448                a > b
449                    || (a == b
450                        && matches!((&lower, &upper), (Bound::Excluded(_), Bound::Excluded(_))))
451            }
452            _ => false,
453        };
454        TreeIter {
455            tree: self,
456            lower,
457            upper,
458            front: None,
459            back: None,
460            exhausted: false,
461            invalid,
462            keys_only: false,
463        }
464    }
465    pub fn keys_range(
466        &self,
467        bounds: impl RangeBounds<K>,
468    ) -> impl DoubleEndedIterator<Item = Result<K>> + '_ {
469        let mut iter = self.range(bounds);
470        iter.keys_only = true;
471        iter.map(|e| e.map(MapEntry::into_key))
472    }
473}
474struct Frame {
475    node: Rc<ReadNode>,
476    index: usize,
477    descend: bool,
478}
479fn decode<T: Storable>(bytes: Vec<u8>) -> Result<T> {
480    T::check_bounds(&bytes)?;
481    Ok(T::from_bytes(Cow::Owned(bytes))?)
482}
483
484type Split = Option<(Entry, Pointer)>;
485struct Transaction<'a, K, V, M: Memory> {
486    tree: &'a Tree<K, V, M>,
487    root: Root,
488    writes: BTreeMap<u64, Vec<u8>>,
489}
490impl<'a, K: Storable + Ord + Clone, V: Storable, M: Memory> Transaction<'a, K, V, M> {
491    fn new(tree: &'a Tree<K, V, M>) -> Self {
492        Self {
493            tree,
494            root: tree.root.borrow().clone(),
495            writes: BTreeMap::new(),
496        }
497    }
498    fn bytes(&self, p: Pointer, magic: [u8; 8]) -> Result<Vec<u8>> {
499        p.check(self.root.cursor)?;
500        if let Some(bytes) = self.writes.get(&p.offset) {
501            Ok(bytes.clone())
502        } else {
503            record::read_bytes(&self.tree.memory, p.offset, p.capacity(), magic)
504        }
505    }
506    fn node(&self, p: Pointer, depth: usize) -> Result<Node> {
507        Ok(self.read_node(p, depth)?.owned())
508    }
509    fn read_node(&self, p: Pointer, depth: usize) -> Result<Rc<ReadNode>> {
510        if let Some(bytes) = self.writes.get(&p.offset) {
511            Ok(Rc::new(ReadNode::decode::<K, V>(
512                bytes.clone(),
513                self.root.cursor,
514            )?))
515        } else {
516            self.tree.read_node(p, depth)
517        }
518    }
519    fn value(&self, v: &Value) -> Result<Vec<u8>> {
520        let bytes = match v {
521            Value::Inline(b) => b.clone(),
522            Value::External(p) => {
523                p.check(self.root.cursor)?;
524                if let Some(bytes) = self.writes.get(&p.offset) {
525                    record::decode_payload(VALUE, bytes)?.to_vec()
526                } else {
527                    record::read_payload(&self.tree.memory, p.offset, p.capacity(), VALUE)?
528                }
529            }
530        };
531        V::check_bounds(&bytes)?;
532        Ok(bytes)
533    }
534    fn free(&mut self, p: Pointer) -> Result<()> {
535        let index = usize::from(p.order);
536        self.writes
537            .insert(p.offset, record::encode(FREE, &self.root.free[index])?);
538        self.root.free[index] = Some(p);
539        Ok(())
540    }
541    fn allocate(&mut self, len: usize) -> Result<Pointer> {
542        let size = len
543            .max(256)
544            .checked_next_power_of_two()
545            .ok_or(Error::Budget)?;
546        let order = size.trailing_zeros() as usize;
547        ensure(order < BINS, Error::Budget)?;
548        for bin in order..BINS {
549            if let Some(mut p) = self.root.free[bin] {
550                let next: Option<Pointer> = record::decode(FREE, &self.bytes(p, FREE)?)?;
551                if let Some(next) = next {
552                    next.check(self.root.cursor)?;
553                    ensure(
554                        next.order == p.order && next != p,
555                        Error::Corrupt("map free-list link"),
556                    )?;
557                }
558                self.root.free[bin] = next;
559                // Return only the requested capacity. Each unused half remains
560                // an ordinary free-list block, staged with the same mutation.
561                while usize::from(p.order) > order {
562                    p.order -= 1;
563                    let sibling = Pointer {
564                        offset: p.offset + p.capacity(),
565                        order: p.order,
566                    };
567                    self.free(sibling)?;
568                }
569                return Ok(p);
570            }
571        }
572        let p = Pointer {
573            offset: self.root.cursor,
574            order: u8::try_from(order).unwrap(),
575        };
576        self.root.cursor = self
577            .root
578            .cursor
579            .checked_add(p.capacity())
580            .ok_or(Error::Budget)?;
581        Ok(p)
582    }
583    fn save_bytes(&mut self, previous: Option<Pointer>, bytes: Vec<u8>) -> Result<Pointer> {
584        let p = if let Some(p) = previous.filter(|p| p.capacity() >= bytes.len() as u64) {
585            let needed = bytes.len().max(256).next_power_of_two() as u64;
586            // Reclaim only into already reusable smaller capacity. Splitting the
587            // live block itself loses its large size class and causes unbounded
588            // growth under repeated large/small replacements without coalescing.
589            let smaller_available = (needed.trailing_zeros() as usize..usize::from(p.order))
590                .any(|order| self.root.free[order].is_some());
591            if p.capacity() / needed >= 4 && smaller_available {
592                let smaller = self.allocate(bytes.len())?;
593                self.free(p)?;
594                smaller
595            } else {
596                p
597            }
598        } else {
599            if let Some(p) = previous {
600                self.free(p)?;
601            }
602            self.allocate(bytes.len())?
603        };
604        self.writes.insert(p.offset, bytes);
605        Ok(p)
606    }
607    fn save(&mut self, p: Option<Pointer>, node: &Node) -> Result<Pointer> {
608        self.save_bytes(p, node.encode()?)
609    }
610    fn save_value(&mut self, previous: Option<&Value>, bytes: Vec<u8>) -> Result<Value> {
611        let old = match previous {
612            Some(Value::External(p)) => Some(*p),
613            _ => None,
614        };
615        if bytes.len() <= INLINE {
616            if let Some(p) = old {
617                self.free(p)?;
618            }
619            Ok(Value::Inline(bytes))
620        } else {
621            Ok(Value::External(
622                self.save_bytes(old, record::encode_payload(VALUE, &bytes)?)?,
623            ))
624        }
625    }
626    fn insert(
627        &mut self,
628        p: Option<Pointer>,
629        key: &K,
630        key_bytes: Vec<u8>,
631        bytes: Vec<u8>,
632        depth: usize,
633    ) -> Result<(Pointer, Split, Option<Vec<u8>>)> {
634        ensure(
635            depth < MAX_DEPTH,
636            Error::Corrupt("map path exceeds height bound"),
637        )?;
638        let read = p.map(|p| self.read_node(p, depth)).transpose()?;
639        let search = read.as_ref().map_or(Ok(Err(0)), |node| node.search(key))?;
640        let (mut node, old) = match search {
641            Ok(i) => {
642                let read = read.as_ref().unwrap();
643                let previous = read.value(i);
644                let old = self.value(&previous)?;
645                let value = self.save_value(Some(&previous), bytes)?;
646                let same_pointer =
647                    matches!((&previous,&value),(Value::External(a),Value::External(b)) if a==b);
648                if same_pointer {
649                    return Ok((p.unwrap(), None, Some(old)));
650                }
651                let mut node = read.owned();
652                node.entries[i].value = value;
653                (node, Some(old))
654            }
655            Err(i) => {
656                if let Some(child) = read.as_ref().and_then(|node| node.children.get(i)).copied() {
657                    let (next, split, old) =
658                        self.insert(Some(child), key, key_bytes, bytes, depth + 1)?;
659                    if split.is_none() && next == child {
660                        return Ok((p.unwrap(), None, old));
661                    }
662                    let mut node = read.as_ref().unwrap().owned();
663                    node.children[i] = next;
664                    if let Some((entry, right)) = split {
665                        node.entries.insert(i, entry);
666                        node.children.insert(i + 1, right);
667                    }
668                    (node, old)
669                } else {
670                    let value = self.save_value(None, bytes)?;
671                    let mut node = read
672                        .as_ref()
673                        .map_or_else(Node::default, |node| node.owned());
674                    node.entries.insert(
675                        i,
676                        Entry {
677                            key: key_bytes,
678                            value,
679                        },
680                    );
681                    self.root.length = self.root.length.checked_add(1).ok_or(Error::Budget)?;
682                    (node, None)
683                }
684            }
685        };
686        let split = if node.entries.len() > MAX_ENTRIES {
687            let right_entries = node.entries.split_off(DEGREE + 1);
688            let median = node.entries.pop().unwrap();
689            let children = if node.children.is_empty() {
690                vec![]
691            } else {
692                node.children.split_off(DEGREE + 1)
693            };
694            let right = self.save(
695                None,
696                &Node {
697                    entries: right_entries,
698                    children,
699                },
700            )?;
701            Some((median, right))
702        } else {
703            None
704        };
705        Ok((self.save(p, &node)?, split, old))
706    }
707    // Return a modified node without encoding it: its parent may still repair
708    // an underflow. None means its persisted routing record remains unchanged.
709    fn remove(
710        &mut self,
711        p: Pointer,
712        key: &K,
713        depth: usize,
714    ) -> Result<(Option<Node>, Option<Vec<u8>>)> {
715        ensure(
716            depth < MAX_DEPTH,
717            Error::Corrupt("map path exceeds height bound"),
718        )?;
719        let read = self.read_node(p, depth)?;
720        match read.search(key)? {
721            Ok(i) => {
722                let mut node = read.owned();
723                let old = self.value(&node.entries[i].value)?;
724                if let Value::External(p) = node.entries[i].value {
725                    self.free(p)?;
726                }
727                if node.children.is_empty() {
728                    node.entries.remove(i);
729                } else {
730                    let child_pointer = node.children[i + 1];
731                    let (child, entry) = self.extract_min(child_pointer, depth + 1)?;
732                    node.entries[i] = entry;
733                    if let Some(child) = child {
734                        self.finish_child(&mut node, i + 1, child, depth)?;
735                    }
736                }
737                Ok((Some(node), Some(old)))
738            }
739            Err(i) => {
740                let Some(child_pointer) = read.children.get(i).copied() else {
741                    return Ok((None, None));
742                };
743                let (child, old) = self.remove(child_pointer, key, depth + 1)?;
744                let node = child
745                    .map(|child| self.changed_parent(&read, i, child, depth))
746                    .transpose()?
747                    .flatten();
748                Ok((node, old))
749            }
750        }
751    }
752    fn extract_min(&mut self, p: Pointer, depth: usize) -> Result<(Option<Node>, Entry)> {
753        ensure(
754            depth < MAX_DEPTH,
755            Error::Corrupt("map path exceeds height bound"),
756        )?;
757        let read = self.read_node(p, depth)?;
758        ensure(read.len() != 0, Error::Corrupt("empty successor node"))?;
759        if read.children.is_empty() {
760            let mut node = read.owned();
761            let entry = node.entries.remove(0);
762            Ok((Some(node), entry))
763        } else {
764            let (child, entry) = self.extract_min(read.children[0], depth + 1)?;
765            let node = child
766                .map(|child| self.changed_parent(&read, 0, child, depth))
767                .transpose()?
768                .flatten();
769            Ok((node, entry))
770        }
771    }
772    // Keep unchanged ancestors borrowed, including when the child was rewritten
773    // in place. Only a moved child or an underflow requires owning the parent.
774    fn changed_parent(
775        &mut self,
776        read: &ReadNode,
777        i: usize,
778        child: Node,
779        depth: usize,
780    ) -> Result<Option<Node>> {
781        if child.entries.len() >= MIN_ENTRIES {
782            let previous = read.children[i];
783            let next = self.save(Some(previous), &child)?;
784            if next == previous {
785                return Ok(None);
786            }
787            let mut parent = read.owned();
788            parent.children[i] = next;
789            Ok(Some(parent))
790        } else {
791            let mut parent = read.owned();
792            self.rebalance(&mut parent, i, child, depth)?;
793            Ok(Some(parent))
794        }
795    }
796    fn finish_child(
797        &mut self,
798        parent: &mut Node,
799        i: usize,
800        child: Node,
801        depth: usize,
802    ) -> Result<()> {
803        if child.entries.len() >= MIN_ENTRIES {
804            parent.children[i] = self.save(Some(parent.children[i]), &child)?;
805            Ok(())
806        } else {
807            self.rebalance(parent, i, child, depth)
808        }
809    }
810    fn rebalance(
811        &mut self,
812        parent: &mut Node,
813        i: usize,
814        mut child: Node,
815        parent_depth: usize,
816    ) -> Result<()> {
817        let depth = parent_depth + 1;
818        let p = parent.children[i];
819        let mut left = if i > 0 {
820            Some(self.node(parent.children[i - 1], depth)?)
821        } else {
822            None
823        };
824        if let Some(left) = &mut left {
825            ensure(
826                left.children.is_empty() == child.children.is_empty(),
827                Error::Corrupt("B-tree sibling levels"),
828            )?;
829            if left.entries.len() > MIN_ENTRIES {
830                child.entries.insert(
831                    0,
832                    std::mem::replace(&mut parent.entries[i - 1], left.entries.pop().unwrap()),
833                );
834                if let Some(p) = left.children.pop() {
835                    child.children.insert(0, p);
836                }
837                parent.children[i - 1] = self.save(Some(parent.children[i - 1]), left)?;
838                parent.children[i] = self.save(Some(p), &child)?;
839                return Ok(());
840            }
841        }
842        let mut right = if i + 1 < parent.children.len() {
843            Some(self.node(parent.children[i + 1], depth)?)
844        } else {
845            None
846        };
847        if let Some(right) = &mut right {
848            ensure(
849                right.children.is_empty() == child.children.is_empty(),
850                Error::Corrupt("B-tree sibling levels"),
851            )?;
852            if right.entries.len() > MIN_ENTRIES {
853                child.entries.push(std::mem::replace(
854                    &mut parent.entries[i],
855                    right.entries.remove(0),
856                ));
857                if !right.children.is_empty() {
858                    child.children.push(right.children.remove(0));
859                }
860                parent.children[i + 1] = self.save(Some(parent.children[i + 1]), right)?;
861                parent.children[i] = self.save(Some(p), &child)?;
862                return Ok(());
863            }
864        }
865        let (left_index, mut left, right) = if let Some(left) = left {
866            (i - 1, left, child)
867        } else {
868            (
869                i,
870                child,
871                right.ok_or(Error::Corrupt("B-tree missing separator"))?,
872            )
873        };
874        ensure(
875            left_index < parent.entries.len(),
876            Error::Corrupt("B-tree missing separator"),
877        )?;
878        let left_p = parent.children[left_index];
879        let right_p = parent.children[left_index + 1];
880        left.entries.push(parent.entries.remove(left_index));
881        left.entries.extend(right.entries);
882        left.children.extend(right.children);
883        self.free(right_p)?;
884        parent.children[left_index] = self.save(Some(left_p), &left)?;
885        parent.children.remove(left_index + 1);
886        Ok(())
887    }
888    fn commit(self) -> Result<()> {
889        let changed = self.root != *self.tree.root.borrow();
890        let header = if changed {
891            Some(record::encode(MAGIC, &self.root)?)
892        } else {
893            None
894        };
895        if let Some(h) = &header {
896            ensure(h.len() as u64 <= record::HEADER_BYTES, Error::Budget)?;
897        }
898        record::reserve(&self.tree.memory, self.root.cursor)?;
899        self.tree.poisoned.set(true);
900        if self.root.cursor < self.tree.root.borrow().cursor
901            || self.root.top != self.tree.root.borrow().top
902        {
903            self.tree.cache.borrow_mut().clear();
904        }
905        for (offset, bytes) in self.writes {
906            self.tree.cache.borrow_mut().invalidate(offset);
907            self.tree.memory.write(offset, &bytes);
908        }
909        if let Some(h) = header {
910            self.tree.memory.write(0, &h);
911        }
912        *self.tree.root.borrow_mut() = self.root;
913        self.tree.poisoned.set(false);
914        Ok(())
915    }
916}
917///
918/// `MapEntry`
919///
920/// An owned key and lazily decoded value from an ordered scan.
921///
922pub struct MapEntry<K, V> {
923    key: K,
924    bytes: Vec<u8>,
925    value: PhantomData<V>,
926}
927impl<K, V: Storable> MapEntry<K, V> {
928    /// Borrow the decoded key.
929    pub const fn key(&self) -> &K {
930        &self.key
931    }
932    /// Decode the value using its declared codec.
933    ///
934    /// # Errors
935    /// Returns the application codec or declared-bound error for this value.
936    pub fn value(&self) -> Result<V> {
937        decode(self.bytes.clone())
938    }
939    /// Consume the entry and decode its value.
940    ///
941    /// # Errors
942    /// Returns the application codec or declared-bound error for this value.
943    pub fn into_pair(self) -> Result<(K, V)> {
944        Ok((self.key, decode(self.bytes)?))
945    }
946    /// Consume the entry without decoding its value.
947    pub fn into_key(self) -> K {
948        self.key
949    }
950    /// Consume the entry and decode only its value.
951    ///
952    /// # Errors
953    /// Returns the application codec or declared-bound error for this value.
954    pub fn into_value(self) -> Result<V> {
955        decode(self.bytes)
956    }
957}
958
959///
960/// `TreeIter`
961///
962/// Lazy bidirectional traversal with bounded routing-node stacks. External values
963/// are read only for in-range entries and decoded when requested by the caller.
964///
965pub struct TreeIter<'a, K, V, M: Memory> {
966    tree: &'a Tree<K, V, M>,
967    lower: Bound<K>,
968    upper: Bound<K>,
969    front: Option<Vec<Frame>>,
970    back: Option<Vec<Frame>>,
971    exhausted: bool,
972    invalid: bool,
973    keys_only: bool,
974}
975impl<K: Storable + Ord + Clone, V: Storable, M: Memory> TreeIter<'_, K, V, M> {
976    fn step(&mut self, forward: bool) -> Result<Option<MapEntry<K, V>>> {
977        ensure(!self.invalid, Error::Bounds)?;
978        self.tree.healthy()?;
979        let empty = match (&self.lower, &self.upper) {
980            (Bound::Included(a), Bound::Included(b)) => a > b,
981            (Bound::Included(a) | Bound::Excluded(a), Bound::Included(b) | Bound::Excluded(b)) => {
982                a >= b
983            }
984            _ => false,
985        };
986        if empty {
987            return Ok(None);
988        }
989        let (path, bound) = if forward {
990            (&mut self.front, &self.lower)
991        } else {
992            (&mut self.back, &self.upper)
993        };
994        if path.is_none() {
995            *path = Some(self.tree.seek_path(bound, forward)?);
996        }
997        let entry = self.tree.advance_path(path.as_mut().unwrap(), forward)?;
998        if let Some(entry) = entry {
999            let key: K = decode(entry.key)?;
1000            let after = match &self.lower {
1001                Bound::Unbounded => true,
1002                Bound::Included(k) => key >= *k,
1003                Bound::Excluded(k) => key > *k,
1004            };
1005            let before = match &self.upper {
1006                Bound::Unbounded => true,
1007                Bound::Included(k) => key <= *k,
1008                Bound::Excluded(k) => key < *k,
1009            };
1010            ensure(
1011                if forward { after } else { before },
1012                Error::Corrupt("map cursor key order"),
1013            )?;
1014            if !(after && before) {
1015                return Ok(None);
1016            }
1017            if forward {
1018                self.lower = Bound::Excluded(key.clone());
1019            } else {
1020                self.upper = Bound::Excluded(key.clone());
1021            }
1022            return Ok(Some(MapEntry {
1023                key,
1024                bytes: if self.keys_only {
1025                    vec![]
1026                } else {
1027                    self.tree.value(entry.value)?
1028                },
1029                value: PhantomData,
1030            }));
1031        }
1032        Ok(None)
1033    }
1034    fn advance(&mut self, forward: bool) -> Option<Result<MapEntry<K, V>>> {
1035        if self.exhausted {
1036            return None;
1037        }
1038        match self.step(forward) {
1039            Ok(Some(entry)) => Some(Ok(entry)),
1040            Ok(None) => {
1041                self.exhausted = true;
1042                None
1043            }
1044            Err(error) => {
1045                self.exhausted = true;
1046                Some(Err(error))
1047            }
1048        }
1049    }
1050}
1051impl<K: Storable + Ord + Clone, V: Storable, M: Memory> Iterator for TreeIter<'_, K, V, M> {
1052    type Item = Result<MapEntry<K, V>>;
1053    fn next(&mut self) -> Option<Self::Item> {
1054        self.advance(true)
1055    }
1056}
1057impl<K: Storable + Ord + Clone, V: Storable, M: Memory> DoubleEndedIterator
1058    for TreeIter<'_, K, V, M>
1059{
1060    fn next_back(&mut self) -> Option<Self::Item> {
1061        self.advance(false)
1062    }
1063}
1064impl<K: Storable + Ord + Clone, V: Storable, M: Memory> std::iter::FusedIterator
1065    for TreeIter<'_, K, V, M>
1066{
1067}
1068
1069#[cfg(test)]
1070mod tests;
ic_storage/adapter/tree.rs

ic_storage/adapter/
tree.rs
