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        record::encode_payload_with(NODE, capacity, |bytes| {
111            bytes.extend_from_slice(&[
112                u8::try_from(self.entries.len()).unwrap(),
113                u8::from(!self.children.is_empty()),
114            ]);
115            for p in &self.children {
116                p.put(bytes);
117            }
118            for entry in &self.entries {
119                bytes.extend_from_slice(
120                    &u32::try_from(entry.key.len())
121                        .map_err(|_| Error::Budget)?
122                        .to_le_bytes(),
123                );
124                bytes.extend_from_slice(&entry.key);
125                match &entry.value {
126                    Value::Inline(value) => {
127                        bytes.push(u8::try_from(value.len()).unwrap());
128                        bytes.extend_from_slice(value);
129                    }
130                    Value::External(p) => {
131                        bytes.push(255);
132                        p.put(bytes);
133                    }
134                }
135            }
136            Ok(())
137        })
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<(Rc<ReadNode>, usize)>> {
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, 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        let Some((node, index)) = self.find(key)? else {
295            return Ok(None);
296        };
297        if let Some(bytes) = node.inline_value(index) {
298            V::check_bounds(bytes)?;
299            Ok(Some(V::from_bytes(Cow::Borrowed(bytes))?))
300        } else {
301            let value = node.value(index);
302            // External decoding does not borrow the routing buffer. Release it
303            // before allocating the payload, as in the original lookup path.
304            drop(node);
305            decode(self.value(value)?).map(Some)
306        }
307    }
308    pub fn contains_key(&self, key: &K) -> Result<bool> {
309        Ok(self.find(key)?.is_some())
310    }
311    pub fn insert(&mut self, key: K, value: V) -> Result<Option<V>> {
312        self.healthy()?;
313        let key_bytes = key.to_bytes_checked()?.into_owned();
314        let bytes = value.into_bytes_checked()?;
315        let mut tx = Transaction::new(self);
316        let (top, split, old) = tx.insert(tx.root.top, &key, key_bytes, bytes, 0)?;
317        tx.root.top = Some(if let Some((entry, right)) = split {
318            tx.save(
319                None,
320                &Node {
321                    entries: vec![entry],
322                    children: vec![top, right],
323                },
324            )?
325        } else {
326            top
327        });
328        drop(key);
329        let old = old.map(decode).transpose()?;
330        tx.commit()?;
331        Ok(old)
332    }
333    pub fn remove(&mut self, key: &K) -> Result<Option<V>> {
334        self.healthy()?;
335        let mut tx = Transaction::new(self);
336        let Some(top) = tx.root.top else {
337            return Ok(None);
338        };
339        let (changed, old) = tx.remove(top, key, 0)?;
340        let Some(old) = old else { return Ok(None) };
341        let value = decode(old)?;
342        if let Some(node) = changed {
343            tx.root.top = if node.entries.is_empty() {
344                tx.free(top)?;
345                node.children.first().copied()
346            } else {
347                Some(tx.save(Some(top), &node)?)
348            };
349        }
350        tx.root.length -= 1;
351        tx.commit()?;
352        Ok(Some(value))
353    }
354    pub fn clear(&mut self) -> Result<()> {
355        self.healthy()?;
356        let mut tx = Transaction::new(self);
357        tx.root.top = None;
358        tx.root.length = 0;
359        tx.root.cursor = record::HEADER_BYTES;
360        tx.root.free.fill(None);
361        tx.commit()
362    }
363    fn seek_path(&self, bound: &Bound<K>, forward: bool) -> Result<Vec<Frame>> {
364        self.healthy()?;
365        let mut path = Vec::new();
366        let mut pointer = self.root.borrow().top;
367        while let Some(p) = pointer {
368            ensure(
369                path.len() < MAX_DEPTH,
370                Error::Corrupt("map cursor exceeds height bound"),
371            )?;
372            let node = self.read_node(p, path.len())?;
373            let index = match bound {
374                Bound::Unbounded => {
375                    if forward {
376                        0
377                    } else {
378                        node.len()
379                    }
380                }
381                Bound::Included(k) => match node.search(k)? {
382                    Ok(i) => {
383                        if forward {
384                            i
385                        } else {
386                            i + 1
387                        }
388                    }
389                    Err(i) => i,
390                },
391                Bound::Excluded(k) => match node.search(k)? {
392                    Ok(i) => {
393                        if forward {
394                            i + 1
395                        } else {
396                            i
397                        }
398                    }
399                    Err(i) => i,
400                },
401            };
402            pointer = node.children.get(index).copied();
403            path.push(Frame {
404                node,
405                index,
406                descend: false,
407            });
408        }
409        Ok(path)
410    }
411    fn advance_path(&self, path: &mut Vec<Frame>, forward: bool) -> Result<Option<Entry>> {
412        self.healthy()?;
413        while let Some(frame) = path.last_mut() {
414            if frame.descend {
415                frame.descend = false;
416                let mut child = frame.node.children.get(frame.index).copied();
417                while let Some(p) = child {
418                    ensure(
419                        path.len() < MAX_DEPTH,
420                        Error::Corrupt("map cursor exceeds height bound"),
421                    )?;
422                    let node = self.read_node(p, path.len())?;
423                    let index = if forward { 0 } else { node.len() };
424                    child = node.children.get(index).copied();
425                    path.push(Frame {
426                        node,
427                        index,
428                        descend: false,
429                    });
430                }
431                continue;
432            }
433            let index = if forward {
434                frame.index
435            } else {
436                if frame.index == 0 {
437                    path.pop();
438                    continue;
439                }
440                frame.index - 1
441            };
442            if index >= frame.node.len() {
443                path.pop();
444                continue;
445            }
446            let entry = frame.node.entry(index);
447            frame.index = if forward { index + 1 } else { index };
448            // A caller may stop at this entry. Read the following subtree only
449            // when another step in this direction is actually requested.
450            frame.descend = !frame.node.children.is_empty();
451            return Ok(Some(entry));
452        }
453        Ok(None)
454    }
455    pub fn range(&self, bounds: impl RangeBounds<K>) -> TreeIter<'_, K, V, M> {
456        let lower = bounds.start_bound().cloned();
457        let upper = bounds.end_bound().cloned();
458        let invalid = match (&lower, &upper) {
459            (Bound::Included(a) | Bound::Excluded(a), Bound::Included(b) | Bound::Excluded(b)) => {
460                a > b
461                    || (a == b
462                        && matches!((&lower, &upper), (Bound::Excluded(_), Bound::Excluded(_))))
463            }
464            _ => false,
465        };
466        TreeIter {
467            tree: self,
468            lower,
469            upper,
470            front: None,
471            back: None,
472            exhausted: false,
473            invalid,
474            keys_only: false,
475        }
476    }
477    pub fn keys_range(
478        &self,
479        bounds: impl RangeBounds<K>,
480    ) -> impl DoubleEndedIterator<Item = Result<K>> + '_ {
481        let mut iter = self.range(bounds);
482        iter.keys_only = true;
483        iter.map(|e| e.map(MapEntry::into_key))
484    }
485}
486struct Frame {
487    node: Rc<ReadNode>,
488    index: usize,
489    descend: bool,
490}
491fn decode<T: Storable>(bytes: Vec<u8>) -> Result<T> {
492    T::check_bounds(&bytes)?;
493    Ok(T::from_bytes(Cow::Owned(bytes))?)
494}
495
496type Split = Option<(Entry, Pointer)>;
497struct Transaction<'a, K, V, M: Memory> {
498    tree: &'a Tree<K, V, M>,
499    root: Root,
500    writes: BTreeMap<u64, Vec<u8>>,
501}
502impl<'a, K: Storable + Ord + Clone, V: Storable, M: Memory> Transaction<'a, K, V, M> {
503    fn new(tree: &'a Tree<K, V, M>) -> Self {
504        Self {
505            tree,
506            root: tree.root.borrow().clone(),
507            writes: BTreeMap::new(),
508        }
509    }
510    fn bytes(&self, p: Pointer, magic: [u8; 8]) -> Result<Vec<u8>> {
511        p.check(self.root.cursor)?;
512        if let Some(bytes) = self.writes.get(&p.offset) {
513            Ok(bytes.clone())
514        } else {
515            record::read_bytes(&self.tree.memory, p.offset, p.capacity(), magic)
516        }
517    }
518    fn node(&self, p: Pointer, depth: usize) -> Result<Node> {
519        Ok(self.read_node(p, depth)?.owned())
520    }
521    fn read_node(&self, p: Pointer, depth: usize) -> Result<Rc<ReadNode>> {
522        if let Some(bytes) = self.writes.get(&p.offset) {
523            Ok(Rc::new(ReadNode::decode::<K, V>(
524                bytes.clone(),
525                self.root.cursor,
526            )?))
527        } else {
528            self.tree.read_node(p, depth)
529        }
530    }
531    fn value(&self, v: &Value) -> Result<Vec<u8>> {
532        let bytes = match v {
533            Value::Inline(b) => b.clone(),
534            Value::External(p) => {
535                p.check(self.root.cursor)?;
536                if let Some(bytes) = self.writes.get(&p.offset) {
537                    record::decode_payload(VALUE, bytes)?.to_vec()
538                } else {
539                    record::read_payload(&self.tree.memory, p.offset, p.capacity(), VALUE)?
540                }
541            }
542        };
543        V::check_bounds(&bytes)?;
544        Ok(bytes)
545    }
546    fn free(&mut self, p: Pointer) -> Result<()> {
547        let index = usize::from(p.order);
548        self.writes
549            .insert(p.offset, record::encode(FREE, &self.root.free[index])?);
550        self.root.free[index] = Some(p);
551        Ok(())
552    }
553    fn allocate(&mut self, len: usize) -> Result<Pointer> {
554        let size = len
555            .max(256)
556            .checked_next_power_of_two()
557            .ok_or(Error::Budget)?;
558        let order = size.trailing_zeros() as usize;
559        ensure(order < BINS, Error::Budget)?;
560        for bin in order..BINS {
561            if let Some(mut p) = self.root.free[bin] {
562                let next: Option<Pointer> = record::decode(FREE, &self.bytes(p, FREE)?)?;
563                if let Some(next) = next {
564                    next.check(self.root.cursor)?;
565                    ensure(
566                        next.order == p.order && next != p,
567                        Error::Corrupt("map free-list link"),
568                    )?;
569                }
570                self.root.free[bin] = next;
571                // Return only the requested capacity. Each unused half remains
572                // an ordinary free-list block, staged with the same mutation.
573                while usize::from(p.order) > order {
574                    p.order -= 1;
575                    let sibling = Pointer {
576                        offset: p.offset + p.capacity(),
577                        order: p.order,
578                    };
579                    self.free(sibling)?;
580                }
581                return Ok(p);
582            }
583        }
584        let p = Pointer {
585            offset: self.root.cursor,
586            order: u8::try_from(order).unwrap(),
587        };
588        self.root.cursor = self
589            .root
590            .cursor
591            .checked_add(p.capacity())
592            .ok_or(Error::Budget)?;
593        Ok(p)
594    }
595    fn save_bytes(&mut self, previous: Option<Pointer>, bytes: Vec<u8>) -> Result<Pointer> {
596        let p = if let Some(p) = previous.filter(|p| p.capacity() >= bytes.len() as u64) {
597            let needed = bytes.len().max(256).next_power_of_two() as u64;
598            // Reclaim only into already reusable smaller capacity. Splitting the
599            // live block itself loses its large size class and causes unbounded
600            // growth under repeated large/small replacements without coalescing.
601            let smaller_available = (needed.trailing_zeros() as usize..usize::from(p.order))
602                .any(|order| self.root.free[order].is_some());
603            if p.capacity() / needed >= 4 && smaller_available {
604                let smaller = self.allocate(bytes.len())?;
605                self.free(p)?;
606                smaller
607            } else {
608                p
609            }
610        } else {
611            if let Some(p) = previous {
612                self.free(p)?;
613            }
614            self.allocate(bytes.len())?
615        };
616        self.writes.insert(p.offset, bytes);
617        Ok(p)
618    }
619    fn save(&mut self, p: Option<Pointer>, node: &Node) -> Result<Pointer> {
620        self.save_bytes(p, node.encode()?)
621    }
622    fn save_value(&mut self, previous: Option<&Value>, bytes: Vec<u8>) -> Result<Value> {
623        let old = match previous {
624            Some(Value::External(p)) => Some(*p),
625            _ => None,
626        };
627        if bytes.len() <= INLINE {
628            if let Some(p) = old {
629                self.free(p)?;
630            }
631            Ok(Value::Inline(bytes))
632        } else {
633            Ok(Value::External(
634                self.save_bytes(old, record::encode_payload(VALUE, &bytes)?)?,
635            ))
636        }
637    }
638    fn insert(
639        &mut self,
640        p: Option<Pointer>,
641        key: &K,
642        key_bytes: Vec<u8>,
643        bytes: Vec<u8>,
644        depth: usize,
645    ) -> Result<(Pointer, Split, Option<Vec<u8>>)> {
646        ensure(
647            depth < MAX_DEPTH,
648            Error::Corrupt("map path exceeds height bound"),
649        )?;
650        let read = p.map(|p| self.read_node(p, depth)).transpose()?;
651        let search = read.as_ref().map_or(Ok(Err(0)), |node| node.search(key))?;
652        let (mut node, old) = match search {
653            Ok(i) => {
654                let read = read.as_ref().unwrap();
655                let previous = read.value(i);
656                let old = self.value(&previous)?;
657                let value = self.save_value(Some(&previous), bytes)?;
658                let same_pointer =
659                    matches!((&previous,&value),(Value::External(a),Value::External(b)) if a==b);
660                if same_pointer {
661                    return Ok((p.unwrap(), None, Some(old)));
662                }
663                let mut node = read.owned();
664                node.entries[i].value = value;
665                (node, Some(old))
666            }
667            Err(i) => {
668                if let Some(child) = read.as_ref().and_then(|node| node.children.get(i)).copied() {
669                    let (next, split, old) =
670                        self.insert(Some(child), key, key_bytes, bytes, depth + 1)?;
671                    if split.is_none() && next == child {
672                        return Ok((p.unwrap(), None, old));
673                    }
674                    let mut node = read.as_ref().unwrap().owned();
675                    node.children[i] = next;
676                    if let Some((entry, right)) = split {
677                        node.entries.insert(i, entry);
678                        node.children.insert(i + 1, right);
679                    }
680                    (node, old)
681                } else {
682                    let value = self.save_value(None, bytes)?;
683                    let mut node = read
684                        .as_ref()
685                        .map_or_else(Node::default, |node| node.owned());
686                    node.entries.insert(
687                        i,
688                        Entry {
689                            key: key_bytes,
690                            value,
691                        },
692                    );
693                    self.root.length = self.root.length.checked_add(1).ok_or(Error::Budget)?;
694                    (node, None)
695                }
696            }
697        };
698        let split = if node.entries.len() > MAX_ENTRIES {
699            let right_entries = node.entries.split_off(DEGREE + 1);
700            let median = node.entries.pop().unwrap();
701            let children = if node.children.is_empty() {
702                vec![]
703            } else {
704                node.children.split_off(DEGREE + 1)
705            };
706            let right = self.save(
707                None,
708                &Node {
709                    entries: right_entries,
710                    children,
711                },
712            )?;
713            Some((median, right))
714        } else {
715            None
716        };
717        Ok((self.save(p, &node)?, split, old))
718    }
719    // Return a modified node without encoding it: its parent may still repair
720    // an underflow. None means its persisted routing record remains unchanged.
721    fn remove(
722        &mut self,
723        p: Pointer,
724        key: &K,
725        depth: usize,
726    ) -> Result<(Option<Node>, Option<Vec<u8>>)> {
727        ensure(
728            depth < MAX_DEPTH,
729            Error::Corrupt("map path exceeds height bound"),
730        )?;
731        let read = self.read_node(p, depth)?;
732        match read.search(key)? {
733            Ok(i) => {
734                let mut node = read.owned();
735                let old = self.value(&node.entries[i].value)?;
736                if let Value::External(p) = node.entries[i].value {
737                    self.free(p)?;
738                }
739                if node.children.is_empty() {
740                    node.entries.remove(i);
741                } else {
742                    let child_pointer = node.children[i + 1];
743                    let (child, entry) = self.extract_min(child_pointer, depth + 1)?;
744                    node.entries[i] = entry;
745                    if let Some(child) = child {
746                        self.finish_child(&mut node, i + 1, child, depth)?;
747                    }
748                }
749                Ok((Some(node), Some(old)))
750            }
751            Err(i) => {
752                let Some(child_pointer) = read.children.get(i).copied() else {
753                    return Ok((None, None));
754                };
755                let (child, old) = self.remove(child_pointer, key, depth + 1)?;
756                let node = child
757                    .map(|child| self.changed_parent(&read, i, child, depth))
758                    .transpose()?
759                    .flatten();
760                Ok((node, old))
761            }
762        }
763    }
764    fn extract_min(&mut self, p: Pointer, depth: usize) -> Result<(Option<Node>, Entry)> {
765        ensure(
766            depth < MAX_DEPTH,
767            Error::Corrupt("map path exceeds height bound"),
768        )?;
769        let read = self.read_node(p, depth)?;
770        ensure(read.len() != 0, Error::Corrupt("empty successor node"))?;
771        if read.children.is_empty() {
772            let mut node = read.owned();
773            let entry = node.entries.remove(0);
774            Ok((Some(node), entry))
775        } else {
776            let (child, entry) = self.extract_min(read.children[0], depth + 1)?;
777            let node = child
778                .map(|child| self.changed_parent(&read, 0, child, depth))
779                .transpose()?
780                .flatten();
781            Ok((node, entry))
782        }
783    }
784    // Keep unchanged ancestors borrowed, including when the child was rewritten
785    // in place. Only a moved child or an underflow requires owning the parent.
786    fn changed_parent(
787        &mut self,
788        read: &ReadNode,
789        i: usize,
790        child: Node,
791        depth: usize,
792    ) -> Result<Option<Node>> {
793        if child.entries.len() >= MIN_ENTRIES {
794            let previous = read.children[i];
795            let next = self.save(Some(previous), &child)?;
796            if next == previous {
797                return Ok(None);
798            }
799            let mut parent = read.owned();
800            parent.children[i] = next;
801            Ok(Some(parent))
802        } else {
803            let mut parent = read.owned();
804            self.rebalance(&mut parent, i, child, depth)?;
805            Ok(Some(parent))
806        }
807    }
808    fn finish_child(
809        &mut self,
810        parent: &mut Node,
811        i: usize,
812        child: Node,
813        depth: usize,
814    ) -> Result<()> {
815        if child.entries.len() >= MIN_ENTRIES {
816            parent.children[i] = self.save(Some(parent.children[i]), &child)?;
817            Ok(())
818        } else {
819            self.rebalance(parent, i, child, depth)
820        }
821    }
822    fn rebalance(
823        &mut self,
824        parent: &mut Node,
825        i: usize,
826        mut child: Node,
827        parent_depth: usize,
828    ) -> Result<()> {
829        let depth = parent_depth + 1;
830        let p = parent.children[i];
831        let mut left = if i > 0 {
832            Some(self.node(parent.children[i - 1], depth)?)
833        } else {
834            None
835        };
836        if let Some(left) = &mut left {
837            ensure(
838                left.children.is_empty() == child.children.is_empty(),
839                Error::Corrupt("B-tree sibling levels"),
840            )?;
841            if left.entries.len() > MIN_ENTRIES {
842                child.entries.insert(
843                    0,
844                    std::mem::replace(&mut parent.entries[i - 1], left.entries.pop().unwrap()),
845                );
846                if let Some(p) = left.children.pop() {
847                    child.children.insert(0, p);
848                }
849                parent.children[i - 1] = self.save(Some(parent.children[i - 1]), left)?;
850                parent.children[i] = self.save(Some(p), &child)?;
851                return Ok(());
852            }
853        }
854        let mut right = if i + 1 < parent.children.len() {
855            Some(self.node(parent.children[i + 1], depth)?)
856        } else {
857            None
858        };
859        if let Some(right) = &mut right {
860            ensure(
861                right.children.is_empty() == child.children.is_empty(),
862                Error::Corrupt("B-tree sibling levels"),
863            )?;
864            if right.entries.len() > MIN_ENTRIES {
865                child.entries.push(std::mem::replace(
866                    &mut parent.entries[i],
867                    right.entries.remove(0),
868                ));
869                if !right.children.is_empty() {
870                    child.children.push(right.children.remove(0));
871                }
872                parent.children[i + 1] = self.save(Some(parent.children[i + 1]), right)?;
873                parent.children[i] = self.save(Some(p), &child)?;
874                return Ok(());
875            }
876        }
877        let (left_index, mut left, right) = if let Some(left) = left {
878            (i - 1, left, child)
879        } else {
880            (
881                i,
882                child,
883                right.ok_or(Error::Corrupt("B-tree missing separator"))?,
884            )
885        };
886        ensure(
887            left_index < parent.entries.len(),
888            Error::Corrupt("B-tree missing separator"),
889        )?;
890        let left_p = parent.children[left_index];
891        let right_p = parent.children[left_index + 1];
892        left.entries.push(parent.entries.remove(left_index));
893        left.entries.extend(right.entries);
894        left.children.extend(right.children);
895        self.free(right_p)?;
896        parent.children[left_index] = self.save(Some(left_p), &left)?;
897        parent.children.remove(left_index + 1);
898        Ok(())
899    }
900    fn commit(self) -> Result<()> {
901        let changed = self.root != *self.tree.root.borrow();
902        let header = if changed {
903            Some(record::encode(MAGIC, &self.root)?)
904        } else {
905            None
906        };
907        if let Some(h) = &header {
908            ensure(h.len() as u64 <= record::HEADER_BYTES, Error::Budget)?;
909        }
910        record::reserve(&self.tree.memory, self.root.cursor)?;
911        self.tree.poisoned.set(true);
912        if self.root.cursor < self.tree.root.borrow().cursor
913            || self.root.top != self.tree.root.borrow().top
914        {
915            self.tree.cache.borrow_mut().clear();
916        }
917        for (offset, bytes) in self.writes {
918            self.tree.cache.borrow_mut().invalidate(offset);
919            self.tree.memory.write(offset, &bytes);
920        }
921        if let Some(h) = header {
922            self.tree.memory.write(0, &h);
923        }
924        *self.tree.root.borrow_mut() = self.root;
925        self.tree.poisoned.set(false);
926        Ok(())
927    }
928}
929///
930/// `MapEntry`
931///
932/// An owned key and lazily decoded value from an ordered scan.
933///
934pub struct MapEntry<K, V> {
935    key: K,
936    bytes: Vec<u8>,
937    value: PhantomData<V>,
938}
939impl<K, V: Storable> MapEntry<K, V> {
940    /// Borrow the decoded key.
941    pub const fn key(&self) -> &K {
942        &self.key
943    }
944    /// Decode the value using its declared codec.
945    ///
946    /// # Errors
947    /// Returns the application codec or declared-bound error for this value.
948    pub fn value(&self) -> Result<V> {
949        decode(self.bytes.clone())
950    }
951    /// Consume the entry and decode its value.
952    ///
953    /// # Errors
954    /// Returns the application codec or declared-bound error for this value.
955    pub fn into_pair(self) -> Result<(K, V)> {
956        Ok((self.key, decode(self.bytes)?))
957    }
958    /// Consume the entry without decoding its value.
959    pub fn into_key(self) -> K {
960        self.key
961    }
962    /// Consume the entry and decode only its value.
963    ///
964    /// # Errors
965    /// Returns the application codec or declared-bound error for this value.
966    pub fn into_value(self) -> Result<V> {
967        decode(self.bytes)
968    }
969}
970
971///
972/// `TreeIter`
973///
974/// Lazy bidirectional traversal with bounded routing-node stacks. External values
975/// are read only for in-range entries and decoded when requested by the caller.
976///
977pub struct TreeIter<'a, K, V, M: Memory> {
978    tree: &'a Tree<K, V, M>,
979    lower: Bound<K>,
980    upper: Bound<K>,
981    front: Option<Vec<Frame>>,
982    back: Option<Vec<Frame>>,
983    exhausted: bool,
984    invalid: bool,
985    keys_only: bool,
986}
987impl<K: Storable + Ord + Clone, V: Storable, M: Memory> TreeIter<'_, K, V, M> {
988    fn step(&mut self, forward: bool) -> Result<Option<MapEntry<K, V>>> {
989        ensure(!self.invalid, Error::Bounds)?;
990        self.tree.healthy()?;
991        let empty = match (&self.lower, &self.upper) {
992            (Bound::Included(a), Bound::Included(b)) => a > b,
993            (Bound::Included(a) | Bound::Excluded(a), Bound::Included(b) | Bound::Excluded(b)) => {
994                a >= b
995            }
996            _ => false,
997        };
998        if empty {
999            return Ok(None);
1000        }
1001        let (path, bound) = if forward {
1002            (&mut self.front, &self.lower)
1003        } else {
1004            (&mut self.back, &self.upper)
1005        };
1006        if path.is_none() {
1007            *path = Some(self.tree.seek_path(bound, forward)?);
1008        }
1009        let entry = self.tree.advance_path(path.as_mut().unwrap(), forward)?;
1010        if let Some(entry) = entry {
1011            let key: K = decode(entry.key)?;
1012            let after = match &self.lower {
1013                Bound::Unbounded => true,
1014                Bound::Included(k) => key >= *k,
1015                Bound::Excluded(k) => key > *k,
1016            };
1017            let before = match &self.upper {
1018                Bound::Unbounded => true,
1019                Bound::Included(k) => key <= *k,
1020                Bound::Excluded(k) => key < *k,
1021            };
1022            ensure(
1023                if forward { after } else { before },
1024                Error::Corrupt("map cursor key order"),
1025            )?;
1026            if !(after && before) {
1027                return Ok(None);
1028            }
1029            if forward {
1030                self.lower = Bound::Excluded(key.clone());
1031            } else {
1032                self.upper = Bound::Excluded(key.clone());
1033            }
1034            return Ok(Some(MapEntry {
1035                key,
1036                bytes: if self.keys_only {
1037                    vec![]
1038                } else {
1039                    self.tree.value(entry.value)?
1040                },
1041                value: PhantomData,
1042            }));
1043        }
1044        Ok(None)
1045    }
1046    fn advance(&mut self, forward: bool) -> Option<Result<MapEntry<K, V>>> {
1047        if self.exhausted {
1048            return None;
1049        }
1050        match self.step(forward) {
1051            Ok(Some(entry)) => Some(Ok(entry)),
1052            Ok(None) => {
1053                self.exhausted = true;
1054                None
1055            }
1056            Err(error) => {
1057                self.exhausted = true;
1058                Some(Err(error))
1059            }
1060        }
1061    }
1062}
1063impl<K: Storable + Ord + Clone, V: Storable, M: Memory> Iterator for TreeIter<'_, K, V, M> {
1064    type Item = Result<MapEntry<K, V>>;
1065    fn next(&mut self) -> Option<Self::Item> {
1066        self.advance(true)
1067    }
1068}
1069impl<K: Storable + Ord + Clone, V: Storable, M: Memory> DoubleEndedIterator
1070    for TreeIter<'_, K, V, M>
1071{
1072    fn next_back(&mut self) -> Option<Self::Item> {
1073        self.advance(false)
1074    }
1075}
1076impl<K: Storable + Ord + Clone, V: Storable, M: Memory> std::iter::FusedIterator
1077    for TreeIter<'_, K, V, M>
1078{
1079}
1080
1081#[cfg(test)]
1082mod tests;
ic_storage/adapter/tree.rs

ic_storage/adapter/
tree.rs
