snapshot.go RawHistoryFolder

1// SPDX-License-Identifier: MIT
2
3package kv
4
5import (
6	"context"
7	"iter"
8)
9
10// Item is the value stored under a key.
11type Item struct {
12	Value   []byte // owned by the snapshot: must not be modified
13	Version uint64 // seq of the batch that last wrote the key
14}
15
16// Snapshot is an immutable, consistent view of the database at one seq. It is
17// safe for concurrent use and stays valid, unchanged, after later writes.
18// Keys yielded by iterators and Item.Value are owned by the snapshot and must
19// not be modified.
20type Snapshot struct {
21	t   tree
22	seq uint64
23}
24
25func newSnapshot(t tree, seq uint64) *Snapshot {
26	return &Snapshot{t: t, seq: seq}
27}
28
29// Seq returns the seq of the last batch applied in this snapshot.
30func (s *Snapshot) Seq() uint64 { return s.seq }
31
32// Len returns the number of keys.
33func (s *Snapshot) Len() int { return s.t.len() }
34
35// Get returns the item stored under key. Reads never block or log: ctx is
36// not checked.
37func (s *Snapshot) Get(_ context.Context, key []byte) (Item, bool) { return s.t.get(key) }
38
39// Range iterates over the keys in [start, end) in ascending order. A nil end
40// (or an empty start) is unbounded. Breaking out of the loop stops the walk.
41func (s *Snapshot) Range(_ context.Context, start, end []byte) iter.Seq2[[]byte, Item] {
42	return s.t.ascend(start, end)
43}
44
45// Prefix iterates over the keys that begin with p in ascending order. An
46// empty p matches every key.
47func (s *Snapshot) Prefix(_ context.Context, p []byte) iter.Seq2[[]byte, Item] {
48	return s.t.ascend(p, prefixEnd(p))
49}
50
51// prefixEnd returns the smallest key greater than every key that begins with
52// p, or nil if there is none (p is empty or all 0xFF).
53func prefixEnd(p []byte) []byte {
54	for i := len(p) - 1; i >= 0; i-- {
55		if p[i] < 0xFF {
56			end := make([]byte, i+1)
57			copy(end, p)
58			end[i]++
59			return end
60		}
61	}
62	return nil
63}