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memiterator.go
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memiterator.go
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package cachekv
import (
"bytes"
dbm "github.com/tendermint/tm-db"
"github.com/cosmos/cosmos-sdk/store/types"
)
// memIterator iterates over iterKVCache items.
// if key is nil, means it was deleted.
// Implements Iterator.
type memIterator struct {
types.Iterator
lastKey []byte
deleted map[string]struct{}
}
func newMemIterator(start, end []byte, items *dbm.MemDB, deleted map[string]struct{}, ascending bool) *memIterator {
var iter types.Iterator
var err error
if ascending {
iter, err = items.Iterator(start, end)
} else {
iter, err = items.ReverseIterator(start, end)
}
if err != nil {
panic(err)
}
return &memIterator{
Iterator: iter,
lastKey: nil,
deleted: deleted,
}
}
func (mi *memIterator) Value() []byte {
key := mi.Iterator.Key()
// We need to handle the case where deleted is modified and includes our current key
// We handle this by maintaining a lastKey object in the iterator.
// If the current key is the same as the last key (and last key is not nil / the start)
// then we are calling value on the same thing as last time.
// Therefore we don't check the mi.deleted to see if this key is included in there.
reCallingOnOldLastKey := (mi.lastKey != nil) && bytes.Equal(key, mi.lastKey)
if _, ok := mi.deleted[string(key)]; ok && !reCallingOnOldLastKey {
return nil
}
mi.lastKey = key
return mi.Iterator.Value()
}