[#216] blobovnicza: Implement main methods and logic

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/blobovnicza/iterate.go

@@ -0,0 +1,46 @@
+package blobovnicza
+
+import (
+	"github.com/pkg/errors"
+	"go.etcd.io/bbolt"
+)
+
+func (b *Blobovnicza) iterateBuckets(tx *bbolt.Tx, f func(uint64, uint64, *bbolt.Bucket) (bool, error)) error {
+	return b.iterateBucketKeys(func(lower uint64, upper uint64, key []byte) (bool, error) {
+		buck := tx.Bucket(key)
+		if buck == nil {
+			// expected to happen:
+			//  - before initialization step (incorrect usage by design)
+			//  - if DB is corrupted (in future this case should be handled)
+			return false, errors.Errorf("(%T) could not get bucket %s", b, stringifyBounds(lower, upper))
+		}
+
+		return f(lower, upper, buck)
+	})
+}
+
+func (b *Blobovnicza) iterateBucketKeys(f func(uint64, uint64, []byte) (bool, error)) error {
+	return b.iterateBounds(func(lower, upper uint64) (bool, error) {
+		return f(lower, upper, bucketKeyFromBounds(upper))
+	})
+}
+
+func (b *Blobovnicza) iterateBounds(f func(uint64, uint64) (bool, error)) error {
+	for upper := firstBucketBound; upper <= b.objSizeLimit; upper *= 2 {
+		var lower uint64
+
+		if upper == firstBucketBound {
+			lower = 0
+		} else {
+			lower = upper/2 + 1
+		}
+
+		if stop, err := f(lower, upper); err != nil {
+			return err
+		} else if stop {
+			break
+		}
+	}
+
+	return nil
+}