[#789] blobstor: Implement iterator

There is a need to be able to process all objects saved in `BlobStor`.

Implement `BlobStor.Iterate` method which iterates over all objects.
Implement `IterateBinaryObjects` and `IterateObjects` helper functions to
simplify the code.

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

pkg/local_object_storage/blobstor/iterate.go

@@ -1,12 +1,33 @@
 package blobstor
 
 import (
+	"fmt"
+
 	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/nspcc-dev/neofs-node/pkg/core/object"
 	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/blobovnicza"
 )
 
-// IterationHandler represents the action to be performed on each iteration.
-type IterationHandler func(*objectSDK.Address, *blobovnicza.ID) error
+// IterationElement represents a unit of elements through which Iterate operation passes.
+type IterationElement struct {
+	data []byte
+
+	blzID *blobovnicza.ID
+}
+
+// ObjectData returns stored object in a binary representation.
+func (x IterationElement) ObjectData() []byte {
+	return x.data
+}
+
+// BlobovniczaID returns identifier of Blobovnicza in which object is stored.
+// Returns nil if object isn't in Blobovnicza.
+func (x IterationElement) BlobovniczaID() *blobovnicza.ID {
+	return x.blzID
+}
+
+// IterationHandler is a generic processor of IterationElement.
+type IterationHandler func(IterationElement) error
 
 // IteratePrm groups the parameters of Iterate operation.
 type IteratePrm struct {
@@ -27,7 +48,78 @@ func (i *IteratePrm) SetIterationHandler(h IterationHandler) {
 // Returns any error encountered that
 // did not allow to completely iterate over the storage.
 //
-// If handler returns an error, method returns it immediately.
-func (b *BlobStor) Iterate(prm *IteratePrm) (*IterateRes, error) {
-	panic("implement me")
+// If handler returns an error, method wraps and returns it immediately.
+func (b *BlobStor) Iterate(prm IteratePrm) (*IterateRes, error) {
+	var elem IterationElement
+
+	err := b.blobovniczas.iterateBlobovniczas(func(p string, blz *blobovnicza.Blobovnicza) error {
+		err := blobovnicza.IterateObjects(blz, func(data []byte) error {
+			var err error
+
+			// decompress the data
+			elem.data, err = b.decompressor(data)
+			if err != nil {
+				return fmt.Errorf("could not decompress object data: %w", err)
+			}
+
+			elem.blzID = blobovnicza.NewIDFromBytes([]byte(p))
+
+			return prm.handler(elem)
+		})
+		if err != nil {
+			return fmt.Errorf("blobovnicza iterator failure %s: %w", p, err)
+		}
+
+		return nil
+	})
+	if err != nil {
+		return nil, fmt.Errorf("blobovniczas iterator failure: %w", err)
+	}
+
+	elem.blzID = nil
+
+	err = b.fsTree.Iterate(func(_ *objectSDK.Address, data []byte) error {
+		// decompress the data
+		elem.data, err = b.decompressor(data)
+		if err != nil {
+			return fmt.Errorf("could not decompress object data: %w", err)
+		}
+
+		return prm.handler(elem)
+	})
+	if err != nil {
+		return nil, fmt.Errorf("fs tree iterator failure: %w", err)
+	}
+
+	return new(IterateRes), nil
+}
+
+// IterateBinaryObjects is a helper function which iterates over BlobStor and passes binary objects to f.
+func IterateBinaryObjects(blz *BlobStor, f func(data []byte, blzID *blobovnicza.ID) error) error {
+	var prm IteratePrm
+
+	prm.SetIterationHandler(func(elem IterationElement) error {
+		return f(elem.ObjectData(), elem.BlobovniczaID())
+	})
+
+	_, err := blz.Iterate(prm)
+
+	return err
+}
+
+// IterateObjects is a helper function which iterates over BlobStor and passes decoded objects to f.
+func IterateObjects(blz *BlobStor, f func(obj *object.Object, blzID *blobovnicza.ID) error) error {
+	var obj *object.Object
+
+	return IterateBinaryObjects(blz, func(data []byte, blzID *blobovnicza.ID) error {
+		if obj == nil {
+			obj = object.New()
+		}
+
+		if err := obj.Unmarshal(data); err != nil {
+			return fmt.Errorf("could not unmarshal the object: %w", err)
+		}
+
+		return f(obj, blzID)
+	})
 }