[#176] localstore: Implement primary BlobStor

Implement primary local BLOB storage based on filesystem tree.

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

pkg/local_object_storage/blobstor/get.go

@@ -0,0 +1,83 @@
+package blobstor
+
+import (
+	"io/ioutil"
+	"os"
+
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/nspcc-dev/neofs-node/pkg/core/object"
+	"github.com/pkg/errors"
+)
+
+// GetPrm groups the parameters of Get operation.
+type GetPrm struct {
+	addr *objectSDK.Address
+}
+
+// GetRes groups resulting values of Get operation.
+type GetRes struct {
+	obj *object.Object
+}
+
+// ErrObjectNotFound is returns on read operations requested on a missing object.
+var ErrObjectNotFound = errors.New("object not found")
+
+// WithAddress is a Get option to set the address of the requested object.
+//
+// Option is required.
+func (p *GetPrm) WithAddress(addr *objectSDK.Address) *GetPrm {
+	if p != nil {
+		p.addr = addr
+	}
+
+	return p
+}
+
+// Object returns the requested object.
+func (r *GetRes) Object() *object.Object {
+	return r.obj
+}
+
+// Get reads the object from BLOB storage.
+//
+// Returns any error encountered that
+// did not allow to completely read the object part.
+func (b *BlobStor) Get(prm *GetPrm) (*GetRes, error) {
+	b.mtx.RLock()
+	defer b.mtx.RUnlock()
+
+	// get compressed object data
+	data, err := b.fsTree.get(prm.addr)
+	if err != nil {
+		if errors.Is(err, errFileNotFound) {
+			return nil, ErrObjectNotFound
+		}
+
+		return nil, errors.Wrap(err, "could not read object from fs tree")
+	}
+
+	data, err = b.decompressor(data)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not decompress object data")
+	}
+
+	// unmarshal the object
+	obj := object.New()
+	if err := obj.Unmarshal(data); err != nil {
+		return nil, errors.Wrap(err, "could not unmarshal the object")
+	}
+
+	return &GetRes{
+		obj: obj,
+	}, nil
+}
+
+func (t *fsTree) get(addr *objectSDK.Address) ([]byte, error) {
+	p := t.treePath(addr)
+
+	if _, err := os.Stat(p); os.IsNotExist(err) {
+		return nil, errFileNotFound
+	}
+
+	return ioutil.ReadFile(p)
+}