[#472] blobstor: implement write-cache

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/local_object_storage/writecache/get.go

@@ -0,0 +1,51 @@
+package writecache
+
+import (
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/nspcc-dev/neofs-node/pkg/core/object"
+	"go.etcd.io/bbolt"
+)
+
+// Get returns object from write-cache.
+func (c *cache) Get(addr *objectSDK.Address) (*object.Object, error) {
+	saddr := addr.String()
+
+	c.mtx.RLock()
+	for i := range c.mem {
+		if saddr == c.mem[i].addr {
+			obj := c.mem[i].obj
+			c.mtx.RUnlock()
+			return obj, nil
+		}
+	}
+	c.mtx.RUnlock()
+
+	var value []byte
+	_ = c.db.View(func(tx *bbolt.Tx) error {
+		b := tx.Bucket(defaultBucket)
+		val := b.Get([]byte(saddr))
+		if val != nil {
+			value = cloneBytes(val)
+		}
+		return nil
+	})
+
+	if value != nil {
+		obj := object.New()
+		c.flushed.Get(saddr)
+		return obj, obj.Unmarshal(value)
+	}
+
+	data, err := c.fsTree.Get(addr)
+	if err != nil {
+		return nil, object.ErrNotFound
+	}
+
+	obj := object.New()
+	if err := obj.Unmarshal(data); err != nil {
+		return nil, err
+	}
+
+	c.flushed.Get(saddr)
+	return obj, nil
+}