[#208] pkg/client: Add function to get container and verify ID

GetContainer method reads container structure by identifier from the
network. In some cases it is required to additionally check the
correspondence of the container structure to the identifier as a hash from
the binary representation. To do this, a new function
GetVerifiedContainerStructure is defined to execute the check after
receiving the container.

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

pkg/client/container.go

@@ -64,6 +64,23 @@ func (c Client) GetContainer(ctx context.Context, id *container.ID, opts ...Call
 	}
 }
 
+// GetVerifiedContainerStructure is a wrapper over Client.GetContainer method
+// which checks if the structure of the resulting container matches its identifier.
+//
+// Returns container.ErrIDMismatch if container does not match the identifier.
+func GetVerifiedContainerStructure(ctx context.Context, c *Client, id *container.ID, opts ...CallOption) (*container.Container, error) {
+	cnr, err := c.GetContainer(ctx, id, opts...)
+	if err != nil {
+		return nil, err
+	}
+
+	if !container.CalculateID(cnr).Equal(id) {
+		return nil, container.ErrIDMismatch
+	}
+
+	return cnr, nil
+}
+
 func (c Client) ListContainers(ctx context.Context, owner *owner.ID, opts ...CallOption) ([]*container.ID, error) {
 	switch c.remoteNode.Version.Major() {
 	case 2: