Cleanup instances of manual resolver construction

License: MIT
Signed-off-by: Łukasz Magiera <magik6k@gmail.com>

util.go

 package iface
 
 import (
+	"context"
 	"io"
 )
 
 type Reader interface {
-	io.ReadSeeker
+	ReadSeekCloser
+	Size() uint64
+	CtxReadFull(context.Context, []byte) (int, error)
+}
+
+// A ReadSeekCloser implements interfaces to read, copy, seek and close.
+type ReadSeekCloser interface {
+	io.Reader
+	io.Seeker
 	io.Closer
+	io.WriterTo
 }