Trim the Domain Name from cached image references

This commit removes the Domain Name, if any, from the cached image
reference before computing the image fingerprint. This way the same
image, if stored in some oter mirror, is still seen as the same one.

Fixes #158

pkg/helpers/references_test.go

@@ -0,0 +1,44 @@
+// Copyright © 2019-2020 Ettore Di Giacinto <mudler@gentoo.org>
+//                       David Cassany <dcassany@suse.com>
+//
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, see <http://www.gnu.org/licenses/>.
+
+package helpers_test
+
+import (
+	. "github.com/mudler/luet/pkg/helpers"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Helpers", func() {
+	Context("StripRegistryFromImage", func() {
+		It("Strips the domain name", func() {
+			out := StripRegistryFromImage("valid.domain.org/base/image:tag")
+			Expect(out).To(Equal("base/image:tag"))
+		})
+		It("Strips the domain name when port is included", func() {
+			out := StripRegistryFromImage("valid.domain.org:5000/base/image:tag")
+			Expect(out).To(Equal("base/image:tag"))
+		})
+		It("Does not strip the domain name", func() {
+			out := StripRegistryFromImage("not-a-domain/base/image:tag")
+			Expect(out).To(Equal("not-a-domain/base/image:tag"))
+		})
+		It("Does not strip the domain name on invalid domains", func() {
+			out := StripRegistryFromImage("-invaliddomain.org/base/image:tag")
+			Expect(out).To(Equal("-invaliddomain.org/base/image:tag"))
+		})
+	})
+})