Check registry repository name against regexp

This regexp is extracted from Docker Distribution 2.4.1 docs, contains
additional `/` element that can be a separator of components.

lib/container_registry/path.rb

@@ -22,7 +22,9 @@ module ContainerRegistry
     end
 
     def valid?
-      @nodes.size > 1 && @nodes.size < Namespace::NUMBER_OF_ANCESTORS_ALLOWED
+      @path =~ Gitlab::Regex.container_repository_name_regex &&
+        @nodes.size > 1 &&
+        @nodes.size < Namespace::NUMBER_OF_ANCESTORS_ALLOWED
     end
 
     def components

lib/gitlab/regex.rb

@@ -121,6 +121,13 @@ module Gitlab
       git_reference_regex
     end
 
+    ##
+    # Docker Distribution Registry 2.4.1 repository name rules
+    #
+    def container_repository_name_regex
+      @container_repository_regex ||= %r{\A[a-z0-9]+(?:[-._/][a-z0-9]+)*\Z}
+    end
+
     def environment_name_regex
       @environment_name_regex ||= /\A[a-zA-Z0-9_\\\/\${}. -]+\z/.freeze
     end

spec/lib/container_registry/path_spec.rb

@@ -36,25 +36,31 @@ describe ContainerRegistry::Path do
     context 'when path has less than two components' do
       let(:path) { 'something/' }
 
-      it 'is not valid' do
-        expect(subject).not_to be_valid
-      end
+      it { is_expected.not_to be_valid }
     end
 
     context 'when path has more than allowed number of components' do
       let(:path) { 'a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/r/s/t/u/w/y/z' }
 
-      it 'is not valid' do
-        expect(subject).not_to be_valid
-      end
+      it { is_expected.not_to be_valid }
+    end
+
+    context 'when path has invalid characters' do
+      let(:path) { 'some\path' }
+
+      it { is_expected.not_to be_valid }
     end
 
     context 'when path has two or more components' do
       let(:path) { 'some/path' }
 
-      it 'is valid' do
-        expect(subject).to be_valid
-      end
+      it { is_expected.to be_valid }
+    end
+
+    context 'when path is related to multi-level image' do
+      let(:path) { 'some/path/my/image' }
+
+      it { is_expected.to be_valid }
     end
   end