tag.Add: allows users to register custom or missing tags into the tags registry

pkg/tag/tag.go

@@ -231,3 +231,12 @@
 	}
 	return Tag{Group: uint16(group), Element: uint16(elem)}, nil
 }
+
+// RegisterCustom allows to add a custom tag. This allows to work arond missing tag definitions
+// and to create private tags.
+// If the tag already exists it will be overridden.
+func RegisterCustom(info Info) {
+	maybeInitTagDict()
+
+	tagDict[info.Tag] = info
+}

pkg/tag/tag_test.go

@@ -45,6 +45,70 @@ func TestSplitTag(t *testing.T) {
 
 }
 
+func TestRegisterCustom(t *testing.T) {
+
+	t.Run("Add new tag", func(t *testing.T) {
+		// Given a certain tag does not exist
+		_, err := FindByName("TestTag")
+		if err == nil {
+			t.Fatalf("expected TestTag to not exist")
+		}
+
+		// When a new tag is registered
+		TagTestTag := Tag{Group: 0x0063, Element: 0x0020}
+		RegisterCustom(Info{
+			Tag:  TagTestTag,
+			VR:   "UT",
+			Name: "TestTag",
+			VM:   "1",
+		})
+
+		// Then the tag is now part of the tag collection
+		_, err = FindByName("TestTag")
+		if err != nil {
+			t.Fatalf("expected TestTag to be accessible with FindByName")
+		}
+		info, err := Find(TagTestTag)
+		if err != nil {
+			t.Fatalf("expected TestTag to be accessible with Find")
+		}
+		if info.VR != "UT" ||
+			info.Name != "TestTag" ||
+			info.VM != "1" {
+			t.Fatal("info of new registered tag is wrong")
+		}
+	})
+	t.Run("override existing tag", func(t *testing.T) {
+		// Given a tag already exists
+		TagTestTag := Tag{Group: 0x0010, Element: 0x0010} // this is the PatientName tag
+		info, err := Find(TagTestTag)
+		if err != nil {
+			t.Fatalf("expected TestTag to be accessible with Find")
+		}
+		if info.VR != "PN" {
+			t.Fatal("expected PatientName VR is originally PN")
+		}
+
+		// When the tag is registered with different content
+		RegisterCustom(Info{
+			Tag:  TagTestTag,
+			VR:   "LO", // originally this is PN
+			Name: "PatientName",
+			VM:   "1",
+		})
+
+		// Then the tag information is overridden
+		info, err = Find(TagTestTag)
+		if err != nil {
+			t.Fatalf("expected TestTag to be accessible with Find")
+		}
+		if info.VR != "LO" {
+			t.Fatal("expected the VR to have changed to LO")
+		}
+	})
+
+}
+
 func BenchmarkFindMetaGroupLengthTag(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		if _, err := Find(Tag{2, 0}); err != nil {