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

pkg/tag/tag.go

@@ -7,6 +7,7 @@ package tag
 //go:generate stringer -type VRKind
 
 import (
+	"errors"
 	"fmt"
 	"strconv"
 	"strings"
@@ -245,3 +246,16 @@ func parseTag(tag string) (Tag, error) {
 	}
 	return Tag{Group: uint16(group), Element: uint16(elem)}, nil
 }
+
+// Add adds a custom tag to the lsit of registered tags. This enables users to work around missing tag definitions
+// and to create private tags.
+// If force == true existing tags will be overwritten.
+// Otherwise an error is returned when attempting to add an already existing tag.
+func Add(info Info, force bool) error {
+	_, found := tagDict[info.Tag]
+	if found && !force {
+		return errors.New("tag already exists")
+	}
+	tagDict[info.Tag] = info
+	return nil
+}

pkg/tag/tag_test.go

@@ -100,6 +100,94 @@ func TestUint32Conversion(t *testing.T) {
 	}
 }
 
+func TestRegisterCustom(t *testing.T) {
+
+	t.Run("Add new tag", func(t *testing.T) {
+		testInfo := Info{
+			Tag:  Tag{Group: 0x0063, Element: 0x0020},
+			VRs:  []string{"UT"},
+			Name: "TestTag",
+			VM:   "1",
+		}
+		// 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
+		err = Add(testInfo, false)
+		if err != nil {
+			t.Fatalf("SetInfo(TestInfo, false) == <error> , expected SetInfo to return nil when a unknown tag is added")
+		}
+
+		// Then the tag is now part of the tag collection
+		_, err = FindByName("TestTag")
+		if err != nil {
+			t.Errorf("expected TestTag to be accessible with FindByName")
+		}
+		info, err := Find(testInfo.Tag)
+		if err != nil {
+			t.Fatalf("expected TestTag to be accessible with Find")
+		}
+		if diff := cmp.Diff(testInfo, info); diff != "" {
+			t.Fatal("info of new registered tag is wrong: \n", diff)
+		}
+	})
+	t.Run("force overwrite existing tag", func(t *testing.T) {
+		// setup a test tag
+		testInfo := Info{
+			Tag:  Tag{Group: 0x0073, Element: 0x0021},
+			VRs:  []string{"UT"},
+			Name: "TestTag",
+			VM:   "1",
+		}
+		err := Add(testInfo, false)
+		if err != nil {
+			t.Fatalf("Add(testInfo, false) = error(%v), expected nil for unknown tag", err)
+		}
+
+		// now change the info
+		testInfo.VRs = []string{"LO"}
+		// and try to overwrite it with force
+		err = Add(testInfo, true)
+		if err != nil {
+			t.Fatalf("Add(testInfo, true) = error(%v), Add with force = true should never return an error", err)
+		}
+
+		// validate that the tag has been overwritten
+		info, err := Find(testInfo.Tag)
+		if err != nil {
+			t.Fatalf("expected added tag to be accessible with Find")
+		}
+		if info.VRs[0] != "LO" {
+			t.Fatal("expected the VR to have changed to LO")
+		}
+	})
+	t.Run("fail to overwrite existing tag", func(t *testing.T) {
+		// setup a test tag
+		testInfo := Info{
+			Tag:  Tag{Group: 0x0083, Element: 0x0031},
+			VRs:  []string{"UT"},
+			Name: "TestTag",
+			VM:   "1",
+		}
+		err := Add(testInfo, false)
+		if err != nil {
+			t.Fatalf("Add(testInfo, false) = error(%v), expected nil for unknown tag", err)
+		}
+
+		// now change the info
+		testInfo.VRs = []string{"LO"}
+		// and try to overwrite it with force
+		err = Add(testInfo, false)
+		if err == nil {
+			t.Fatalf("Add(testInfo, true) = nil, Add with force = false should return an error when trying to overwrite a tag")
+		}
+	})
+
+}
+
 func BenchmarkFindMetaGroupLengthTag(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		if _, err := Find(Tag{2, 0}); err != nil {