add method to get name sanitized for tag value

this is going to be useful to implement the change documented
here in Metrictank:

https://github.com/graphite-project/graphite-web/pull/2458/files

Author: replay

metric.go

@@ -166,6 +166,22 @@ func (m *MetricDefinition) NameWithTags() string {
 	return m.nameWithTags
 }
 
+func (m *MetricDefinition) NameSanitizedAsTagValue() string {
+	if !strings.Contains(m.Name, "~") {
+		return m.Name
+	}
+
+	sanitized := []byte(m.Name)
+	for i := 0; i < len(sanitized); i++ {
+		if sanitized[i] == '~' {
+			sanitized = append(sanitized[:i], sanitized[i+1:]...)
+			i--
+		}
+	}
+
+	return string(sanitized)
+}
+
 func (m *MetricDefinition) SetId() {
 	sort.Strings(m.Tags)
 

metric_test.go

@@ -132,3 +132,38 @@ func TestNameWithTags(t *testing.T) {
 		}
 	}
 }
+
+func TestNameSanitizedAsTagValue(t *testing.T) {
+	type testCase struct {
+		originalName string
+		expectedName string
+	}
+	cases := []testCase{
+		{
+			originalName: "my~.test.abc",
+			expectedName: "my.test.abc",
+		}, {
+			originalName: "a.b.c",
+			expectedName: "a.b.c",
+		}, {
+			originalName: "~~a~~.~~~b~~~.~~~c~~~",
+			expectedName: "a.b.c",
+		}, {
+			originalName: "a.b.c~",
+			expectedName: "a.b.c",
+		}, {
+			originalName: "~a.b.c",
+			expectedName: "a.b.c",
+		}, {
+			originalName: "~a~",
+			expectedName: "a",
+		},
+	}
+	for i := range cases {
+		md := MetricDefinition{Name: cases[i].originalName}
+		sanitized := md.NameSanitizedAsTagValue()
+		if sanitized != cases[i].expectedName {
+			t.Fatalf("TC %d: Expected sanitized version of %s to be %s, but it was %s", i, md.Name, cases[i].expectedName, sanitized)
+		}
+	}
+}