Check if tag value is empty before allocation

closes #2390
closes #2404

metric/metric.go

@@ -44,13 +44,18 @@ func New(
 	// pre-allocate exact size of the tags slice
 	taglen := 0
 	for k, v := range tags {
-		// TODO check that length of tag key & value are > 0
+		if len(k) == 0 || len(v) == 0 {
+			continue
+		}
 		taglen += 2 + len(escape(k, "tagkey")) + len(escape(v, "tagval"))
 	}
 	m.tags = make([]byte, taglen)
 
 	i := 0
 	for k, v := range tags {
+		if len(k) == 0 || len(v) == 0 {
+			continue
+		}
 		m.tags[i] = ','
 		i++
 		i += copy(m.tags[i:], escape(k, "tagkey"))

metric/metric_test.go

@@ -625,3 +625,26 @@ func TestNewMetricFailNaN(t *testing.T) {
 	_, err := New("cpu", tags, fields, now)
 	assert.NoError(t, err)
 }
+
+func TestEmptyTagValueOrKey(t *testing.T) {
+	now := time.Now()
+
+	tags := map[string]string{
+		"host":     "localhost",
+		"emptytag": "",
+		"":         "valuewithoutkey",
+	}
+	fields := map[string]interface{}{
+		"usage_idle": float64(99),
+	}
+	m, err := New("cpu", tags, fields, now)
+
+	assert.True(t, m.HasTag("host"))
+	assert.False(t, m.HasTag("emptytag"))
+	assert.Equal(t,
+		fmt.Sprintf("cpu,host=localhost usage_idle=99 %d\n", now.UnixNano()),
+		m.String())
+
+	assert.NoError(t, err)
+
+}