add librato tagging support

conn.go

@@ -195,7 +195,7 @@ func isNegative(v interface{}) bool {
 func (c *conn) appendBucket(prefix, bucket string, tags string) {
 	c.appendString(prefix)
 	c.appendString(bucket)
-	if c.tagFormat == InfluxDB {
+	if c.tagFormat == InfluxDB || c.tagFormat == Librato {
 		c.appendString(tags)
 	}
 	c.appendByte(':')
@@ -247,13 +247,12 @@ func (c *conn) flush(n int) {
 		n = len(c.buf)
 	}
 
-	// Trim the last \n, StatsD does not like it.
-	_, err := c.w.Write(c.buf[:n-1])
+	total, err := c.w.Write(c.buf[:n])
 	c.handleError(err)
-	if n < len(c.buf) {
-		copy(c.buf, c.buf[n:])
+	if total < len(c.buf) {
+		copy(c.buf, c.buf[total:])
 	}
-	c.buf = c.buf[:len(c.buf)-n]
+	c.buf = c.buf[:len(c.buf)-total]
 }
 
 func (c *conn) handleError(err error) {

options.go

@@ -191,6 +191,7 @@ const (
 	// Datadog tag format.
 	// See http://docs.datadoghq.com/guides/metrics/#tags
 	Datadog
+	Librato
 )
 
 var (
@@ -224,6 +225,20 @@ var (
 			}
 			return buf.String()
 		},
+		Librato: func(tags []tag) string {
+			var buf bytes.Buffer
+			for i, tag := range tags {
+				if i == 0 {
+					_ = buf.WriteByte('#')
+				} else {
+					_ = buf.WriteByte(',')
+				}
+				_, _ = buf.WriteString(tag.K)
+				_ = buf.WriteByte('=')
+				_, _ = buf.WriteString(tag.V)
+			}
+			return buf.String()
+		},
 	}
 	splitFuncs = map[TagFormat]func(string) []tag{
 		InfluxDB: func(s string) []tag {
@@ -246,5 +261,15 @@ var (
 			}
 			return tags
 		},
+		Librato: func(s string) []tag {
+			s = s[1:]
+			pairs := strings.Split(s, ",")
+			tags := make([]tag, len(pairs))
+			for i, pair := range pairs {
+				kv := strings.Split(pair, ":")
+				tags[i] = tag{K: kv[0], V: kv[1]}
+			}
+			return tags
+		},
 	}
 )

statsd_test.go

@@ -179,6 +179,12 @@ func TestDatadogTags(t *testing.T) {
 	}, TagsFormat(Datadog), Tags("tag1", "value1", "tag2", "value2"))
 }
 
+func TestLibratoTags(t *testing.T) {
+	testOutput(t, "test_key#tag1=value1,tag2=value2:1|c", func(c *Client) {
+		c.Increment(testKey)
+	}, TagsFormat(Librato), Tags("tag1", "value1", "tag2", "value2"))
+}
+
 func TestNoTagFormat(t *testing.T) {
 	testOutput(t, "test_key:1|c", func(c *Client) {
 		c.Increment(testKey)