graphite parser, handle multiple templates empty filter

Previously, the graphite parser would simply overwrite any template that
had an identical filter to a previous template. This included the empty
filter.

This change automatically creates a "*." filter for any template
specified with an empty filter. This allows users to specify only a
template, and Telegraf will auto-match based on the most specific
template.

closes #1731

plugins/parsers/graphite/parser.go

@@ -73,6 +73,20 @@ func NewGraphiteParser(
 			}
 		}
 
+		// if the template did not have a filter defined for it, then create a
+		// dummy filter of all '*'
+		// ie,
+		//   "measurement.host.metric"               -> *.*.*
+		//   "measurement.host.metric.metric.metric" -> *.*.*.*.*
+		//   "measurement.host.metric.metric"        -> *.*.*.*
+		if filter == "" {
+			stars := []string{}
+			for _, _ = range strings.Split(template, ".") {
+				stars = append(stars, "*")
+			}
+			filter = strings.Join(stars, ".")
+		}
+
 		// Parse out the default tags specific to this template
 		tags := map[string]string{}
 		if strings.Contains(parts[len(parts)-1], "=") {

plugins/parsers/graphite/parser_test.go

@@ -747,6 +747,31 @@ func TestApplyTemplateGreedyField(t *testing.T) {
 	}
 }
 
+func TestApplyTemplateMostSpecificTemplate(t *testing.T) {
+	p, err := NewGraphiteParser(
+		".",
+		[]string{
+			"measurement.host.metric",
+			"measurement.host.metric.metric.metric",
+			"measurement.host.metric.metric",
+		},
+		nil,
+	)
+	assert.NoError(t, err)
+
+	measurement, tags, _, err := p.ApplyTemplate("net.server001.a.b.c 2")
+	assert.Equal(t, "net", measurement)
+	assert.Equal(t,
+		map[string]string{"host": "server001", "metric": "a.b.c"},
+		tags)
+
+	measurement, tags, _, err = p.ApplyTemplate("net.server001.a.b 2")
+	assert.Equal(t, "net", measurement)
+	assert.Equal(t,
+		map[string]string{"host": "server001", "metric": "a.b"},
+		tags)
+}
+
 // Test Helpers
 func errstr(err error) string {
 	if err != nil {