lib/protoparser/prometheus: allow trailing comma in tags list

The trailing comma is generated by cloudwatch exporter.
See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/350

lib/protoparser/prometheus/parser.go

@@ -193,12 +193,12 @@ func unmarshalRow(dst []Row, s string, tagsPool []Tag, noEscapes bool, errLogger
 var invalidLines = metrics.NewCounter(`vm_rows_invalid_total{type="prometheus"}`)
 
 func unmarshalTags(dst []Tag, s string, noEscapes bool) (string, []Tag, error) {
-	s = skipLeadingWhitespace(s)
-	if len(s) > 0 && s[0] == '}' {
-		// End of tags found.
-		return s[1:], dst, nil
-	}
 	for {
+		s = skipLeadingWhitespace(s)
+		if len(s) > 0 && s[0] == '}' {
+			// End of tags found.
+			return s[1:], dst, nil
+		}
 		n := strings.IndexByte(s, '=')
 		if n < 0 {
 			return s, dst, fmt.Errorf("missing value for tag %q", s)
@@ -248,7 +248,7 @@ func unmarshalTags(dst []Tag, s string, noEscapes bool) (string, []Tag, error) {
 		if len(s) == 0 || s[0] != ',' {
 			return s, dst, fmt.Errorf("missing comma after tag %s=%q", key, value)
 		}
-		s = skipLeadingWhitespace(s[1:])
+		s = s[1:]
 	}
 }
 

lib/protoparser/prometheus/parser_test.go

@@ -111,15 +111,14 @@ func TestRowsUnmarshalFailure(t *testing.T) {
 	f("a{")
 	f("a { ")
 	f("a {foo")
-	f("a {foo}")
+	f("a {foo} 3")
 	f("a {foo  =")
 	f(`a {foo  ="bar`)
 	f(`a {foo  ="b\ar`)
 	f(`a {foo  = "bar"`)
 	f(`a {foo  ="bar",`)
 	f(`a {foo  ="bar" , `)
-	f(`a {foo  ="bar" , }`)
+	f(`a {foo  ="bar" , baz } 2`)
-	f(`a {foo  ="bar" , baz }`)
 
 	// empty metric name
 	f(`{foo="bar"}`)
@@ -232,6 +231,20 @@ func TestRowsUnmarshalSuccess(t *testing.T) {
 		}},
 	})
 
+	// Trailing comma after tag
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/350
+	f(`foo{bar="baz",} 1 2`, &Rows{
+		Rows: []Row{{
+			Metric: "foo",
+			Tags: []Tag{{
+				Key:   "bar",
+				Value: "baz",
+			}},
+			Value:     1,
+			Timestamp: 2,
+		}},
+	})
+
 	// Multi lines
 	f("# foo\n # bar ba zzz\nfoo 0.3 2\naaa 3\nbar.baz 0.34 43\n", &Rows{
 		Rows: []Row{