Strips invalid characters in `promAdjust`.

The `promAdjust` function in `auto.go` previously allowed characters
that were not valid in prometheus metric names (e.g. '>'). This commit
updates `promAdjust` to remove invalid characters. The `TestPromAdjust`
function is updated with testcases that include invalid characters.

metrics/auto.go

@@ -1,22 +1,30 @@
 package metrics
 
 import (
+	"regexp"
 	"strings"
 	"sync"
 
 	"github.com/prometheus/client_golang/prometheus"
 )
 
+// per `prometheus/common/model/metric.go` and the `IsValidMetricName` function
+// only alphanumeric characters, underscore and `:` are valid characters in
+// a Prometheus metric name
+var invalidPromChars = regexp.MustCompile(`[^[:alnum:]\_:]+`)
+
 // promAdjust adjusts a name for use by Prometheus: It strips off a single label
 // of prefix (which is always the name of the service, and therefore duplicated
-// by Prometheus' instance labels), and replaces "-" and "." with "_".
+// by Prometheus' instance labels), and replaces "-" and "." with "_". Invalid
+// metric name characters that remain (e.g. `>`) are removed.
 func promAdjust(name string) string {
 	name = strings.Replace(name, "-", "_", -1)
 	labels := strings.Split(name, ".")
 	if len(labels) < 2 {
-		return labels[0]
+		return invalidPromChars.ReplaceAllString(labels[0], "")
 	}
-	return strings.Join(labels[1:], "_")
+	name = strings.Join(labels[1:], "_")
+	return invalidPromChars.ReplaceAllString(name, "")
 }
 
 // autoProm implements a bridge from statsd-style metrics to Prometheus-style

metrics/auto_test.go

@@ -16,11 +16,13 @@ func TestPromAdjust(t *testing.T) {
 		{"RA.FOO-BAR", "FOO_BAR"},
 		{"RA.FOO-BAR", "FOO_BAR"},
 		{"RA", "RA"},
+		{"RA>CA", "RACA"},
+		{"RA?CA!- 99 @#$%&()", "RACA_99"},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.input, func(t *testing.T) {
-			if promAdjust(tc.input) != tc.output {
+			if result := promAdjust(tc.input); result != tc.output {
-				t.Errorf("expected %q, got %q", tc.input, tc.output)
+				t.Errorf("promAdjust(%q) - expected %q, got %q", tc.input, tc.output, result)
 			}
 		})
 	}