rework metricLineRE to support matching segments that start with a number

Signed-off-by: glightfoot <glightfoot@rsglab.com>

pkg/mapper/mapper.go

@@ -28,10 +28,14 @@ import (
 )
 
 var (
-	statsdMetricRE    = `[a-zA-Z_](-?[a-zA-Z0-9_])*`
-	templateReplaceRE = `(\$\{?\d+\}?)`
+	// The first segment of a match cannot start with a number
+	statsdMetricRE = `[a-zA-Z_](-?[a-zA-Z0-9_])*`
+	// The subsequent segments of a match can start with a number
+	// See https://github.com/prometheus/statsd_exporter/issues/328
+	statsdMetricSubsequentRE = `[a-zA-Z0-9_](-?[a-zA-Z0-9_])*`
+	templateReplaceRE        = `(\$\{?\d+\}?)`
 
-	metricLineRE = regexp.MustCompile(`^(\*\.|` + statsdMetricRE + `\.)+(\*|` + statsdMetricRE + `)$`)
+	metricLineRE = regexp.MustCompile(`^(\*|` + statsdMetricRE + `)(\.\*|\.` + statsdMetricSubsequentRE + `)*$`)
 	metricNameRE = regexp.MustCompile(`^([a-zA-Z_]|` + templateReplaceRE + `)([a-zA-Z0-9_]|` + templateReplaceRE + `)*$`)
 	labelNameRE  = regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_]+$`)
 )

pkg/mapper/mapper_test.go

@@ -337,6 +337,39 @@ mappings:
 				},
 			},
 		},
+		{
+			testName: "Match metric segment starting with a number",
+			config: `
+mappings:
+- match: test.99.myapp.*
+  name: "name"
+  labels:
+    label: "${1}_foo"
+  `,
+			mappings: mappings{
+				{
+					statsdMetric: "test.99.myapp.create",
+					name:         "name",
+					labels: map[string]string{
+						"label": "create_foo",
+					},
+				},
+			},
+		},
+		{
+			testName: "Match metric segment starting with a number #328 example",
+			config: `
+mappings:
+- match: kafka.server.FetcherStats.brokerHost.hostname.brokerPort.9092.clientId.ReplicaFetcherThread-0-1.BytesPerSec.1MinuteRate.gauge
+  name: "example_name"
+  `,
+			mappings: mappings{
+				{
+					statsdMetric: "kafka.server.FetcherStats.brokerHost.hostname.brokerPort.9092.clientId.ReplicaFetcherThread-0-1.BytesPerSec.1MinuteRate.gauge",
+					name:         "example_name",
+				},
+			},
+		},
 		{
 			testName: "Config with bad metric line",
 			config: `---