allow for dynamic metric name

README.md

@@ -123,7 +123,17 @@ follows:
     test.web-server.foo.bar
      => test_web_server_foo_bar{}
 
-Each mapping in the configuration file must define a `name` for the metric.
+Each mapping in the configuration file must define a `name` for the metric. The
+metric's name can contain `$n`-style references to be replaced by the n-th
+wildcard match in the matching line. That allows for dynamic rewrites, such as:
+
+```yaml
+mappings:
+- match: test.*.*.counter
+  name: "${2}_counter"
+  labels:
+    provider: "$1"
+```
 
 If the default metric help text is insufficient for your needs you may use the YAML
 configuration to specify a custom help text for each mapping:

exporter.go

@@ -263,7 +263,7 @@ func (b *Exporter) Listen(e <-chan Events) {
 				help = mapping.HelpText
 			}
 			if present {
-				metricName = mapping.Name
+				metricName = escapeMetricName(mapping.Name)
 				for label, value := range labels {
 					prometheusLabels[label] = value
 				}

mapper.go

@@ -25,12 +25,12 @@ import (
 )
 
 var (
-	identifierRE   = `[a-zA-Z_][a-zA-Z0-9_]+`
-	statsdMetricRE = `[a-zA-Z_](-?[a-zA-Z0-9_])+`
+	statsdMetricRE    = `[a-zA-Z_](-?[a-zA-Z0-9_])+`
+	templateReplaceRE = `(\$\{?\d+\}?)`
 
 	metricLineRE = regexp.MustCompile(`^(\*\.|` + statsdMetricRE + `\.)+(\*|` + statsdMetricRE + `)$`)
-	labelLineRE  = regexp.MustCompile(`^(` + identifierRE + `)\s*=\s*"(.*)"$`)
-	metricNameRE = regexp.MustCompile(`^` + identifierRE + `$`)
+	metricNameRE = regexp.MustCompile(`^([a-zA-Z_]|` + templateReplaceRE + `)([a-zA-Z0-9_]|` + templateReplaceRE + `)*$`)
+	labelNameRE  = regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_]+$`)
 )
 
 type mapperConfigDefaults struct {
@@ -77,7 +77,7 @@ func (m *metricMapper) initFromYAMLString(fileContents string) error {
 
 		// check that label is correct
 		for k := range currentMapping.Labels {
-			if !metricNameRE.MatchString(k) {
+			if !labelNameRE.MatchString(k) {
 				return fmt.Errorf("invalid label key: %s", k)
 			}
 		}
@@ -150,11 +150,19 @@ func (m *metricMapper) getMapping(statsdMetric string) (*metricMapping, promethe
 			continue
 		}
 
+		mapping.Name = string(mapping.regex.ExpandString(
+			[]byte{},
+			mapping.Name,
+			statsdMetric,
+			matches,
+		))
+
 		labels := prometheus.Labels{}
 		for label, valueExpr := range mapping.Labels {
 			value := mapping.regex.ExpandString([]byte{}, valueExpr, statsdMetric, matches)
 			labels[label] = string(value)
 		}
+
 		return &mapping, labels, true
 	}
 

mapper_test.go

@@ -184,6 +184,33 @@ mappings:
   `,
 			configBad: true,
 		},
+		// Config with dynamic metric name.
+		{
+			config: `---
+mappings:
+- match: test1.*.*
+  name: "$1"
+  labels: {}
+- match: test2.*.*
+  name: "${1}_$2"
+  labels: {}
+- match: test3\.(\w+)\.(\w+)
+  match_type: regex
+  name: "${2}_$1"
+  labels: {}
+  `,
+			mappings: mappings{
+				"test1.total_requests.count": {
+					name: "total_requests",
+				},
+				"test2.total_requests.count": {
+					name: "total_requests_count",
+				},
+				"test3.total_requests.count": {
+					name: "count_total_requests",
+				},
+			},
+		},
 		// Config with bad metric name.
 		{
 			config: `---