Add drop action for matches

README.md

@@ -204,6 +204,27 @@ mappings:
     job: "${1}_server_other"
 ```
 
+You may also drop metrics by specifying a "drop" action on a match. For example:
+
+```yaml
+mappings:
+# This metric would match as normal.
+- match: test.timing.*.*.*
+  name: "my_timer"
+  labels: 
+    provider: "$2"
+    outcome: "$3"
+    job: "${1}_server"
+# Any metric not matched will be dropped because "." matches all metrics.
+- match: .
+  match_type: regex
+  action: drop
+  name: "dropped"
+```
+
+You can drop any metric using the normal match syntax.
+The default action is "map" which does the normal metrics mapping.
+
 ## Using Docker
 
 You can deploy this exporter using the [prom/statsd-exporter](https://registry.hub.docker.com/u/prom/statsd-exporter/) Docker image.

action.go

@@ -0,0 +1,42 @@
+// Copyright 2018 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import "fmt"
+
+type actionType string
+
+const (
+	actionTypeMap     actionType = "map"
+	actionTypeDrop    actionType = "drop"
+	actionTypeDefault actionType = ""
+)
+
+func (t *actionType) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var v string
+
+	if err := unmarshal(&v); err != nil {
+		return err
+	}
+
+	switch actionType(v) {
+	case actionTypeDrop:
+		*t = actionTypeDrop
+	case actionTypeMap, actionTypeDefault:
+		*t = actionTypeMap
+	default:
+		return fmt.Errorf("invalid action type %q", v)
+	}
+	return nil
+}

exporter.go

@@ -252,6 +252,11 @@ func (b *Exporter) Listen(e <-chan Events) {
 			if mapping == nil {
 				mapping = &metricMapping{}
 			}
+
+			if mapping.Action == actionTypeDrop {
+				continue
+			}
+
 			if mapping.HelpText == "" {
 				help = defaultHelp
 			} else {

mapper.go

@@ -54,6 +54,7 @@ type metricMapping struct {
 	Buckets   []float64         `yaml:"buckets"`
 	MatchType matchType         `yaml:"match_type"`
 	HelpText  string            `yaml:"help"`
+	Action    actionType        `yaml:"action"`
 }
 
 func (m *metricMapper) initFromYAMLString(fileContents string) error {
@@ -93,6 +94,10 @@ func (m *metricMapper) initFromYAMLString(fileContents string) error {
 			currentMapping.MatchType = n.Defaults.MatchType
 		}
 
+		if currentMapping.Action == "" {
+			currentMapping.Action = actionTypeMap
+		}
+
 		if currentMapping.MatchType == matchTypeGlob {
 			if !metricLineRE.MatchString(currentMapping.Match) {
 				return fmt.Errorf("invalid match: %s", currentMapping.Match)

mapper_test.go

@@ -360,6 +360,39 @@ mappings:
 				},
 			},
 		},
+		// Config that drops all.
+		{
+			config: `mappings:
+- match: .
+  match_type: regex
+  name: "drop"
+  action: drop`,
+			mappings: mappings{
+				"test.a": {},
+				"abc":    {},
+			},
+		},
+		// Config that has a catch-all to drop all.
+		{
+			config: `mappings:
+- match: web.*
+  name: "web"
+  labels:
+    site: "$1"
+- match: .
+  match_type: regex
+  name: "drop"
+  action: drop`,
+			mappings: mappings{
+				"test.a": {},
+				"web.localhost": {
+					name: "web",
+					labels: map[string]string{
+						"site": "localhost",
+					},
+				},
+			},
+		},
 	}
 
 	mapper := metricMapper{}
@@ -374,7 +407,7 @@ mappings:
 
 		for metric, mapping := range scenario.mappings {
 			m, labels, present := mapper.getMapping(metric)
-			if present && m.Name != mapping.name {
+			if present && mapping.name != "" && m.Name != mapping.name {
 				t.Fatalf("%d.%q: Expected name %v, got %v", i, metric, m.Name, mapping.name)
 			}
 			if mapping.notPresent && present {
@@ -392,3 +425,73 @@ mappings:
 		}
 	}
 }
+
+func TestAction(t *testing.T) {
+	scenarios := []struct {
+		config         string
+		configBad      bool
+		expectedAction actionType
+	}{
+		{
+			// no action set
+			config: `---
+mappings:
+- match: test.*.*
+  name: "foo"
+`,
+			configBad:      false,
+			expectedAction: actionTypeMap,
+		},
+		{
+			// map action set
+			config: `---
+mappings:
+- match: test.*.*
+  name: "foo"
+  action: map
+`,
+			configBad:      false,
+			expectedAction: actionTypeMap,
+		},
+		{
+			// drop action set
+			config: `---
+mappings:
+- match: test.*.*
+  name: "foo"
+  action: drop
+`,
+			configBad:      false,
+			expectedAction: actionTypeDrop,
+		},
+		{
+			// invalid action set
+			config: `---
+mappings:
+- match: test.*.*
+  name: "foo"
+  action: xyz
+`,
+			configBad:      true,
+			expectedAction: actionTypeDrop,
+		},
+	}
+
+	for i, scenario := range scenarios {
+		mapper := metricMapper{}
+		err := mapper.initFromYAMLString(scenario.config)
+		if err != nil && !scenario.configBad {
+			t.Fatalf("%d. Config load error: %s %s", i, scenario.config, err)
+		}
+		if err == nil && scenario.configBad {
+			t.Fatalf("%d. Expected bad config, but loaded ok: %s", i, scenario.config)
+		}
+
+		if !scenario.configBad {
+			a := mapper.Mappings[0].Action
+			if scenario.expectedAction != a {
+				t.Fatalf("%d: Expected action %v, got %v", i, scenario.expectedAction, a)
+			}
+		}
+	}
+}