feat: Extend regexp processor do allow renaming of measurements, tags and fields (#9561)

plugins/processors/regex/README.md

@@ -4,6 +4,8 @@ The `regex` plugin transforms tag and field values with regex pattern. If `resul
 
 For tags transforms, if `append` is set to `true`, it will append the transformation to the existing tag value, instead of overwriting it.
 
+For metrics transforms, `key` denotes the element that should be transformed. Furthermore, `result_key` allows control over the behavior applied in case the resulting `tag` or `field` name already exists.
+
 ### Configuration:
 
 ```toml
@@ -38,6 +40,38 @@ For tags transforms, if `append` is set to `true`, it will append the transforma
     pattern = ".*category=(\\w+).*"
     replacement = "${1}"
     result_key = "search_category"
+
+  # Rename metric fields
+  [[processors.regex.field_rename]]
+    ## Regular expression to match on a field name
+    pattern = "^search_(\\w+)d$"
+    ## Matches of the pattern will be replaced with this string.  Use ${1}
+    ## notation to use the text of the first submatch.
+    replacement = "${1}"
+    ## If the new field name already exists, you can either "overwrite" the
+    ## existing one with the value of the renamed field OR you can "keep"
+    ## both the existing and source field.
+    # result_key = "keep"
+
+  # Rename metric tags
+  # [[processors.regex.tag_rename]]
+  #   ## Regular expression to match on a tag name
+  #   pattern = "^search_(\\w+)d$"
+  #   ## Matches of the pattern will be replaced with this string.  Use ${1}
+  #   ## notation to use the text of the first submatch.
+  #   replacement = "${1}"
+  #   ## If the new tag name already exists, you can either "overwrite" the
+  #   ## existing one with the value of the renamed tag OR you can "keep"
+  #   ## both the existing and source tag.
+  #   # result_key = "keep"
+
+  # Rename metrics
+  # [[processors.regex.metric_rename]]
+  #   ## Regular expression to match on an metric name
+  #   pattern = "^search_(\\w+)d$"
+  #   ## Matches of the pattern will be replaced with this string.  Use ${1}
+  #   ## notation to use the text of the first submatch.
+  #   replacement = "${1}"
 ```
 
 ### Tags:
@@ -46,5 +80,5 @@ No tags are applied by this processor.
 
 ### Example Output:
 ```
-nginx_requests,verb=GET,resp_code=2xx request="/api/search/?category=plugins&q=regex&sort=asc",method="/search/",search_category="plugins",referrer="-",ident="-",http_version=1.1,agent="UserAgent",client_ip="127.0.0.1",auth="-",resp_bytes=270i 1519652321000000000
+nginx_requests,verb=GET,resp_code=2xx request="/api/search/?category=plugins&q=regex&sort=asc",method="/search/",category="plugins",referrer="-",ident="-",http_version=1.1,agent="UserAgent",client_ip="127.0.0.1",auth="-",resp_bytes=270i 1519652321000000000
 ```

plugins/processors/regex/regex.go

@@ -1,24 +1,30 @@
 package regex
 
 import (
+	"fmt"
 	"regexp"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal/choice"
 	"github.com/influxdata/telegraf/plugins/processors"
 )
 
 type Regex struct {
-	Tags       []converter
+	Tags         []converter     `toml:"tags"`
-	Fields     []converter
+	Fields       []converter     `toml:"fields"`
+	TagRename    []converter     `toml:"tag_rename"`
+	FieldRename  []converter     `toml:"field_rename"`
+	MetricRename []converter     `toml:"metric_rename"`
+	Log          telegraf.Logger `toml:"-"`
 	regexCache   map[string]*regexp.Regexp
 }
 
 type converter struct {
-	Key         string
+	Key         string `toml:"key"`
-	Pattern     string
+	Pattern     string `toml:"pattern"`
-	Replacement string
+	Replacement string `toml:"replacement"`
-	ResultKey   string
+	ResultKey   string `toml:"result_key"`
-	Append      bool
+	Append      bool   `toml:"append"`
 }
 
 const sampleConfig = `
@@ -50,12 +56,105 @@ const sampleConfig = `
   #   pattern = ".*category=(\\w+).*"
   #   replacement = "${1}"
   #   result_key = "search_category"
+
+  ## Rename metric fields
+  # [[processors.regex.field_rename]]
+  #   ## Regular expression to match on a field name
+  #   pattern = "^search_(\\w+)d$"
+  #   ## Matches of the pattern will be replaced with this string.  Use ${1}
+  #   ## notation to use the text of the first submatch.
+  #   replacement = "${1}"
+  #   ## If the new field name already exists, you can either "overwrite" the
+  #   ## existing one with the value of the renamed field OR you can "keep"
+  #   ## both the existing and source field.
+  #   # result_key = "keep"
+
+  ## Rename metric tags
+  # [[processors.regex.tag_rename]]
+  #   ## Regular expression to match on a tag name
+  #   pattern = "^search_(\\w+)d$"
+  #   ## Matches of the pattern will be replaced with this string.  Use ${1}
+  #   ## notation to use the text of the first submatch.
+  #   replacement = "${1}"
+  #   ## If the new tag name already exists, you can either "overwrite" the
+  #   ## existing one with the value of the renamed tag OR you can "keep"
+  #   ## both the existing and source tag.
+  #   # result_key = "keep"
+
+  ## Rename metrics
+  # [[processors.regex.metric_rename]]
+  #   ## Regular expression to match on an metric name
+  #   pattern = "^search_(\\w+)d$"
+  #   ## Matches of the pattern will be replaced with this string.  Use ${1}
+  #   ## notation to use the text of the first submatch.
+  #   replacement = "${1}"
 `
 
-func NewRegex() *Regex {
+func (r *Regex) Init() error {
-	return &Regex{
+	r.regexCache = make(map[string]*regexp.Regexp)
-		regexCache: make(map[string]*regexp.Regexp),
+
+	// Compile the regular expressions
+	for _, c := range r.Tags {
+		if _, compiled := r.regexCache[c.Pattern]; !compiled {
+			r.regexCache[c.Pattern] = regexp.MustCompile(c.Pattern)
 		}
+	}
+	for _, c := range r.Fields {
+		if _, compiled := r.regexCache[c.Pattern]; !compiled {
+			r.regexCache[c.Pattern] = regexp.MustCompile(c.Pattern)
+		}
+	}
+
+	resultOptions := []string{"overwrite", "keep"}
+	for _, c := range r.TagRename {
+		if c.Key != "" {
+			r.Log.Info("'tag_rename' section contains a key which is ignored during processing")
+		}
+
+		if c.ResultKey == "" {
+			c.ResultKey = "keep"
+		}
+		if err := choice.Check(c.ResultKey, resultOptions); err != nil {
+			return fmt.Errorf("invalid metrics result_key: %v", err)
+		}
+
+		if _, compiled := r.regexCache[c.Pattern]; !compiled {
+			r.regexCache[c.Pattern] = regexp.MustCompile(c.Pattern)
+		}
+	}
+
+	for _, c := range r.FieldRename {
+		if c.Key != "" {
+			r.Log.Info("'field_rename' section contains a key which is ignored during processing")
+		}
+
+		if c.ResultKey == "" {
+			c.ResultKey = "keep"
+		}
+		if err := choice.Check(c.ResultKey, resultOptions); err != nil {
+			return fmt.Errorf("invalid metrics result_key: %v", err)
+		}
+
+		if _, compiled := r.regexCache[c.Pattern]; !compiled {
+			r.regexCache[c.Pattern] = regexp.MustCompile(c.Pattern)
+		}
+	}
+
+	for _, c := range r.MetricRename {
+		if c.Key != "" {
+			r.Log.Info("'metric_rename' section contains a key which is ignored during processing")
+		}
+
+		if c.ResultKey != "" {
+			r.Log.Info("'metric_rename' section contains a 'result_key' ignored during processing as metrics will ALWAYS the name")
+		}
+
+		if _, compiled := r.regexCache[c.Pattern]; !compiled {
+			r.regexCache[c.Pattern] = regexp.MustCompile(c.Pattern)
+		}
+	}
+
+	return nil
 }
 
 func (r *Regex) SampleConfig() string {
@@ -63,7 +162,7 @@ func (r *Regex) SampleConfig() string {
 }
 
 func (r *Regex) Description() string {
-	return "Transforms tag and field values with regex pattern"
+	return "Transforms tag and field values as well as measurement, tag and field names with regex pattern"
 }
 
 func (r *Regex) Apply(in ...telegraf.Metric) []telegraf.Metric {
@@ -83,27 +182,96 @@ func (r *Regex) Apply(in ...telegraf.Metric) []telegraf.Metric {
 
 		for _, converter := range r.Fields {
 			if value, ok := metric.GetField(converter.Key); ok {
-				switch value := value.(type) {
+				if v, ok := value.(string); ok {
-				case string:
+					if key, newValue := r.convert(converter, v); newValue != "" {
-					if key, newValue := r.convert(converter, value); newValue != "" {
 						metric.AddField(key, newValue)
 					}
 				}
 			}
 		}
+
+		for _, converter := range r.TagRename {
+			regex := r.regexCache[converter.Pattern]
+			replacements := make(map[string]string)
+			for _, tag := range metric.TagList() {
+				name := tag.Key
+				if regex.MatchString(name) {
+					newName := regex.ReplaceAllString(name, converter.Replacement)
+
+					if !metric.HasTag(newName) {
+						// There is no colliding tag, we can just change the name.
+						tag.Key = newName
+						continue
+					}
+
+					if converter.ResultKey == "overwrite" {
+						// We got a colliding tag, remember the replacement and do it later
+						replacements[name] = newName
+					}
+				}
+			}
+			// We needed to postpone the replacement as we cannot modify the tag-list
+			// while iterating it as this will result in invalid memory dereference panic.
+			for oldName, newName := range replacements {
+				value, ok := metric.GetTag(oldName)
+				if !ok {
+					// Just in case the tag got removed in the meantime
+					continue
+				}
+				metric.AddTag(newName, value)
+				metric.RemoveTag(oldName)
+			}
+		}
+
+		for _, converter := range r.FieldRename {
+			regex := r.regexCache[converter.Pattern]
+			replacements := make(map[string]string)
+			for _, field := range metric.FieldList() {
+				name := field.Key
+				if regex.MatchString(name) {
+					newName := regex.ReplaceAllString(name, converter.Replacement)
+
+					if !metric.HasField(newName) {
+						// There is no colliding field, we can just change the name.
+						field.Key = newName
+						continue
+					}
+
+					if converter.ResultKey == "overwrite" {
+						// We got a colliding field, remember the replacement and do it later
+						replacements[name] = newName
+					}
+				}
+			}
+			// We needed to postpone the replacement as we cannot modify the field-list
+			// while iterating it as this will result in invalid memory dereference panic.
+			for oldName, newName := range replacements {
+				value, ok := metric.GetField(oldName)
+				if !ok {
+					// Just in case the field got removed in the meantime
+					continue
+				}
+				metric.AddField(newName, value)
+				metric.RemoveField(oldName)
+			}
+		}
+
+		for _, converter := range r.MetricRename {
+			regex := r.regexCache[converter.Pattern]
+			value := metric.Name()
+			if regex.MatchString(value) {
+				newValue := regex.ReplaceAllString(value, converter.Replacement)
+				metric.SetName(newValue)
+			}
+		}
 	}
 
 	return in
 }
 
-func (r *Regex) convert(c converter, src string) (string, string) {
+func (r *Regex) convert(c converter, src string) (key string, value string) {
-	regex, compiled := r.regexCache[c.Pattern]
+	regex := r.regexCache[c.Pattern]
-	if !compiled {
-		regex = regexp.MustCompile(c.Pattern)
-		r.regexCache[c.Pattern] = regex
-	}
 
-	value := ""
 	if c.ResultKey == "" || regex.MatchString(src) {
 		value = regex.ReplaceAllString(src, c.Replacement)
 	}
@@ -116,7 +284,5 @@ func (r *Regex) convert(c converter, src string) (string, string) {
 }
 
 func init() {
-	processors.Add("regex", func() telegraf.Processor {
+	processors.Add("regex", func() telegraf.Processor { return &Regex{} })
-		return NewRegex()
-	})
 }

plugins/processors/regex/regex_test.go

@@ -5,12 +5,14 @@ import (
 	"time"
 
 	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/metric"
+	"github.com/influxdata/telegraf/testutil"
-	"github.com/stretchr/testify/assert"
+
+	"github.com/stretchr/testify/require"
 )
 
 func newM1() telegraf.Metric {
-	m1 := metric.New("access_log",
+	return testutil.MustMetric(
+		"access_log",
 		map[string]string{
 			"verb":      "GET",
 			"resp_code": "200",
@@ -20,11 +22,11 @@ func newM1() telegraf.Metric {
 		},
 		time.Now(),
 	)
-	return m1
 }
 
 func newM2() telegraf.Metric {
-	m2 := metric.New("access_log",
+	return testutil.MustMetric(
+		"access_log",
 		map[string]string{
 			"verb":      "GET",
 			"resp_code": "200",
@@ -36,7 +38,6 @@ func newM2() telegraf.Metric {
 		},
 		time.Now(),
 	)
-	return m2
 }
 
 func TestFieldConversions(t *testing.T) {
@@ -72,10 +73,11 @@ func TestFieldConversions(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		regex := NewRegex()
+		regex := Regex{
-		regex.Fields = []converter{
+			Fields: []converter{test.converter},
-			test.converter,
+			Log:    testutil.Logger{},
 		}
+		require.NoError(t, regex.Init())
 
 		processed := regex.Apply(newM1())
 
@@ -84,9 +86,9 @@ func TestFieldConversions(t *testing.T) {
 			"resp_code": "200",
 		}
 
-		assert.Equal(t, test.expectedFields, processed[0].Fields(), test.message)
+		require.Equal(t, test.expectedFields, processed[0].Fields(), test.message)
-		assert.Equal(t, expectedTags, processed[0].Tags(), "Should not change tags")
+		require.Equal(t, expectedTags, processed[0].Tags(), "Should not change tags")
-		assert.Equal(t, "access_log", processed[0].Name(), "Should not change name")
+		require.Equal(t, "access_log", processed[0].Name(), "Should not change name")
 	}
 }
 
@@ -139,10 +141,11 @@ func TestTagConversions(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		regex := NewRegex()
+		regex := Regex{
-		regex.Tags = []converter{
+			Tags: []converter{test.converter},
-			test.converter,
+			Log:  testutil.Logger{},
 		}
+		require.NoError(t, regex.Init())
 
 		processed := regex.Apply(newM1())
 
@@ -150,15 +153,549 @@ func TestTagConversions(t *testing.T) {
 			"request": "/users/42/",
 		}
 
-		assert.Equal(t, expectedFields, processed[0].Fields(), test.message, "Should not change fields")
+		require.Equal(t, expectedFields, processed[0].Fields(), test.message, "Should not change fields")
-		assert.Equal(t, test.expectedTags, processed[0].Tags(), test.message)
+		require.Equal(t, test.expectedTags, processed[0].Tags(), test.message)
-		assert.Equal(t, "access_log", processed[0].Name(), "Should not change name")
+		require.Equal(t, "access_log", processed[0].Name(), "Should not change name")
+	}
+}
+
+func TestMetricNameConversions(t *testing.T) {
+	inputTemplate := []telegraf.Metric{
+		testutil.MustMetric(
+			"access_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "200",
+			},
+			map[string]interface{}{
+				"request": "/users/42/",
+			},
+			time.Unix(1627646243, 0),
+		),
+		testutil.MustMetric(
+			"access_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "200",
+			},
+			map[string]interface{}{
+				"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+				"ignore_number": int64(200),
+				"ignore_bool":   true,
+			},
+			time.Unix(1627646253, 0),
+		),
+		testutil.MustMetric(
+			"error_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "404",
+			},
+			map[string]interface{}{
+				"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+				"ignore_number": int64(404),
+				"ignore_flag":   true,
+				"error_message": "request too silly",
+			},
+			time.Unix(1627646263, 0),
+		),
+	}
+
+	tests := []struct {
+		name      string
+		converter converter
+		expected  []telegraf.Metric
+	}{
+		{
+			name: "Should change metric name",
+			converter: converter{
+				Pattern:     "^(\\w+)_log$",
+				Replacement: "${1}",
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"access",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request": "/users/42/",
+					},
+					time.Unix(1627646243, 0),
+				),
+				testutil.MustMetric(
+					"access",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(200),
+						"ignore_bool":   true,
+					},
+					time.Unix(1627646253, 0),
+				),
+				testutil.MustMetric(
+					"error",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "404",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(404),
+						"ignore_flag":   true,
+						"error_message": "request too silly",
+					},
+					time.Unix(1627646263, 0),
+				),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		// Copy the inputs as they will be modified by the processor
+		input := make([]telegraf.Metric, len(inputTemplate))
+		for i, m := range inputTemplate {
+			input[i] = m.Copy()
+		}
+
+		t.Run(test.name, func(t *testing.T) {
+			regex := Regex{
+				MetricRename: []converter{test.converter},
+				Log:          testutil.Logger{},
+			}
+			require.NoError(t, regex.Init())
+
+			actual := regex.Apply(input...)
+			testutil.RequireMetricsEqual(t, test.expected, actual)
+		})
+	}
+}
+
+func TestFieldRenameConversions(t *testing.T) {
+	inputTemplate := []telegraf.Metric{
+		testutil.MustMetric(
+			"access_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "200",
+			},
+			map[string]interface{}{
+				"request": "/users/42/",
+			},
+			time.Unix(1627646243, 0),
+		),
+		testutil.MustMetric(
+			"access_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "200",
+			},
+			map[string]interface{}{
+				"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+				"ignore_number": int64(200),
+				"ignore_bool":   true,
+			},
+			time.Unix(1627646253, 0),
+		),
+		testutil.MustMetric(
+			"error_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "404",
+			},
+			map[string]interface{}{
+				"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+				"ignore_number": int64(404),
+				"ignore_flag":   true,
+				"error_message": "request too silly",
+			},
+			time.Unix(1627646263, 0),
+		),
+	}
+
+	tests := []struct {
+		name      string
+		converter converter
+		expected  []telegraf.Metric
+	}{
+		{
+			name: "Should change field name",
+			converter: converter{
+				Pattern:     "^(?:ignore|error)_(\\w+)$",
+				Replacement: "result_${1}",
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request": "/users/42/",
+					},
+					time.Unix(1627646243, 0),
+				),
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"result_number": int64(200),
+						"result_bool":   true,
+					},
+					time.Unix(1627646253, 0),
+				),
+				testutil.MustMetric(
+					"error_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "404",
+					},
+					map[string]interface{}{
+						"request":        "/api/search/?category=plugins&q=regex&sort=asc",
+						"result_number":  int64(404),
+						"result_flag":    true,
+						"result_message": "request too silly",
+					},
+					time.Unix(1627646263, 0),
+				),
+			},
+		},
+		{
+			name: "Should keep existing field name",
+			converter: converter{
+				Pattern:     "^(?:ignore|error)_(\\w+)$",
+				Replacement: "request",
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request": "/users/42/",
+					},
+					time.Unix(1627646243, 0),
+				),
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(200),
+						"ignore_bool":   true,
+					},
+					time.Unix(1627646253, 0),
+				),
+				testutil.MustMetric(
+					"error_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "404",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(404),
+						"ignore_flag":   true,
+						"error_message": "request too silly",
+					},
+					time.Unix(1627646263, 0),
+				),
+			},
+		},
+		{
+			name: "Should overwrite existing field name",
+			converter: converter{
+				Pattern:     "^ignore_bool$",
+				Replacement: "request",
+				ResultKey:   "overwrite",
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request": "/users/42/",
+					},
+					time.Unix(1627646243, 0),
+				),
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"ignore_number": int64(200),
+						"request":       true,
+					},
+					time.Unix(1627646253, 0),
+				),
+				testutil.MustMetric(
+					"error_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "404",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(404),
+						"ignore_flag":   true,
+						"error_message": "request too silly",
+					},
+					time.Unix(1627646263, 0),
+				),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		// Copy the inputs as they will be modified by the processor
+		input := make([]telegraf.Metric, len(inputTemplate))
+		for i, m := range inputTemplate {
+			input[i] = m.Copy()
+		}
+
+		t.Run(test.name, func(t *testing.T) {
+			regex := Regex{
+				FieldRename: []converter{test.converter},
+				Log:         testutil.Logger{},
+			}
+			require.NoError(t, regex.Init())
+
+			actual := regex.Apply(input...)
+			testutil.RequireMetricsEqual(t, test.expected, actual)
+		})
+	}
+}
+
+func TestTagRenameConversions(t *testing.T) {
+	inputTemplate := []telegraf.Metric{
+		testutil.MustMetric(
+			"access_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "200",
+			},
+			map[string]interface{}{
+				"request": "/users/42/",
+			},
+			time.Unix(1627646243, 0),
+		),
+		testutil.MustMetric(
+			"access_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "200",
+			},
+			map[string]interface{}{
+				"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+				"ignore_number": int64(200),
+				"ignore_bool":   true,
+			},
+			time.Unix(1627646253, 0),
+		),
+		testutil.MustMetric(
+			"error_log",
+			map[string]string{
+				"verb":      "GET",
+				"resp_code": "404",
+			},
+			map[string]interface{}{
+				"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+				"ignore_number": int64(404),
+				"ignore_flag":   true,
+				"error_message": "request too silly",
+			},
+			time.Unix(1627646263, 0),
+		),
+	}
+
+	tests := []struct {
+		name      string
+		converter converter
+		expected  []telegraf.Metric
+	}{
+		{
+			name: "Should change tag name",
+			converter: converter{
+				Pattern:     "^resp_(\\w+)$",
+				Replacement: "${1}",
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb": "GET",
+						"code": "200",
+					},
+					map[string]interface{}{
+						"request": "/users/42/",
+					},
+					time.Unix(1627646243, 0),
+				),
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb": "GET",
+						"code": "200",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(200),
+						"ignore_bool":   true,
+					},
+					time.Unix(1627646253, 0),
+				),
+				testutil.MustMetric(
+					"error_log",
+					map[string]string{
+						"verb": "GET",
+						"code": "404",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(404),
+						"ignore_flag":   true,
+						"error_message": "request too silly",
+					},
+					time.Unix(1627646263, 0),
+				),
+			},
+		},
+		{
+			name: "Should keep existing tag name",
+			converter: converter{
+				Pattern:     "^resp_(\\w+)$",
+				Replacement: "verb",
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request": "/users/42/",
+					},
+					time.Unix(1627646243, 0),
+				),
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "200",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(200),
+						"ignore_bool":   true,
+					},
+					time.Unix(1627646253, 0),
+				),
+				testutil.MustMetric(
+					"error_log",
+					map[string]string{
+						"verb":      "GET",
+						"resp_code": "404",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(404),
+						"ignore_flag":   true,
+						"error_message": "request too silly",
+					},
+					time.Unix(1627646263, 0),
+				),
+			},
+		},
+		{
+			name: "Should overwrite existing tag name",
+			converter: converter{
+				Pattern:     "^resp_(\\w+)$",
+				Replacement: "verb",
+				ResultKey:   "overwrite",
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb": "200",
+					},
+					map[string]interface{}{
+						"request": "/users/42/",
+					},
+					time.Unix(1627646243, 0),
+				),
+				testutil.MustMetric(
+					"access_log",
+					map[string]string{
+						"verb": "200",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(200),
+						"ignore_bool":   true,
+					},
+					time.Unix(1627646253, 0),
+				),
+				testutil.MustMetric(
+					"error_log",
+					map[string]string{
+						"verb": "404",
+					},
+					map[string]interface{}{
+						"request":       "/api/search/?category=plugins&q=regex&sort=asc",
+						"ignore_number": int64(404),
+						"ignore_flag":   true,
+						"error_message": "request too silly",
+					},
+					time.Unix(1627646263, 0),
+				),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		// Copy the inputs as they will be modified by the processor
+		input := make([]telegraf.Metric, len(inputTemplate))
+		for i, m := range inputTemplate {
+			input[i] = m.Copy()
+		}
+
+		t.Run(test.name, func(t *testing.T) {
+			regex := Regex{
+				TagRename: []converter{test.converter},
+				Log:       testutil.Logger{},
+			}
+			require.NoError(t, regex.Init())
+
+			actual := regex.Apply(input...)
+			testutil.RequireMetricsEqual(t, test.expected, actual)
+		})
 	}
 }
 
 func TestMultipleConversions(t *testing.T) {
-	regex := NewRegex()
+	regex := Regex{
-	regex.Tags = []converter{
+		Tags: []converter{
 			{
 				Key:         "resp_code",
 				Pattern:     "^(\\d)\\d\\d$",
@@ -171,8 +708,8 @@ func TestMultipleConversions(t *testing.T) {
 				Replacement: "OK",
 				ResultKey:   "resp_code_text",
 			},
-	}
+		},
-	regex.Fields = []converter{
+		Fields: []converter{
 			{
 				Key:         "request",
 				Pattern:     "^/api(?P<method>/[\\w/]+)\\S*",
@@ -185,7 +722,10 @@ func TestMultipleConversions(t *testing.T) {
 				Replacement: "${1}",
 				ResultKey:   "search_category",
 			},
+		},
+		Log: testutil.Logger{},
 	}
+	require.NoError(t, regex.Init())
 
 	processed := regex.Apply(newM2())
 
@@ -203,8 +743,8 @@ func TestMultipleConversions(t *testing.T) {
 		"resp_code_text":  "OK",
 	}
 
-	assert.Equal(t, expectedFields, processed[0].Fields())
+	require.Equal(t, expectedFields, processed[0].Fields())
-	assert.Equal(t, expectedTags, processed[0].Tags())
+	require.Equal(t, expectedTags, processed[0].Tags())
 }
 
 func TestNoMatches(t *testing.T) {
@@ -250,34 +790,38 @@ func TestNoMatches(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		regex := NewRegex()
+		regex := Regex{
-		regex.Fields = []converter{
+			Fields: []converter{test.converter},
-			test.converter,
+			Log:    testutil.Logger{},
 		}
+		require.NoError(t, regex.Init())
 
 		processed := regex.Apply(newM1())
 
-		assert.Equal(t, test.expectedFields, processed[0].Fields(), test.message)
+		require.Equal(t, test.expectedFields, processed[0].Fields(), test.message)
 	}
 }
 
 func BenchmarkConversions(b *testing.B) {
-	regex := NewRegex()
+	regex := Regex{
-	regex.Tags = []converter{
+		Tags: []converter{
 			{
 				Key:         "resp_code",
 				Pattern:     "^(\\d)\\d\\d$",
 				Replacement: "${1}xx",
 				ResultKey:   "resp_code_group",
 			},
-	}
+		},
-	regex.Fields = []converter{
+		Fields: []converter{
 			{
 				Key:         "request",
 				Pattern:     "^/users/\\d+/$",
 				Replacement: "/users/{id}/",
 			},
+		},
+		Log: testutil.Logger{},
 	}
+	require.NoError(b, regex.Init())
 
 	for n := 0; n < b.N; n++ {
 		processed := regex.Apply(newM1())