LIBBEAT: Enhancement replace_string processor for replacing strings values of fields.

CHANGELOG.next.asciidoc

@@ -198,6 +198,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Update RPM packages contained in Beat Docker images. {issue}17035[17035]
 - Update supported versions of `redis` output. {pull}17198[17198]
 - Update documentation for system.process.memory fields to include clarification on Windows os's. {pull}17268[17268]
+- Add `replace` processor for replacing string values of fields. {pull}17342[17342]
 - Add optional regex based cid extractor to `add_kubernetes_metadata` processor. {pull}17360[17360]
 - Add `urldecode` processor to for decoding URL-encoded fields. {pull}17505[17505]
 - Add support for AWS IAM `role_arn` in credentials config. {pull}17658[17658] {issue}12464[12464]

libbeat/processors/actions/docs/replace.asciidoc

@@ -0,0 +1,49 @@
+[[replace-fields]]
+=== Replace fields from events
+
+++++
+<titleabbrev>replace</titleabbrev>
+++++
+
+The `replace` processor takes a list of fields to replace the field value 
+matching a pattern with replacement string. Under the `fields` key, each entry 
+contains a `field: field-name`, `pattern: regex-pattern` and 
+`replacement: replacement-string`, where:
+
+* `field` is the original field name
+* `pattern` is regex pattern to match field's value
+* `replacement` is the replacement string to use for updating the field's value
+
+The `replace` processor cannot be used to replace value with a completely new value. 
+
+TIP: You can replace field value to truncate part of field value or replace 
+it with a new string. It can also be used for masking PII information.
+
+Following example will change path from /usr/bin to /usr/local/bin
+
+[source,yaml]
+-------
+processors:
+- replace:
+    fields:
+     - field: "file.path"
+       pattern: "/usr/"
+       replacement: "/usr/local/"
+    ignore_missing: false
+    fail_on_error: true
+-------
+
+The `replace` processor has following configuration settings:
+
+`ignore_missing`:: (Optional) If set to true, no error is logged in case a specifiedfield 
+is missing. Default is `false`.
+
+`fail_on_error`:: (Optional) If set to true, in case of an error the replacement of
+field values is stopped and the original event is returned. If set to false, replacement
+continues even if an error occurs during replacement. Default is `true`.
+
+See <<conditions>> for a list of supported conditions.
+
+You can specify multiple `ignore_missing` processors under the `processors`
+section.
+

libbeat/processors/actions/replace.go

@@ -0,0 +1,118 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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 actions
+
+import (
+	"fmt"
+	"regexp"
+
+	"github.com/pkg/errors"
+
+	"github.com/elastic/beats/v7/libbeat/beat"
+	"github.com/elastic/beats/v7/libbeat/common"
+	"github.com/elastic/beats/v7/libbeat/logp"
+	"github.com/elastic/beats/v7/libbeat/processors"
+	"github.com/elastic/beats/v7/libbeat/processors/checks"
+	jsprocessor "github.com/elastic/beats/v7/libbeat/processors/script/javascript/module/processor"
+)
+
+type replaceString struct {
+	config replaceStringConfig
+}
+
+type replaceStringConfig struct {
+	Fields        []replaceConfig `config:"fields"`
+	IgnoreMissing bool            `config:"ignore_missing"`
+	FailOnError   bool            `config:"fail_on_error"`
+}
+
+type replaceConfig struct {
+	Field       string         `config:"field"`
+	Pattern     *regexp.Regexp `config:"pattern"`
+	Replacement string         `config:"replacement"`
+}
+
+func init() {
+	processors.RegisterPlugin("replace",
+		checks.ConfigChecked(NewReplaceString,
+			checks.RequireFields("fields")))
+
+	jsprocessor.RegisterPlugin("Replace", NewReplaceString)
+}
+
+// NewReplaceString returns a new replace processor.
+func NewReplaceString(c *common.Config) (processors.Processor, error) {
+	config := replaceStringConfig{
+		IgnoreMissing: false,
+		FailOnError:   true,
+	}
+	err := c.Unpack(&config)
+	if err != nil {
+		return nil, fmt.Errorf("failed to unpack the replace configuration: %s", err)
+	}
+
+	f := &replaceString{
+		config: config,
+	}
+	return f, nil
+}
+
+func (f *replaceString) Run(event *beat.Event) (*beat.Event, error) {
+	var backup common.MapStr
+	// Creates a copy of the event to revert in case of failure
+	if f.config.FailOnError {
+		backup = event.Fields.Clone()
+	}
+
+	for _, field := range f.config.Fields {
+		err := f.replaceField(field.Field, field.Pattern, field.Replacement, event.Fields)
+		if err != nil {
+			errMsg := fmt.Errorf("Failed to replace fields in processor: %s", err)
+			logp.Debug("replace", errMsg.Error())
+			if f.config.FailOnError {
+				event.Fields = backup
+				event.PutValue("error.message", errMsg.Error())
+				return event, err
+			}
+		}
+	}
+
+	return event, nil
+}
+
+func (f *replaceString) replaceField(field string, pattern *regexp.Regexp, replacement string, fields common.MapStr) error {
+	currentValue, err := fields.GetValue(field)
+	if err != nil {
+		// Ignore ErrKeyNotFound errors
+		if f.config.IgnoreMissing && errors.Cause(err) == common.ErrKeyNotFound {
+			return nil
+		}
+		return fmt.Errorf("could not fetch value for key: %s, Error: %s", field, err)
+	}
+
+	updatedString := pattern.ReplaceAllString(currentValue.(string), replacement)
+	_, err = fields.Put(field, updatedString)
+	if err != nil {
+		return fmt.Errorf("could not put value: %s: %v, %v", replacement, currentValue, err)
+	}
+	return nil
+}
+
+func (f *replaceString) String() string {
+	return "replace=" + fmt.Sprintf("%+v", f.config.Fields)
+}