Add the take_over mode for filestream inputs

CHANGELOG.next.asciidoc

@@ -172,6 +172,7 @@ https://github.com/elastic/beats/compare/v8.2.0\...main[Check the HEAD diff]
 - Add support for recognizing the log level in Elasticsearch JVM logs {pull}34159[34159]
 - Add metrics for TCP packet processing. {pull}34333[34333]
 - Add metrics for unix socket packet processing. {pull}34335[34335]
+- Add beta `take over` mode for `filestream` for simple migration from `log` inputs {pull}34292[34292]
 
 *Auditbeat*
 

filebeat/_meta/config/filebeat.inputs.reference.yml.tmpl

@@ -402,7 +402,7 @@ filebeat.inputs:
        # Source of container events. Available options: all, stdin, stderr.
        #stream: all
 
-       # Format of the container events. Available options: auto, cri, docker, json-file 
+       # Format of the container events. Available options: auto, cri, docker, json-file
        #format: auto
 
   ### Log rotation
@@ -412,7 +412,7 @@ filebeat.inputs:
   #rotation.external.strategy.copytruncate:
   # Regex that matches the rotated files.
   #  suffix_regex: \.\d$
-  # If the rotated filename suffix is a datetime, set it here. 
+  # If the rotated filename suffix is a datetime, set it here.
   #  dateformat: -20060102
 
   ### State options
@@ -452,6 +452,11 @@ filebeat.inputs:
   # Available options: since_first_start, since_last_start.
   #ignore_inactive: ""
 
+  # If `take_over` is set to `true`, this `filestream` will take over all files
+  # from `log` inputs if they match at least one of the `paths` set in the `filestream`.
+  # This functionality is still in beta.
+  #take_over: false
+
   # Defines the buffer size every harvester uses when fetching the file
   #harvester_buffer_size: 16384
 
@@ -609,7 +614,7 @@ filebeat.inputs:
   #hosts:
     #- kafka-broker-1:9092
     #- kafka-broker-2:9092
-  
+
   # A list of topics to read from.
   #topics: ["my-topic", "important-logs"]
 
@@ -644,7 +649,7 @@ filebeat.inputs:
 
   # The minimum number of bytes to wait for.
   #fetch.min: 1
-  
+
   # The default number of bytes to read per request.
   #fetch.default: 1MB
 
@@ -777,4 +782,3 @@ filebeat.inputs:
   #- multiline:
     #type: count
     #count_lines: 3
-

filebeat/backup/backup.go

@@ -0,0 +1,47 @@
+// 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 backup
+
+import (
+	"errors"
+	"os"
+)
+
+const (
+	backupSuffix = ".bak"
+)
+
+// Backuper defines backup-related operations
+type Backuper interface {
+	// Backup performs the backup
+	Backup() error
+	// Removes all backups created by this backuper
+	Remove() error
+}
+
+// fileExists checks if the given file exists
+func fileExists(name string) (bool, error) {
+	_, err := os.Stat(name)
+	if err == nil {
+		return true, nil
+	}
+	if errors.Is(err, os.ErrNotExist) {
+		return false, nil
+	}
+	return false, err
+}

filebeat/backup/files.go

@@ -0,0 +1,99 @@
+// 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 backup
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"time"
+
+	"github.com/elastic/elastic-agent-libs/logp"
+)
+
+// NewFileBackuper creates a new backuper that creates backups for the given files.
+func NewFileBackuper(log *logp.Logger, files []string) Backuper {
+	return &fileBackuper{
+		log:   log,
+		files: files,
+	}
+}
+
+type fileBackuper struct {
+	log     *logp.Logger
+	files   []string
+	backups []string
+}
+
+// Backup creates temporary backups for given files and returns a callback that
+// removes every created backup file
+func (fb *fileBackuper) Backup() error {
+	var (
+		buf = make([]byte, 64*1024) // 64KB
+	)
+
+	for _, file := range fb.files {
+		err := func() error {
+			src, err := os.Open(file)
+			if err != nil {
+				return err
+			}
+			defer src.Close()
+
+			// we must put the timestamp as a prefix, so after the restart the new backups don't override the previous ones
+			backupFilename := fmt.Sprintf("%s-%d%s", file, time.Now().UnixNano(), backupSuffix)
+			dst, err := os.OpenFile(backupFilename, os.O_CREATE|os.O_EXCL|os.O_APPEND|os.O_WRONLY, 0600)
+			if err != nil {
+				return err
+			}
+			defer dst.Close()
+
+			_, err = io.CopyBuffer(dst, src, buf)
+			if err != nil {
+				return err
+			}
+
+			fb.backups = append(fb.backups, backupFilename)
+			return nil
+		}()
+		if err != nil {
+			return fmt.Errorf("failed to backup a file %s: %w", file, err)
+		}
+	}
+
+	return nil
+}
+
+// Remove removes all backups created by this backuper
+func (fb fileBackuper) Remove() error {
+	fb.log.Infof("Removing backup files: %v...", fb.backups)
+
+	var errs []error
+	for _, backup := range fb.backups {
+		err := os.Remove(backup)
+		if err != nil {
+			errs = append(errs, err)
+		}
+	}
+
+	if len(errs) != 0 {
+		return fmt.Errorf("failed to remove some backups: %v", errs)
+	}
+
+	return nil
+}

filebeat/backup/files_test.go

@@ -0,0 +1,91 @@
+// 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 backup
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/elastic/elastic-agent-libs/logp"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestFileBackup(t *testing.T) {
+	log := logp.NewLogger("backup-test")
+	files := createFiles(t, 3)
+
+	backuper := NewFileBackuper(log, files)
+
+	t.Run("creates exactly one backup per given file", func(t *testing.T) {
+		err := backuper.Backup()
+		require.NoError(t, err)
+		requireBackups(t, files, 1)
+	})
+
+	t.Run("creates second round of backups", func(t *testing.T) {
+		// there is a unix time with nanosecond precision in the filename
+		// we can create only one backup per nanosecond
+		// if there is already a file created in the same nanosecond, the backup fails
+		time.Sleep(time.Microsecond)
+
+		err := backuper.Backup()
+		require.NoError(t, err)
+
+		requireBackups(t, files, 2)
+	})
+
+	t.Run("removes all created backups", func(t *testing.T) {
+		err := backuper.Remove()
+		require.NoError(t, err)
+
+		requireBackups(t, files, 0)
+	})
+}
+
+func createFiles(t *testing.T, count int) (created []string) {
+	t.Helper()
+
+	tmp := t.TempDir()
+
+	for i := 0; i < count; i++ {
+		file, err := os.CreateTemp(tmp, "file-*")
+		require.NoError(t, err)
+		_, err = file.WriteString(file.Name())
+		require.NoError(t, err)
+		file.Close()
+		created = append(created, file.Name())
+	}
+
+	return created
+}
+
+func requireBackups(t *testing.T, files []string, expectedCount int) {
+	for _, file := range files {
+		matches, err := filepath.Glob(file + "-*" + backupSuffix)
+		require.NoError(t, err)
+		require.Len(t, matches, expectedCount, "expected a different amount of created backups")
+		for _, match := range matches {
+			content, err := os.ReadFile(match)
+			require.NoError(t, err)
+			require.Equal(t, file, string(content))
+		}
+	}
+}