fix(outputs.remotefile): Create a new serializer instance per output file

config/config.go

@@ -1010,6 +1010,25 @@ func (c *Config) addParser(parentcategory, parentname string, table *ast.Table)
 	return running, err
 }
 
+func (c *Config) probeSerializer(table *ast.Table) bool {
+	dataFormat := c.getFieldString(table, "data_format")
+	if dataFormat == "" {
+		dataFormat = "influx"
+	}
+
+	creator, ok := serializers.Serializers[dataFormat]
+	if !ok {
+		return false
+	}
+
+	// Try to parse the options to detect if any of them is misspelled
+	serializer := creator()
+	//nolint:errcheck // We don't actually use the parser, so no need to check the error.
+	c.toml.UnmarshalTable(table, serializer)
+
+	return true
+}
+
 func (c *Config) addSerializer(parentname string, table *ast.Table) (*models.RunningSerializer, error) {
 	conf := &models.SerializerConfig{
 		Parent: parentname,
@@ -1140,6 +1159,15 @@ func (c *Config) setupProcessor(name string, creator processors.StreamingCreator
 		t.SetSerializer(serializer)
 		optionTestCount++
 	}
+	if t, ok := processor.(telegraf.SerializerFuncPlugin); ok {
+		if !c.probeSerializer(table) {
+			return nil, 0, errors.New("serializer not found")
+		}
+		t.SetSerializerFunc(func() (telegraf.Serializer, error) {
+			return c.addSerializer(name, table)
+		})
+		optionTestCount++
+	}
 
 	if err := c.toml.UnmarshalTable(table, processor); err != nil {
 		return nil, 0, fmt.Errorf("unmarshalling failed: %w", err)
@@ -1154,8 +1182,8 @@ func (c *Config) addOutput(name string, table *ast.Table) error {
 		return nil
 	}
 
-	// For inputs with parsers we need to compute the set of
-	// options that is not covered by both, the parser and the input.
+	// For outputs with serializers we need to compute the set of
+	// options that is not covered by both, the serializer and the input.
 	// We achieve this by keeping a local book of missing entries
 	// that counts the number of misses. In case we have a parser
 	// for the input both need to miss the entry. We count the
@@ -1196,6 +1224,16 @@ func (c *Config) addOutput(name string, table *ast.Table) error {
 		t.SetSerializer(serializer)
 	}
 
+	if t, ok := output.(telegraf.SerializerFuncPlugin); ok {
+		missThreshold = 1
+		if !c.probeSerializer(table) {
+			return errors.New("serializer not found")
+		}
+		t.SetSerializerFunc(func() (telegraf.Serializer, error) {
+			return c.addSerializer(name, table)
+		})
+	}
+
 	outputConfig, err := c.buildOutput(name, table)
 	if err != nil {
 		return err

parser.go

@@ -22,6 +22,7 @@ type Parser interface {
 	SetDefaultTags(tags map[string]string)
 }
 
+// ParserFunc is a function to create a new instance of a parser
 type ParserFunc func() (Parser, error)
 
 // ParserPlugin is an interface for plugins that are able to parse

plugins/outputs/remotefile/README.md

@@ -63,6 +63,15 @@ to use them.
   ## Maximum size of the cache on disk (infinite by default)
   # cache_max_size = -1
 
+  ## Forget files after not being touched for longer than the given time
+  ## This is useful to prevent memory leaks when using time-based filenames
+  ## as it allows internal structures to be cleaned up.
+  ## Note: When writing to a file after is has been forgotten, the file is
+  ##       treated as a new file which might cause file-headers to be appended
+  ##       again by certain serializers like CSV.
+  ## By default files will be kept indefinitely.
+  # forget_files_after = "0s"
+
   ## Data format to output.
   ## Each data format has its own unique set of configuration options, read
   ## more about them here:

plugins/outputs/remotefile/remotefile.go

@@ -21,7 +21,6 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/config"
 	"github.com/influxdata/telegraf/plugins/outputs"
-	"github.com/influxdata/telegraf/plugins/serializers"
 )
 
 //go:embed sample.conf
@@ -35,22 +34,25 @@ type File struct {
 	MaxCacheSize      config.Size     `toml:"cache_max_size"`
 	UseBatchFormat    bool            `toml:"use_batch_format"`
 	Trace             bool            `toml:"trace" deprecated:"1.33.0;1.35.0;use 'log_level = \"trace\"' instead"`
+	ForgetFiles       config.Duration `toml:"forget_files_after"`
 	Log               telegraf.Logger `toml:"-"`
 
 	root     *vfs.VFS
 	fscancel context.CancelFunc
 	vfsopts  vfscommon.Options
 
-	templates  []*template.Template
-	serializer serializers.Serializer
+	templates      []*template.Template
+	serializerFunc telegraf.SerializerFunc
+	serializers    map[string]telegraf.Serializer
+	modified       map[string]time.Time
 }
 
 func (*File) SampleConfig() string {
 	return sampleConfig
 }
 
-func (f *File) SetSerializer(serializer serializers.Serializer) {
-	f.serializer = serializer
+func (f *File) SetSerializerFunc(sf telegraf.SerializerFunc) {
+	f.serializerFunc = sf
 }
 
 func (f *File) Init() error {
@@ -101,6 +103,9 @@ func (f *File) Init() error {
 		f.templates = append(f.templates, tmpl)
 	}
 
+	f.serializers = make(map[string]telegraf.Serializer)
+	f.modified = make(map[string]time.Time)
+
 	return nil
 }
 
@@ -187,16 +192,24 @@ func (f *File) Write(metrics []telegraf.Metric) error {
 	// Serialize the metric groups
 	groupBuffer := make(map[string][]byte, len(groups))
 	for fn, fnMetrics := range groups {
+		if _, found := f.serializers[fn]; !found {
+			var err error
+			if f.serializers[fn], err = f.serializerFunc(); err != nil {
+				return fmt.Errorf("creating serializer failed: %w", err)
+			}
+		}
+		serializer := f.serializers[fn]
+
 		if f.UseBatchFormat {
-			serialized, err := f.serializer.SerializeBatch(fnMetrics)
+			serialized, err := serializer.SerializeBatch(fnMetrics)
 			if err != nil {
 				f.Log.Errorf("Could not serialize metrics: %v", err)
 				continue
 			}
 			groupBuffer[fn] = serialized
 		} else {
 			for _, m := range fnMetrics {
-				serialized, err := f.serializer.Serialize(m)
+				serialized, err := serializer.Serialize(m)
 				if err != nil {
 					f.Log.Debugf("Could not serialize metric: %v", err)
 					continue
@@ -207,6 +220,7 @@ func (f *File) Write(metrics []telegraf.Metric) error {
 	}
 
 	// Write the files
+	t := time.Now()
 	for fn, serialized := range groupBuffer {
 		// Make sure the directory exists
 		dir := filepath.Dir(filepath.ToSlash(fn))
@@ -232,6 +246,18 @@ func (f *File) Write(metrics []telegraf.Metric) error {
 			return fmt.Errorf("writing metrics to file %q failed: %w", fn, err)
 		}
 		file.Close()
+
+		f.modified[fn] = t
+	}
+
+	// Cleanup internal structures for old files
+	if f.ForgetFiles > 0 {
+		for fn, tmod := range f.modified {
+			if t.Sub(tmod) > time.Duration(f.ForgetFiles) {
+				delete(f.serializers, fn)
+				delete(f.modified, fn)
+			}
+		}
 	}
 
 	return nil

plugins/outputs/remotefile/remotefile_test.go

@@ -13,6 +13,7 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/config"
 	"github.com/influxdata/telegraf/metric"
+	"github.com/influxdata/telegraf/plugins/serializers/csv"
 	"github.com/influxdata/telegraf/plugins/serializers/influx"
 	"github.com/influxdata/telegraf/testutil"
 )
@@ -40,9 +41,11 @@ func TestStaticFileCreation(t *testing.T) {
 		Log:               &testutil.Logger{},
 	}
 
-	serializer := &influx.Serializer{}
-	require.NoError(t, serializer.Init())
-	plugin.SetSerializer(serializer)
+	plugin.SetSerializerFunc(func() (telegraf.Serializer, error) {
+		serializer := &influx.Serializer{}
+		err := serializer.Init()
+		return serializer, err
+	})
 
 	require.NoError(t, plugin.Init())
 	require.NoError(t, plugin.Connect())
@@ -93,9 +96,11 @@ func TestStaticFileAppend(t *testing.T) {
 		Log:               &testutil.Logger{},
 	}
 
-	serializer := &influx.Serializer{}
-	require.NoError(t, serializer.Init())
-	plugin.SetSerializer(serializer)
+	plugin.SetSerializerFunc(func() (telegraf.Serializer, error) {
+		serializer := &influx.Serializer{}
+		err := serializer.Init()
+		return serializer, err
+	})
 
 	require.NoError(t, plugin.Init())
 	require.NoError(t, plugin.Connect())
@@ -180,9 +185,11 @@ func TestDynamicFiles(t *testing.T) {
 		Log:               &testutil.Logger{},
 	}
 
-	serializer := &influx.Serializer{}
-	require.NoError(t, serializer.Init())
-	plugin.SetSerializer(serializer)
+	plugin.SetSerializerFunc(func() (telegraf.Serializer, error) {
+		serializer := &influx.Serializer{}
+		err := serializer.Init()
+		return serializer, err
+	})
 
 	require.NoError(t, plugin.Init())
 	require.NoError(t, plugin.Connect())
@@ -246,9 +253,11 @@ func TestCustomTemplateFunctions(t *testing.T) {
 		Log:               &testutil.Logger{},
 	}
 
-	serializer := &influx.Serializer{}
-	require.NoError(t, serializer.Init())
-	plugin.SetSerializer(serializer)
+	plugin.SetSerializerFunc(func() (telegraf.Serializer, error) {
+		serializer := &influx.Serializer{}
+		err := serializer.Init()
+		return serializer, err
+	})
 
 	require.NoError(t, plugin.Init())
 	require.NoError(t, plugin.Connect())
@@ -266,3 +275,121 @@ func TestCustomTemplateFunctions(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, expected, string(actual))
 }
+
+func TestCSVSerialization(t *testing.T) {
+	input := []telegraf.Metric{
+		metric.New(
+			"test",
+			map[string]string{"source": "a"},
+			map[string]interface{}{"value": 42},
+			time.Unix(1587686400, 0),
+		),
+		metric.New(
+			"test",
+			map[string]string{"source": "b"},
+			map[string]interface{}{"value": 23},
+			time.Unix(1587686400, 0),
+		),
+	}
+	expected := map[string]string{
+		"test-a.csv": "timestamp,measurement,source,value\n1587686400,test,a,42\n",
+		"test-b.csv": "timestamp,measurement,source,value\n1587686400,test,b,23\n",
+	}
+
+	tmpdir, err := os.MkdirTemp("", "telegraf-remotefile-*")
+	require.NoError(t, err)
+	defer os.RemoveAll(tmpdir)
+
+	// Setup the plugin including the serializer
+	plugin := &File{
+		Remote:            config.NewSecret([]byte("local:" + tmpdir)),
+		Files:             []string{`test-{{.Tag "source"}}.csv`},
+		WriteBackInterval: config.Duration(100 * time.Millisecond),
+		Log:               &testutil.Logger{},
+	}
+
+	plugin.SetSerializerFunc(func() (telegraf.Serializer, error) {
+		serializer := &csv.Serializer{Header: true}
+		err := serializer.Init()
+		return serializer, err
+	})
+
+	require.NoError(t, plugin.Init())
+	require.NoError(t, plugin.Connect())
+	defer plugin.Close()
+
+	// Write the input metrics and close the plugin. This is required to
+	// actually flush the data to disk
+	require.NoError(t, plugin.Write(input))
+	plugin.Close()
+
+	// Check the result
+	for expectedFilename, expectedContent := range expected {
+		require.FileExists(t, filepath.Join(tmpdir, expectedFilename))
+		buf, err := os.ReadFile(filepath.Join(tmpdir, expectedFilename))
+		require.NoError(t, err)
+		actual := strings.ReplaceAll(string(buf), "\r\n", "\n")
+		require.Equal(t, expectedContent, actual)
+	}
+
+	require.Len(t, plugin.modified, 2)
+	require.Contains(t, plugin.modified, "test-a.csv")
+	require.Contains(t, plugin.modified, "test-b.csv")
+	require.Len(t, plugin.serializers, 2)
+	require.Contains(t, plugin.serializers, "test-a.csv")
+	require.Contains(t, plugin.serializers, "test-b.csv")
+}
+
+func TestForgettingFiles(t *testing.T) {
+	input := []telegraf.Metric{
+		metric.New(
+			"test",
+			map[string]string{"source": "a"},
+			map[string]interface{}{"value": 42},
+			time.Unix(1587686400, 0),
+		),
+		metric.New(
+			"test",
+			map[string]string{"source": "b"},
+			map[string]interface{}{"value": 23},
+			time.Unix(1587686400, 0),
+		),
+	}
+
+	tmpdir, err := os.MkdirTemp("", "telegraf-remotefile-*")
+	require.NoError(t, err)
+	defer os.RemoveAll(tmpdir)
+
+	// Setup the plugin including the serializer
+	plugin := &File{
+		Remote:            config.NewSecret([]byte("local:" + tmpdir)),
+		Files:             []string{`test-{{.Tag "source"}}.csv`},
+		WriteBackInterval: config.Duration(100 * time.Millisecond),
+		ForgetFiles:       config.Duration(10 * time.Millisecond),
+		Log:               &testutil.Logger{},
+	}
+
+	plugin.SetSerializerFunc(func() (telegraf.Serializer, error) {
+		serializer := &csv.Serializer{Header: true}
+		err := serializer.Init()
+		return serializer, err
+	})
+
+	require.NoError(t, plugin.Init())
+	require.NoError(t, plugin.Connect())
+	defer plugin.Close()
+
+	// Write the input metrics and close the plugin. This is required to
+	// actually flush the data to disk
+	require.NoError(t, plugin.Write(input[:1]))
+	time.Sleep(100 * time.Millisecond)
+	require.NoError(t, plugin.Write(input[1:]))
+
+	plugin.Close()
+
+	// Check the result
+	require.Len(t, plugin.modified, 1)
+	require.Contains(t, plugin.modified, "test-b.csv")
+	require.Len(t, plugin.serializers, 1)
+	require.Contains(t, plugin.serializers, "test-b.csv")
+}