Adding upstream version 1.34.4.

Signed-off-by: Daniel Baumann <daniel@debian.org>

persister/persister.go

@@ -0,0 +1,103 @@
+package persister
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"reflect"
+
+	"github.com/influxdata/telegraf"
+)
+
+type Persister struct {
+	Filename string
+
+	register map[string]telegraf.StatefulPlugin
+}
+
+func (p *Persister) Init() error {
+	p.register = make(map[string]telegraf.StatefulPlugin)
+
+	return nil
+}
+
+func (p *Persister) Register(id string, plugin telegraf.StatefulPlugin) error {
+	if _, found := p.register[id]; found {
+		return fmt.Errorf("plugin with ID %q already registered", id)
+	}
+	p.register[id] = plugin
+
+	return nil
+}
+
+func (p *Persister) Load() error {
+	// Read the states from disk
+	in, err := os.ReadFile(p.Filename)
+	if err != nil {
+		return fmt.Errorf("reading states file failed: %w", err)
+	}
+
+	// Unmarshal the id to serialized states map
+	var states map[string][]byte
+	if err := json.Unmarshal(in, &states); err != nil {
+		return fmt.Errorf("unmarshalling states failed: %w", err)
+	}
+
+	// Get the initialized state as blueprint for unmarshalling
+	for id, serialized := range states {
+		// Check if we have a plugin with that ID
+		plugin, found := p.register[id]
+		if !found {
+			continue
+		}
+
+		// Create a new empty state of the "state"-type. As we need a pointer
+		// of the state, we cannot dereference it here due to the unknown
+		// nature of the state-type.
+		nstate := reflect.New(reflect.TypeOf(plugin.GetState())).Interface()
+		if err := json.Unmarshal(serialized, &nstate); err != nil {
+			return fmt.Errorf("unmarshalling state for %q failed: %w", id, err)
+		}
+		state := reflect.ValueOf(nstate).Elem().Interface()
+
+		// Set the state in the plugin
+		if err := plugin.SetState(state); err != nil {
+			return fmt.Errorf("setting state of %q failed: %w", id, err)
+		}
+	}
+
+	return nil
+}
+
+func (p *Persister) Store() error {
+	states := make(map[string][]byte)
+
+	// Collect the states and serialize the individual data chunks
+	// to later serialize all items in the id / serialized-states map
+	for id, plugin := range p.register {
+		state, err := json.Marshal(plugin.GetState())
+		if err != nil {
+			return fmt.Errorf("marshalling state for id %q failed: %w", id, err)
+		}
+		states[id] = state
+	}
+
+	// Serialize the states
+	serialized, err := json.Marshal(states)
+	if err != nil {
+		return fmt.Errorf("marshalling states failed: %w", err)
+	}
+
+	// Write the states to disk
+	f, err := os.Create(p.Filename)
+	if err != nil {
+		return fmt.Errorf("creating states file %q failed: %w", p.Filename, err)
+	}
+	defer f.Close()
+
+	if _, err := f.Write(serialized); err != nil {
+		return fmt.Errorf("writing states failed: %w", err)
+	}
+
+	return nil
+}