[AGNTLOG-56 ] Create Auditor Component

.github/CODEOWNERS

@@ -327,6 +327,7 @@
 /comp/forwarder/eventplatform @DataDog/agent-log-pipelines
 /comp/forwarder/eventplatformreceiver @DataDog/agent-log-pipelines
 /comp/forwarder/orchestrator @DataDog/agent-log-pipelines
+/comp/logs/auditor @DataDog/agent-metrics-logs
 /comp/metadata/haagent @DataDog/ndm-core
 /comp/metadata/packagesigning @DataDog/agent-delivery
 /comp/trace/etwtracer @DataDog/windows-agent

comp/README.md

@@ -289,6 +289,14 @@ Package adscheduler is glue code to connect autodiscovery to the logs agent. It
 
 Package agent contains logs agent component.
 
+### [comp/logs/auditor](https://pkg.go.dev/github.com/DataDog/datadog-agent/comp/logs/auditor)
+
+*Datadog Team*: agent-metrics-logs
+
+Package auditor records the log files the agent is tracking. It tracks
+filename, time last updated, offset (how far into the file the agent has
+read), and tailing mode for each log file.
+
 ### [comp/logs/integrations](https://pkg.go.dev/github.com/DataDog/datadog-agent/comp/logs/integrations)
 
 Package integrations adds a go interface for integrations to register and

comp/logs/auditor/def/component.go

@@ -0,0 +1,30 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2025-present Datadog, Inc.
+
+// Package auditor records the log files the agent is tracking. It tracks
+// filename, time last updated, offset (how far into the file the agent has
+// read), and tailing mode for each log file.
+package auditor
+
+import (
+	"github.com/DataDog/datadog-agent/pkg/logs/message"
+)
+
+// team: agent-metrics-logs
+
+// Component is the component type.
+type Component interface {
+	Registry
+
+	// Start starts the auditor
+	Start()
+
+	// Stop stops the auditor
+	Stop()
+
+	// Channel returns the channel to use to communicate with the auditor or nil
+	// if the auditor is currently stopped.
+	Channel() chan *message.Payload
+}

comp/logs/auditor/def/types.go

@@ -0,0 +1,12 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2025-present Datadog, Inc.
+
+package auditor
+
+// Registry holds a list of offsets.
+type Registry interface {
+	GetOffset(identifier string) string
+	GetTailingMode(identifier string) string
+}

comp/logs/auditor/fx/fx.go

@@ -0,0 +1,21 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2025-present Datadog, Inc.
+
+// Package fx provides the fx module for the auditor component
+package fx
+
+import (
+	auditorimpl "github.com/DataDog/datadog-agent/comp/logs/auditor/impl"
+	"github.com/DataDog/datadog-agent/pkg/util/fxutil"
+)
+
+// Module defines the fx options for this component
+func Module() fxutil.Module {
+	return fxutil.Component(
+		fxutil.ProvideComponentConstructor(
+			auditorimpl.NewAuditor,
+		),
+	)
+}

comp/logs/auditor/impl-none/auditor_noop.go

@@ -0,0 +1,66 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2025-present Datadog, Inc.
+
+// Package noneimpl provides the noop auditor component
+package noneimpl
+
+import (
+	"github.com/DataDog/datadog-agent/pkg/logs/message"
+)
+
+// NullAuditor is an auditor that does nothing but empties the channel it
+// receives messages from
+type NullAuditor struct {
+	channel     chan *message.Payload
+	stopChannel chan struct{}
+}
+
+// NewAuditor creates a new noop auditor comoponent
+func NewAuditor() *NullAuditor {
+	nullAuditor := &NullAuditor{
+		channel:     make(chan *message.Payload),
+		stopChannel: make(chan struct{}),
+	}
+
+	return nullAuditor
+}
+
+// GetOffset returns an empty string
+func (a *NullAuditor) GetOffset(_ string) string {
+	return ""
+}
+
+// GetTailingMode returns an empty string
+func (a *NullAuditor) GetTailingMode(_ string) string {
+	return ""
+}
+
+// Start starts the NullAuditor main loop
+func (a *NullAuditor) Start() {
+	go a.run()
+}
+
+// Stop stops the NullAuditor main loop
+func (a *NullAuditor) Stop() {
+	a.stopChannel <- struct{}{}
+}
+
+// Channel returns the channel messages should be sent on
+func (a *NullAuditor) Channel() chan *message.Payload {
+	return a.channel
+}
+
+// run is the main run loop for the null auditor
+func (a *NullAuditor) run() {
+	for {
+		select {
+		case <-a.channel:
+		// drain the channel, we're not doing anything with the channel
+		case <-a.stopChannel:
+			// TODO(remy): close the message channel
+			return
+		}
+	}
+}

comp/logs/auditor/impl/api_v0.go

@@ -0,0 +1,47 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2016-present Datadog, Inc.
+
+//nolint:revive // TODO(AML) Fix revive linter
+package auditorimpl
+
+import (
+	"encoding/json"
+	"fmt"
+	"strconv"
+	"time"
+)
+
+// v0: In the first version of the auditor, we were only recording file offsets
+
+type registryEntryV0 struct {
+	Path      string
+	Timestamp time.Time
+	Offset    int64
+}
+
+type jsonRegistryV0 struct {
+	Version  int
+	Registry map[string]registryEntryV0
+}
+
+func unmarshalRegistryV0(b []byte) (map[string]*RegistryEntry, error) {
+	var r jsonRegistryV0
+	err := json.Unmarshal(b, &r)
+	if err != nil {
+		return nil, err
+	}
+	registry := make(map[string]*RegistryEntry)
+	for identifier, entry := range r.Registry {
+		switch {
+		case entry.Offset > 0:
+			// from v0 to v1 and further, we also prefixed path with file:
+			newIdentifier := fmt.Sprintf("file:%s", identifier)
+			registry[newIdentifier] = &RegistryEntry{LastUpdated: entry.Timestamp, Offset: strconv.FormatInt(entry.Offset, 10)}
+		default:
+			// no valid offset for this entry
+		}
+	}
+	return registry, nil
+}

comp/logs/auditor/impl/api_v1.go

@@ -0,0 +1,45 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2016-present Datadog, Inc.
+
+package auditorimpl
+
+import (
+	"encoding/json"
+	"strconv"
+	"time"
+)
+
+// v1: In the second version of the auditor, Timestamp became LastUpdated and we added Timestamp to record container offsets.
+
+type registryEntryV1 struct {
+	Timestamp   string
+	Offset      int64
+	LastUpdated time.Time
+}
+
+type jsonRegistryV1 struct {
+	Version  int
+	Registry map[string]registryEntryV1
+}
+
+func unmarshalRegistryV1(b []byte) (map[string]*RegistryEntry, error) {
+	var r jsonRegistryV1
+	err := json.Unmarshal(b, &r)
+	if err != nil {
+		return nil, err
+	}
+	registry := make(map[string]*RegistryEntry)
+	for identifier, entry := range r.Registry {
+		switch {
+		case entry.Offset > 0:
+			registry[identifier] = &RegistryEntry{LastUpdated: entry.LastUpdated, Offset: strconv.FormatInt(entry.Offset, 10)}
+		case entry.Timestamp != "":
+			registry[identifier] = &RegistryEntry{LastUpdated: entry.LastUpdated, Offset: entry.Timestamp}
+		default:
+			// no valid offset for this entry
+		}
+	}
+	return registry, nil
+}

comp/logs/auditor/impl/api_v2.go

@@ -0,0 +1,27 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2016-present Datadog, Inc.
+
+package auditorimpl
+
+import (
+	"encoding/json"
+)
+
+// v2: In the third version of the auditor, we dropped Timestamp and used a generic Offset instead to reinforce the separation of concerns
+// between the auditor and log sources.
+
+func unmarshalRegistryV2(b []byte) (map[string]*RegistryEntry, error) {
+	var r JSONRegistry
+	err := json.Unmarshal(b, &r)
+	if err != nil {
+		return nil, err
+	}
+	registry := make(map[string]*RegistryEntry)
+	for identifier, entry := range r.Registry {
+		newEntry := entry
+		registry[identifier] = &newEntry
+	}
+	return registry, nil
+}