refactor fleet mode detection and storage (#40667)

* refactor fleet mode detection and storage

libbeat/cfgfile/cfgfile.go

@@ -18,6 +18,7 @@
 package cfgfile
 
 import (
+	"flag"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -97,6 +98,8 @@ func GetDefaultCfgfile() string {
 }
 
 // HandleFlags adapts default config settings based on command line flags.
+// This also stores if -E management.enabled=true was set on command line
+// to determine if running the Beat under agent.
 func HandleFlags() error {
 	// default for the home path is the binary location
 	home, err := filepath.Abs(filepath.Dir(os.Args[0]))
@@ -114,6 +117,27 @@ func HandleFlags() error {
 		common.PrintConfigDebugf(overwrites, "CLI setting overwrites (-E flag):")
 	}
 
+	// Enable check to see if beat is running under Agent
+	// This is stored in a package so the modules which don't have
+	// access to the config can check this value.
+	type management struct {
+		Enabled bool `config:"management.enabled"`
+	}
+	var managementSettings management
+	cfgFlag := flag.Lookup("E")
+	if cfgFlag == nil {
+		fleetmode.SetAgentMode(false)
+		return nil
+	}
+	cfgObject, _ := cfgFlag.Value.(*config.SettingsFlag)
+	cliCfg := cfgObject.Config()
+
+	err = cliCfg.Unpack(&managementSettings)
+	if err != nil {
+		fleetmode.SetAgentMode(false)
+		return nil //nolint:nilerr // unpacking failing isn't an error for this case
+	}
+	fleetmode.SetAgentMode(managementSettings.Enabled)
 	return nil
 }
 

libbeat/common/fleetmode/fleet_mode.go

@@ -17,33 +17,18 @@
 
 package fleetmode
 
-import (
-	"flag"
-
-	"github.com/elastic/elastic-agent-libs/config"
-)
+var managementEnabled bool
+
+// SetAgentMode stores if the Beat is running under Elastic Agent.
+// Normally this is called when the command line flags are parsed.
+// This is stored as a package level variable because some components
+// (like filebeat/metricbeat modules) don't have access to the
+// configuration information to determine this on their own.
+func SetAgentMode(enabled bool) {
+	managementEnabled = enabled
+}
 
-// Enabled checks to see if filebeat/metricbeat is running under Agent
-// The management setting is stored in the main Beat runtime object, but we can't see that from a module
-// So instead we check the CLI flags, since Agent starts filebeat/metricbeat with "-E", "management.enabled=true"
+// Enabled returns true if the Beat is running under Elastic Agent.
 func Enabled() bool {
-	type management struct {
-		Enabled bool `config:"management.enabled"`
-	}
-	var managementSettings management
-
-	cfgFlag := flag.Lookup("E")
-	if cfgFlag == nil {
-		return false
-	}
-
-	cfgObject, _ := cfgFlag.Value.(*config.SettingsFlag)
-	cliCfg := cfgObject.Config()
-
-	err := cliCfg.Unpack(&managementSettings)
-	if err != nil {
-		return false
-	}
-
-	return managementSettings.Enabled
+	return managementEnabled
 }