feat: add fingerprint command to agent (#1726)

Co-authored-by: henrygd <hank@henrygd.me>

agent/agent.go

@@ -5,11 +5,8 @@
 package agent
 
 import (
-	"crypto/sha256"
-	"encoding/hex"
 	"log/slog"
 	"os"
-	"path/filepath"
 	"strings"
 	"sync"
 	"time"
@@ -19,7 +16,6 @@ import (
 	"github.com/henrygd/beszel/agent/deltatracker"
 	"github.com/henrygd/beszel/internal/common"
 	"github.com/henrygd/beszel/internal/entities/system"
-	"github.com/shirou/gopsutil/v4/host"
 	gossh "golang.org/x/crypto/ssh"
 )
 
@@ -65,7 +61,7 @@ func NewAgent(dataDir ...string) (agent *Agent, err error) {
 	agent.netIoStats = make(map[uint16]system.NetIoStats)
 	agent.netInterfaceDeltaTrackers = make(map[uint16]*deltatracker.DeltaTracker[string, uint64])
 
-	agent.dataDir, err = getDataDir(dataDir...)
+	agent.dataDir, err = GetDataDir(dataDir...)
 	if err != nil {
 		slog.Warn("Data directory not found")
 	} else {
@@ -228,40 +224,12 @@ func (a *Agent) gatherStats(options common.DataRequestOptions) *system.CombinedD
 	return data
 }
 
-// StartAgent initializes and starts the agent with optional WebSocket connection
+// Start initializes and starts the agent with optional WebSocket connection
 func (a *Agent) Start(serverOptions ServerOptions) error {
 	a.keys = serverOptions.Keys
 	return a.connectionManager.Start(serverOptions)
 }
 
 func (a *Agent) getFingerprint() string {
-	// first look for a fingerprint in the data directory
-	if a.dataDir != "" {
-		if fp, err := os.ReadFile(filepath.Join(a.dataDir, "fingerprint")); err == nil {
-			if s := strings.TrimSpace(string(fp)); s != "" {
-				return s
-			}
-		}
-	}
-
-	// if no fingerprint is found, generate one
-	fingerprint, err := host.HostID()
-	// we ignore a commonly known "product_uuid" known not to be unique
-	if err != nil || fingerprint == "" || fingerprint == "03000200-0400-0500-0006-000700080009" {
-		fingerprint = a.systemDetails.Hostname + a.systemDetails.CpuModel
-	}
-
-	// hash fingerprint
-	sum := sha256.Sum256([]byte(fingerprint))
-	fingerprint = hex.EncodeToString(sum[:24])
-
-	// save fingerprint to data directory
-	if a.dataDir != "" {
-		err = os.WriteFile(filepath.Join(a.dataDir, "fingerprint"), []byte(fingerprint), 0644)
-		if err != nil {
-			slog.Warn("Failed to save fingerprint", "err", err)
-		}
-	}
-
-	return fingerprint
+	return GetFingerprint(a.dataDir, a.systemDetails.Hostname, a.systemDetails.CpuModel)
 }

agent/data_dir.go

@@ -8,10 +8,10 @@ import (
 	"runtime"
 )
 
-// getDataDir returns the path to the data directory for the agent and an error
+// GetDataDir returns the path to the data directory for the agent and an error
 // if the directory is not valid. Attempts to find the optimal data directory if
 // no data directories are provided.
-func getDataDir(dataDirs ...string) (string, error) {
+func GetDataDir(dataDirs ...string) (string, error) {
 	if len(dataDirs) > 0 {
 		return testDataDirs(dataDirs)
 	}

agent/data_dir_test.go

@@ -17,7 +17,7 @@ func TestGetDataDir(t *testing.T) {
 	// Test with explicit dataDir parameter
 	t.Run("explicit data dir", func(t *testing.T) {
 		tempDir := t.TempDir()
-		result, err := getDataDir(tempDir)
+		result, err := GetDataDir(tempDir)
 		require.NoError(t, err)
 		assert.Equal(t, tempDir, result)
 	})
@@ -26,7 +26,7 @@ func TestGetDataDir(t *testing.T) {
 	t.Run("explicit data dir - create new", func(t *testing.T) {
 		tempDir := t.TempDir()
 		newDir := filepath.Join(tempDir, "new-data-dir")
-		result, err := getDataDir(newDir)
+		result, err := GetDataDir(newDir)
 		require.NoError(t, err)
 		assert.Equal(t, newDir, result)
 
@@ -52,7 +52,7 @@ func TestGetDataDir(t *testing.T) {
 
 		os.Setenv("BESZEL_AGENT_DATA_DIR", tempDir)
 
-		result, err := getDataDir()
+		result, err := GetDataDir()
 		require.NoError(t, err)
 		assert.Equal(t, tempDir, result)
 	})
@@ -60,7 +60,7 @@ func TestGetDataDir(t *testing.T) {
 	// Test with invalid explicit dataDir
 	t.Run("invalid explicit data dir", func(t *testing.T) {
 		invalidPath := "/invalid/path/that/cannot/be/created"
-		_, err := getDataDir(invalidPath)
+		_, err := GetDataDir(invalidPath)
 		assert.Error(t, err)
 	})
 
@@ -79,7 +79,7 @@ func TestGetDataDir(t *testing.T) {
 
 		// This will try platform-specific defaults, which may or may not work
 		// We're mainly testing that it doesn't panic and returns some result
-		result, err := getDataDir()
+		result, err := GetDataDir()
 		// We don't assert success/failure here since it depends on system permissions
 		// Just verify we get a string result if no error
 		if err == nil {

agent/fingerprint.go

@@ -0,0 +1,87 @@
+package agent
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/shirou/gopsutil/v4/cpu"
+	"github.com/shirou/gopsutil/v4/host"
+)
+
+const fingerprintFileName = "fingerprint"
+
+// knownBadUUID is a commonly known "product_uuid" that is not unique across systems.
+const knownBadUUID = "03000200-0400-0500-0006-000700080009"
+
+// GetFingerprint returns the agent fingerprint. It first tries to read a saved
+// fingerprint from the data directory. If not found (or dataDir is empty), it
+// generates one from system properties. The hostname and cpuModel parameters are
+// used as fallback material if host.HostID() fails. If either is empty, they
+// are fetched from the system automatically.
+//
+// If a new fingerprint is generated and a dataDir is provided, it is saved.
+func GetFingerprint(dataDir, hostname, cpuModel string) string {
+	if dataDir != "" {
+		if fp, err := readFingerprint(dataDir); err == nil {
+			return fp
+		}
+	}
+	fp := generateFingerprint(hostname, cpuModel)
+	if dataDir != "" {
+		_ = SaveFingerprint(dataDir, fp)
+	}
+	return fp
+}
+
+// generateFingerprint creates a fingerprint from system properties.
+// It tries host.HostID() first, falling back to hostname + cpuModel.
+// If hostname or cpuModel are empty, they are fetched from the system.
+func generateFingerprint(hostname, cpuModel string) string {
+	fingerprint, err := host.HostID()
+	if err != nil || fingerprint == "" || fingerprint == knownBadUUID {
+		if hostname == "" {
+			hostname, _ = os.Hostname()
+		}
+		if cpuModel == "" {
+			if info, err := cpu.Info(); err == nil && len(info) > 0 {
+				cpuModel = info[0].ModelName
+			}
+		}
+		fingerprint = hostname + cpuModel
+	}
+
+	sum := sha256.Sum256([]byte(fingerprint))
+	return hex.EncodeToString(sum[:24])
+}
+
+// readFingerprint reads the saved fingerprint from the data directory.
+func readFingerprint(dataDir string) (string, error) {
+	fp, err := os.ReadFile(filepath.Join(dataDir, fingerprintFileName))
+	if err != nil {
+		return "", err
+	}
+	s := strings.TrimSpace(string(fp))
+	if s == "" {
+		return "", errors.New("fingerprint file is empty")
+	}
+	return s, nil
+}
+
+// SaveFingerprint writes the fingerprint to the data directory.
+func SaveFingerprint(dataDir, fingerprint string) error {
+	return os.WriteFile(filepath.Join(dataDir, fingerprintFileName), []byte(fingerprint), 0o644)
+}
+
+// DeleteFingerprint removes the saved fingerprint file from the data directory.
+// Returns nil if the file does not exist (idempotent).
+func DeleteFingerprint(dataDir string) error {
+	err := os.Remove(filepath.Join(dataDir, fingerprintFileName))
+	if errors.Is(err, os.ErrNotExist) {
+		return nil
+	}
+	return err
+}

agent/fingerprint_test.go

@@ -0,0 +1,103 @@
+//go:build testing
+// +build testing
+
+package agent
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetFingerprint(t *testing.T) {
+	t.Run("reads existing fingerprint from file", func(t *testing.T) {
+		dir := t.TempDir()
+		expected := "abc123def456"
+		err := os.WriteFile(filepath.Join(dir, fingerprintFileName), []byte(expected), 0644)
+		require.NoError(t, err)
+
+		fp := GetFingerprint(dir, "", "")
+		assert.Equal(t, expected, fp)
+	})
+
+	t.Run("trims whitespace from file", func(t *testing.T) {
+		dir := t.TempDir()
+		err := os.WriteFile(filepath.Join(dir, fingerprintFileName), []byte("  abc123  \n"), 0644)
+		require.NoError(t, err)
+
+		fp := GetFingerprint(dir, "", "")
+		assert.Equal(t, "abc123", fp)
+	})
+
+	t.Run("generates fingerprint when file does not exist", func(t *testing.T) {
+		dir := t.TempDir()
+		fp := GetFingerprint(dir, "", "")
+		assert.NotEmpty(t, fp)
+	})
+
+	t.Run("generates fingerprint when dataDir is empty", func(t *testing.T) {
+		fp := GetFingerprint("", "", "")
+		assert.NotEmpty(t, fp)
+	})
+
+	t.Run("generates consistent fingerprint for same inputs", func(t *testing.T) {
+		fp1 := GetFingerprint("", "myhost", "mycpu")
+		fp2 := GetFingerprint("", "myhost", "mycpu")
+		assert.Equal(t, fp1, fp2)
+	})
+
+	t.Run("prefers saved fingerprint over generated", func(t *testing.T) {
+		dir := t.TempDir()
+		require.NoError(t, SaveFingerprint(dir, "saved-fp"))
+
+		fp := GetFingerprint(dir, "anyhost", "anycpu")
+		assert.Equal(t, "saved-fp", fp)
+	})
+}
+
+func TestSaveFingerprint(t *testing.T) {
+	t.Run("saves fingerprint to file", func(t *testing.T) {
+		dir := t.TempDir()
+		err := SaveFingerprint(dir, "abc123")
+		require.NoError(t, err)
+
+		content, err := os.ReadFile(filepath.Join(dir, fingerprintFileName))
+		require.NoError(t, err)
+		assert.Equal(t, "abc123", string(content))
+	})
+
+	t.Run("overwrites existing fingerprint", func(t *testing.T) {
+		dir := t.TempDir()
+		require.NoError(t, SaveFingerprint(dir, "old"))
+		require.NoError(t, SaveFingerprint(dir, "new"))
+
+		content, err := os.ReadFile(filepath.Join(dir, fingerprintFileName))
+		require.NoError(t, err)
+		assert.Equal(t, "new", string(content))
+	})
+}
+
+func TestDeleteFingerprint(t *testing.T) {
+	t.Run("deletes existing fingerprint", func(t *testing.T) {
+		dir := t.TempDir()
+		fp := filepath.Join(dir, fingerprintFileName)
+		err := os.WriteFile(fp, []byte("abc123"), 0644)
+		require.NoError(t, err)
+
+		err = DeleteFingerprint(dir)
+		require.NoError(t, err)
+
+		// Verify file is gone
+		_, err = os.Stat(fp)
+		assert.True(t, os.IsNotExist(err))
+	})
+
+	t.Run("no error when file does not exist", func(t *testing.T) {
+		dir := t.TempDir()
+		err := DeleteFingerprint(dir)
+		assert.NoError(t, err)
+	})
+}

agent/update.go

@@ -63,9 +63,9 @@ func detectRestarter() restarter {
 	if path, err := exec.LookPath("rc-service"); err == nil {
 		return &openRCRestarter{cmd: path}
 	}
-    if path, err := exec.LookPath("procd"); err == nil {
-        return &openWRTRestarter{cmd: path}
-    }
+	if path, err := exec.LookPath("procd"); err == nil {
+		return &openWRTRestarter{cmd: path}
+	}
 	if path, err := exec.LookPath("service"); err == nil {
 		if runtime.GOOS == "freebsd" {
 			return &freeBSDRestarter{cmd: path}
@@ -79,7 +79,7 @@ func detectRestarter() restarter {
 func Update(useMirror bool) error {
 	exePath, _ := os.Executable()
 
-	dataDir, err := getDataDir()
+	dataDir, err := GetDataDir()
 	if err != nil {
 		dataDir = os.TempDir()
 	}
@@ -125,4 +125,3 @@ func Update(useMirror bool) error {
 
 	return nil
 }
-

internal/cmd/agent/agent.go

@@ -38,6 +38,9 @@ func (opts *cmdOptions) parse() bool {
 		}
 		fmt.Print("ok")
 		return true
+	case "fingerprint":
+		handleFingerprint()
+		return true
 	}
 
 	// pflag.CommandLine.ParseErrorsWhitelist.UnknownFlags = true
@@ -71,9 +74,9 @@ func (opts *cmdOptions) parse() bool {
 		builder.WriteString(os.Args[0])
 		builder.WriteString(" [command] [flags]\n")
 		builder.WriteString("\nCommands:\n")
-		builder.WriteString("  health    Check if the agent is running\n")
-		// builder.WriteString("  help      Display this help message\n")
-		builder.WriteString("  update    Update to the latest version\n")
+		builder.WriteString("  fingerprint  View or reset the agent fingerprint\n")
+		builder.WriteString("  health       Check if the agent is running\n")
+		builder.WriteString("  update       Update to the latest version\n")
 		builder.WriteString("\nFlags:\n")
 		fmt.Print(builder.String())
 		pflag.PrintDefaults()
@@ -134,6 +137,38 @@ func (opts *cmdOptions) getAddress() string {
 	return agent.GetAddress(opts.listen)
 }
 
+// handleFingerprint handles the "fingerprint" command with subcommands "view" and "reset".
+func handleFingerprint() {
+	subCmd := ""
+	if len(os.Args) > 2 {
+		subCmd = os.Args[2]
+	}
+
+	switch subCmd {
+	case "", "view":
+		dataDir, _ := agent.GetDataDir()
+		fp := agent.GetFingerprint(dataDir, "", "")
+		fmt.Println(fp)
+	case "help", "-h", "--help":
+		fmt.Print(fingerprintUsage())
+	case "reset":
+		dataDir, err := agent.GetDataDir()
+		if err != nil {
+			log.Fatal(err)
+		}
+		if err := agent.DeleteFingerprint(dataDir); err != nil {
+			log.Fatal(err)
+		}
+		fmt.Println("Fingerprint reset. A new one will be generated on next start.")
+	default:
+		log.Fatalf("Unknown command: %q\n\n%s", subCmd, fingerprintUsage())
+	}
+}
+
+func fingerprintUsage() string {
+	return fmt.Sprintf("Usage: %s fingerprint [view|reset]\n\nCommands:\n  view   Print fingerprint (default)\n  reset  Reset saved fingerprint\n", os.Args[0])
+}
+
 func main() {
 	var opts cmdOptions
 	subcommandHandled := opts.parse()