| 36 | var deviceIDFunc = getOrCreateDeviceID |
| 37 | |
| 38 | func getOrCreateDeviceID() (string, error) { |
| 39 | stateDir := stateDirFunc() |
| 40 | idPath := filepath.Join(stateDir, deviceIDFileName) |
| 41 | |
| 42 | data, err := os.ReadFile(idPath) |
| 43 | if err == nil { |
| 44 | return strings.TrimSpace(string(data)), nil |
| 45 | } |
| 46 | if !errors.Is(err, os.ErrNotExist) { |
| 47 | return "", err |
| 48 | } |
| 49 | |
| 50 | id := uuid.New().String() |
| 51 | if err := os.MkdirAll(stateDir, 0o755); err != nil { |
| 52 | return "", err |
| 53 | } |
| 54 | |
| 55 | // Write the ID to a temp file in the same directory, then hard-link it |
| 56 | // to the target path. os.Link fails atomically if the target already |
| 57 | // exists, so exactly one concurrent caller wins. Losers read the |
| 58 | // winner's ID. The temp file is always cleaned up. |
| 59 | tmpFile, err := os.CreateTemp(stateDir, deviceIDFileName+".tmp.*") |
| 60 | if err != nil { |
| 61 | return "", err |
| 62 | } |
| 63 | tmpPath := tmpFile.Name() |
| 64 | |
| 65 | if _, err := tmpFile.WriteString(id); err != nil { |
| 66 | tmpFile.Close() |
| 67 | os.Remove(tmpPath) |
| 68 | return "", err |
| 69 | } |
| 70 | if err := tmpFile.Close(); err != nil { |
| 71 | os.Remove(tmpPath) |
| 72 | return "", err |
| 73 | } |
| 74 | |
| 75 | linkErr := os.Link(tmpPath, idPath) |
| 76 | os.Remove(tmpPath) |
| 77 | |
| 78 | if linkErr != nil { |
| 79 | // Another caller won — read their ID. |
| 80 | data, readErr := os.ReadFile(idPath) |
| 81 | if readErr != nil { |
| 82 | return "", linkErr |
| 83 | } |
| 84 | return strings.TrimSpace(string(data)), nil |
| 85 | } |
| 86 | |
| 87 | return id, nil |
| 88 | } |
| 89 | |
| 90 | var falseyValues = []string{"", "0", "false", "no", "disabled", "off"} |
| 91 | |