Building a Playful File Locker with GoFr

├── file-locker
│   ├── handlers
│   │   ├── unix
│   │   │   ├── handler.go
│   ├── services
│   │   ├── unix
│   │   │   ├── service.go
│   │   ├── crypt
│   │   │   ├── crypt.go
│   ├── constants
│   │   ├── contants.go
│   ├── main.go
│   ├── go.mod

  const (  
     fileName = `private`  
     hiddenFileName = `.private`  
     encryptedDataFileName = `.encrypted-data`  
  )  

  type unix struct {  
     crypt services.Crypt  
  }  

  func New(crypt services.Crypt) services.FileLocker {  
     return &unix{crypt: crypt}  
  }  

  func (m *unix) Init(password string) error {  
     _, err := os.Stat(fileName)  
     if err == nil {  
        return errors.New("file locker already initialized")  
     }  

     err = os.Mkdir(fileName, os.ModePerm)  
     if err != nil {  
        return err  
     }  

     _, err = os.Create(filepath.Join(fileName, ".nomedia"))  
     if err != nil {  
        return err  
     }  

     encryptedPassword := m.crypt.Encrypt([]byte(password))  

     err = os.WriteFile(filepath.Join(fileName, encryptedDataFileName), encryptedPassword, os.ModePerm)  
     if err != nil {  
        return err  
     }  

     return nil  
  }  

  func (m *unix) Lock() error {  
     _, err := os.Stat(fileName)  
     if err != nil {  
        if err == os.ErrNotExist {  
           return errors.New("file locker not initialized or is still locked")  
        }  

        return err  
     }  

     return os.Rename(fileName, hiddenFileName)  
  }  

  func (m *unix) Unlock(password string) error {  
     _, err := os.Stat(hiddenFileName)  
     if err != nil {  
        if err == os.ErrNotExist {  
           return errors.New("file locker not initialized or is still unlocked")  
        }  

        return err  
     }  

     data, err := os.ReadFile(filepath.Join(hiddenFileName, encryptedDataFileName))  
     if err != nil {  
        return err  
     }  

     decryptedData, err := m.crypt.Decrypt(string(data))  
     if err != nil {  
        return err  
     }  

     if password != string(decryptedData) {  
        return errors.New("unauthorized")  
     }  

     return os.Rename(hiddenFileName, fileName)  
  }

- Struct `unix` implements `FileLocker` interface.
- `New` is the factory function that returns a `FileLocker` instance
- `Init` method will create a directory named `private` in the current directory and will store the encrypted password in file named `.encrypted-data`. If `private` directory is already present or there occurs some error while creating it then `Init` method will return error otherwise will return nil.
- `Lock` method will hide the `private` directory by renaming it to `.private`. If the `private` directory is not present in the current directory then it means that either `file-locker` has not been initialised or it is already in locked state.
- `Unlock` method will read the password from `.private/.encrypted-data` file and compare with the password received in the parameter. If it matches, then it will unhide the `private` file otherwise return `unauthorized` error.

  const secret = `qwertyuiopasdfghjklzxcvb`  

  type crypt struct {  
     block cipher.Block  
  }  

  func New() (services.Crypt, error) {  
     block, err := aes.NewCipher([]byte(secret))  
     if err != nil {  
        return nil, err  
     }  

     return &crypt{block: block}, nil  
  }  

  func (c *crypt) Encrypt(data []byte) []byte {  
     ciphertext := make([]byte, aes.BlockSize+len(data))  
     iv := ciphertext[:aes.BlockSize]  

     cfb := cipher.NewCFBEncrypter(c.block, iv)  
     cipherText := make([]byte, len(data))  
     cfb.XORKeyStream(cipherText, data)  

     dst := make([]byte, base64.StdEncoding.EncodedLen(len(cipherText)))  

     base64.StdEncoding.Encode(dst, cipherText)  

     return dst  
  }  

  func (c *crypt) Decrypt(data string) ([]byte, error) {  
     ciphertext := make([]byte, aes.BlockSize+len(data))  

     iv := ciphertext[:aes.BlockSize]  
     cfb := cipher.NewCFBDecrypter(c.block, iv)  

     cipherText, err := base64.StdEncoding.DecodeString(data)  
     if err != nil {  
        return []byte{}, err  
     }  

     plainText := make([]byte, len(cipherText))  
     cfb.XORKeyStream(plainText, cipherText)  

     return plainText, nil  
  }

- `Encrypt` method will encrypt the data given in the parameter and will return the encrypted string.
- `Decrypt` method will decrypt the string given in the parameter and will return the decrypted string.
- `secret` is a constant that has random string that will be used to encrypt and decrypt the data. You are free to update the value of secret but keeping a strong secret is advisable.

  type Handler interface {  
     Init(ctx *gofr.Context) (interface{}, error)  
     Lock(ctx *gofr.Context) (interface{}, error)  
     Unlock(ctx *gofr.Context) (interface{}, error)  
     Help(_ *gofr.Context) (interface{}, error)  
  }  

  type handler struct {  
     service services.FileLocker  
  }  

  func New(service services.FileLocker) Handler {  
     return &handler{service: service}  
  }  

  func (h *handler) Init(ctx *gofr.Context) (interface{}, error) {  
     password := ctx.Param("password")  
     if password == "" {  
        return nil, errors.New("password is required")  
     }  

     err := h.service.Init(password)  
     if err != nil {  
        return nil, err  
     }  

     return "file locker initialized", nil  
  }  

  func (h *handler) Lock(_ *gofr.Context) (interface{}, error) {  
     err := h.service.Lock()  
     if err != nil {  
        return nil, err  
     }  

     return "file locked", nil  
  }  

  func (h *handler) Unlock(ctx *gofr.Context) (interface{}, error) {  
     password := ctx.Param("password")  
     if password == "" {  
        return nil, errors.New("password is required")  
     }  

     err := h.service.Unlock(password)  
     if err != nil {  
        return nil, err  
     }  

     return "file unlocked", nil  
  }  

  func (h *handler) Help(_ *gofr.Context) (interface{}, error) {  
     return `File Locker CLI Tool  

  Usage:  
   file-locker [command]  
  Available Commands:  
   init      Create a directory named private and initialize the file locker lock      Hide the private directory unlock    Unhides the private directory`, nil  
  }

- `handler` is the struct that implements `Handler` interface.
- `Init` is the handler for `init` command. It takes `password` as the flag. The value for this flag will be used in unlocking.
- `Lock` method is the handler for `lock` command.
- `Unlock` method is the handler for `unlock` command. It takes `password` flag for password to unlock.
- `Help` method is the handler for `help` command. It returns the help string for the app.

  func main() {  
     var service services.FileLocker  

    app := gofr.NewCMD()  

     crypt, err := cryptPkg.New()  
     if err != nil {  
        app.Logger().Fatalf("Error occurred: %v", err)  
     }  

     switch runtime.GOOS {  
     case constants.Darwin, constants.Linux:  
        service = unix.New(crypt)  
     default:  
        app.Logger().Fatalf("Unsupported architecture: %v", runtime.GOOS)  
     }  

     handler := handlers.New(service)  

     app.SubCommand("init", handler.Init)  
     app.SubCommand("unlock", handler.Unlock)  
     app.SubCommand("lock", handler.Lock)  
     app.SubCommand("help", handler.Help)  

     app.Run()  
  }

- `NewCMD()` function creates a command line application
- Depending upon the architecture of the underlying OS, we are creating service. This service will be injected in the handler. Currently, we have only implemented service layer for Unix based OS hence in the switch statement we only have case for `Darwin` (for MacOS) and `Linux`.
- `SubCommand` method adds a sub-command to the CLI application. Here, we have added four sub-commands, viz. `init`, `unlock`, `lock`, `help`. The second argument in the `SubCommand` method is the handler that will be called for execution when that particular sub-command is given.
- `Run()` method will run the application.

const (  
   Darwin = `darwin`  
   Linux = `linux`  
)