When building command-line tools or applications that need to store configuration files, it’s common to use the user’s home directory. In this post, we’ll explore how to safely create and manage a hidden directory in the user’s home folder using Go, with a focus on security.

Getting the User’s Home Directory

Go provides a straightforward way to get the user’s home directory through the os package:

homeDir, err := os.UserHomeDir()

This works cross-platform, handling the differences between Windows (C:\Users\username), Unix (/home/username), and macOS (/Users/username).

Creating a Hidden Directory

In Unix-like systems, directories starting with a dot (.) are hidden by default. Let’s create a .spike directory in the user’s home folder:

package main

import (
    "os"
    "path/filepath"
)

func main() {
    homeDir, err := os.UserHomeDir()
    if err != nil {
        panic(err)
    }

    spikeDir := filepath.Join(homeDir, ".spike")
    
    err = os.MkdirAll(spikeDir, 0600)
    if err != nil {
        panic(err)
    }
}

Understanding File Permissions

The permission value 0600 in the code above is crucial for security:

• 6 (owner): Read (4) + Write (2) = 6
• 0 (group): No permissions
• 0 (others): No permissions

This ensures that only the owner can read and write to the directory, while all other users on the system are denied access.

Handling Existing Directories

MkdirAll has some interesting behavior when the directory already exists:

1. If the directory doesn’t exist, it creates it with the specified permissions
2. If the directory exists, it does nothing and returns nil
3. It won’t modify permissions of an existing directory

To ensure consistent permissions, we should explicitly set them:

// Create if doesn't exist
err = os.MkdirAll(spikeDir, 0600)
if err != nil {
    panic(err)
}

// Ensure correct permissions even if directory already existed
err = os.Chmod(spikeDir, 0600)
if err != nil {
    panic(err)
}

Platform Considerations

While Unix-style permissions (0600) work well on Unix-like systems, Windows handles permissions differently. Go will attempt to map these permissions to Windows Access Control Lists (ACLs), but the exact behavior might vary.

Best Practices

1. Always check for errors when dealing with file operations
2. Use filepath.Join() instead of string concatenation for paths
3. Set restrictive permissions for directories containing sensitive data
4. Consider explicitly setting permissions after directory creation
5. Use os.UserHomeDir() instead of environment variables for better cross-platform support

Conclusion

When creating directories in a user’s home folder, it’s crucial to consider security implications. By using appropriate permissions and handling existing directories correctly, we can ensure our application safely stores its data while preventing unauthorized access.

Remember, security is not just about functionality—it’s about protecting user data and maintaining trust in your application.