Information Disclosure in Sinatra (Go)

To prevent information disclosure in Go-based Sinatra applications, implement strict output validation and struct-level field control. Start by auditing all HTTP handlers for unintentional data leaks. Replace generic error responses with sanitized messages and ensure that error details are logged server-side only, never returned to the client.

Use explicit struct tags to control JSON serialization. Define separate structs for input, output, and internal use. For example, instead of marshaling a domain model directly, create a view model that excludes sensitive fields:

// Internal user model (never exposed)
type user struct {
	ID           string
	Email        string
	HashedPassword string `json:"-"` // Never serialize
	SessionToken string `json:"-"`
	CreatedAt    time.Time
}

// Public-facing response model
type userResponse struct {
	ID        string `json:"id"`
	Email     string `json:"email"`
	CreatedAt string `json:"created_at"` // Format as needed
}

func getUserHandler(w http.ResponseWriter, r *http.Request) {
	// ... fetch user from DB into `u` of type `user`
	resp := userResponse{
		ID:        u.ID,
		Email:     u.Email,
		CreatedAt: u.CreatedAt.Format(time.RFC3339),
	}
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(resp)
}

This ensures that even if the internal user struct changes, sensitive fields are not accidentally exposed due to missing json:"-" tags.

For error handling, centralize response writing with a helper that never leaks internals:

func respondWithError(w http.ResponseWriter, status int, message string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(map[string]string{"error": message})
}

// Usage
if err != nil {
	// Log the real error for debugging
	log.Printf("Internal error: %v", err)
	// Return generic message to client
	respondWithError(w, http.StatusInternalServerError, "something went wrong")
	return
}

Finally, disable debug modes and stack trace output in production. If using a framework like gin or echo (common in Go microservices that may interface with Sinatra-like patterns), ensure SetMode(gin.ReleaseMode) is called. Regularly scan endpoints with tools like middleBrick to detect lingering information disclosure issues — its unauthenticated scanning can identify exposed debug endpoints, error messages, or excessive data in responses before attackers do.