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sec-design.md

File metadata and controls

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Okay, let's create a design document for the flutter_file_picker project.

BUSINESS POSTURE

Business Priorities and Goals:

  • Enable developers to easily integrate file picking functionality into their Flutter applications across various platforms (iOS, Android, Web, Desktop).
  • Provide a consistent and user-friendly API for accessing files from different sources (local storage, cloud providers).
  • Maintain a high level of platform compatibility and adapt to evolving operating system file access mechanisms.
  • Minimize external dependencies to reduce the risk of supply chain attacks and maintain a small package size.
  • Provide good documentation and examples to facilitate easy adoption by developers.
  • Offer a flexible and customizable solution to cater to diverse application needs.

Business Risks:

  • Inconsistent behavior across different platforms, leading to application instability or user frustration.
  • Security vulnerabilities related to file access, potentially exposing sensitive user data.
  • Dependency on deprecated or insecure platform APIs, causing compatibility issues or security risks.
  • Lack of support for emerging file sources or storage mechanisms.
  • Difficult integration or usage, hindering developer adoption.
  • Failure to comply with platform-specific file access guidelines and permissions, leading to application rejection or runtime errors.

SECURITY POSTURE

Existing Security Controls:

  • security control: Leverages platform-specific file access APIs (e.g., Android Intents, iOS Document Picker) to delegate file selection to the operating system, inheriting the OS's built-in security mechanisms.
  • security control: Uses standard Flutter/Dart mechanisms for inter-process communication (MethodChannel) to interact with native platform code, reducing the attack surface.
  • security control: The project is open-source, allowing for community review and identification of potential vulnerabilities.
  • security control: Follows semantic versioning, allowing users to control updates and avoid unexpected breaking changes.
  • security control: Implemented in Dart - memory-safe language.

Accepted Risks:

  • accepted risk: Relies on the security of the underlying platform's file access APIs and user's granting of appropriate permissions.
  • accepted risk: Limited control over the UI/UX of the native file pickers, as they are provided by the operating system.
  • accepted risk: Potential for future platform API changes to introduce compatibility issues or require updates to the plugin.

Recommended Security Controls:

  • security control: Implement robust input validation and sanitization for file paths and names returned by the platform APIs to prevent path traversal or other injection vulnerabilities.
  • security control: Provide clear documentation and guidelines on secure file handling practices for developers using the plugin, including recommendations for data encryption and storage.
  • security control: Regularly review and update dependencies to address known vulnerabilities.
  • security control: Consider implementing a mechanism for verifying the integrity of downloaded files (e.g., checksum validation) if the plugin supports downloading files from remote sources.
  • security control: Add static code analysis to CI pipeline.

Security Requirements:

  • Authentication:

    • The plugin itself does not handle user authentication. Authentication, if required, is the responsibility of the application using the plugin or the underlying platform APIs (e.g., when accessing cloud storage).

  • Authorization:

    • The plugin relies on the operating system's permission model to control access to files. The application using the plugin must request the necessary permissions (e.g., READ_EXTERNAL_STORAGE on Android) from the user.

  • Input Validation:

    • File paths and names returned by the platform APIs should be treated as untrusted input and validated/sanitized before being used by the application. This is crucial to prevent path traversal vulnerabilities.

  • Cryptography:

    • The plugin does not directly handle encryption. If encryption is required, it is the responsibility of the application using the plugin to encrypt/decrypt files before/after using the file picker.

DESIGN

C4 CONTEXT

graph LR
    User["User"]
    FlutterApp["Flutter Application\n(using flutter_file_picker)"]
    FilePickerPlugin["flutter_file_picker\nPlugin"]
    OperatingSystem["Operating System\n(iOS, Android, Web, Desktop)"]
    CloudStorage["Cloud Storage\n(Optional)"]

    User -- Uses --> FlutterApp
    FlutterApp -- Uses --> FilePickerPlugin
    FilePickerPlugin -- Interacts with --> OperatingSystem
    OperatingSystem -- Accesses --> CloudStorage
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Element Descriptions:

  • Element:

    • Name: User
    • Type: Person
    • Description: The end-user interacting with the Flutter application.
    • Responsibilities: Initiates file picking operations within the application.
    • Security controls: N/A - The user is external to the system.

  • Element:

    • Name: Flutter Application (using flutter_file_picker)
    • Type: Software System
    • Description: A Flutter application developed by a third party that utilizes the flutter_file_picker plugin.
    • Responsibilities: Integrates the flutter_file_picker plugin, handles file picking results, and processes the selected files.
    • Security controls: Responsible for implementing secure file handling practices, including input validation, data encryption, and secure storage.

  • Element:

    • Name: flutter_file_picker Plugin
    • Type: Software System
    • Description: The flutter_file_picker plugin itself.
    • Responsibilities: Provides a platform-agnostic API for file picking, interacts with native platform APIs, and returns file information to the Flutter application.
    • Security controls: Leverages platform-specific security mechanisms, uses secure inter-process communication.

  • Element:

    • Name: Operating System (iOS, Android, Web, Desktop)
    • Type: Software System
    • Description: The underlying operating system on which the Flutter application is running.
    • Responsibilities: Provides the native file picking UI and handles file access permissions.
    • Security controls: Enforces platform-specific security policies, including file access permissions and sandboxing.

  • Element:

    • Name: Cloud Storage (Optional)
    • Type: Software System
    • Description: Cloud storage services (e.g., Google Drive, Dropbox, iCloud) that may be accessed through the native file picker.
    • Responsibilities: Provides storage and retrieval of files.
    • Security controls: Implements its own security mechanisms, including authentication, authorization, and data encryption.

C4 CONTAINER

graph LR
    FlutterApp["Flutter Application"]
    FilePickerAPI["File Picker API\n(Dart)"]
    MethodChannel["Method Channel\n(Flutter)"]
    PlatformSpecificImpl["Platform-Specific\nImplementation\n(Native Code)"]
    OSFilePicker["OS File Picker\n(Native)"]

    FlutterApp -- Calls --> FilePickerAPI
    FilePickerAPI -- Uses --> MethodChannel
    MethodChannel -- Invokes --> PlatformSpecificImpl
    PlatformSpecificImpl -- Interacts with --> OSFilePicker
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Element Descriptions:

  • Element:

    • Name: Flutter Application
    • Type: Container
    • Description: The application using the flutter_file_picker plugin.
    • Responsibilities: Initiates file picking, handles results, and processes files.
    • Security controls: Implements application-level security measures.

  • Element:

    • Name: File Picker API (Dart)
    • Type: Container
    • Description: The platform-agnostic Dart API exposed by the plugin.
    • Responsibilities: Provides a consistent interface for file picking across different platforms.
    • Security controls: Input validation (to the extent possible at the Dart level).

  • Element:

    • Name: Method Channel (Flutter)
    • Type: Container
    • Description: Flutter's mechanism for inter-process communication between Dart and native code.
    • Responsibilities: Facilitates communication between the Dart code and the platform-specific implementation.
    • Security controls: Uses a defined protocol for communication, reducing the risk of injection attacks.

  • Element:

    • Name: Platform-Specific Implementation (Native Code)
    • Type: Container
    • Description: The native code (Java/Kotlin for Android, Objective-C/Swift for iOS, etc.) that interacts with the OS file picker.
    • Responsibilities: Bridges the gap between the Flutter plugin and the native file picking APIs.
    • Security controls: Relies on the security of the underlying platform APIs.

  • Element:

    • Name: OS File Picker (Native)
    • Type: Container
    • Description: The native file picker UI provided by the operating system.
    • Responsibilities: Presents the file selection interface to the user and handles file access permissions.
    • Security controls: Enforces OS-level security policies.

DEPLOYMENT

Possible Deployment Solutions:

  1. Flutter Package Deployment: The primary deployment method is as a Flutter package hosted on pub.dev. Developers add the package as a dependency in their pubspec.yaml file.
  2. Direct GitHub Repository Inclusion: Developers can also include the plugin directly from the GitHub repository, although this is less common.
  3. Local Copy: A developer could download a copy of the repository and include it locally in their project. This is not recommended due to update and maintenance issues.

Chosen Solution (Flutter Package Deployment):

graph LR
    Developer["Developer"]
    FlutterProject["Flutter Project\n(pubspec.yaml)"]
    PubDev["pub.dev"]
    FlutterBuild["Flutter Build Process"]
    TargetDevice["Target Device\n(iOS, Android, Web, Desktop)"]
    OS["Operating System"]

    Developer -- Adds dependency to --> FlutterProject
    FlutterProject -- Fetches from --> PubDev
    PubDev -- Provides package to --> FlutterBuild
    FlutterBuild -- Compiles and deploys to --> TargetDevice
    TargetDevice -- Runs on --> OS
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Element Descriptions:

  • Element:

    • Name: Developer
    • Type: Person
    • Description: The developer integrating the flutter_file_picker plugin into their Flutter application.
    • Responsibilities: Adds the plugin as a dependency and uses its API.
    • Security controls: N/A

  • Element:

    • Name: Flutter Project (pubspec.yaml)
    • Type: Configuration File
    • Description: The pubspec.yaml file of the Flutter application, which declares the dependency on flutter_file_picker.
    • Responsibilities: Specifies the required version of the plugin.
    • Security controls: Semantic versioning allows developers to control updates.

  • Element:

    • Name: pub.dev
    • Type: Package Repository
    • Description: The official package repository for Flutter and Dart packages.
    • Responsibilities: Hosts the flutter_file_picker package and its different versions.
    • Security controls: Provides a central, trusted source for Flutter packages.

  • Element:

    • Name: Flutter Build Process
    • Type: Process
    • Description: The process of building the Flutter application, including fetching dependencies and compiling code.
    • Responsibilities: Retrieves the flutter_file_picker package from pub.dev and integrates it into the application.
    • Security controls: Relies on the integrity of pub.dev and the downloaded package.

  • Element:

    • Name: Target Device (iOS, Android, Web, Desktop)
    • Type: Device
    • Description: The device on which the Flutter application is running.
    • Responsibilities: Executes the application code, including the flutter_file_picker plugin.
    • Security controls: Relies on the operating system's security mechanisms.

  • Element: * Name: Operating System * Type: Software System * Description: OS on target device. * Responsibilities: Provides native file picker. * Security controls: OS level security controls.

BUILD

graph LR
    Developer["Developer"] --> LocalMachine["Local Machine"]
    LocalMachine --> GitHub["GitHub Repository"]
    GitHub --> GitHubActions["GitHub Actions (CI)"]
    GitHubActions --> DartAnalyzer["Dart Analyzer"]
    GitHubActions --> FlutterTest["Flutter Test"]
    GitHubActions --> PubDev["pub.dev"]

    DartAnalyzer -- Static Analysis --> GitHubActions
    FlutterTest -- Unit & Integration Tests --> GitHubActions
    GitHubActions -- Publishes Package --> PubDev
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Build Process Description:

  1. Development: Developers write code and commit changes to the GitHub repository.
  2. Continuous Integration (GitHub Actions):
    • A GitHub Actions workflow is triggered on each push or pull request.
    • Static Analysis: Dart Analyzer performs static code analysis to identify potential issues and enforce code style.
    • Testing: Flutter Test runs unit and integration tests to ensure code quality and functionality.
    • Publishing (on tagged commits): If the workflow is triggered by a tagged commit, and all checks pass, the package is automatically published to pub.dev.
  3. Package Publication: The flutter pub publish command is used (within the GitHub Actions workflow) to upload the package to pub.dev.

Security Controls in Build Process:

  • security control: GitHub Actions: Automates the build, test, and publishing process, ensuring consistency and reducing manual errors.
  • security control: Dart Analyzer: Enforces code style and identifies potential issues through static analysis.
  • security control: Flutter Test: Runs automated tests to verify code correctness and prevent regressions.
  • security control: Semantic Versioning: Uses semantic versioning to manage releases and allow users to control updates.
  • security control: Signed Commits: Developers should sign their commits to ensure authenticity and prevent tampering.
  • security control: Dependency Management: Regularly review and update dependencies to address known vulnerabilities.

RISK ASSESSMENT

Critical Business Processes:

  • File Selection: The core functionality of the plugin, enabling users to select files from various sources.
  • Cross-Platform Compatibility: Ensuring consistent behavior across different operating systems.
  • Application Stability: Preventing crashes or errors related to file picking.
  • User Data Privacy: Protecting user data accessed through the file picker.

Data Sensitivity:

  • File Paths: May reveal information about the user's file system structure. Sensitivity: Low to Medium.
  • File Names: May contain sensitive information, depending on the user's naming conventions. Sensitivity: Low to High.
  • File Contents: The actual content of the selected files, which can range from non-sensitive to highly sensitive (e.g., personal documents, financial records, medical information). Sensitivity: Variable, potentially High.

QUESTIONS & ASSUMPTIONS

Questions:

  • Are there any specific compliance requirements (e.g., GDPR, HIPAA) that need to be considered when handling user files?
  • Are there any plans to support specific cloud storage providers directly (beyond what is offered by the native file pickers)?
  • What level of logging and error reporting is desired for the plugin?
  • Are there any specific performance requirements or limitations for file picking (e.g., maximum file size)?

Assumptions:

  • BUSINESS POSTURE: The primary goal is to provide a convenient and reliable file picking solution for Flutter developers.
  • BUSINESS POSTURE: The project prioritizes ease of use and cross-platform compatibility.
  • SECURITY POSTURE: The plugin relies heavily on the security of the underlying operating system's file access mechanisms.
  • SECURITY POSTURE: Developers using the plugin are responsible for implementing appropriate security measures in their applications, such as input validation and data encryption.
  • DESIGN: The plugin acts as a bridge between the Flutter application and the native file picking APIs.
  • DESIGN: The plugin does not directly handle file storage or management.
  • DESIGN: The plugin does not require any specific authentication mechanisms beyond what is provided by the operating system or cloud storage providers.