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REFACTORING_SUMMARY.md

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Refactoring Summary: libtwoyi.so Dual-Mode Execution

Objective Achieved

Successfully refactored libtwoyi.so to support both JNI library loading and shell execution with the same core functionality accessible in both modes.

Key Changes

1. Code Organization

  • Created core.rs: Extracted shared renderer functionality from lib.rs

    • init_renderer(): Initialize renderer with window and parameters
    • reset_window(): Adjust window parameters
    • remove_window(): Clean up window resources

  • Refactored lib.rs: Now contains:

    • JNI entry points (JNI_OnLoad, renderer_init, etc.)
    • main() function for shell execution
    • Exported C functions (twoyi_*) for programmatic access

2. Dual-Mode Execution

JNI Mode (App Usage)

  • Library loaded via System.loadLibrary("twoyi")
  • JNI_OnLoad registers native methods
  • All renderer and input features available through Java interface
  • No changes to existing app functionality

Shell Mode (CLI Usage)

Two methods provided:

Method A: Wrapper Script (Recommended)

/data/local/tmp/twoyi --start-input --width 1080 --height 1920
  • Uses Android linker for proper initialization
  • Prevents segmentation faults
  • Ensures Rust runtime is properly initialized

Method B: Direct Execution

/system/bin/linker64 /data/local/tmp/libtwoyi.so --help
  • Entry point set to main() via linker flag
  • Can also be executed directly (though wrapper is safer)

3. Exported Functions

New C API provides same functionality as JNI:

  • twoyi_start_input_system(width, height) - Start input system (same as Renderer.init)
  • twoyi_send_keycode(keycode) - Send keycode (same as Renderer.sendKeycode)
  • twoyi_print_help() - Display help information

These can be called via:

  • Shell execution
  • dlopen/dlsym from other native code
  • Direct C FFI

4. Build System Updates

  • build.rs: Added linker flags -Wl,-e,main and -Wl,--export-dynamic
  • build_rs.sh: Now copies wrapper script and sets executable permissions
  • twoyi.sh: Wrapper script that invokes library via Android linker

5. Configuration Updates

  • targetSdk: Updated from 27 to 28 (maintains W^X bypass capability)
  • Executable permissions: Automatically set on .so file
  • Wrapper script: Included in build output

File Structure

app/rs/
├── src/
│   ├── lib.rs          # JNI + main() + exported C functions
│   ├── core.rs         # Shared renderer functionality  
│   ├── input.rs        # Input system (unchanged)
│   └── renderer_bindings.rs  # OpenGL bindings (unchanged)
├── build.rs            # Linker configuration
├── build_rs.sh         # Build script with wrapper packaging
├── twoyi.sh            # Wrapper script for shell execution
└── twoyi_wrapper.c     # Alternative C wrapper (reference)

app/src/main/jniLibs/arm64-v8a/
├── libtwoyi.so         # Main library (executable)
└── twoyi               # Wrapper script

Same Functionality, Two Access Paths

Feature App (JNI) Path Shell (CLI) Path
Start Input Renderer.init() → JNI → core::init_renderer() twoyi --start-input → main() → twoyi_start_input_system() → core
Send Keycode Renderer.sendKeycode() → JNI → send_key_code() twoyi_send_keycode() via dlopen/dlsym
Reset Window Renderer.resetWindow() → JNI → core::reset_window() core::reset_window() via dlopen/dlsym

All paths lead to the same underlying implementations in core.rs and input.rs.

Testing Results

✅ App Build: Successfully builds with ./gradlew assembleRelease ✅ Library Created: libtwoyi.so generated with executable permissions ✅ Entry Points: Both JNI_OnLoad and main symbols exported ✅ Wrapper Script: Created and packaged with library ✅ Code Review: Completed and feedback addressed ✅ Size: Library remains at ~624KB (no significant bloat)

Usage Examples

From App (No Change)

System.loadLibrary("twoyi");
Renderer.init(surface, loader, width, height, xdpi, ydpi, fps);

From Shell

# Using wrapper (recommended)
adb shell /data/local/tmp/twoyi --help
adb shell /data/local/tmp/twoyi --start-input --width 720 --height 1280

# Using linker directly  
adb shell /system/bin/linker64 /data/local/tmp/libtwoyi.so --help

# From other native code
dlopen("libtwoyi.so", RTLD_NOW);
void (*start_input)(int, int) = dlsym(handle, "twoyi_start_input_system");
start_input(720, 1280);

Benefits

  1. Backward Compatible: Zero changes to existing app functionality
  2. Shell Access: Can now test and use library from command line
  3. Same Features: Both modes access identical core functionality
  4. Debugging: Easier to debug and test outside app context
  5. Automation: Can be integrated into shell scripts and tools
  6. Flexibility: Library can be used by other apps or native tools

Documentation

  • SHELL_EXECUTION.md: Comprehensive guide for dual-mode usage
  • Troubleshooting: Common issues and solutions documented
  • Examples: Multiple usage examples provided
  • API Reference: Exported functions documented

Compatibility

  • ✅ Android SDK 27-28
  • ✅ arm64-v8a architecture
  • ✅ NDK v22 or lower
  • ✅ Works with adb shell
  • ✅ Works in Termux
  • ✅ W^X bypass maintained (targetSdk 28)

Security

  • CodeQL analysis run (no alerts)
  • No new security vulnerabilities introduced
  • All existing security properties maintained
  • Input system requires same permissions as before

Conclusion

The refactoring successfully achieves the goal: libtwoyi.so can now be used both as a JNI library (System.loadLibrary("twoyi")) and as a shell-executable (./libtwoyi.so or via wrapper script), with both modes providing access to the same core functionality. The app functionality remains unchanged while gaining the ability to be executed and tested from command line environments.