Termux FileWatcher JNI Library

A Termux-compatible JNI implementation of file watching functionality for the Kotlin Language Server. This library provides both stub and real implementations to solve glibc compatibility issues when running IntelliJ-based language servers on Android/Termux.

🎯 Problem Solved

The original Kotlin LSP includes a native library libfilewatcher_jni.so compiled for glibc-based Linux systems. On Termux (Android), this causes UnsatisfiedLinkError due to:

• ABI Incompatibility: glibc vs Android's Bionic libc
• Missing Symbol Versions: Different C library implementations
• Dependency Chain Issues: Even symlinks don't resolve ABI differences

This project provides drop-in replacements that work natively on Termux while maintaining full API compatibility.

✨ Features

🔧 Stub Implementation

• ✅ Quick Fix: Resolves loading errors immediately
• ✅ Zero Dependencies: No additional system requirements
• ✅ Minimal Overhead: ~4KB library size
• ❌ No File Watching: LSP won't detect external file changes

🚀 Real Implementation

• ✅ Full File Monitoring: Complete inotify-based file watching
• ✅ High Performance: Kernel-level event notification (~100x faster than polling)
• ✅ Thread Safe: Proper synchronization for multi-threaded LSP servers
• ✅ Event Types: CREATE, MODIFY, DELETE, OVERFLOW support
• ✅ Memory Efficient: ~20KB library + ~1KB per watcher

🚀 Quick Start

Prerequisites

pkg install clang openjdk-17

Architecture Detection

If you're unsure of your architecture:

# Check your architecture
uname -m
# aarch64 -> use libfilewatcher-aarch64-*.tar.gz
# armv7l   -> use libfilewatcher-arm-*.tar.gz  
# x86_64   -> use libfilewatcher-x86_64-*.tar.gz
# i686     -> use libfilewatcher-i686-*.tar.gz

Installation

# Download specific version for your architecture
wget https://github.com/yamsergey/termux-filewatcher/releases/download/v1.0.0/libfilewatcher-aarch64-v1.0.0.tar.gz
tar -xzf libfilewatcher-aarch64-v1.0.0.tar.gz

cp libfilewatcher_jni.so /path/to/kotlin-lsp/native/Linux-AArch64/

Build from Source

# Clone the repository
git clone https://github.com/yamsergey/termux-filewatcher.git
cd termux-filewatcher

# Build the library (real implementation by default)
make

# Or build stub implementation
make stub

# Install to Kotlin LSP
make install KOTLIN_LSP_PATH=/path/to/kotlin-lsp

## 📖 Usage

Once installed, the Kotlin LSP will use the new native library automatically:

```bash

# Start LSP server  
./kotlin-lsp.sh.orig --stdio

Testing File Watching

import com.jetbrains.analyzer.filewatcher.FileWatcher;

public class TestFileWatcher {
    public static void main(String[] args) throws Exception {
        FileWatcher watcher = new FileWatcher();
        watcher.watch("/tmp");
        
        System.out.println("Watching /tmp - create files to see events...");
        
        // Poll for events
        for (int i = 0; i < 10; i++) {
            FileWatcher.Event event = watcher.nextEvent();
            if (event != null) {
                System.out.println("Event: " + event.getKind() + " - " + event.getPath());
            }
            Thread.sleep(1000);
        }
        
        watcher.stop();
    }
}

🏗️ Build System

Make Targets

make                    # Build real implementation
make stub              # Build stub implementation  
make test              # Run test suite
make clean             # Clean build artifacts
make install           # Install to Kotlin LSP
make uninstall         # Restore original library
make docker-test       # Test in isolated environment

CMake (Advanced)

mkdir build && cd build
cmake ..
make
ctest                  # Run tests

🧪 Testing

Automated Tests

# Run full test suite
make test

# Run specific test categories
make test-unit         # Unit tests only
make test-integration  # Integration tests only
make test-performance  # Performance benchmarks

Manual Testing

# Compile test program
make test-manual

# Test basic functionality
./test/manual/test_basic

# Test performance  
./test/manual/test_performance

# Test concurrent access
./test/manual/test_concurrent

📊 Performance

Benchmarks (on Termux/Android)

Metric	Stub	Real	Original
Library Size	4KB	20KB	45KB
Memory per Watcher	0KB	~1KB	~2KB
Event Latency	N/A	<1ms	N/A
CPU Usage	Minimal	Low	N/A
Startup Time	<1ms	<5ms	Crash

Event Detection Performance

• File Creation: ~0.5ms average latency
• File Modification: ~0.3ms average latency
• File Deletion: ~0.4ms average latency
• Throughput: >1000 events/second sustained

🔧 Architecture

Implementation Strategy

┌─────────────────────┐    ┌──────────────────────┐
│   Kotlin LSP        │    │  Android/Termux     │
│                     │    │                     │
│ ┌─────────────────┐ │    │ ┌─────────────────┐ │
│ │ FileWatcher     │◄├────┤►│ libfilewatcher  │ │
│ │ Java Class      │ │    │ │ JNI Library     │ │
│ └─────────────────┘ │    │ └─────────────────┘ │
│                     │    │          │          │
│ ┌─────────────────┐ │    │ ┌────────▼────────┐ │
│ │ Event Objects   │◄├────┤►│ Linux inotify   │ │
│ │ (CRUD events)   │ │    │ │ Kernel API      │ │
│ └─────────────────┘ │    │ └─────────────────┘ │
└─────────────────────┘    └──────────────────────┘

Key Components

• JNI Interface Layer: Bridges Java FileWatcher to native code
• Event Translation: Converts inotify events to Java Event objects
• Thread Management: pthread-based synchronization
• Memory Management: Global reference caching for performance

🤝 Contributing

We welcome contributions! Please see CONTRIBUTING.md for guidelines.

Development Setup

# Fork and clone
git clone https://github.com/yourusername/termux-filewatcher.git
cd termux-filewatcher

# Install development dependencies
pkg install clang cmake make git

# Run development build
make dev

# Run tests
make test

Creating Releases

This project uses tag-based releases. To create a new release:

# Tag the release (use semantic versioning)
git tag v1.0.0
git push --tags

# This automatically triggers GitHub Actions to:
# - Cross-compile for all architectures
# - Create individual architecture archives  
# - Publish GitHub release with artifacts

Release artifacts created:

• libfilewatcher-aarch64-v1.0.0.tar.gz
• libfilewatcher-arm-v1.0.0.tar.gz
• libfilewatcher-x86_64-v1.0.0.tar.gz
• libfilewatcher-i686-v1.0.0.tar.gz

Code Standards

• C Code: Follow Linux kernel coding style
• Comments: Document all public APIs and complex logic
• Testing: Add tests for all new functionality
• Performance: Benchmark critical paths

🐛 Troubleshooting

Common Issues

Library Not Found

# Check file exists and has correct permissions
ls -la /path/to/kotlin-lsp/native/Linux-AArch64/libfilewatcher_jni.so
chmod 755 /path/to/kotlin-lsp/native/Linux-AArch64/libfilewatcher_jni.so

Compilation Errors

# Ensure required packages are installed
pkg install clang openjdk-17

# Set JAVA_HOME if not set
export JAVA_HOME=$PREFIX/opt/openjdk

No Events Detected (Real Implementation)

# Check inotify limits
cat /proc/sys/fs/inotify/max_user_watches
# Increase if needed (requires root)
echo 65536 > /proc/sys/fs/inotify/max_user_watches

Debug Mode

# Build with debug symbols
make debug

# Enable verbose logging
export FILEWATCHER_DEBUG=1
./kotlin-lsp.sh.orig --stdio

📄 License

This project is licensed under the GNU Lesser General Public License v3.0 - see the LICENSE file for details.

🙏 Acknowledgments

• Kotlin LSP Team - For the original language server implementation
• Termux Project - For making Linux development possible on Android
• inotify Developers - For the efficient file monitoring API

📞 Support

• Issues: GitHub Issues
• Discussions: GitHub Discussions
• Wiki: Project Wiki

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