Device2Device

A feature-rich Android application for peer-to-peer communication and multimedia processing between devices.

Core capabilities:

• 🔵 Bluetooth RFCOMM serial communication with device discovery and data logging
• 🌐 Multi-protocol networking: TCP, UDP (multicast), KCP (reliable UDP)
• 📨 Pub/Sub messaging via scadup message queue library
• 🎨 GPU (OpenGL ES) and CPU image/video rendering
• 🎤 Audio recording (16kHz PCM) with real-time waveform visualization and speech recognition
• 📊 Real-time sensor monitoring (accelerometer, gravity, linear acceleration)
• 🤖 AI chat powered by DeepSeek API (Chat + Deep Think models)
• 📁 Embedded HTTP file server with directory browsing

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Architecture

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Technology Stack

Category	Technologies
Platform	Android (API 21+, target 31)
Language	Java, C++ (C++11)
Native	JNI, CMake 2.8+, OpenGL ES 2.0, OpenSL ES, NDK 23
Network	UDP (Multicast), TCP, KCP (Reliable UDP), HTTP, Bluetooth
Media	AudioRecord, AudioTrack, MediaExtractor, OpenGL ES, YUV↔RGB, PCM↔WAV
UI	Material Design, ConstraintLayout, Custom Views, System Overlay
Build	Gradle 7.x, CMake, NDK (ARM NEON optimizations)

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Project Structure

app/src/main/
├── java/com/tsymiar/device2device/
│   ├── activity/                  # Activities (12)
│   │   ├── MainActivity           # Splash screen → auto-navigate
│   │   ├── SelectActivity         # Main dashboard (network, sensor, chat, files, Bluetooth)
│   │   ├── TextureActivity        # Image/Video GPU & CPU rendering
│   │   ├── WaveActivity           # Audio recording & real-time waveform + speech recognition
│   │   ├── GraphActivity          # Sensor real-time data display
│   │   ├── SensorActivity         # List all device sensors
│   │   ├── CommitActivity         # Bluetooth serial communication (RFCOMM)
│   │   ├── ConnectActivity        # Bluetooth discoverability & device scanning
│   │   ├── DevicesActivity        # Paired & discovered Bluetooth devices list
│   │   ├── BuggerActivity         # Bug report / email feedback
│   │   ├── MyGitActivity          # Open project GitHub page
│   │   └── ThanksActivity         # Acknowledgements page
│   ├── service/                   # Background services (7)
│   │   ├── SubscribeService       # Pub/Sub subscribe floating window
│   │   ├── PublishService         # Pub/Sub publish floating window
│   │   ├── HttpFileService        # Embedded HTTP file server (File & SAF modes)
│   │   ├── ToastNotificationService  # Global floating toast notifications
│   │   ├── ReceiverService        # Bluetooth data receive floating window
│   │   ├── WindowService          # Generic text overlay floating window
│   │   ├── SaveDataService        # Persist Bluetooth received data to file
│   │   └── Voice                  # Audio alert playback service
│   ├── acceleration/              # Sensor & Voice modules
│   │   ├── SensorFragment         # Real-time accelerometer chart (Bézier-smoothed)
│   │   ├── DefaultFragment        # Basic sensor chart variant
│   │   └── Voice                  # Over-acceleration warning (threshold: 7.0 m/s²)
│   ├── dialog/                    # UI dialogs
│   │   ├── ChatBoxDialog          # DeepSeek AI chat (Chat / Reasoner models)
│   │   └── FileMsgDialog          # File transfer with progress & SAF file picker
│   ├── entity/                    # Data entities (PubSubSetting, Receiver)
│   ├── event/                     # Observer-pattern event system (EventHandle, EventNotify)
│   ├── utils/                     # Utilities (Atom, MP4Header, WAVHeader, SoundRecord, WaveCanvas, HttpsRequest, Utils, etc.)
│   ├── view/                      # Custom views (WaveSurface, WaveformsView)
│   └── wrapper/                   # JNI native bridge (Callback, Network, View, Media, Time)
├── cpp/                           # Native C++ code
│   ├── JniMethods.cpp/h           # All JNI entry points
│   ├── bitmap/                    # BMP image processing
│   ├── callback/                  # Java↔C++ bidirectional callbacks
│   ├── convert/                   # PCM↔WAV, YUV↔RGB format conversion
│   ├── display/                   # GPU (EGL/GLES2) & CPU rendering
│   ├── message/                   # Thread-safe message queue
│   ├── socket/                    # UDP / TCP / KCP / FileMsg protocol
│   ├── scadup/                    # Message queue library (tsymiar/scadup)
│   ├── test/                      # Unit tests (FileMsgSocket)
│   ├── time/                      # Timestamp utilities
│   └── utils/                     # File utilities, logging, constants

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Features

Bluetooth Communication

Feature	Description
Device Scanning	Scan for nearby Bluetooth devices
Pairing	List paired devices and discover new ones
Serial Comm	Bidirectional RFCOMM communication with directional control commands
Data Logging	Auto-save received data to local file
Floating Window	Receive data display in draggable system overlay

Network Communication

Feature	Description
UDP Server	Start a UDP multicast server to receive data
UDP Client	Start a UDP multicast client to send data
TCP Server	Start a TCP server to receive data
KCP	KCP (Reliable UDP) protocol for low-latency transmission
Pub/Sub	Subscribe & Publish messages via floating dialog windows; async connection with real-time status feedback
File Transfer	Custom binary protocol with chunked transfer (64KB/chunk) and progress callback
HTTP Server	Embedded HTTP server with HTML directory listing; supports SAF mode (Android 10+)

Message System (C++ ↔ Java)

The app uses a thread-safe message queue (Message.h) to bridge C++ native code with Java UI. Messages are dispatched via the MASSAGER enum:

Type	Direction	Description
MESSAGE	C++ → Java	General toast notifications
TOAST	C++ → Java	Status text update (txt_status)
MSG_HINT	C++ → Java	Hint text update (txt_hint)
SUBSCRIBER	C++ → Java	Subscribe service feedback
PUBLISHER	C++ → Java	Publish service feedback
FILE_PROGRESS	C++ → Java	File transfer progress update
TEXTURE	C++ → Java	Texture rendering callback
UDP_SERVER	C++ → Java	UDP server status
UDP_CLIENT	C++ → Java	UDP client status
KCP_VIEW	C++ → Java	KCP connection status

The SelectActivity UI features a dual-status display: txt_hint (italic, light gray) for supplementary hints and txt_status (bold, dark) for primary status, separated by a divider line.

Multimedia Processing

Feature	Description
GPU Rendering	Image/video rendering via OpenGL ES 2.0 (EGL/GLESv2)
CPU Rendering	Software-based image/video decoding and display
Audio Recording	16kHz PCM recording with real-time waveform visualization
Audio Playback	Play WAV/MP4/OGG/MP3/AAC/AMR files with waveform analysis
Speech to Text	Built-in speech recognition (STT) integration
Sensor Monitor	Real-time accelerometer, gravity, and linear acceleration data display

Intelligent Features

Feature	Description
AI Chat	DeepSeek API integration with Chat / Reasoner (Deep Think) models
Sensor Alert	Automatic warning audio when acceleration exceeds 7.0 m/s² threshold

System Integration

Feature	Description
Event System	Observer-pattern event broadcast for inter-component communication
Time Sync	Native timestamp acquisition and synchronization
Global Toast	Floating toast notification service (3s auto-dismiss)
One-Tap Exit	Global exit manager to terminate all activities and services

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Build Requirements

Component	Version
Android SDK	31 (compileSdk) / 21+ (minSdk)
Android NDK	23.0.7599858
Build Tools	30.0.3
Gradle	7.x
CMake	2.8+
JDK	8 or 11
ABIs	arm64-v8a, armeabi-v7a, x86_64
C++ Standard	C++11 (ARM NEON optimized)

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Permissions

<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
<uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
<uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />
<uses-permission android:name="android.permission.HIGH_SAMPLING_RATE_SENSORS" />

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Building

# Local build
./build.sh

# CI build (Azure Pipelines)
# See azure-pipelines.yml

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CI/CD

This project uses Azure Pipelines for continuous integration on macos-latest. The pipeline:

• Checks out the main repo and tsymiar/scadup submodule
• Copies scadup native library to app/src/main/cpp/scadup/
• Installs Android SDK components (NDK 23, build-tools 30.0.3, platform 31)
• Sets up JDK 11 and builds with Gradle 7.0.2
• Produces debug APK for arm64-v8a, armeabi-v7a, x86_64

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Screenshots

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License

MIT License

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Recent Changes

2026-06

• MSG_HINT Message Type: Added MSG_HINT = 9 to MASSAGER enum for displaying auxiliary hint text in SelectActivity. C++ can now send hints via Message::instance().setMessage(msg, MSG_HINT).
• UI Layout Improvements: sample_text moved to fixed footer (outside ScrollView). txt_hint added above txt_status with visual differentiation: italic 12sp gray hint vs. bold 14sp dark status, separated by a divider line.
• Pub/Sub Async Overhaul (JniMethods.cpp): StartSubscribe now returns immediately (non-blocking), connection results sent asynchronously via Message system. Publish moved to detached thread to prevent UI thread blocking (ANR). Added real-time feedback (Toast) for both Subscribe and Publish operations.
• Publish/Subscribe Topic Isolation (PubSubSetting.java): Separate topic (subscribe) and pubTopic (publish) fields to prevent cross-contamination between services.
• Subscriber Use-After-Free Fix (Subscriber.cpp): Fixed random trailing characters in received messages. Root cause: body buffer was freed immediately after enqueuing callback to thread pool, but the callback's content pointer still referenced freed memory. Fixed by using shared_ptr<vector<char>> to manage buffer lifecycle, ensuring it persists until callback completion.
• Port Parsing Protection (SubscribeService.java): Added try-catch around Integer.parseInt() calls for port input, falling back to default port 9999 on invalid input.