This example demonstrates how to use NNG (Nanomsg Next Generation) with Unix Domain Sockets for inter-process communication using the PUB/SUB pattern.

The PUB/SUB pattern is ideal for:

• Event broadcasting: System events, status updates, notifications
• Log streaming: Centralized logging distribution
• Module communication: Inter-module event passing within the same machine
• Real-time monitoring: Status updates to multiple monitoring clients

• Unix Domain Socket (IPC): File-based communication (ipc:///tmp/nng_pubsub)
• Signal handling: Graceful shutdown with Ctrl+C
• Memory management: Proper cleanup of allocated buffers
• Error handling: Comprehensive error checking and reporting

nng-example/
├── pub_server.c    # Publisher (server)
├── sub_client.c    # Subscriber (client)
├── CMakeLists.txt  # CMake build configuration
├── Makefile        # Alternative Makefile build
└── README.md       # This file

Ubuntu/Debian:

sudo apt-get update
sudo apt-get install -y libnng-dev

macOS (with Homebrew):

brew install nng

Manual Installation:

git clone https://github.com/nanomsg/nng.git
cd nng
mkdir build && cd build
cmake ..
make -j$(nproc)
sudo make install

# Create build directory
mkdir build && cd build

# Configure and build
cmake ..
make

# Or build individually
make pub_server
make sub_client

# Build both publisher and subscriber
make all

# Or build individually
make pub_server
make sub_client

./pub_server

The publisher will:

• Create a Unix Domain Socket at /tmp/nng_pubsub
• Start publishing messages every second
• Display published messages with timestamps

In separate terminal windows:

./sub_client

You can run multiple subscribers simultaneously - they will all receive the same messages.

Press Ctrl+C in any terminal to gracefully shut down the application.

Publisher:

Publisher started on ipc:///tmp/nng_pubsub
Press Ctrl+C to stop...

PUB: tick 0 - timestamp: 1703123456
PUB: tick 1 - timestamp: 1703123457
PUB: tick 2 - timestamp: 1703123458

Subscriber:

Subscriber connected to ipc:///tmp/nng_pubsub
Waiting for messages... (Press Ctrl+C to stop)

SUB: tick 0 - timestamp: 1703123456
SUB: tick 1 - timestamp: 1703123457
SUB: tick 2 - timestamp: 1703123458

# From build directory
make help              # Show all available targets
make run-pub           # Run publisher
make run-sub           # Run subscriber
make clean-socket      # Remove socket file
make clean             # Remove build artifacts

make help              # Show all available commands
make clean             # Remove build artifacts and socket file
make install-deps      # Install NNG library (Ubuntu/Debian)
make install-deps-macos # Install NNG library (macOS)
make run-pub           # Run publisher in background
make run-sub           # Run subscriber
make stop              # Stop all running processes

1. File-based (ipc:///tmp/nng_pubsub):

   • Creates a socket file at the specified path
   • Requires proper file permissions
   • Visible in filesystem

2. Abstract namespace (ipc://@nng_pubsub):

   • Linux-specific feature
   • No filesystem representation
   • Automatically cleaned up on process exit

• Fire-and-forget: No delivery guarantees
• Fan-out: One publisher can serve multiple subscribers
• Topic filtering: Subscribers can filter by message prefixes
• Late joiners: New subscribers only receive messages published after they connect

The example includes comprehensive error handling for:

• Socket creation failures
• Connection errors
• Send/receive failures
• Signal handling for graceful shutdown

// Publisher sends system status
snprintf(msg, sizeof(msg), "CPU: %.1f%% MEM: %.1f%%", cpu_usage, mem_usage);
nng_send(pub, msg, strlen(msg) + 1, 0);

// Publisher sends log events
snprintf(msg, sizeof(msg), "LOG: [%s] %s", level, message);
nng_send(pub, msg, strlen(msg) + 1, 0);

// Publisher sends module events
snprintf(msg, sizeof(msg), "MODULE: %s STATUS: %s", module_name, status);
nng_send(pub, msg, strlen(msg) + 1, 0);

# Check socket file permissions
ls -la /tmp/nng_pubsub

# Remove old socket file if needed
rm -f /tmp/nng_pubsub

• Ensure publisher is running before starting subscribers
• Check if socket file exists and has proper permissions
• Verify no other process is using the same socket path

• Ensure NNG library is properly installed
• Check that development headers are available
• Verify compiler supports C99 standard

// Subscribe to specific topics
nng_setopt(sub, NNG_OPT_SUB_SUBSCRIBE, "ERROR", 5);  // Only error messages
nng_setopt(sub, NNG_OPT_SUB_SUBSCRIBE, "WARN", 4);   // Only warning messages

You can extend this example to support multiple publishers by using different socket paths or implementing a more sophisticated routing mechanism.

This example is provided as-is for educational purposes. NNG is licensed under the MIT License.