golib/socket/server/udp

UDP Server

Lightweight, high-performance UDP server implementation with atomic state management, graceful shutdown, lifecycle callbacks, and comprehensive monitoring capabilities.

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Table of Contents

• Overview
  • Design Philosophy
  • Key Features
• Architecture
  • Component Diagram
  • Data Flow
  • State Management
• Performance
  • Throughput
  • Memory Usage
  • Scalability
• Use Cases
• Quick Start
  • Installation
  • Basic Echo Server
  • Server with Callbacks
  • Production Server
• Best Practices
• API Reference
  • ServerUdp Interface
  • Configuration
  • Error Codes
• Contributing
• Limitations
• Resources
• AI Transparency
• License

---

Overview

The udp package provides a production-ready UDP server optimized for connectionless datagram processing. It implements an atomic state management model suitable for stateless request/response patterns and event streaming use cases.

Design Philosophy

1. Connectionless First: Optimized for stateless UDP datagram processing
2. Lock-Free Operations: Atomic operations for zero-contention state management
3. Simplicity: Minimal API surface with clear semantics
4. Observable: Real-time monitoring via callbacks and state methods
5. Context-Aware: Full integration with Go's context for lifecycle control

Key Features

• ✅ UDP Server: Pure UDP datagram processing (connectionless)
• ✅ Atomic State: Lock-free state management with atomic operations
• ✅ Graceful Shutdown: Context-based shutdown with configurable timeouts
• ✅ Lifecycle Callbacks: Hook into server events (error, info, connection updates)
• ✅ Thread-Safe: All operations safe for concurrent use
• ✅ Context Integration: Full context support for cancellation and deadlines
• ✅ Zero Connection Tracking: Stateless design (OpenConnections always returns 0)
• ✅ TLS N/A: UDP is connectionless; no TLS at transport layer
• ✅ Zero Dependencies: Only standard library + golib packages

---

Architecture

Component Diagram

┌────────────────────────────────────────────────────────┐
│                   UDP Server                           │
├────────────────────────────────────────────────────────┤
│                                                        │
│  ┌────────────────┐       ┌───────────────────┐        │
│  │    Listener    │       │  Context Manager  │        │
│  │  (net.UDPConn) │       │  (cancellation)   │        │
│  └────────┬───────┘       └─────────┬─────────┘        │
│           │                         │                  │
│           ▼                         ▼                  │
│  ┌──────────────────────────────────────────┐          │
│  │       Datagram Read Loop                 │          │
│  │     (single goroutine per server)        │          │
│  └──────────────┬───────────────────────────┘          │
│                 │                                      │
│                 ▼                                      │
│         Per-Datagram Handler                           │
│         ┌──────────────────────┐                       │
│         │  sCtx (I/O wrapper)  │                       │
│         │   - Read (from buf)  │                       │
│         │   - Write (no-op)    │                       │
│         │   - Remote/Local     │                       │
│         └──────────┬───────────┘                       │
│                    │                                   │
│                    ▼                                   │
│         ┌──────────────────────┐                       │
│         │   User Handler       │                       │
│         │  (processes dgram)   │                       │
│         └──────────────────────┘                       │
│                                                        │
│  ┌──────────────────────────────────────────┐          │
│  │         Atomic State (libatm.Value)      │          │
│  │   - run: server running                  │          │
│  │   - gon: server terminated               │          │
│  │   - ad:  server address                  │          │
│  │   - fe:  error callback                  │          │
│  │   - fi:  info callback                   │          │
│  │   - fs:  server info callback            │          │
│  └──────────────────────────────────────────┘          │
│                                                        │
└────────────────────────────────────────────────────────┘

Data Flow

Client                     UDP Server                Handler
  │                             │                       │
  │───── Datagram ─────────────▶│                       │
  │                             │                       │
  │                             │──── sCtx ────────────▶│
  │                             │                       │
  │                             │                  Process
  │                             │                       │
  │                             │◀───── Close ──────────│
  │                             │                       │
  │◀──── Response ──────────────│                       │
  │    (via client socket)      │                       │

Key Points:

• Stateless: Each datagram is independent
• No Connection Tracking: UDP is connectionless by nature
• Handler Per Datagram: Each datagram spawns a goroutine
• Context Per Datagram: sCtx wraps datagram buffer and remote address

State Management

The server uses atomic operations for lock-free state management:

type srv struct {
    run atomic.Bool          // Server running state
    gon atomic.Bool          // Server gone (terminated)
    ad  libatm.Value[string] // Listen address
    fe  libatm.Value[FuncError]     // Error callback
    fi  libatm.Value[FuncInfo]      // Info callback
    fs  libatm.Value[FuncInfoSrv]   // Server info callback
}

State Transitions:

1. New() → gon=true, run=false (created but not started)
2. Listen() → gon=false, run=true (active)
3. Shutdown()/Close() → gon=true, run=false (terminated)

---

Performance

Throughput

Metric	Value	Conditions
Datagram Processing	~50,000 dgrams/sec	Single server, 1KB datagrams
Handler Spawn	<100 µs/datagram	Goroutine creation overhead
State Query	<10 ns	Atomic read operations
Shutdown Latency	<50 ms	Graceful shutdown time

Memory Usage

Component	Memory	Notes
Base Server	~500 bytes	Struct + atomics
Per Datagram	~4 KB	sCtx + buffer (configurable)
UDP Buffer	65,507 bytes	Max UDP datagram size
Goroutine Stack	2-8 KB	Per handler goroutine

Total per active datagram: ~12 KB

Scalability

• Datagrams: Unlimited (stateless)
• Concurrent Handlers: Limited by OS (typically 10,000+)
• Listeners: 1 per server instance
• CPU Cores: Scales linearly with available cores

Recommended:

• Use UDP for stateless, high-throughput scenarios
• Keep handler processing time minimal (<1ms)
• Consider datagram size vs. MTU (~1,500 bytes for Ethernet)

---

Use Cases

1. Syslog Server

Receive log messages over UDP from distributed systems.

handler := func(ctx libsck.Context) {
    defer ctx.Close()
    buf := make([]byte, 4096)
    n, _ := ctx.Read(buf)
    processSyslogMessage(buf[:n])
}

2. Metrics Collector (StatsD)

High-throughput metric ingestion with stateless processing.

handler := func(ctx libsck.Context) {
    defer ctx.Close()
    buf := make([]byte, 1024)
    n, _ := ctx.Read(buf)
    parseAndStoreMetric(buf[:n])
}

3. DNS Server

Stateless query/response over UDP.

handler := func(ctx libsck.Context) {
    defer ctx.Close()
    buf := make([]byte, 512)
    n, _ := ctx.Read(buf)
    response := resolveDNSQuery(buf[:n])
    // Send response via separate client socket
}

4. Game Server (Real-time)

Low-latency state updates for multiplayer games.

handler := func(ctx libsck.Context) {
    defer ctx.Close()
    buf := make([]byte, 2048)
    n, _ := ctx.Read(buf)
    processGameState(buf[:n], ctx.RemoteHost())
}

5. IoT Data Ingestion

High-volume sensor data from embedded devices.

handler := func(ctx libsck.Context) {
    defer ctx.Close()
    buf := make([]byte, 256)
    n, _ := ctx.Read(buf)
    storeSensorData(buf[:n])
}

---

Quick Start

Installation

go get github.com/nabbar/golib/socket/server/udp

Basic Echo Server

package main

import (
    "context"
    "fmt"
    "log"
    
    libsck "github.com/nabbar/golib/socket"
    sckcfg "github.com/nabbar/golib/socket/config"
    "github.com/nabbar/golib/socket/server/udp"
)

func main() {
    // Create server configuration
    cfg := sckcfg.Server{
        Network: "udp",
        Address: ":8080",
    }
    
    // Define handler
    handler := func(ctx libsck.Context) {
        defer ctx.Close()
        
        buf := make([]byte, 1024)
        n, err := ctx.Read(buf)
        if err != nil {
            log.Printf("Read error: %v", err)
            return
        }
        
        fmt.Printf("Received: %s from %s\n", buf[:n], ctx.RemoteHost())
    }
    
    // Create server
    srv, err := udp.New(nil, handler, cfg)
    if err != nil {
        log.Fatal(err)
    }
    
    // Listen
    ctx := context.Background()
    if err := srv.Listen(ctx); err != nil {
        log.Fatal(err)
    }
}

Server with Callbacks

// Error callback
srv.RegisterFuncError(func(err error) {
    log.Printf("[ERROR] %v", err)
})

// Info callback (connection events)
srv.RegisterFuncInfo(func(local, remote string, state libsck.ConnState) {
    log.Printf("[INFO] %s -> %s: %s", remote, local, state)
})

// Server info callback (lifecycle events)
srv.RegisterFuncInfoSrv(func(local string, state libsck.ConnState) {
    log.Printf("[SERVER] %s: %s", local, state)
})

Production Server

// Production setup with graceful shutdown
ctx, cancel := context.WithCancel(context.Background())
defer cancel()

// Register callbacks
srv.RegisterFuncError(logError)
srv.RegisterFuncInfo(logConnection)

// Start server in goroutine
go func() {
    if err := srv.Listen(ctx); err != nil {
        log.Printf("Listen error: %v", err)
    }
}()

// Wait for running state
time.Sleep(100 * time.Millisecond)
if !srv.IsRunning() {
    log.Fatal("Server failed to start")
}

// Graceful shutdown on signal
sigChan := make(chan os.Signal, 1)
signal.Notify(sigChan, os.Interrupt, syscall.SIGTERM)
<-sigChan

shutdownCtx, shutdownCancel := context.WithTimeout(context.Background(), 5*time.Second)
defer shutdownCancel()

if err := srv.Shutdown(shutdownCtx); err != nil {
    log.Printf("Shutdown error: %v", err)
}

---

Best Practices

Handler Design

1. Keep Handlers Fast: Process datagrams in <1ms when possible
2. Always Close Context: Use defer ctx.Close() at handler start
3. Handle Read Errors: UDP reads can fail, check errors
4. Avoid Blocking: Don't block in handlers (spawn goroutines if needed)

// ✅ Good: Fast, non-blocking
handler := func(ctx libsck.Context) {
    defer ctx.Close()
    buf := make([]byte, 1024)
    n, err := ctx.Read(buf)
    if err != nil {
        return
    }
    processQuickly(buf[:n])
}

// ❌ Bad: Slow, blocking
handler := func(ctx libsck.Context) {
    defer ctx.Close()
    buf := make([]byte, 1024)
    n, _ := ctx.Read(buf)
    time.Sleep(1 * time.Second) // Blocks goroutine
    database.Query(buf[:n])     // Slow I/O
}

Buffer Sizing

1. MTU Awareness: Keep buffers ≤1,500 bytes for Ethernet
2. Max UDP Size: Maximum UDP datagram is 65,507 bytes
3. Typical Sizes: 512-2,048 bytes for most use cases

// For DNS queries
buf := make([]byte, 512)

// For general use
buf := make([]byte, 1500)

// For jumbo frames
buf := make([]byte, 9000)

Error Handling

1. Register Error Callback: Always log errors
2. Handle Context Errors: Check for cancellation
3. Graceful Degradation: Don't crash on malformed datagrams

srv.RegisterFuncError(func(err error) {
    log.Printf("[UDP ERROR] %v", err)
})

handler := func(ctx libsck.Context) {
    defer ctx.Close()
    
    select {
    case <-ctx.Done():
        return // Context cancelled
    default:
    }
    
    buf := make([]byte, 1024)
    n, err := ctx.Read(buf)
    if err != nil {
        return // Log via error callback
    }
    
    // Process...
}

Lifecycle Management

1. Context for Shutdown: Use context cancellation
2. Check IsRunning: Verify server state
3. Graceful Shutdown: Use Shutdown() with timeout

// Start
go srv.Listen(ctx)
time.Sleep(100 * time.Millisecond)
if !srv.IsRunning() {
    log.Fatal("Failed to start")
}

// Shutdown
shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
defer cancel()
if err := srv.Shutdown(shutdownCtx); err != nil {
    log.Printf("Shutdown timeout: %v", err)
}

Testing

See TESTING.md for comprehensive testing guidelines.

---

API Reference

ServerUdp Interface

type ServerUdp interface {
    libsck.Server // Extends base Server interface
}

Extends github.com/nabbar/golib/socket.Server:

type Server interface {
    // Lifecycle
    Listen(ctx context.Context) error
    Shutdown(ctx context.Context) error
    Close() error
    
    // State
    IsRunning() bool
    IsGone() bool
    OpenConnections() int64 // Always returns 0 for UDP
    
    // Configuration
    RegisterServer(address string) error
    SetTLS(enable bool, tlsConfig libtls.TLSConfig) // No-op for UDP
    
    // Callbacks
    RegisterFuncError(fct FuncError)
    RegisterFuncInfo(fct FuncInfo)
    RegisterFuncInfoSrv(fct FuncInfoSrv)
}

Configuration

Server Config

type Server struct {
    Network string           // Must be "udp", "udp4", or "udp6"
    Address string           // Listen address (e.g., ":8080", "0.0.0.0:9000")
    
    // UDP-specific (unused but part of base config)
    PermFile       os.FileMode  // N/A for UDP
    GroupPerm      int32        // N/A for UDP
    ConIdleTimeout time.Duration // N/A for UDP (connectionless)
    TLS            struct{...}  // N/A for UDP (no TLS at transport layer)
}

Constructor

func New(
    updateConn libsck.UpdateConn, // Optional: Called when listener is created (can be nil)
    handler libsck.HandlerFunc,   // Required: Datagram handler
    cfg sckcfg.Server,            // Required: Server configuration
) (ServerUdp, error)

Error Codes

var (
    ErrInvalidAddress   = errors.New("invalid address")
    ErrInvalidHandler   = errors.New("invalid handler")
    ErrShutdownTimeout  = errors.New("shutdown timeout")
    ErrInvalidInstance  = errors.New("invalid instance")
)

---

Contributing

Contributions are welcome! Please follow these guidelines:

1. Fork & Branch: Create a feature branch from main
2. Test Coverage: Maintain >70% coverage
3. Race Detector: All tests must pass with -race
4. Documentation: Update docs for API changes
5. BDD Style: Use Ginkgo/Gomega for tests

See CONTRIBUTING.md for details.

---

Limitations

By Design

1. No Connection Tracking: OpenConnections() always returns 0 (UDP is stateless)
2. No TLS Support: TLS requires connection-oriented protocol (use DTLS separately)
3. No Idle Timeout: UDP has no persistent connections to timeout
4. Write is No-Op: Context.Write() returns io.ErrClosedPipe (response via client socket)

UDP Protocol Limits

1. Datagram Size: Maximum 65,507 bytes (65,535 - 8-byte header - 20-byte IP header)
2. No Ordering: Datagrams may arrive out of order
3. No Reliability: Datagrams may be lost or duplicated
4. No Flow Control: No backpressure mechanism

Implementation Constraints

1. Single Listener: One net.UDPConn per server
2. Goroutine Per Datagram: Can exhaust goroutines under extreme load
3. No Connection Pooling: Each datagram is independent
4. Context Deadline: Inherited from Listen() context, not per-datagram

---

Resources

• Go net package: https://pkg.go.dev/net
• UDP RFC 768: https://tools.ietf.org/html/rfc768
• Ginkgo BDD: https://onsi.github.io/ginkgo/
• Gomega Matchers: https://onsi.github.io/gomega/
• Testing Guide: TESTING.md

---

AI Transparency

In compliance with EU AI Act Article 50.4: AI assistance was used for documentation generation, test creation, and code review under human supervision. All core functionality is human-designed and validated.

---

License

License: MIT License - See LICENSE file for details
Maintained By: Nicolas JUHEL
Package: github.com/nabbar/golib/socket/server/udp