onvif-go/ARCHITECTURE.md

go-onvif Architecture & Design

Overview

go-onvif is a modern, performant Go library for communicating with ONVIF-compliant IP cameras and devices. It provides a clean, type-safe API with comprehensive support for device management, media streaming, PTZ control, and imaging settings.

Architecture

Core Components

┌─────────────────────────────────────────────────────────────┐
│                         Client Layer                         │
│  - onvif.Client: Main entry point                           │
│  - Context-aware operations                                  │
│  - Connection pooling                                        │
│  - Credential management                                     │
└─────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────┐
│                       Service Layer                          │
│  - Device Service  (device.go)                              │
│  - Media Service   (media.go)                               │
│  - PTZ Service     (ptz.go)                                 │
│  - Imaging Service (imaging.go)                             │
└─────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────┐
│                      Transport Layer                         │
│  - SOAP Client (soap/soap.go)                               │
│  - WS-Security Authentication                                │
│  - XML Marshaling/Unmarshaling                              │
└─────────────────────────────────────────────────────────────┘
                              ↓
┌─────────────────────────────────────────────────────────────┐
│                      Network Layer                           │
│  - HTTP Client with connection pooling                       │
│  - TLS support                                               │
│  - Timeout management                                        │
└─────────────────────────────────────────────────────────────┘

Discovery Component

┌─────────────────────────────────────────────────────────────┐
│                    WS-Discovery Service                      │
│  - Multicast UDP probe                                       │
│  - Device enumeration                                        │
│  - Service endpoint discovery                                │
└─────────────────────────────────────────────────────────────┘

Key Design Decisions

1. Context-First Design

All network operations accept context.Context as the first parameter, enabling:

• Request cancellation
• Timeout control
• Request tracing
• Graceful shutdown

ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()

info, err := client.GetDeviceInformation(ctx)

2. Functional Options Pattern

Client configuration uses functional options for flexibility:

client, err := onvif.NewClient(
    endpoint,
    onvif.WithCredentials(username, password),
    onvif.WithTimeout(30*time.Second),
    onvif.WithHTTPClient(customClient),
)

3. Type Safety

Strong typing throughout the API with comprehensive struct definitions:

• Clear data structures for all ONVIF types
• Type-safe service methods
• Compile-time error detection

4. Error Handling

Multiple error handling strategies:

• Sentinel errors for common cases (ErrServiceNotSupported, ErrAuthenticationFailed)
• Typed ONVIFError for SOAP faults
• Wrapped errors with context

if err := client.ContinuousMove(ctx, profileToken, velocity, nil); err != nil {
    if errors.Is(err, onvif.ErrServiceNotSupported) {
        // Handle missing PTZ support
    } else if onvif.IsONVIFError(err) {
        // Handle SOAP fault
    }
}

5. Concurrency Safety

Thread-safe operations with proper locking:

• Mutex-protected credential management
• Safe concurrent API calls
• Connection pool management

6. Performance Optimization

Multiple performance optimizations:

• HTTP connection pooling
• Reusable HTTP client
• Efficient XML marshaling
• Minimal allocations in hot paths

Service Implementations

Device Service

Provides device management functionality:

• Device information retrieval
• Capability discovery
• System operations (reboot, date/time)
• Service endpoint enumeration

Media Service

Handles media profiles and streaming:

• Profile management
• Stream URI generation (RTSP/HTTP)
• Snapshot URI retrieval
• Encoder configuration

PTZ Service

Controls pan-tilt-zoom operations:

• Continuous movement
• Absolute positioning
• Relative positioning
• Preset management
• Status monitoring

Imaging Service

Manages image settings:

• Brightness, contrast, saturation
• Exposure control
• Focus management
• White balance
• Wide dynamic range (WDR)

Security

WS-Security Implementation

Authentication uses WS-Security UsernameToken with password digest:

1. Generate random nonce (16 bytes)
2. Get current UTC timestamp
3. Calculate digest: Base64(SHA1(nonce + created + password))
4. Include in SOAP header

<Security>
  <UsernameToken>
    <Username>admin</Username>
    <Password Type="...#PasswordDigest">digest</Password>
    <Nonce EncodingType="...#Base64Binary">nonce</Nonce>
    <Created>2024-01-01T12:00:00Z</Created>
  </UsernameToken>
</Security>

Transport Security

• Supports HTTP and HTTPS
• Configurable TLS settings via custom HTTP client
• Certificate validation control

Discovery Protocol

WS-Discovery implementation:

1. Send multicast probe to 239.255.255.250:3702
2. Listen for probe matches
3. Parse device information from responses
4. Extract service endpoints (XAddrs)
5. Deduplicate devices by endpoint reference

SOAP Message Flow

Client Request
     ↓
Build SOAP Envelope
     ↓
Add WS-Security Header (if authenticated)
     ↓
Marshal to XML
     ↓
HTTP POST
     ↓
Receive Response
     ↓
Parse SOAP Envelope
     ↓
Check for Fault
     ↓
Unmarshal Response Data
     ↓
Return to Caller

Testing Strategy

Unit Tests

• Client initialization and configuration
• Error handling
• Type validation
• Option application

Integration Tests (with mock servers)

• SOAP message formatting
• Response parsing
• Error handling

Real Device Tests

• Full service workflows
• PTZ operations
• Media streaming
• Discovery

Performance Characteristics

Benchmarks (typical)

• Client creation: ~100 µs
• SOAP call: ~10-50 ms (network dependent)
• Discovery: ~1-5 seconds
• Memory usage: ~1-5 MB per client

Scalability

• Supports hundreds of concurrent clients
• Connection pooling reduces overhead
• Minimal memory footprint per device

Future Enhancements

Planned Features

• Event service (event subscription, pull-point)
• Analytics service (rule engine, motion detection)
• Recording service (recording management)
• Replay service (playback control)
• Advanced security (X.509 certificates)

Optimizations

• Response caching for static data
• Batch operations support
• Streaming data handling
• WebSocket support for events

Best Practices

Client Lifecycle

// Create client once
client, err := onvif.NewClient(endpoint, options...)
if err != nil {
    return err
}

// Initialize to discover services
if err := client.Initialize(ctx); err != nil {
    return err
}

// Reuse client for multiple operations
// ...

// No explicit cleanup needed (HTTP client manages connections)

Error Handling

info, err := client.GetDeviceInformation(ctx)
if err != nil {
    // Check for specific errors
    if errors.Is(err, context.DeadlineExceeded) {
        // Handle timeout
    }
    return fmt.Errorf("failed to get device info: %w", err)
}

Resource Management

// Use contexts with timeouts
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()

// Operations automatically respect context cancellation
result, err := client.Operation(ctx, ...)

Dependencies

Minimal external dependencies:

• golang.org/x/net: HTTP/2 support and IDNA
• golang.org/x/text: Character encoding
• Go standard library: Everything else

Compliance

• ONVIF Core Specification: ✓
• ONVIF Profile S (Streaming): ✓
• ONVIF Profile T (Advanced Streaming): Partial
• ONVIF Profile G (Recording): Planned
• WS-Security: ✓ (UsernameToken)
• WS-Discovery: ✓

Conclusion

go-onvif provides a modern, performant, and easy-to-use Go library for ONVIF camera integration. Its architecture prioritizes:

• Developer experience (simple, intuitive API)
• Type safety (compile-time error detection)
• Performance (connection pooling, efficient operations)
• Reliability (comprehensive error handling)
• Standards compliance (ONVIF specifications)