SignalR

Overview

Great Nuget package for real-time communication, has easy implementation and structure. Quite hard to create a client on Delphi 2009, though.

It has a lot of cool transport protocols with automatic fallback

Key Concepts

• Hubs: The main abstraction for real-time communication
• Connections: Persistent connections between clients and servers
• Groups: Logical grouping of connections
• Transports: Different ways to establish connections (WebSockets, Server-Sent Events, Long Polling)

SignalR Protocols

SignalR supports multiple transport protocols with automatic fallback:

1. WebSockets (Primary)

• Best performance: Full-duplex communication
• Lowest latency: Real-time bidirectional communication
• Automatic reconnection: Built-in connection management
• Browser support: Modern browsers (IE10+, Chrome, Firefox, Safari)

2. Server-Sent Events (SSE)

• Fallback option: When WebSockets unavailable
• Server-to-client only: One-way communication from server
• Automatic reconnection: Built-in retry mechanism
• Browser support: IE10+, Chrome, Firefox, Safari

3. Long Polling

• Final fallback: When other transports fail
• Universal compatibility: Works in all browsers
• Higher latency: Polling-based communication
• Resource intensive: More server resources required

4. Forever Frame (Legacy)

• IE8/IE9 support: Only used for older Internet Explorer
• Deprecated: Not recommended for new applications
• Limited functionality: Basic communication only

Transport Fallback Order

SignalR automatically tries transports in this order:

1. WebSockets (if supported)
2. Server-Sent Events (if WebSockets fail)
3. Long Polling (if SSE fails)
4. Forever Frame (IE8/IE9 only)

Protocol Selection Logic

// SignalR automatically negotiates the best available transport
var connection = new HubConnectionBuilder()
    .WithUrl("https://your-server/signalr")
    .Build();
 
// You can also force a specific transport
var connection = new HubConnectionBuilder()
    .WithUrl("https://your-server/signalr")
    .WithTransport(HttpTransportType.WebSockets) // Force WebSockets only
    .Build();

Transport Detection

SignalR performs transport negotiation:

1. Negotiation request: Client requests available transports
2. Server response: Server provides supported transports
3. Transport selection: Client chooses best available transport
4. Connection establishment: Client connects using selected transport