SignalR (Push Services with Hubs)–Part 1

ASP.NET SignalR is a library for ASP.NET developers that simplifies the process of adding real-time web functionality to applications. Real-time web functionality is the ability to have server code push content to connected clients instantly as it becomes available, rather than having the server wait for a client to request new data.

• Push services is something like whenever data changes in any of the devices (web, mobile, ssms) the data displayed on other devices will be updated instantly.
  Push Pattern:
  
  • Push services are not an official pattern.
  • Technical approaches for push
    • Periodical polling
    • Long polling
    • Forever Frame
    • Service Sent Events (SSE)
    • Web Sockets
  SignalR:
  
  • A server side framework to write push services
  • A set of client libraries to make push services communication easy to use on any platform
  • Optimized for asynchronous processing
  • Two Programming Models
    • Persistent connections
    • Hubs
  • NOTE: SignalR packages are available through NuGet packages
  SignalR Hubs:
  
  • Hubs are classes to implement push services in SignalR
    • Abstraction on top of persistent connection
    • Convention-over-configuration
  • Hubs provide a high level RPD framework
    • Perfect for different type of messages to send between server and client
  • Hub Conventions
    • Public methods are callable from the outside
    • Send messages to the clients by invoking client-side methods
  • Simple steps to get going
    • Write hub class
    • Add route in host process
    • Done
  • Hub Class:
    • [HubName] attribute is used to reflect the Name of Hub in API
    • Can return Simple Type or Complex Type Or Task
    • Complex objects and arrays are automatically serialized/deserialized to/from JSON
    • Context holds connection and request specific information like ConnectionId, Request, headers, Query string, User and Request Cookies
  • Hubs Protocol
    • Base endpoint is /signalr
    • Optional: get JS meta data from /signalr/hubs
    • Basically two protocol steps(details vary by transport)
      • /negotiate – which transport do you support?
      • (Optional: /ping server)
      • /connect – Okay. Here is my persistent connection.
    • 'BEST' transport negotiation( Try to open a connection with below options, if one fails it will try for next tech)
      • Web Sockets -> SSE -> Forever Frame -> Long Polling
    • Pre-defined pay load
    • Any data is JSON encoded
  • Pushing Data: Clients
    • Clients property as dispatching point to send messages to clients
    • Holds dynamic properties and methods
    • Target methods with parameters are dynamically injected into code path, serialized, and embedded into protocol response.
  • Pushing Data: Groups
    • Typical base pattern in push scenarios
    • Can add connections to group and send messages to particular groups
    • Groups are not persisted on the server
      • We need to keep track of what connections are in what group
      • No automatic group count
  • Hub Lifecycle
    • Hub Connections have a     life cycle
      • Override Async pipeline event handles( OnConnected(), OnDisconnected(), OnReconnected())
      • Sending data from outside a hub
        • Retrieve hub context via dependency resolver
  • Sample:
    • Create Service:
      • Need to add Hub Class.
      • Need to add RouteTables.Routes.MapHubs();
      • Create method with simple type or complex type or Task.
      • The Response in browser will show java script code which builds the proxy class what we mentioned in Hub Class.
      • The request will contain the message, hub name, client method name in JSON format. (Request details can be only viewable in ling-polling transport approach.