LightImage.Networking

This repository contains basic networking functionality for software components that need to discover each other, exchange information about available services and connect via these services.

Note: This repository is still under development. Breaking changes will be introduced in upcoming versions.

All logic is built on top of the following dependencies. You will need a basic understanding of each of these libraries in order to use the networking packages.

• The awesome NetMQ library for low-level networking and actors.
• Microsoft.Extensions.Logging abstractions for logging
• Microsoft.Extensions.Configuration abstractions for configuration
• Autofac for dependency injection

Introduction

Services

The repository supports the creation of connected software components called nodes that run one or more services. These nodes automatically find each other and exchange information about their services and how to connect those, through a disovery protocol. Each node may join a session; its services then connect with all corresponding services in other nodes in that same session. Services may be symmetrical (e.g. all nodes with this service behave the same) or have different roles. These roles can further determine which nodes connect to each other for that particular service.

Actors

Each service borrows some concepts from the actor model to perform its communication with other nodes and maintain state. The service is the class responsible to the outside world that exposes events for incoming data and commands for sending data to connected peers. Internally it creates a shim (handler) which performs the actual work and communication with the outside world. This handler does not share any data with the service, as it runs on a separate thread. Communication between the two takes place via NetMQ sockets.

Getting started

Below are the steps to get a simple cluster of nodes to work. Have a look at the LightImage.Networking.Samples.Chat project for details.

Implementing a service

• Define a subclass of ClusterShimPeer. In this class you may store additional state related to a specific peer.
• Define a subclass of ClusterShim. It should do the following:
  • Return an instance of your new peer class from method CreatePeer.
  • Handle incoming network messages from peer nodes in HandleRouterMessage.
  • Handle incoming commands from the service in HandleShimMessage.
  • When necessary, provide feedback to the service by sending messages to the Shim socket property.
• Define a subclass of ClusterService. It should do the following:
  • Return an instance of your shim class from method CreateShim.
  • Process incoming messages from the shim in HandleActorEvent. Expose relevant triggers to consuming classes using C# events.
  • Expose methods to control the service to its consumers. These typically send messages to the shim via the Actor socket property.

Running the service

Note: The steps below relate to WPF desktop applications. For console applications, some more steps are involved to set up a proper SynchronizationContext.

• Setup an IConfiguration instance; you may create an empty one using new ConfigurationBuilder().Build().
• Setup an AutoFac IContainer by registering the following components in a ContainerBuilder:
  • Module NetworkingServicesModule
  • Module DiscoveryModule
  • Your service as an IService
  • Logging, for example using builder.AddTestLogging()
• Retrieve an IDiscoveryNode instance; you may call node.Join(1) to join a particular session on startup.
• Retrieve your service instance and use it.

Packages

The libraries are distributed as NuGet packages.

Package	NuGet
LightImage.Networking.Services
LightImage.Networking.Discovery
LightImage.Networking.FileSharing

Todo

• Simplify and document Getting started for console applications.
• Document configuration options
• Replace Autofac dependency by microsoft.Extensions.DependencyInjection.