This project implements a distributed broadcast system, where nodes reach eventual consistency on validated news.

Note that each node could join or leave the system at any time, make sure nodes can discover each other (with or without a centural registry).

Here lists pseudocode of behaviour offered to clients by a single node:

package server
type Data struct {
 id string 
 raw string
 signature string
}
 
type BroadcastService interface {
 // Returns true if data is valid and accepted
 PostNewData(data Data)
 // Return all data received in the past 24h
 ListAllRecentData() []Data
}

A server discovers other servers and establish connections with them, which compose a broadcast system with high availability. User can interact with server through http to post or get rencent data.

The whole broadcast system keeps working as long as any server survives.

A server is composed with 5 modules:

• HTTP:HTTP module receives request from client, it offers apis for data access. You can also implement your own version with different protocols like grpc or homemade protocol.
• EventBus: EventBus is responsible for data transmission through the whole server. The EventBus interface defines Publish and Subscribe method. A naive implementation with native buffered channel in golng is offered, you are free to implement your own version and integrate it to the server.
• Cluster: Cluster module manages discovered node and handles communication with them. This project offers implementation based on go-libp2p PubSubService.
• Storage: Storage stores data in recent 24 hours. This project use go-cache which offers time-expiration.
• Validator: Validator validates the genuineness of the incoming data.
• Core: Core offers Deliver, Events methods: Deliver handles incoming data from client or other servers, a valid data will be stored it doesn't exist or have former timestamp. After that a broadcast event will be published and you can get notified by subscribing Event method. Additionally, Core scans and broadcast all stored data periodically(20 seconds) make sure that the whole system reaches eventual consistency.

Pick executable listed in build directory for your operating system, for example, build/macos/distributed-broad-systemserver-1.0. To start a broadcast server, run following comand to start a node listening port8080:

./build/macos/distributed-broad-systemserver-1.0 -httpport=8080

then send a http request to post new data, signature is MD5 digest of raw data, for example, echo -n newmessage | md5:

curl --location --request POST 'http://localhost:8081/postNewData' \
--header 'Content-Type: application/json;' \
--data-raw '{
 "id": "id",
 "raw": "newmessage",
 "signature": "fbf9957b19f15006367d7702a10d6463"
}'

You can fetch all recent data with

curl --location --request POST 'http://localhost:8080/listAllRecentData' \
--header 'Content-Type: application/json'

open a new terminal, start another server on 8081:

./build/macos/distributed-broad-systemserver-1.0 -httpport=8081

Wait for 20 seconds and fetch data from new server, you can see that new server reach consistency with other servers on all post data:

curl --location --request POST 'http://localhost:8081/listAllRecentData' \
--header 'Content-Type: application/json'