Getting Started

Update resources/project-config.edn

Update the :connection and :db-name keys with your Datomic Cloud configuration

{:db-name    "ws-demo"
 :connection {:server-type :ion
              :region      "eu-west-1"
              :system      "knox"
              :endpoint    "http://entry.knox.eu-west-1.datomic.net:8182/"
              :proxy-port  8182}}

Database setup

Create a new Datomic database (if necessary)

(in-ns 'wsdemo.client)
(d/create-database (get-conn) {:db-name "ws-demo"})

And transact the demo schema:

(d/transact (get-conn) {:tx-data (-> "schema.edn" io/resource slurp read-string)})

Deploy lambda functions

The project uses Datomic Ions to deploy 3 Clojure Lambda functions which handle websocket connections via an AWS API Gateway:

wsdemo.handlers/gateway-authorizer (Re)authorizes connections to the gateway

wsdemo.handlers/handle-connection-proxy Links one or more gateway connection IDs with database users

wsdemo.io/handle-message-proxy Handles all communications after a successful connection

Deploy them to your AWS infrastructure

$ clj -Adeploy-to-aws <system-name>

API Gateway

In the AWS Console, create a new WebSocket API

• Route Selection Expression = $request.body.event (default)
• $connect
  • Route Request
    • Authorizer = gateway-authorizer Ion
  • Integration Response
    • Integration type: Lambda Function
    • Use Lambda Proxy Integration
    • Lambda function = ws-handle-connection-proxy
• $disconnect
  • Integration Response
    • Integration type: Lambda Function
    • Use Lambda Proxy Integration
    • Lambda function = ws-handle-connection-proxy
• $default
  • Integration Response
    • Integration type: Lambda Function
    • Use Lambda Proxy Integration
    • Lambda function = ws-handle-message-proxy

Deploy the API, and then update resources/project-config.edn

{:api-gw {:hostname "n3giprj0y8.execute-api.eu-west-1.amazonaws.com"
          :stage    "dev"
          :path     "/dev/@connections/"}}

Testing

REPL

The wsdemo.test-connections namespace will estabish two connections when loaded. The broadcast-from-conn-1 function will send a message from conn-1 to all connections, in this case conn-1 and conn-2:

(in-ns 'wsdemo.test-connections)
(broadcast-from-conn-1)
Message received: {:message Hello everyone, :sender eb50a8b9-f285-4ca7-ac99-0c876a5daa5d}
Message received: {:message Hello everyone, :sender eb50a8b9-f285-4ca7-ac99-0c876a5daa5d}

wscat

Install wscat

$ yarn global add wscat  

Get a valid JWT sign with the secret from project-config.edn

(in-ns 'wsdemo.test-connections)
(jwt/sign {:sub (UUID/randomUUID)} secret)
=>
"eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIwZmEyNTVkZS1jOGJkLTQ0M2EtODY0Yy1jODkyZGFmY2ZjNTgifQ.ZMcAEwd3JHP7HqBnprvz_38uPtNmp_cNl14mGCI1E_U"

Connect and broadcast a message

$ wscat -c wss://n3giprj0y8.execute-api.eu-west-1.amazonaws.com/dev -H Authorization:<JWT>
> {:action :broadcast :message "Hello everyone"}
< {:message "Hello everyone", :sender "0fa255de-c8bd-443a-864c-c892dafcfc58"}