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Using a WebSocket Endpoint

WebSocket is a protocol that provides full-duplex communication channels over a single TCP connection. This can be used by any client or server application. The Micro Integrator provides WebSocket support via the WebSocket Transport and the WebSocket Inbound Protocol.

Example 1: Sending a Message from a WebSocket Client to a WebSocket Endpoint

If you need to send a message from a WebSocket client to a WebSocket endpoint via WSO2 MI, you need to establish a persistent WebSocket connection from the WebSocket client to WSO2 MI as well as from WSO2 MI to the WebSocket back-end.

To demonstrate this scenario, you need to create two dispatching sequences. One for the client to back-end mediation, and another for the back-end to client mediation. Finally you need to configure the WebSocket inbound endpoint of WSO2 MI to use the created sequences and listen on port 9092.

For sample synapse configs, see Websocket Inbound.

If you analyze the log, you will see that a connection from the WebSocket client to WSO2 MI is established, and the sequences are executed by the WebSocket inbound endpoint. You will also see that the message sent to the WebSocket server is not transformed, and that the response injected to the out sequence is also not transformed.

Example 2: Sending a Message from a HTTP Client to a WebSocket Endpoint

If you need to send a message from a HTTP client to a WebSocket endpoint via the Micro Integrator, you need to establish a persistent Websocket connection from WSO2 MI to the WebSocket back-end.

To demonstrate this scenario, you need to create two dispatching sequences. One for the client to back-end mediation, and another for the back-end to client mediation. Then you need to create a proxy service to call the created sequences.

Synapse configuration

Following is a sample REST API configuration that we can used to implement this scenario. See the instructions on how to build and run this example.

Create the sequence for client to backend mediation, sequence for the backend to client mediation, and a proxy service as to call the sequences.

<sequence name="dispatchSeq" xmlns="http://ws.apache.org/ns/synapse">
    <in>
        <property name="OUT_ONLY" value="true"/>
        <property name="FORCE_SC_ACCEPTED" scope="axis2" type="STRING" value="true"/>
        <property name="websocket.accept.contenType" scope="axis2" value="application/json"/>
             <send>
                <endpoint>
                     <address uri="ws://localhost:8082/websocket"/>
                </endpoint>
            </send>
     </in>
</sequence>
<sequence name="outDispatchSeq" xmlns="http://ws.apache.org/ns/synapse">
   <log level="full"/>
</sequence>
<proxy xmlns="http://ws.apache.org/ns/synapse"
                   name="websocketProxy1"
                   transports="http,https"
                   statistics="disable"
                   trace="disable"
                   startOnLoad="true">
    <target inSequence="dispatchSeq" faultSequence="outDispatchSeq"/>
    <description/>
</proxy>

Build and run

Create the artifacts:

  1. Set up WSO2 Integration Studio.

    Note

    The Websocket sender functionality of the Micro Integrator is disabled by default. To enable the transport, open the deployment.toml file from the MI_TOOLING_HOME/Contents/Eclipse/runtime/microesb/conf/ directory and add the following:

    [transport.ws]
    sender.enable = true
  2. Create an ESB Solution project

  3. Create the mediation sequences and the proxy service with the configurations given above.
  4. Deploy the artifacts in your Micro Integrator.

Starting the Websocket client:

  • Download the netty artifacts zip file from here and extract it. The extracted folder will be shown as ESB-master.
  • Open a terminal, navigate to ESB-master/ESB-Artifacts/Netty_artifacts_for_WebSocket_samples and execute the following command to start the WebSocket server on port 8082:
    java -cp netty-example-4.0.30.Final.jar:lib/*:. io.netty.example.http.websocketx.server.WebSocketServer

If you analyze the log, you will see that an HTTP request is sent to the Websocket server, and that the Websocket server injects the response to the out sequence.

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