Replacing Disconnect Handling

In some cases, an application does not want the AMPS Client to reconnect, but instead wants to take a different action if disconnection occurs. For example, a stateless publisher that sends ephemeral data (such as telemetry or prices) may want to exit with an error if the connection is lost rather than risk falling behind and providing outdated messages. Often, in this case, a monitoring process will start another publisher if a publisher fails, and it is better for a message to be lost than to arrive late.

To cover cases where the application has unusual needs, the AMPS client library allows an application to provide custom disconnect handling.

Your application gets to specify exactly what happens when a disconnect occurs by supplying a function to client.setDisconnectHandler(), which is invoked whenever a disconnect occurs. This may be helpful for situations where a particular connection needs to do something completely different than reconnecting or failing over to another AMPS server.

warning

Setting the disconnect handler completely replaces the disconnection failover behavior for a Client.

The example below shows the basics:

/**
* Call this function to establish a connection to AMPS.
*/
const connectToAMPS = async () => {
  try {
    await client.connect('ws://localhost:9000/amps/json');
    // Successfully connected
  }
  catch (err) {
    // Can't establish connection
  }
};

// create a client object
const client = new Client('disconnect-handler-demo');

/*
* disconnectHandler() method is called to supply a function for use
* when AMPS detects a disconnect. At any time, this function may be
* called by AMPS to indicate that the client has disconnected from
* the server, and to allow your application to choose what to do
* about it.
*/
client.disconnectHandler(
    /**
    * Our disconnect handler’s implementation begins here.
    *
    * Any custom disconnect handler would be application-specific
    * so, for demonstration purposes, we simply log the error.
    *
    * Notice that this disconnect handler replaces all other
    * disconnect handling behavior. When the client is disconnected,
    * it will simply log an error to the console. The client
    * will not reconnect or take any other action.
    */
    (client, error) => {
         console.log(error);
    }
);

// We begin by connecting and subscribing
connectToAMPS();