WebSocket Client Service

The WebSocket Client service is a component of the Cloud Gateway. It enables applications to establish a WebSocket connection with a WebSocket server endpoint. The Predix Edge implementation exposes the WebSocket Client through the Java WebSocket API (JSR-356). This allows applications running on Predix Edge to be WebSocket-provider agnostic.

Example Use Cases

The WebSocket Client Service supports the following use cases:

A service attempts to connect to a WebSocket endpoint to send and receive data. The component first gets an instance of the client container, which implements the WebSocketContainer interface through a dependency injection. The service then calls a connectToServer() method and passes a ClientEndpoint-annotated WebSocket class to the method.
A service attempts to connect to a WebSocket endpoint to transfer/receive data. The component first gets an instance of the client container, which implements the WebSocketContainer interface through dependency injection. It then calls a connectToServer() method and passes a ClientEndpoint-annotated WebSocket object instance to the method. This method allows the consumer to register a WebSocket ClientEndpoint with a configured state as opposed to an uninstantiated class.

SSL Context

The WebSocket Client uses the global SSLContext set in the Security Admin configuration file at <Predix Machine runtime container location>/security to enable WebSockets over TLS. After being configured, the client automatically establishes a TLS connection when connecting to a WSS URI.

Dependencies

Maven dependencies and an OSGI import package are required to consume the service.

The following Maven dependency is required:

<dependency>
    <groupId>javax.websocket</groupId>
    <artifactId>javax.websocket-api</artifactId>
    <version>1.0</version>
</dependency>

The following OSGi import is required to consume the bundle:
```
Import-Package: javax.websocket;version="[1.0,2)"
```