Websockets
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Websocket support was present prior to Pedestal 0.7, but was a container-specific option for Jetty. In Pedestal 0.7, websocket support was refactored to be more universal and declarative, part of the service-map.adoc. |
Websockets are an asynchronous and bidirectional connection between a client and a server. Once a Websocket connection is established, either party may send messages to the other party - this unleashes truly unbounded possibilities for creating dynamic, real-time, and asynchronous applications.
A service-map.adoc may define a :io.pedestal.http/websockets key. This key [1] is a map of strings to a endpoint maps [2]. Each map key is the path for the websocket; the corresponding endpoint map is a collection of callback functions.
The path and endpoint map are ultimately passed to the api:add-endpoint[] function, which describes in detail how the callbacks are used in detail.
Essentially, the :on-open callback is invoked when the client initiates the connection.
It is intended that, when the client connects, some form of server-side process will be initiated capable of sending messages to the client asynchronously. It is the responsibility of the :on-open callback to create such a process. One common option is to use api:on-open-start-ws-connection[] to create the callback, or construct the :on-open callback around the api:start-ws-connection[] function.
The :on-string and :on-binary callbacks are invoked when a text or binary message from the client is received.
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