@jsenv/core/src/plugins/server_events/server_events_dispatcher.js

Tool to develop, test and build js projects

export const createServerEventsDispatcher = () => {
  const clients = [];
  const MAX_CLIENTS = 100;

  const addClient = (client) => {
    clients.push(client);
    if (clients.length >= MAX_CLIENTS) {
      const firstClient = clients.shift();
      firstClient.close();
    }
    const removeClient = () => {
      const index = clients.indexOf(client);
      if (index > -1) {
        clients.splice(index, 1);
      }
    };
    client.onclose = () => {
      removeClient(client);
    };
    return () => {
      client.close();
    };
  };

  return {
    addWebsocket: (websocket, request) => {
      const client = {
        request,
        getReadystate: () => {
          return websocket.readyState;
        },
        sendEvent: (event) => {
          websocket.send(JSON.stringify(event));
        },
        close: (reason) => {
          const closePromise = new Promise((resolve, reject) => {
            websocket.onclose = () => {
              websocket.onclose = null;
              websocket.onerror = null;
              resolve();
            };
            websocket.onerror = (e) => {
              websocket.onclose = null;
              websocket.onerror = null;
              reject(e);
            };
          });
          websocket.close(reason);
          return closePromise;
        },
        destroy: () => {
          websocket.terminate();
        },
      };
      client.sendEvent({ type: "welcome" });
      websocket.onclose = () => {
        client.onclose();
      };
      client.onclose = () => {};
      return addClient(client);
    },
    // we could add "addEventSource" and let clients connect using
    // new WebSocket or new EventSource
    // in practice the new EventSource won't be used
    // so "serverEventsDispatcher.addEventSource" is not implemented
    // addEventSource: (request) => {},
    dispatch: (event) => {
      clients.forEach((client) => {
        if (client.getReadystate() === 1) {
          client.sendEvent(event);
        }
      });
    },
    dispatchToClientsMatching: (event, predicate) => {
      clients.forEach((client) => {
        if (client.getReadystate() === 1 && predicate(client)) {
          client.sendEvent(event);
        }
      });
    },
    close: async (reason) => {
      await Promise.all(
        clients.map(async (client) => {
          await client.close(reason);
        }),
      );
    },
    destroy: () => {
      clients.forEach((client) => {
        client.destroy();
      });
    },
  };
};