@tanstack/offline-transactions/dist/esm/coordination/BroadcastChannelLeader.js

Offline-first transaction capabilities for TanStack DB

import { BaseLeaderElection } from "./LeaderElection.js";
class BroadcastChannelLeader extends BaseLeaderElection {
  constructor(channelName = `offline-executor-leader`) {
    super();
    this.channel = null;
    this.heartbeatInterval = null;
    this.electionTimeout = null;
    this.lastLeaderHeartbeat = 0;
    this.heartbeatIntervalMs = 5e3;
    this.electionTimeoutMs = 1e4;
    this.handleMessage = (event) => {
      const { type, tabId, timestamp } = event.data;
      if (tabId === this.tabId) {
        return;
      }
      switch (type) {
        case `heartbeat`:
          if (this.isLeaderState && tabId < this.tabId) {
            this.releaseLeadership();
          } else if (!this.isLeaderState) {
            this.lastLeaderHeartbeat = timestamp;
            this.cancelElection();
          }
          break;
        case `election`:
          if (this.isLeaderState) {
            this.sendHeartbeat();
          } else if (tabId > this.tabId) {
            this.startElection();
          }
          break;
        case `leadership-claim`:
          if (this.isLeaderState && tabId < this.tabId) {
            this.releaseLeadership();
          }
          break;
      }
    };
    this.channelName = channelName;
    this.tabId = crypto.randomUUID();
    this.setupChannel();
  }
  setupChannel() {
    if (!this.isBroadcastChannelSupported()) {
      return;
    }
    this.channel = new BroadcastChannel(this.channelName);
    this.channel.addEventListener(`message`, this.handleMessage);
  }
  async requestLeadership() {
    if (!this.isBroadcastChannelSupported()) {
      return false;
    }
    if (this.isLeaderState) {
      return true;
    }
    this.startElection();
    return new Promise((resolve) => {
      setTimeout(() => {
        resolve(this.isLeaderState);
      }, 1e3);
    });
  }
  startElection() {
    if (this.electionTimeout) {
      return;
    }
    this.sendMessage({
      type: `election`,
      tabId: this.tabId,
      timestamp: Date.now()
    });
    this.electionTimeout = window.setTimeout(() => {
      const timeSinceLastHeartbeat = Date.now() - this.lastLeaderHeartbeat;
      if (timeSinceLastHeartbeat > this.electionTimeoutMs) {
        this.claimLeadership();
      }
      this.electionTimeout = null;
    }, this.electionTimeoutMs);
  }
  cancelElection() {
    if (this.electionTimeout) {
      clearTimeout(this.electionTimeout);
      this.electionTimeout = null;
    }
  }
  claimLeadership() {
    this.notifyLeadershipChange(true);
    this.sendMessage({
      type: `leadership-claim`,
      tabId: this.tabId,
      timestamp: Date.now()
    });
    this.startHeartbeat();
  }
  startHeartbeat() {
    if (this.heartbeatInterval) {
      return;
    }
    this.sendHeartbeat();
    this.heartbeatInterval = window.setInterval(() => {
      this.sendHeartbeat();
    }, this.heartbeatIntervalMs);
  }
  stopHeartbeat() {
    if (this.heartbeatInterval) {
      clearInterval(this.heartbeatInterval);
      this.heartbeatInterval = null;
    }
  }
  sendHeartbeat() {
    this.sendMessage({
      type: `heartbeat`,
      tabId: this.tabId,
      timestamp: Date.now()
    });
  }
  sendMessage(message) {
    if (this.channel) {
      this.channel.postMessage(message);
    }
  }
  releaseLeadership() {
    this.stopHeartbeat();
    this.cancelElection();
    this.notifyLeadershipChange(false);
  }
  isBroadcastChannelSupported() {
    return typeof BroadcastChannel !== `undefined`;
  }
  static isSupported() {
    return typeof BroadcastChannel !== `undefined`;
  }
  dispose() {
    this.releaseLeadership();
    if (this.channel) {
      this.channel.removeEventListener(`message`, this.handleMessage);
      this.channel.close();
      this.channel = null;
    }
  }
}
export {
  BroadcastChannelLeader
};
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