@ledgerhq/hw-transport-web-ble/src/monitorCharacteristic.ts

Ledger Hardware Wallet Web Bluetooth implementation of the communication layer

import { Observable } from "rxjs";
import type { Characteristic } from "./types";
import { log } from "@ledgerhq/logs";

export const monitorCharacteristic = (characteristic: Characteristic): Observable<Buffer> =>
  Observable.create(o => {
    log("ble-verbose", "start monitor " + characteristic.uuid);

    function onCharacteristicValueChanged(event) {
      const characteristic = event.target;

      if (characteristic.value) {
        o.next(Buffer.from(characteristic.value.buffer));
      }
    }

    characteristic.startNotifications().then(() => {
      characteristic.addEventListener("characteristicvaluechanged", onCharacteristicValueChanged);
    });
    return () => {
      log("ble-verbose", "end monitor " + characteristic.uuid);
      characteristic.stopNotifications();
    };
  });