Only poll USB devices list when a change is detected

packages/hw-transport-node-hid/package.json

@@ -26,7 +26,9 @@
   "license": "Apache-2.0",
   "dependencies": {
     "@ledgerhq/hw-transport": "^4.19.0",
-    "node-hid": "^0.7.2"
+    "lodash.debounce": "^4.0.8",
+    "node-hid": "^0.7.2",
+    "usb-detection": "^3.1.0"
   },
   "devDependencies": {
     "flow-bin": "^0.68.0",

packages/hw-transport-node-hid/src/TransportNodeHid.js

@@ -28,6 +28,7 @@ function defer<T>(): Defer<T> {
 
 let listenDevicesPollingInterval = 500;
 let listenDevicesPollingSkip = () => false;
+let listenDevicesDebug = () => {};
 
 /**
  * node-hid Transport implementation
@@ -68,6 +69,15 @@ export default class TransportNodeHid extends Transport<string> {
     listenDevicesPollingSkip = conditionToSkip;
   };
 
+  static setListenDevicesDebug = (debug: boolean | ((log: string) => void)) => {
+    listenDevicesDebug =
+      typeof debug === "function"
+        ? debug
+        : debug
+          ? (...log) => console.log("[listenDevices]", ...log)
+          : () => {};
+  };
+
   /**
    */
   static listen = (
@@ -85,7 +95,8 @@ export default class TransportNodeHid extends Transport<string> {
     });
     const { events, stop } = listenDevices(
       listenDevicesPollingInterval,
-      listenDevicesPollingSkip
+      listenDevicesPollingSkip,
+      listenDevicesDebug
     );
 
     const onAdd = device => {

packages/hw-transport-node-hid/src/listenDevices.js

@@ -1,19 +1,23 @@
 // @flow
 
 import EventEmitter from "events";
+import usbDetect from "usb-detection";
+import debounce from "lodash.debounce";
 import getDevices from "./getDevices";
 
+const VENDOR_ID = 11415; // Ledger's Vendor ID for filtering
+
 export default (
   delay: number,
-  listenDevicesPollingSkip: () => boolean
+  listenDevicesPollingSkip: () => boolean,
+  debug: (...any) => void
 ): {
   events: EventEmitter,
   stop: () => void
 } => {
   const events = new EventEmitter();
   events.setMaxListeners(0);
 
-  let timeoutDetection;
   let listDevices = getDevices();
 
   const flatDevice = d => d.path;
@@ -27,37 +31,75 @@ export default (
 
   let lastDevices = getFlatDevices();
 
-  const checkDevices = () => {
+  const poll = () => {
     if (!listenDevicesPollingSkip()) {
-      const currentDevices = getFlatDevices();
+      debug("Polling for added or removed devices");
 
+      let changeFound = false;
+      const currentDevices = getFlatDevices();
       const newDevices = currentDevices.filter(d => !lastDevices.includes(d));
-      const removeDevices = lastDevices.filter(
-        d => !currentDevices.includes(d)
-      );
 
       if (newDevices.length > 0) {
+        debug("New device found:", newDevices);
+
         listDevices = getDevices();
         events.emit("add", getDeviceByPaths(newDevices));
+
+        changeFound = true;
+      } else {
+        debug("No new device found");
       }
 
+      const removeDevices = lastDevices.filter(
+        d => !currentDevices.includes(d)
+      );
+
       if (removeDevices.length > 0) {
+        debug("Removed device found:", removeDevices);
+
         events.emit("remove", getDeviceByPaths(removeDevices));
         listDevices = listDevices.filter(
           d => !removeDevices.includes(flatDevice(d))
         );
+
+        changeFound = true;
+      } else {
+        debug("No removed device found");
       }
 
-      lastDevices = currentDevices;
+      if (changeFound) {
+        lastDevices = currentDevices;
+      }
+    } else {
+      debug("Polling skipped, re-debouncing");
+      debouncedPoll();
     }
-    setTimeout(checkDevices, delay);
   };
 
-  timeoutDetection = setTimeout(checkDevices, delay);
+  const debouncedPoll = debounce(poll, delay);
+
+  debug("Starting to monitor USB for ledger devices");
+  usbDetect.startMonitoring();
+
+  // Detect add
+  usbDetect.on(`add:${VENDOR_ID}`, device => {
+    debug("Device add detected:", device.deviceName);
+
+    debouncedPoll();
+  });
+
+  // Detect remove
+  usbDetect.on(`remove:${VENDOR_ID}`, device => {
+    debug("Device removal detected:", device.deviceName);
+
+    debouncedPoll();
+  });
 
   return {
     stop: () => {
-      clearTimeout(timeoutDetection);
+      debug("Stopping USB monitoring");
+      debouncedPoll.cancel();
+      usbDetect.stopMonitoring();
     },
     events
   };