add device interfaces

Author: e.khalilov

README.md

@@ -78,14 +78,33 @@ interface UsbDevice {
   manufacturer?: string
   product?: string
   serialNumber?: string
-  deviceClass: number
+  deviceClass: number       // raw bDeviceClass; 0 for HID/composite devices (see note)
   deviceSubclass: number
   deviceProtocol: number
   busId: string
   deviceAddress: number
+  interfaces: UsbInterface[] // per-interface class info (the real function class)
+}
+
+interface UsbInterface {
+  interfaceNumber: number
+  class: number
+  subclass: number
+  protocol: number
+  interfaceString?: string
 }
 ```
 
+> **Note on `deviceClass`**
+>
+> The device-level `deviceClass` (`bDeviceClass` in the USB spec) is
+> legitimately `0x00` for HID and composite devices -- keyboards, trackpads,
+> mice, iPhones, etc. A value of `0x00` means the class is declared
+> *per-interface*, not at the device level. To determine what such a device
+> actually is, read `interfaces[].class` (e.g. `0x03` = HID, `0x06` =
+> still-image/PTP, `0xFF` = vendor-specific). On Windows, `interfaces` may be
+> empty for non-composite devices bound to a single driver.
+
 ## Platform support
 
 | Platform | Architecture | Status |

index.d.ts

@@ -15,11 +15,21 @@ export interface UsbDevice {
   manufacturer?: string
   product?: string
   serialNumber?: string
+  /**
+   * Raw `bDeviceClass` from the device descriptor. This is legitimately
+   * `0x00` for HID and composite devices, which declare their class
+   * per-interface. Inspect `interfaces` for the actual function class.
+   */
   deviceClass: number
   deviceSubclass: number
   deviceProtocol: number
   busId: string
   deviceAddress: number
+  /**
+   * Interfaces in the device's active configuration. May be empty on
+   * Windows for non-composite devices bound to a single driver.
+   */
+  interfaces: Array<UsbInterface>
 }
 
 export interface UsbEvent {
@@ -34,6 +44,22 @@ export declare const enum UsbEventType {
   Disconnected = 'Disconnected'
 }
 
+/**
+ * Summary information about a single USB interface, taken from the
+ * interface descriptor of the device's active configuration.
+ *
+ * This is where the real device function class lives for HID and
+ * composite devices (keyboards, trackpads, iPhones, etc.), whose
+ * device-level `bDeviceClass` is `0x00` per the USB specification.
+ */
+export interface UsbInterface {
+  interfaceNumber: number
+  class: number
+  subclass: number
+  protocol: number
+  interfaceString?: string
+}
+
 /**
  * Start watching for USB device connect/disconnect events.
  * The callback receives `(err, event)` for each hotplug event.