Class: UsbTransport

USB transport over libusb for Node.js.

Defaults to interface 0 — covering single-interface printer-class devices used by @thermal-label/* drivers (LabelManager, LabelWriter, Brother QL). Pass { bInterfaceNumber } to claim a different interface; this is needed for composite devices like the LabelWriter 450 Duo, which exposes one interface per engine.

Two transports may be opened against the same (vid, pid) device on different interfaces; they share the underlying libusb handle via an internal refcounted cache so that closing one does not invalidate the other.

Implements

• Transport

Accessors

connected

Get Signature

get connected(): boolean;

Whether the transport is currently connected.

Returns

boolean

Implementation of

Transport.connected

Methods

close()

close(): Promise<void>;

Close the connection.

Always safe to call multiple times. Always await the result.

Returns

Promise<void>

Implementation of

Transport.close

---

read()

read(length: number, timeout?: number): Promise<Uint8Array>;

Read bytes from the printer.

Buffers until length bytes are available or the timeout fires.

BLE implementations: there is no "read N bytes" primitive in BLE. Implementations must buffer incoming GATT notifications internally and satisfy read() calls from that buffer. Document this in your transport class — every BLE implementation must handle buffering consistently so drivers get the same pull-based API on every transport.

Parameters

Parameter	Type
length	number
timeout?	number

Returns

Promise<Uint8Array>

Throws

TransportTimeoutError on timeout.

Throws

TransportClosedError if the transport is closed mid-read.

Implementation of

Transport.read

---

write()

write(data: Uint8Array): Promise<void>;

Send bytes to the printer.

Parameters

Parameter	Type
data	Uint8Array

Returns

Promise<void>

Implementation of

Transport.write

---

open()

static open(
   vid: number, 
   pid: number, 
options?: UsbOpenOptions): Promise<UsbTransport>;

Open a USB Printer Class device by VID/PID.

Enumerates via libusb, opens (or refcount-acquires) the device, claims the requested interface, detaches the usblp kernel driver on Linux if attached, and locates Bulk IN / OUT endpoints on that interface.

Parameters

Parameter	Type
vid	number
pid	number
options?	UsbOpenOptions

Returns

Promise<UsbTransport>

Throws

DeviceNotFoundError if no matching device is attached.

---

openDevice()

static openDevice(entry: DeviceEntry, options?: UsbOpenOptions): Promise<UsbTransport>;

Convenience wrapper for opening a device from a DeviceEntry.

Parameters

Parameter	Type
entry	DeviceEntry
options?	UsbOpenOptions

Returns

Promise<UsbTransport>

Throws

DeviceNotFoundError if the entry has no transports.usb block (network-only printers cannot be opened over USB).