Crate nusb

A new library for cross-platform low-level access to USB devices.

nusb is comparable to the C library libusb and its Rust bindings rusb, but written in pure Rust. It’s built on and exposes async APIs by default, but can be made blocking using futures_lite::future::block_on or similar.

Use nusb to write user-space drivers in Rust for non-standard USB devices or those without kernel support. For devices implementing a standard USB class such as Mass Storage, CDC (Serial), HID, Audio, or Video, this is probably not the library you’re looking for – use something built on the existing kernel driver instead. (On some platforms you could detach or replace the kernel driver and program the device from user-space using this library, but you’d have to re-implement the class functionality yourself.)

USB and usage overview

When a USB device connects, the OS queries the device descriptor containing basic device information such as the vendor and product ID (VID / PID) and string descriptors like the manufacturer, product, and serial number strings. list_devices returns an iterator listing connected USB devices, which can be filtered by these fields to identify and select the desired device.

Call device_info.open() to open a selected device. Additional information about the device can be queried with device.active_configuration().

USB devices consist of one or more interfaces exposing a group of functionality. A device with multiple interfaces is known as a composite device. To open an interface, call Device::claim_interface. Only one program (or kernel driver) may claim an interface at a time.

Use the resulting Interface to transfer data on the device’s control, bulk or interrupt endpoints. Transfers are async by default, and can be awaited as individual Futures, or use a Queue to manage streams of data.

For more details on how USB works, USB in a Nutshell is a good overview.

Logging

nusb uses the log crate to log debug and error information.

When submitting a bug report, please include the logs: use a log backend like env_logger and configure it to enable log output for this crate (for env_logger set environment variable RUST_LOG=nusb=debug.)

Platform support

Linux

nusb is built on the kernel’s usbfs API.

A user must have write access on the /dev/bus/usb/XXX/YYY nodes to successfully open a device. Use udev rules to configure these permissions.

For a single-user system used for development, it may be desirable to give your user account access to all USB devices by placing the following in /etc/udev/rules.d/70-plugdev-usb.rules:

SUBSYSTEM=="usb", MODE="0660", GROUP="plugdev"

This grants access on all USB devices to the plugdev group, which your user may be a member of by default on Debian/Ubuntu-based distros. If you are developing an app for others to install, you should scope the permissions more narrowly using the ATTRS{idVendor}=="ZZZZ", ATTRS{idProduct}=="ZZZZ" filters to only apply to your device.

Windows

nusb uses WinUSB on Windows.

On Windows, devices are associated with a particular driver, which persists across connections and reboots. Composite devices appear as multiple devices in the Windows device model, and each interface can be associated with a separate driver.

To use nusb, your device or interface must be associated with the WinUSB driver. If you control the device firmware, the recommended way is to use a WCID descriptor to tell Windows to install the WinUSB driver automatically when the device is first connected. Alternatively Zadig (GUI) or libwdi (CLI / C library) can be used to manually install the WinUSB driver for a device.

macOS

nusb uses IOKit on macOS.

Users have access to USB devices by default, with no permission configuration needed. Devices with a kernel driver are not accessible.

Modules

descriptors

Utilities for parsing USB descriptors.

hotplug

Types for receiving notifications when USB devices are connected or disconnected from the system.

transfer

Transfer-related types.

Structs

Device

An opened USB device.

DeviceId

Opaque device identifier

DeviceInfo

Information about a device that can be obtained without opening it.

Interface

An opened interface of a USB device.

InterfaceInfo

Summary information about a device’s interface, available before opening a device.

Enums

Speed

USB connection speed

Functions

list_devices

Get an iterator listing the connected devices.

watch_devices

Get a Stream that yields an event when a USB device is connected or disconnected from the system.

Type Aliases

Error

OS error returned from operations other than transfers.