hid

README

Gopher Interface Devices (USB HID)

The hid package is a cross platform library for accessing and communicating with USB Human Interface Devices (HID). It is an alternative package to gousb for use cases where devices support this ligher mode of operation (e.g. input devices, hardware crypto wallets).

The package wraps hidapi for accessing OS specific USB HID APIs directly instead of using low level USB constructs, which might have permission issues on some platforms. On Linux the package uses either libusb (default) or hidraw as backend. All of these dependencies are vendored directly into the repository and wrapped using CGO, making the hid package self-contained and go-gettable.

Supported platforms at the moment are Linux, macOS and Windows (exclude constraints are also specified for Android and iOS to allow smoother vendoring into cross platform projects).

Libusb backend selection (linux only)

If nothing is specified, libusb is used as backend for hidapi. To use the hidraw backend, build it with

go build -tags hidraw

Cross-compiling

Using go get the embedded C library is compiled into the binary format of your host OS. Cross compiling to a different platform or architecture entails disabling CGO by default in Go, causing device enumeration hid.Enumerate() to yield no results.

To cross compile a functional version of this library, you'll need to enable CGO during cross compilation via CGO_ENABLED=1 and you'll need to install and set a cross compilation enabled C toolkit via CC=your-cross-gcc.

Acknowledgements

Although the hid package is an implementation from scratch, it was heavily inspired by the existing go.hid library, which seems abandoned since 2015; is incompatible with Go 1.6+; and has various external dependencies. Given its inspirational roots, I thought it important to give credit to the author of said package too.

Wide character support in the hid package is done via the gowchar library, unmaintained since 2013; non buildable with a modern Go release and failing go vet checks. As such, gowchar was also vendored in inline (copyright headers and origins preserved).

License

The components of hid are licensed as such:

• hidapi is released under the GNU LGPL 3/3-clause BSD/HIDAPI license.
• libusb is released under the GNU LGPL 2.1 license.
• go.hid is released under the 2-clause BSD license.
• gowchar is released under the 3-clause BSD license.

Given the above, hid is licensed under GNU LGPL 2.1 or later on Linux and 3-clause BSD on other platforms.

Documentation

Overview

Package hid provides an interface for USB HID devices.

Index

• Variables
• func Supported() bool
• type Device
  • func (dev *Device) Close() error
  • func (dev *Device) GetFeatureReport(b []byte) (int, error)
  • func (dev *Device) GetInputReport(b []byte) (int, error)
  • func (dev *Device) Read(b []byte) (int, error)
  • func (dev *Device) ReadTimeout(b []byte, timeout int) (int, error)
  • func (dev *Device) SendFeatureReport(b []byte) (int, error)
  • func (dev *Device) SetNonblocking(b bool) error
  • func (dev *Device) Write(b []byte) (int, error)
• type DeviceInfo
  • func Enumerate(vendorID uint16, productID uint16) []DeviceInfo
  • func (info DeviceInfo) Open() (*Device, error)

Variables

var ErrDeviceClosed = errors.New("hid: device closed")

ErrDeviceClosed is returned for operations where the device closed before or during the execution.

var ErrUnsupportedPlatform = errors.New("hid: unsupported platform")

ErrUnsupportedPlatform is returned for all operations where the underlying operating system is not supported by the library.

Functions

func Supported

func Supported() bool

Supported returns whether this platform is supported by the HID library or not. The goal of this method is to allow programatically handling platforms that do not support USB HID and not having to fall back to build constraints.

Types

type Device

type Device struct {
	DeviceInfo // Embed the infos for easier access
	// contains filtered or unexported fields
}

Device is a live HID USB connected device handle.

func (*Device) Close

func (dev *Device) Close() error

Close releases the HID USB device handle.

func (*Device) GetFeatureReport

func (dev *Device) GetFeatureReport(b []byte) (int, error)

GetFeatureReport retrieves a feature report from a HID device

Set the first byte of []b to the Report ID of the report to be read. Make sure to allow space for this extra byte in []b. Upon return, the first byte will still contain the Report ID, and the report data will start in b[1].

func (*Device) GetInputReport

func (dev *Device) GetInputReport(b []byte) (int, error)

GetInputReport retrieves a input report from a HID device

Set the first byte of []b to the Report ID of the report to be read. Make sure to allow space for this extra byte in []b. Upon return, the first byte will still contain the Report ID, and the report data will start in b[1].

func (*Device) Read

func (dev *Device) Read(b []byte) (int, error)

Read is a wrapper to ReadTimeout that will check if device blocking is enabled and set timeout accordingly.

This reproduces C.hid_read() behaviour in wrapping hid_read_timeout: return hid_read_timeout(dev, data, length, (dev->blocking)? -1: 0);

func (*Device) ReadTimeout

func (dev *Device) ReadTimeout(b []byte, timeout int) (int, error)

ReadTimeout retrieves an input report from a HID device with a timeout. If timeout is -1 a blocking read is performed, else a non-blocking that waits timeout milliseconds

func (*Device) SendFeatureReport

func (dev *Device) SendFeatureReport(b []byte) (int, error)

SendFeatureReport sends a feature report to a HID device

Feature reports are sent over the Control endpoint as a Set_Report transfer. The first byte of b must contain the Report ID. For devices which only support a single report, this must be set to 0x0. The remaining bytes contain the report data. Since the Report ID is mandatory, calls to SendFeatureReport() will always contain one more byte than the report contains. For example, if a hid report is 16 bytes long, 17 bytes must be passed to SendFeatureReport(): the Report ID (or 0x0, for devices which do not use numbered reports), followed by the report data (16 bytes). In this example, the length passed in would be 17.

func (*Device) SetNonblocking

func (dev *Device) SetNonblocking(b bool) error

SetNonblocking sets the device handle to be non-blocking.

In non-blocking mode calls to Read() will return immediately with a value of 0 if there is no data to be read. In blocking mode, Read() will wait (block) until there is data to read before returning.

func (*Device) Write

func (dev *Device) Write(b []byte) (int, error)

Write sends an output report to a HID device.

Write will send the data on the first OUT endpoint, if one exists. If it does not, it will send the data through the Control Endpoint (Endpoint 0).

type DeviceInfo

type DeviceInfo struct {
	Path          string // Platform-specific device path
	LegacyMacPath string
	VendorID      uint16 // Device Vendor ID
	ProductID     uint16 // Device Product ID
	Release       uint16 // Device Release Number in binary-coded decimal, also known as Device Version Number
	Serial        string // Serial Number
	Manufacturer  string // Manufacturer String
	Product       string // Product string
	UsagePage     uint16 // Usage Page for this Device/Interface (Windows/Mac only)
	Usage         uint16 // Usage for this Device/Interface (Windows/Mac only)

	// The USB interface which this logical device
	// represents. Valid on both Linux implementations
	// in all cases, and valid on the Windows implementation
	// only if the device contains more than one interface.
	Interface int
}

DeviceInfo is a hidapi info structure.

func Enumerate

func Enumerate(vendorID uint16, productID uint16) []DeviceInfo

Enumerate returns a list of all the HID devices attached to the system which match the vendor and product id:

• If the vendor id is set to 0 then any vendor matches.
• If the product id is set to 0 then any product matches.
• If the vendor and product id are both 0, all HID devices are returned.

func (DeviceInfo) Open

func (info DeviceInfo) Open() (*Device, error)

Open connects to an HID device by its path name.