hid_enabled.go

// usb - Self contained USB and HID library for Go
// Copyright 2017 The library Authors
//
// This library is free software: you can redistribute it and/or modify it under
// the terms of the GNU Lesser General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option) any
// later version.
//
// The library is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License along
// with the library. If not, see <http://www.gnu.org/licenses/>.

// +build freebsd,cgo linux,cgo darwin,!ios,cgo windows,cgo

package usb

/*
#include <stdlib.h>
#include "./hidapi/hidapi/hidapi.h"
*/
import "C"

import (
	"errors"
	"runtime"
	"sync"
	"unsafe"
)

// enumerateHid 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 enumerateHid(vendorID uint16, productID uint16) ([]DeviceInfo, error) {
	// Gather all device infos and ensure they are freed before returning
	head := C.hid_enumerate(C.ushort(vendorID), C.ushort(productID))
	if head == nil {
		return nil, nil
	}
	defer C.hid_free_enumeration(head)

	// Iterate the list and retrieve the device details
	var infos []DeviceInfo
	for ; head != nil; head = head.next {
		info := DeviceInfo{
			Path:      C.GoString(head.path),
			VendorID:  uint16(head.vendor_id),
			ProductID: uint16(head.product_id),
			Release:   uint16(head.release_number),
			UsagePage: uint16(head.usage_page),
			Usage:     uint16(head.usage),
			Interface: int(head.interface_number),
		}
		if head.serial_number != nil {
			info.Serial, _ = wcharTToString(head.serial_number)
		}
		if head.product_string != nil {
			info.Product, _ = wcharTToString(head.product_string)
		}
		if head.manufacturer_string != nil {
			info.Manufacturer, _ = wcharTToString(head.manufacturer_string)
		}
		infos = append(infos, info)
	}
	return infos, nil
}

// openHid connects to an HID device by its path name.
func openHid(info DeviceInfo) (*hidDevice, error) {
	path := C.CString(info.Path)
	defer C.free(unsafe.Pointer(path))

	device := C.hid_open_path(path)
	if device == nil {
		return nil, errors.New("hidapi: failed to open device")
	}
	return &hidDevice{
		DeviceInfo: info,
		device:     device,
	}, nil
}

// hidDevice is a live HID USB connected device handle.
type hidDevice struct {
	DeviceInfo // Embed the infos for easier access

	device *C.hid_device // Low level HID device to communicate through
	lock   sync.Mutex
}

// Close releases the HID USB device handle.
func (dev *hidDevice) Close() error {
	dev.lock.Lock()
	defer dev.lock.Unlock()

	if dev.device != nil {
		C.hid_close(dev.device)
		dev.device = nil
	}
	return nil
}

// 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).
func (dev *hidDevice) Write(b []byte) (int, error) {
	// Abort if nothing to write
	if len(b) == 0 {
		return 0, nil
	}
	// Abort if device closed in between
	dev.lock.Lock()
	device := dev.device
	dev.lock.Unlock()

	if device == nil {
		return 0, ErrDeviceClosed
	}
	// Prepend a HID report ID on Windows, other OSes don't need it
	var report []byte
	if runtime.GOOS == "windows" {
		report = append([]byte{0x00}, b...)
	} else {
		report = b
	}
	// Execute the write operation
	written := int(C.hid_write(device, (*C.uchar)(&report[0]), C.size_t(len(report))))
	if written == -1 {
		// If the write failed, verify if closed or other error
		dev.lock.Lock()
		device = dev.device
		dev.lock.Unlock()

		if device == nil {
			return 0, ErrDeviceClosed
		}
		// Device not closed, some other error occurred
		message := C.hid_error(device)
		if message == nil {
			return 0, errors.New("hidapi: unknown failure")
		}
		failure, _ := wcharTToString(message)
		return 0, errors.New("hidapi: " + failure)
	}
	return written, nil
}

// Read retrieves an input report from a HID device.
func (dev *hidDevice) Read(b []byte) (int, error) {
	// Aborth if nothing to read
	if len(b) == 0 {
		return 0, nil
	}
	// Abort if device closed in between
	dev.lock.Lock()
	device := dev.device
	dev.lock.Unlock()

	if device == nil {
		return 0, ErrDeviceClosed
	}
	// Execute the read operation
	read := int(C.hid_read(device, (*C.uchar)(&b[0]), C.size_t(len(b))))
	if read == -1 {
		// If the read failed, verify if closed or other error
		dev.lock.Lock()
		device = dev.device
		dev.lock.Unlock()

		if device == nil {
			return 0, ErrDeviceClosed
		}
		// Device not closed, some other error occurred
		message := C.hid_error(device)
		if message == nil {
			return 0, errors.New("hidapi: unknown failure")
		}
		failure, _ := wcharTToString(message)
		return 0, errors.New("hidapi: " + failure)
	}
	return read, nil
}