move all libusb wrappers to libusb.go.

usb/config.go

@@ -15,13 +15,8 @@
 
 package usb
 
-// #include <libusb.h>
-import "C"
-
 import (
 	"fmt"
-	"reflect"
-	"unsafe"
 )
 
 type EndpointInfo struct {
@@ -87,73 +82,3 @@ type ConfigInfo struct {
 func (c ConfigInfo) String() string {
 	return fmt.Sprintf("Config %02x", c.Config)
 }
-
-func newConfig(dev *C.libusb_device, cfg *C.struct_libusb_config_descriptor) ConfigInfo {
-	c := ConfigInfo{
-		Config:     uint8(cfg.bConfigurationValue),
-		Attributes: uint8(cfg.bmAttributes),
-		MaxPower:   uint8(cfg.MaxPower),
-	}
-
-	var ifaces []C.struct_libusb_interface
-	*(*reflect.SliceHeader)(unsafe.Pointer(&ifaces)) = reflect.SliceHeader{
-		Data: uintptr(unsafe.Pointer(cfg._interface)),
-		Len:  int(cfg.bNumInterfaces),
-		Cap:  int(cfg.bNumInterfaces),
-	}
-	c.Interfaces = make([]InterfaceInfo, 0, len(ifaces))
-	for _, iface := range ifaces {
-		if iface.num_altsetting == 0 {
-			continue
-		}
-
-		var alts []C.struct_libusb_interface_descriptor
-		*(*reflect.SliceHeader)(unsafe.Pointer(&alts)) = reflect.SliceHeader{
-			Data: uintptr(unsafe.Pointer(iface.altsetting)),
-			Len:  int(iface.num_altsetting),
-			Cap:  int(iface.num_altsetting),
-		}
-		descs := make([]InterfaceSetup, 0, len(alts))
-		for _, alt := range alts {
-			i := InterfaceSetup{
-				Number:     uint8(alt.bInterfaceNumber),
-				Alternate:  uint8(alt.bAlternateSetting),
-				IfClass:    uint8(alt.bInterfaceClass),
-				IfSubClass: uint8(alt.bInterfaceSubClass),
-				IfProtocol: uint8(alt.bInterfaceProtocol),
-			}
-			var ends []C.struct_libusb_endpoint_descriptor
-			*(*reflect.SliceHeader)(unsafe.Pointer(&ends)) = reflect.SliceHeader{
-				Data: uintptr(unsafe.Pointer(alt.endpoint)),
-				Len:  int(alt.bNumEndpoints),
-				Cap:  int(alt.bNumEndpoints),
-			}
-			i.Endpoints = make([]EndpointInfo, 0, len(ends))
-			for _, end := range ends {
-				ei := EndpointInfo{
-					Address:       uint8(end.bEndpointAddress),
-					Attributes:    uint8(end.bmAttributes),
-					MaxPacketSize: uint16(end.wMaxPacketSize),
-					PollInterval:  uint8(end.bInterval),
-					RefreshRate:   uint8(end.bRefresh),
-					SynchAddress:  uint8(end.bSynchAddress),
-				}
-				if ei.TransferType() == TRANSFER_TYPE_ISOCHRONOUS {
-					// bits 0-10 identify the packet size, bits 11-12 are the number of additional transactions per microframe.
-					// Don't use libusb_get_max_iso_packet_size, as it has a bug where it returns the same value
-					// regardless of alternative setting used, where different alternative settings might define different
-					// max packet sizes.
-					// See http://libusb.org/ticket/77 for more background.
-					ei.MaxIsoPacket = uint32(end.wMaxPacketSize) & 0x07ff * (uint32(end.wMaxPacketSize)>>11&3 + 1)
-				}
-				i.Endpoints = append(i.Endpoints, ei)
-			}
-			descs = append(descs, i)
-		}
-		c.Interfaces = append(c.Interfaces, InterfaceInfo{
-			Number: descs[0].Number,
-			Setups: descs,
-		})
-	}
-	return c
-}

usb/descriptor.go

@@ -15,9 +15,6 @@
 
 package usb
 
-// #include <libusb.h>
-import "C"
-
 type Descriptor struct {
 	// Bus information
 	Bus     uint8 // The bus on which the device was detected
@@ -39,34 +36,3 @@ type Descriptor struct {
 	// Configuration information
 	Configs []ConfigInfo
 }
-
-func newDescriptor(dev *C.libusb_device) (*Descriptor, error) {
-	var desc C.struct_libusb_device_descriptor
-	if errno := C.libusb_get_device_descriptor(dev, &desc); errno < 0 {
-		return nil, usbError(errno)
-	}
-
-	// Enumerate configurations
-	var cfgs []ConfigInfo
-	for i := 0; i < int(desc.bNumConfigurations); i++ {
-		var cfg *C.struct_libusb_config_descriptor
-		if errno := C.libusb_get_config_descriptor(dev, C.uint8_t(i), &cfg); errno < 0 {
-			return nil, usbError(errno)
-		}
-		cfgs = append(cfgs, newConfig(dev, cfg))
-		C.libusb_free_config_descriptor(cfg)
-	}
-
-	return &Descriptor{
-		Bus:      uint8(C.libusb_get_bus_number(dev)),
-		Address:  uint8(C.libusb_get_device_address(dev)),
-		Spec:     BCD(desc.bcdUSB),
-		Device:   BCD(desc.bcdDevice),
-		Vendor:   ID(desc.idVendor),
-		Product:  ID(desc.idProduct),
-		Class:    uint8(desc.bDeviceClass),
-		SubClass: uint8(desc.bDeviceSubClass),
-		Protocol: uint8(desc.bDeviceProtocol),
-		Configs:  cfgs,
-	}, nil
-}

usb/device.go

@@ -15,15 +15,10 @@
 
 package usb
 
-// #include <libusb.h>
-import "C"
-
 import (
 	"fmt"
-	"reflect"
 	"sync"
 	"time"
-	"unsafe"
 )
 
 var DefaultReadTimeout = 1 * time.Second
@@ -31,7 +26,7 @@ var DefaultWriteTimeout = 1 * time.Second
 var DefaultControlTimeout = 250 * time.Millisecond //5 * time.Second
 
 type Device struct {
-	handle *C.libusb_device_handle
+	handle *libusbDevHandle
 
 	// Embed the device information for easy access
 	*Descriptor
@@ -46,7 +41,7 @@ type Device struct {
 	claimed map[uint8]int
 }
 
-func newDevice(handle *C.libusb_device_handle, desc *Descriptor) *Device {
+func newDevice(handle *libusbDevHandle, desc *Descriptor) *Device {
 	ifaces := 0
 	d := &Device{
 		handle:         handle,
@@ -62,48 +57,24 @@ func newDevice(handle *C.libusb_device_handle, desc *Descriptor) *Device {
 }
 
 func (d *Device) Reset() error {
-	if errno := C.libusb_reset_device(d.handle); errno != 0 {
-		return usbError(errno)
-	}
-	return nil
+	return libusb.reset(d.handle)
 }
 
 func (d *Device) Control(rType, request uint8, val, idx uint16, data []byte) (int, error) {
-	//log.Printf("control xfer: %d:%d/%d:%d %x", idx, rType, request, val, string(data))
-	dataSlice := (*reflect.SliceHeader)(unsafe.Pointer(&data))
-	n := C.libusb_control_transfer(
-		d.handle,
-		C.uint8_t(rType),
-		C.uint8_t(request),
-		C.uint16_t(val),
-		C.uint16_t(idx),
-		(*C.uchar)(unsafe.Pointer(dataSlice.Data)),
-		C.uint16_t(len(data)),
-		C.uint(d.ControlTimeout/time.Millisecond))
-	if n < 0 {
-		return int(n), usbError(n)
-	}
-	return int(n), nil
+	return libusb.control(d.handle, d.ControlTimeout, rType, request, val, idx, data)
 }
 
 // ActiveConfig returns the config id (not the index) of the active configuration.
 // This corresponds to the ConfigInfo.Config field.
 func (d *Device) ActiveConfig() (uint8, error) {
-	var cfg C.int
-	if errno := C.libusb_get_configuration(d.handle, &cfg); errno < 0 {
-		return 0, usbError(errno)
-	}
-	return uint8(cfg), nil
+	return libusb.getConfig(d.handle)
 }
 
 // SetConfig attempts to change the active configuration.
 // The cfg provided is the config id (not the index) of the configuration to set,
 // which corresponds to the ConfigInfo.Config field.
 func (d *Device) SetConfig(cfg uint8) error {
-	if errno := C.libusb_set_configuration(d.handle, C.int(cfg)); errno < 0 {
-		return usbError(errno)
-	}
-	return nil
+	return libusb.setConfig(d.handle, cfg)
 }
 
 // Close the device.
@@ -114,9 +85,9 @@ func (d *Device) Close() error {
 	d.lock.Lock()
 	defer d.lock.Unlock()
 	for iface := range d.claimed {
-		C.libusb_release_interface(d.handle, C.int(iface))
+		libusb.release(d.handle, iface)
 	}
-	C.libusb_close(d.handle)
+	libusb.close(d.handle)
 	d.handle = nil
 	return nil
 }
@@ -162,19 +133,19 @@ func (d *Device) OpenEndpoint(conf, iface, setup, epoint uint8) (Endpoint, error
 found:
 
 	// Set the configuration
-	var activeConf C.int
-	if errno := C.libusb_get_configuration(d.handle, &activeConf); errno < 0 {
-		return nil, fmt.Errorf("usb: getcfg: %s", usbError(errno))
+	activeConf, err := libusb.getConfig(d.handle)
+	if err != nil {
+		return nil, fmt.Errorf("usb: getcfg: %s", err)
 	}
-	if int(activeConf) != int(conf) {
-		if errno := C.libusb_set_configuration(d.handle, C.int(conf)); errno < 0 {
-			return nil, fmt.Errorf("usb: setcfg: %s", usbError(errno))
+	if activeConf != conf {
+		if err := libusb.setConfig(d.handle, conf); err != nil {
+			return nil, fmt.Errorf("usb: setcfg: %s", err)
 		}
 	}
 
 	// Claim the interface
-	if errno := C.libusb_claim_interface(d.handle, C.int(iface)); errno < 0 {
-		return nil, fmt.Errorf("usb: claim: %s", usbError(errno))
+	if err := libusb.claim(d.handle, iface); err != nil {
+		return nil, fmt.Errorf("usb: claim: %s", err)
 	}
 
 	// Increment the claim count
@@ -184,9 +155,8 @@ found:
 
 	// Choose the alternate
 	if setAlternate {
-		if errno := C.libusb_set_interface_alt_setting(d.handle, C.int(iface), C.int(setup)); errno < 0 {
-			debug.Printf("altsetting error: %s", usbError(errno))
-			return nil, fmt.Errorf("usb: setalt: %s", usbError(errno))
+		if err := libusb.setAlt(d.handle, iface, setup); err != nil {
+			return nil, fmt.Errorf("usb: setalt: %s", err)
 		}
 	}
 
@@ -194,26 +164,7 @@ found:
 }
 
 func (d *Device) GetStringDescriptor(desc_index int) (string, error) {
-
-	// allocate 200-byte array limited the length of string descriptor
-	goBuffer := make([]byte, 200)
-
-	// get string descriptor from libusb. if errno < 0 then there are any errors.
-	// if errno >= 0; it is a length of result string descriptor
-	errno := C.libusb_get_string_descriptor_ascii(
-		d.handle,
-		C.uint8_t(desc_index),
-		(*C.uchar)(unsafe.Pointer(&goBuffer[0])),
-		200)
-
-	// if any errors occur
-	if errno < 0 {
-		return "", fmt.Errorf("usb: getstr: %s", usbError(errno))
-	}
-	// convert slice of byte to string with limited length from errno
-	stringDescriptor := string(goBuffer[:errno])
-
-	return stringDescriptor, nil
+	return libusb.getStringDesc(d.handle, desc_index)
 }
 
 // SetAutoDetach enables/disables libusb's automatic kernel driver detachment.
@@ -221,20 +172,12 @@ func (d *Device) GetStringDescriptor(desc_index int) (string, error) {
 // on the interface and reattach it when releasing the interface.
 // Automatic kernel driver detachment is disabled on newly opened device handles by default.
 func (d *Device) SetAutoDetach(autodetach bool) error {
-	autodetachInt := 0
-	if autodetach {
+	var autodetachInt int
+	switch autodetach {
+	case true:
 		autodetachInt = 1
+	case false:
+		autodetachInt = 0
 	}
-
-	err := C.libusb_set_auto_detach_kernel_driver(
-		d.handle,
-		C.int(autodetachInt),
-	)
-
-	// TODO LIBUSB_ERROR_NOT_SUPPORTED (-12) handling
-	// if any errors occur
-	if err != C.int(SUCCESS) {
-		return fmt.Errorf("usb: setautodetach: %s", usbError(err))
-	}
-	return nil
+	return libusb.setAutoDetach(d.handle, autodetachInt)
 }

usb/endpoint.go

@@ -34,7 +34,7 @@ type transferIntf interface {
 }
 
 type endpoint struct {
-	h *deviceHandle
+	h *libusbDevHandle
 
 	InterfaceSetup
 	EndpointInfo
@@ -92,7 +92,7 @@ func (e *endpoint) transfer(buf []byte, timeout time.Duration) (int, error) {
 
 func newEndpoint(d *Device) *endpoint {
 	ep := &endpoint{
-		h:            (*deviceHandle)(d.handle),
+		h:            d.handle,
 		readTimeout:  d.ReadTimeout,
 		writeTimeout: d.WriteTimeout,
 	}

usb/error.go

@@ -28,6 +28,14 @@ func (e usbError) Error() string {
 	return fmt.Sprintf("libusb: %s [code %d]", usbErrorString[e], int(e))
 }
 
+func fromUSBError(errno C.int) error {
+	err := usbError(errno)
+	if err == SUCCESS {
+		return nil
+	}
+	return err
+}
+
 const (
 	SUCCESS             usbError = C.LIBUSB_SUCCESS
 	ERROR_IO            usbError = C.LIBUSB_ERROR_IO

usb/transfer.go

@@ -14,14 +14,6 @@
 
 package usb
 
-/*
-#include <libusb.h>
-
-int compact_iso_data(struct libusb_transfer *xfer, unsigned char *status);
-int submit(struct libusb_transfer *xfer);
-*/
-import "C"
-
 import (
 	"errors"
 	"fmt"
@@ -31,32 +23,8 @@ import (
 	"unsafe"
 )
 
-// libusb hooks used as injection points for tests.
-var (
-	cCancel = func(t *libusbTransfer) usbError {
-		return usbError(C.libusb_cancel_transfer((*C.struct_libusb_transfer)(t)))
-	}
-	cSubmit = func(t *libusbTransfer) usbError {
-		return usbError(C.submit((*C.struct_libusb_transfer)(t)))
-	}
-)
-
-// because of a limitation of cgo, tests cannot import C.
-type deviceHandle C.libusb_device_handle
-type libusbTransfer C.struct_libusb_transfer
-type libusbIso C.struct_libusb_iso_packet_descriptor
-
-// also for tests
-var (
-	libusbIsoSize   = C.sizeof_struct_libusb_iso_packet_descriptor
-	libusbIsoOffset = unsafe.Offsetof(C.struct_libusb_transfer{}.iso_packet_desc)
-)
-
-//export xfer_callback
-func xfer_callback(cptr unsafe.Pointer) {
-	ch := *(*chan struct{})(cptr)
-	close(ch)
-}
+// #include <libusb.h>
+import "C"
 
 type usbTransfer struct {
 	// mu protects the transfer state.
@@ -84,7 +52,7 @@ func (t *usbTransfer) submit() error {
 	}
 	t.done = make(chan struct{})
 	t.xfer.user_data = (unsafe.Pointer)(&t.done)
-	if err := cSubmit(t.xfer); err != SUCCESS {
+	if err := libusb.submit(t.xfer); err != nil {
 		return err
 	}
 	t.submitted = true
@@ -111,10 +79,9 @@ func (t *usbTransfer) wait() (n int, err error) {
 	var status TransferStatus
 	switch TransferType(t.xfer._type) {
 	case TRANSFER_TYPE_ISOCHRONOUS:
-		n = int(C.compact_iso_data((*C.struct_libusb_transfer)(t.xfer), (*C.uchar)(unsafe.Pointer(&status))))
+		n, status = libusb.compactIsoData(t.xfer)
 	default:
-		n = int(t.xfer.actual_length)
-		status = TransferStatus(t.xfer.status)
+		n, status = int(t.xfer.actual_length), TransferStatus(t.xfer.status)
 	}
 	if status != LIBUSB_TRANSFER_COMPLETED {
 		return n, status
@@ -130,15 +97,12 @@ func (t *usbTransfer) cancel() error {
 	if !t.submitted {
 		return nil
 	}
-	err := usbError(cCancel(t.xfer))
+	err := libusb.cancel(t.xfer)
 	if err == ERROR_NOT_FOUND {
 		// transfer already completed
-		err = SUCCESS
+		return nil
 	}
-	if err != SUCCESS {
-		return err
-	}
-	return nil
+	return err
 }
 
 // free releases the memory allocated for the transfer.
@@ -150,7 +114,7 @@ func (t *usbTransfer) free() error {
 	if t.submitted {
 		return errors.New("free() cannot be called on a submitted transfer until wait() returns")
 	}
-	C.libusb_free_transfer((*C.struct_libusb_transfer)(t.xfer))
+	libusb.free(t.xfer)
 	t.xfer = nil
 	t.buf = nil
 	t.done = nil
@@ -159,7 +123,7 @@ func (t *usbTransfer) free() error {
 
 // newUSBTransfer allocates a new transfer structure for communication with a
 // given device/endpoint, with buf as the underlying transfer buffer.
-func newUSBTransfer(dev *deviceHandle, ei EndpointInfo, buf []byte, timeout time.Duration) (*usbTransfer, error) {
+func newUSBTransfer(dev *libusbDevHandle, ei EndpointInfo, buf []byte, timeout time.Duration) (*usbTransfer, error) {
 	var isoPackets int
 	tt := ei.TransferType()
 	if tt == TRANSFER_TYPE_ISOCHRONOUS {
@@ -169,9 +133,9 @@ func newUSBTransfer(dev *deviceHandle, ei EndpointInfo, buf []byte, timeout time
 		}
 	}
 
-	xfer := C.libusb_alloc_transfer(C.int(isoPackets))
-	if xfer == nil {
-		return nil, fmt.Errorf("libusb_alloc_transfer(%d) failed", isoPackets)
+	xfer, err := libusb.alloc(isoPackets)
+	if err != nil {
+		return nil, err
 	}
 
 	xfer.dev_handle = (*C.struct_libusb_device_handle)(dev)
@@ -183,8 +147,7 @@ func newUSBTransfer(dev *deviceHandle, ei EndpointInfo, buf []byte, timeout time
 	xfer.length = C.int(len(buf))
 
 	if tt == TRANSFER_TYPE_ISOCHRONOUS {
-		xfer.num_iso_packets = C.int(isoPackets)
-		C.libusb_set_iso_packet_lengths(xfer, C.uint(ei.MaxIsoPacket))
+		libusb.setIsoPacketLengths(xfer, ei.MaxIsoPacket)
 	}
 
 	t := &usbTransfer{

usb/transfer_fakelibusb_test.go

@@ -19,19 +19,20 @@ import "sync"
 type fakeLibusb struct {
 	sync.Mutex
 	ts map[*libusbTransfer]chan struct{}
+	libusbIntf
 }
 
-func (f *fakeLibusb) submit(t *libusbTransfer) usbError {
+func (f *fakeLibusb) submit(t *libusbTransfer) error {
 	f.Lock()
 	defer f.Unlock()
 	if f.ts[t] == nil {
 		f.ts[t] = make(chan struct{})
 	}
 	close(f.ts[t])
-	return SUCCESS
+	return nil
 }
 
-func (f *fakeLibusb) cancel(t *libusbTransfer) usbError { return SUCCESS }
+func (f *fakeLibusb) cancel(t *libusbTransfer) error { return nil }
 
 func (f *fakeLibusb) waitForSubmit(t *usbTransfer) {
 	f.Lock()
@@ -52,5 +53,8 @@ func (f *fakeLibusb) runCallback(t *usbTransfer, cb func(*usbTransfer)) {
 }
 
 func newFakeLibusb() *fakeLibusb {
-	return &fakeLibusb{ts: make(map[*libusbTransfer]chan struct{})}
+	return &fakeLibusb{
+		ts:         make(map[*libusbTransfer]chan struct{}),
+		libusbIntf: libusbImpl{},
+	}
 }

usb/transfer_test.go

@@ -87,12 +87,10 @@ func TestNewTransfer(t *testing.T) {
 }
 
 func TestTransferProtocol(t *testing.T) {
-	origSubmit, origCancel := cSubmit, cCancel
-	defer func() { cSubmit, cCancel = origSubmit, origCancel }()
+	defer func(i libusbIntf) { libusb = i }(libusb)
 
 	f := newFakeLibusb()
-	cSubmit = f.submit
-	cCancel = f.cancel
+	libusb = f
 
 	xfers := make([]*usbTransfer, 2)
 	var err error
@@ -167,12 +165,10 @@ func TestTransferProtocol(t *testing.T) {
 }
 
 func TestIsoPackets(t *testing.T) {
-	origSubmit, origCancel := cSubmit, cCancel
-	defer func() { cSubmit, cCancel = origSubmit, origCancel }()
+	defer func(i libusbIntf) { libusb = i }(libusb)
 
 	f := newFakeLibusb()
-	cSubmit = f.submit
-	cCancel = f.cancel
+	libusb = f
 
 	xfer, err := newUSBTransfer(nil, EndpointInfo{
 		Address:       0x82,

usb/usb.go

@@ -20,50 +20,26 @@ package usb
 // #include <libusb.h>
 import "C"
 
-import (
-	"log"
-	"reflect"
-	"unsafe"
-)
-
 type Context struct {
-	ctx  *C.libusb_context
+	ctx  *libusbContext
 	done chan struct{}
 }
 
 func (c *Context) Debug(level int) {
-	C.libusb_set_debug(c.ctx, C.int(level))
+	libusb.setDebug(c.ctx, level)
 }
 
 func NewContext() *Context {
-	c := &Context{
+	c, err := libusb.init()
+	if err != nil {
+		panic(err)
+	}
+	ctx := &Context{
+		ctx:  c,
 		done: make(chan struct{}),
 	}
-
-	if errno := C.libusb_init(&c.ctx); errno != 0 {
-		panic(usbError(errno))
-	}
-
-	go func() {
-		tv := C.struct_timeval{
-			tv_sec:  0,
-			tv_usec: 100000,
-		}
-		for {
-			select {
-			case <-c.done:
-				return
-			default:
-			}
-			if errno := C.libusb_handle_events_timeout_completed(c.ctx, &tv, nil); errno < 0 {
-				log.Printf("handle_events: error: %s", usbError(errno))
-				continue
-			}
-			//log.Printf("handle_events returned")
-		}
-	}()
-
-	return c
+	go libusb.handleEvents(ctx.ctx, ctx.done)
+	return ctx
 }
 
 // ListDevices calls each with each enumerated device.
@@ -72,36 +48,30 @@ func NewContext() *Context {
 // If there are any errors enumerating the devices,
 // the final one is returned along with any successfully opened devices.
 func (c *Context) ListDevices(each func(desc *Descriptor) bool) ([]*Device, error) {
-	var list **C.libusb_device
-	cnt := C.libusb_get_device_list(c.ctx, &list)
-	if cnt < 0 {
-		return nil, usbError(cnt)
-	}
-	defer C.libusb_free_device_list(list, 1)
-
-	var slice []*C.libusb_device
-	*(*reflect.SliceHeader)(unsafe.Pointer(&slice)) = reflect.SliceHeader{
-		Data: uintptr(unsafe.Pointer(list)),
-		Len:  int(cnt),
-		Cap:  int(cnt),
+	list, err := libusb.getDevices(c.ctx)
+	if err != nil {
+		return nil, err
 	}
 
 	var reterr error
 	var ret []*Device
-	for _, dev := range slice {
-		desc, err := newDescriptor(dev)
+	for _, dev := range list {
+		desc, err := libusb.getDeviceDesc(dev)
 		if err != nil {
+			libusb.dereference(dev)
 			reterr = err
 			continue
 		}
 
 		if each(desc) {
-			var handle *C.libusb_device_handle
-			if errno := C.libusb_open(dev, &handle); errno != 0 {
-				reterr = usbError(errno)
+			handle, err := libusb.open(dev)
+			if err != nil {
+				reterr = err
 				continue
 			}
 			ret = append(ret, newDevice(handle, desc))
+		} else {
+			libusb.dereference(dev)
 		}
 	}
 	return ret, reterr
@@ -110,21 +80,14 @@ func (c *Context) ListDevices(each func(desc *Descriptor) bool) ([]*Device, erro
 // OpenDeviceWithVidPid opens Device from specific VendorId and ProductId.
 // If there are any errors, it'll returns at second value.
 func (c *Context) OpenDeviceWithVidPid(vid, pid int) (*Device, error) {
-
-	handle := C.libusb_open_device_with_vid_pid(c.ctx, (C.uint16_t)(vid), (C.uint16_t)(pid))
-	if handle == nil {
-		return nil, ERROR_NOT_FOUND
+	dev, handle, err := libusb.openVIDPID(c.ctx, vid, pid)
+	if err != nil {
+		return nil, err
 	}
-
-	dev := C.libusb_get_device(handle)
-	if dev == nil {
-		return nil, ERROR_NO_DEVICE
-	}
-
-	desc, err := newDescriptor(dev)
-
+	desc, err := libusb.getDeviceDesc(dev)
 	// return an error from nil-handle and nil-device
 	if err != nil {
+		libusb.dereference(dev)
 		return nil, err
 	}
 
@@ -135,7 +98,7 @@ func (c *Context) OpenDeviceWithVidPid(vid, pid int) (*Device, error) {
 func (c *Context) Close() error {
 	close(c.done)
 	if c.ctx != nil {
-		C.libusb_exit(c.ctx)
+		libusb.exit(c.ctx)
 	}
 	c.ctx = nil
 	return nil