Merge pull request #39 from kylelemons/libusb_wrappers

Libusb wrappers
2017-03-10 06:52:56 -05:00
parent 77a5315a11 810a98e9fa
commit b5abadf3f0
13 changed files with 699 additions and 553 deletions
--- a/usb/config.go
+++ b/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
-}
--- a/usb/descriptor.go
+++ b/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
-}
--- a/usb/device.go
+++ b/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.
@@ -114,79 +85,89 @@ 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
 }

-func (d *Device) OpenEndpoint(conf, iface, setup, epoint uint8) (Endpoint, error) {
-	end := newEndpoint(d)
+func (d *Device) OpenEndpoint(cfgNum, ifNum, setNum, epNum uint8) (Endpoint, error) {
+	var cfg *ConfigInfo
+	for _, c := range d.Configs {
+		if c.Config == cfgNum {
+			debug.Printf("found conf: %#v\n", c)
+			cfg = &c
+			break
+		}
+	}
+	if cfg == nil {
+		return nil, fmt.Errorf("usb: unknown configuration %02x", cfgNum)
+	}
+
+	var intf *InterfaceInfo
+	for _, i := range cfg.Interfaces {
+		if i.Number == ifNum {
+			debug.Printf("found iface: %#v\n", i)
+			intf = &i
+			break
+		}
+	}
+	if intf == nil {
+		return nil, fmt.Errorf("usb: unknown interface %02x", ifNum)
+	}

 	var setAlternate bool
-	for _, c := range d.Configs {
-		if c.Config != conf {
-			continue
+	var ifs *InterfaceSetup
+	for i, s := range intf.Setups {
+		if s.Alternate == setNum {
+			setAlternate = i != 0
+			debug.Printf("found setup: %#v [default: %v]\n", s, !setAlternate)
+			ifs = &s
 		}
-		debug.Printf("found conf: %#v\n", c)
-		for _, i := range c.Interfaces {
-			if i.Number != iface {
-				continue
-			}
-			debug.Printf("found iface: %#v\n", i)
-			for i, s := range i.Setups {
-				if s.Alternate != setup {
-					continue
-				}
-				setAlternate = i != 0
-
-				debug.Printf("found setup: %#v [default: %v]\n", s, !setAlternate)
-				for _, e := range s.Endpoints {
-					debug.Printf("ep %02x search: %#v\n", epoint, s)
-					if e.Address != epoint {
-						continue
-					}
-					end.InterfaceSetup = s
-					end.EndpointInfo = e
-					goto found
-				}
-				return nil, fmt.Errorf("usb: unknown endpoint %02x", epoint)
-			}
-			return nil, fmt.Errorf("usb: unknown setup %02x", setup)
-		}
-		return nil, fmt.Errorf("usb: unknown interface %02x", iface)
 	}
-	return nil, fmt.Errorf("usb: unknown configuration %02x", conf)
+	if ifs == nil {
+		return nil, fmt.Errorf("usb: unknown setup %02x", setNum)
+	}

-found:
+	var ep *EndpointInfo
+	for _, e := range ifs.Endpoints {
+		if e.Address == epNum {
+			debug.Printf("found ep %02x in %#v\n", epNum, *ifs)
+			ep = &e
+		}
+	}
+	if ep == nil {
+		return nil, fmt.Errorf("usb: unknown endpoint %02x", epNum)
+	}
+
+	end := newEndpoint(d.handle, *ifs, *ep, d.ReadTimeout, d.WriteTimeout)

 	// 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 != cfgNum {
+		if err := libusb.setConfig(d.handle, cfgNum); 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, ifNum); err != nil {
+		return nil, fmt.Errorf("usb: claim: %s", err)
 	}

 	// Increment the claim count
 	d.lock.Lock()
-	d.claimed[iface]++
+	d.claimed[ifNum]++
 	d.lock.Unlock() // unlock immediately because the next calls may block

 	// 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, ifNum, setNum); err != nil {
+			return nil, fmt.Errorf("usb: setalt: %s", err)
 		}
 	}

@@ -194,26 +175,7 @@ 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 +183,12 @@ 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)
 }
--- a/usb/endpoint.go
+++ b/usb/endpoint.go
@@ -27,22 +27,14 @@ type Endpoint interface {
 	Info() EndpointInfo
 }

-type transferIntf interface {
-	submit() error
-	wait() (int, error)
-	free() error
-}
-
 type endpoint struct {
-	h *deviceHandle
+	h *libusbDevHandle

 	InterfaceSetup
 	EndpointInfo

 	readTimeout  time.Duration
 	writeTimeout time.Duration
-
-	newUSBTransfer func([]byte, time.Duration) (transferIntf, error)
 }

 func (e *endpoint) Read(buf []byte) (int, error) {
@@ -64,16 +56,12 @@ func (e *endpoint) Write(buf []byte) (int, error) {
 func (e *endpoint) Interface() InterfaceSetup { return e.InterfaceSetup }
 func (e *endpoint) Info() EndpointInfo        { return e.EndpointInfo }

-func (e *endpoint) newLibUSBTransfer(buf []byte, timeout time.Duration) (transferIntf, error) {
-	return newUSBTransfer(e.h, e.EndpointInfo, buf, timeout)
-}
-
 func (e *endpoint) transfer(buf []byte, timeout time.Duration) (int, error) {
 	if len(buf) == 0 {
 		return 0, nil
 	}

-	t, err := e.newUSBTransfer(buf, timeout)
+	t, err := newUSBTransfer(e.h, e.EndpointInfo, buf, timeout)
 	if err != nil {
 		return 0, err
 	}
@@ -90,12 +78,12 @@ func (e *endpoint) transfer(buf []byte, timeout time.Duration) (int, error) {
 	return n, nil
 }

-func newEndpoint(d *Device) *endpoint {
-	ep := &endpoint{
-		h:            (*deviceHandle)(d.handle),
-		readTimeout:  d.ReadTimeout,
-		writeTimeout: d.WriteTimeout,
+func newEndpoint(h *libusbDevHandle, s InterfaceSetup, e EndpointInfo, rt, wt time.Duration) *endpoint {
+	return &endpoint{
+		InterfaceSetup: s,
+		EndpointInfo:   e,
+		h:              h,
+		readTimeout:    rt,
+		writeTimeout:   wt,
 	}
-	ep.newUSBTransfer = ep.newLibUSBTransfer
-	return ep
 }
--- a/usb/endpoint_test.go
+++ b/usb/endpoint_test.go
@@ -15,23 +15,13 @@
 package usb

 import (
-	"errors"
 	"reflect"
 	"testing"
 	"time"
 )

-type fakeTransfer struct {
-	buf []byte
-	ret int
-	err error
-}
-
-func (t *fakeTransfer) submit() error      { return nil }
-func (t *fakeTransfer) wait() (int, error) { return t.ret, t.err }
-func (t *fakeTransfer) free() error        { return nil }
-
 func TestEndpoint(t *testing.T) {
+	defer func(i libusbIntf) { libusb = i }(libusb)
 	for _, epCfg := range []struct {
 		method string
 		InterfaceSetup
@@ -42,35 +32,55 @@ func TestEndpoint(t *testing.T) {
 	} {
 		t.Run(epCfg.method, func(t *testing.T) {
 			for _, tc := range []struct {
+				desc    string
 				buf     []byte
 				ret     int
-				err     error
+				status  TransferStatus
 				want    int
 				wantErr bool
 			}{
-				{buf: nil, ret: 10, want: 0},
-				{buf: make([]byte, 128), ret: 60, want: 60},
-				{buf: make([]byte, 128), ret: 10, err: errors.New("some error"), want: 10, wantErr: true},
+				{
+					desc: "empty buffer",
+					buf:  nil,
+					ret:  10,
+					want: 0,
+				},
+				{
+					desc: "128B buffer, 60 transferred",
+					buf:  make([]byte, 128),
+					ret:  60,
+					want: 60,
+				},
+				{
+					desc:    "128B buffer, 10 transferred and then error",
+					buf:     make([]byte, 128),
+					ret:     10,
+					status:  LIBUSB_TRANSFER_ERROR,
+					want:    10,
+					wantErr: true,
+				},
 			} {
-				ep := &endpoint{
-					InterfaceSetup: epCfg.InterfaceSetup,
-					EndpointInfo:   epCfg.EndpointInfo,
-					newUSBTransfer: func(buf []byte, timeout time.Duration) (transferIntf, error) {
-						return &fakeTransfer{buf: buf, ret: tc.ret, err: tc.err}, nil
-					},
-				}
+				lib := newFakeLibusb()
+				libusb = lib
+				ep := newEndpoint(nil, epCfg.InterfaceSetup, epCfg.EndpointInfo, time.Second, time.Second)
 				op, ok := reflect.TypeOf(ep).MethodByName(epCfg.method)
 				if !ok {
 					t.Fatalf("method %s not found in endpoint struct", epCfg.method)
 				}
+				go func() {
+					fakeT := lib.waitForSubmitted()
+					fakeT.length = tc.ret
+					fakeT.status = tc.status
+					close(fakeT.done)
+				}()
 				opv := op.Func.Interface().(func(*endpoint, []byte) (int, error))
 				got, err := opv(ep, tc.buf)
 				if (err != nil) != tc.wantErr {
-					t.Errorf("bulkInEP.Read(): got err: %v, err != nil is %v, want %v", err, err != nil, tc.wantErr)
+					t.Errorf("%s: bulkInEP.Read(): got err: %v, err != nil is %v, want %v", tc.desc, err, err != nil, tc.wantErr)
 					continue
 				}
 				if got != tc.want {
-					t.Errorf("bulkInEP.Read(): got %d bytes, want %d", got, tc.want)
+					t.Errorf("%s: bulkInEP.Read(): got %d bytes, want %d", tc.desc, got, tc.want)
 				}
 			}
 		})
--- a/usb/error.go
+++ b/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
--- a/usb/fakelibusb_test.go
+++ b/usb/fakelibusb_test.go
@@ -0,0 +1,85 @@
+// Copyright 2017 the gousb Authors.  All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package usb
+
+import (
+	"sync"
+	"time"
+)
+
+type fakeTransfer struct {
+	// done is the channel that needs to be closed when the transfer has finished.
+	done chan struct{}
+	// buf is the slice for reading/writing data between the submit() and wait() returning.
+	buf []byte
+	// status will be returned by wait() on this transfer
+	status TransferStatus
+	// length is the number of bytes used from the buffer (write) or available
+	// in the buffer (read).
+	length int
+}
+
+type fakeLibusb struct {
+	libusbIntf
+
+	mu sync.Mutex
+	// ts has a map of all allocated transfers, indexed by the pointer of
+	// underlying libusbTransfer.
+	ts map[*libusbTransfer]*fakeTransfer
+	// submitted receives a fakeTransfers when submit() is called.
+	submitted chan *fakeTransfer
+}
+
+func (f *fakeLibusb) alloc(_ *libusbDevHandle, _ uint8, _ TransferType, _ time.Duration, _ int, buf []byte) (*libusbTransfer, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	t := new(libusbTransfer)
+	f.ts[t] = &fakeTransfer{buf: buf}
+	return t, nil
+}
+
+func (f *fakeLibusb) submit(t *libusbTransfer, done chan struct{}) error {
+	f.mu.Lock()
+	ft := f.ts[t]
+	f.mu.Unlock()
+	ft.done = done
+	f.submitted <- ft
+	return nil
+}
+
+func (f *fakeLibusb) cancel(t *libusbTransfer) error { return nil }
+func (f *fakeLibusb) free(t *libusbTransfer) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	delete(f.ts, t)
+}
+
+func (f *fakeLibusb) data(t *libusbTransfer) (int, TransferStatus) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	return f.ts[t].length, f.ts[t].status
+}
+
+func (f *fakeLibusb) waitForSubmitted() *fakeTransfer {
+	return <-f.submitted
+}
+
+func newFakeLibusb() *fakeLibusb {
+	return &fakeLibusb{
+		ts:         make(map[*libusbTransfer]*fakeTransfer),
+		submitted:  make(chan *fakeTransfer, 10),
+		libusbIntf: libusbImpl{},
+	}
+}
--- a/usb/libusb.go
+++ b/usb/libusb.go
@@ -0,0 +1,388 @@
+// Copyright 2017 the gousb Authors.  All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package usb
+
+import (
+	"fmt"
+	"log"
+	"reflect"
+	"time"
+	"unsafe"
+)
+
+/*
+#cgo pkg-config: libusb-1.0
+#include <libusb.h>
+
+int compact_iso_data(struct libusb_transfer *xfer, unsigned char *status);
+int submit(struct libusb_transfer *xfer);
+*/
+import "C"
+
+type libusbContext C.libusb_context
+type libusbDevice C.libusb_device
+type libusbDevHandle C.libusb_device_handle
+type libusbTransfer C.struct_libusb_transfer
+type libusbIso C.struct_libusb_iso_packet_descriptor
+
+// libusbIntf is a set of trivial idiomatic Go wrappers around libusb C functions.
+// The underlying code is generally not testable or difficult to test,
+// since libusb interacts directly with the host USB stack.
+//
+// All functions here should operate on types defined on C.libusb* data types,
+// and occasionally on convenience data types (like TransferType or Descriptor).
+type libusbIntf interface {
+	// context
+	init() (*libusbContext, error)
+	handleEvents(*libusbContext, <-chan struct{})
+	getDevices(*libusbContext) ([]*libusbDevice, error)
+	exit(*libusbContext)
+	setDebug(*libusbContext, int)
+	openVIDPID(*libusbContext, int, int) (*libusbDevice, *libusbDevHandle, error)
+
+	// device
+	dereference(*libusbDevice)
+	getDeviceDesc(*libusbDevice) (*Descriptor, error)
+	open(*libusbDevice) (*libusbDevHandle, error)
+
+	close(*libusbDevHandle)
+	reset(*libusbDevHandle) error
+	control(*libusbDevHandle, time.Duration, uint8, uint8, uint16, uint16, []byte) (int, error)
+	getConfig(*libusbDevHandle) (uint8, error)
+	setConfig(*libusbDevHandle, uint8) error
+	getStringDesc(*libusbDevHandle, int) (string, error)
+	setAutoDetach(*libusbDevHandle, int) error
+
+	// interface
+	claim(*libusbDevHandle, uint8) error
+	release(*libusbDevHandle, uint8)
+	setAlt(*libusbDevHandle, uint8, uint8) error
+
+	// transfer
+	alloc(*libusbDevHandle, uint8, TransferType, time.Duration, int, []byte) (*libusbTransfer, error)
+	cancel(*libusbTransfer) error
+	submit(*libusbTransfer, chan struct{}) error
+	data(*libusbTransfer) (int, TransferStatus)
+	free(*libusbTransfer)
+	setIsoPacketLengths(*libusbTransfer, uint32)
+}
+
+// libusbImpl is an implementation of libusbIntf using real CGo-wrapped libusb.
+type libusbImpl struct{}
+
+func (libusbImpl) init() (*libusbContext, error) {
+	var ctx *C.libusb_context
+	if err := fromUSBError(C.libusb_init(&ctx)); err != nil {
+		return nil, err
+	}
+	return (*libusbContext)(ctx), nil
+}
+
+func (libusbImpl) handleEvents(c *libusbContext, done <-chan struct{}) {
+	tv := C.struct_timeval{tv_usec: 100e3}
+	for {
+		select {
+		case <-done:
+			return
+		default:
+		}
+		if errno := C.libusb_handle_events_timeout_completed((*C.libusb_context)(c), &tv, nil); errno < 0 {
+			log.Printf("handle_events: error: %s", usbError(errno))
+		}
+	}
+}
+
+func (libusbImpl) getDevices(ctx *libusbContext) ([]*libusbDevice, error) {
+	var list **C.libusb_device
+	cnt := C.libusb_get_device_list((*C.libusb_context)(ctx), &list)
+	if cnt < 0 {
+		return nil, fromUSBError(C.int(cnt))
+	}
+	var devs []*C.libusb_device
+	*(*reflect.SliceHeader)(unsafe.Pointer(&devs)) = reflect.SliceHeader{
+		Data: uintptr(unsafe.Pointer(list)),
+		Len:  int(cnt),
+		Cap:  int(cnt),
+	}
+	var ret []*libusbDevice
+	for _, d := range devs {
+		ret = append(ret, (*libusbDevice)(d))
+	}
+	// devices will be dereferenced later, during close.
+	C.libusb_free_device_list(list, 0)
+	return ret, nil
+}
+
+func (libusbImpl) exit(c *libusbContext) {
+	C.libusb_exit((*C.libusb_context)(c))
+}
+
+func (libusbImpl) setDebug(c *libusbContext, lvl int) {
+	C.libusb_set_debug((*C.libusb_context)(c), C.int(lvl))
+}
+
+func (libusbImpl) openVIDPID(ctx *libusbContext, vid, pid int) (*libusbDevice, *libusbDevHandle, error) {
+	h := C.libusb_open_device_with_vid_pid((*C.libusb_context)(ctx), (C.uint16_t)(vid), (C.uint16_t)(pid))
+	if h == nil {
+		return nil, nil, ERROR_NOT_FOUND
+	}
+	dev := C.libusb_get_device(h)
+	if dev == nil {
+		return nil, nil, ERROR_NO_DEVICE
+	}
+	C.libusb_ref_device(dev)
+	return (*libusbDevice)(dev), (*libusbDevHandle)(h), nil
+}
+
+func (libusbImpl) getDeviceDesc(d *libusbDevice) (*Descriptor, error) {
+	var desc C.struct_libusb_device_descriptor
+	if err := fromUSBError(C.libusb_get_device_descriptor((*C.libusb_device)(d), &desc)); err != nil {
+		return nil, err
+	}
+	// Enumerate configurations
+	var cfgs []ConfigInfo
+	for i := 0; i < int(desc.bNumConfigurations); i++ {
+		var cfg *C.struct_libusb_config_descriptor
+		if err := fromUSBError(C.libusb_get_config_descriptor((*C.libusb_device)(d), C.uint8_t(i), &cfg)); err != nil {
+			return nil, err
+		}
+		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,
+			})
+		}
+		C.libusb_free_config_descriptor(cfg)
+		cfgs = append(cfgs, c)
+	}
+
+	return &Descriptor{
+		Bus:      uint8(C.libusb_get_bus_number((*C.libusb_device)(d))),
+		Address:  uint8(C.libusb_get_device_address((*C.libusb_device)(d))),
+		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
+}
+
+func (libusbImpl) dereference(d *libusbDevice) {
+	C.libusb_unref_device((*C.libusb_device)(d))
+}
+
+func (libusbImpl) open(d *libusbDevice) (*libusbDevHandle, error) {
+	var handle *C.libusb_device_handle
+	if err := fromUSBError(C.libusb_open((*C.libusb_device)(d), &handle)); err != nil {
+		return nil, err
+	}
+	return (*libusbDevHandle)(handle), nil
+}
+
+func (libusbImpl) close(d *libusbDevHandle) {
+	C.libusb_close((*C.libusb_device_handle)(d))
+}
+
+func (libusbImpl) reset(d *libusbDevHandle) error {
+	return fromUSBError(C.libusb_reset_device((*C.libusb_device_handle)(d)))
+}
+
+func (libusbImpl) control(d *libusbDevHandle, timeout time.Duration, rType, request uint8, val, idx uint16, data []byte) (int, error) {
+	dataSlice := (*reflect.SliceHeader)(unsafe.Pointer(&data))
+	n := C.libusb_control_transfer(
+		(*C.libusb_device_handle)(d),
+		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(timeout/time.Millisecond))
+	if n < 0 {
+		return int(n), fromUSBError(n)
+	}
+	return int(n), nil
+}
+
+func (libusbImpl) getConfig(d *libusbDevHandle) (uint8, error) {
+	var cfg C.int
+	if errno := C.libusb_get_configuration((*C.libusb_device_handle)(d), &cfg); errno < 0 {
+		return 0, fromUSBError(errno)
+	}
+	return uint8(cfg), nil
+}
+
+func (libusbImpl) setConfig(d *libusbDevHandle, cfg uint8) error {
+	return fromUSBError(C.libusb_set_configuration((*C.libusb_device_handle)(d), C.int(cfg)))
+}
+
+func (libusbImpl) getStringDesc(d *libusbDevHandle, index int) (string, error) {
+	// allocate 200-byte array limited the length of string descriptor
+	buf := 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(
+		(*C.libusb_device_handle)(d),
+		C.uint8_t(index),
+		(*C.uchar)(unsafe.Pointer(&buf[0])),
+		200)
+	if errno < 0 {
+		return "", fmt.Errorf("usb: getstr: %s", fromUSBError(errno))
+	}
+	return string(buf[:errno]), nil
+}
+
+func (libusbImpl) setAutoDetach(d *libusbDevHandle, val int) error {
+	err := fromUSBError(C.libusb_set_auto_detach_kernel_driver((*C.libusb_device_handle)(d), C.int(val)))
+	if err != nil && err != ERROR_NOT_SUPPORTED {
+		return err
+	}
+	return nil
+}
+
+func (libusbImpl) claim(d *libusbDevHandle, iface uint8) error {
+	return fromUSBError(C.libusb_claim_interface((*C.libusb_device_handle)(d), C.int(iface)))
+}
+
+func (libusbImpl) release(d *libusbDevHandle, iface uint8) {
+	C.libusb_release_interface((*C.libusb_device_handle)(d), C.int(iface))
+}
+
+func (libusbImpl) setAlt(d *libusbDevHandle, iface, setup uint8) error {
+	return fromUSBError(C.libusb_set_interface_alt_setting((*C.libusb_device_handle)(d), C.int(iface), C.int(setup)))
+}
+
+func (libusbImpl) alloc(d *libusbDevHandle, addr uint8, tt TransferType, timeout time.Duration, isoPackets int, buf []byte) (*libusbTransfer, error) {
+	xfer := C.libusb_alloc_transfer(C.int(isoPackets))
+	if xfer == nil {
+		return nil, fmt.Errorf("libusb_alloc_transfer(%d) failed", isoPackets)
+	}
+	xfer.dev_handle = (*C.libusb_device_handle)(d)
+	xfer.endpoint = C.uchar(addr)
+	xfer.timeout = C.uint(timeout / time.Millisecond)
+	xfer._type = C.uchar(tt)
+	xfer.num_iso_packets = C.int(isoPackets)
+	xfer.buffer = (*C.uchar)((unsafe.Pointer)(&buf[0]))
+	xfer.length = C.int(len(buf))
+	return (*libusbTransfer)(xfer), nil
+}
+
+func (libusbImpl) cancel(t *libusbTransfer) error {
+	return fromUSBError(C.libusb_cancel_transfer((*C.struct_libusb_transfer)(t)))
+}
+
+func (libusbImpl) submit(t *libusbTransfer, done chan struct{}) error {
+	t.user_data = (unsafe.Pointer)(&done)
+	return fromUSBError(C.submit((*C.struct_libusb_transfer)(t)))
+}
+
+func (libusbImpl) data(t *libusbTransfer) (int, TransferStatus) {
+	if TransferType(t._type) == TRANSFER_TYPE_ISOCHRONOUS {
+		var status TransferStatus
+		n := int(C.compact_iso_data((*C.struct_libusb_transfer)(t), (*C.uchar)(unsafe.Pointer(&status))))
+		return n, status
+	}
+	return int(t.actual_length), TransferStatus(t.status)
+}
+
+func (libusbImpl) free(t *libusbTransfer) {
+	C.libusb_free_transfer((*C.struct_libusb_transfer)(t))
+}
+
+func (libusbImpl) setIsoPacketLengths(t *libusbTransfer, length uint32) {
+	C.libusb_set_iso_packet_lengths((*C.struct_libusb_transfer)(t), C.uint(length))
+}
+
+// libusb is an injection point for tests
+var libusb libusbIntf = libusbImpl{}
+
+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)
+}
+
+// for benchmarking
+func libusbSetDebug(c *libusbContext, lvl int) {
+	C.libusb_set_debug((*C.libusb_context)(c), C.int(lvl))
+}
--- a/usb/libusb_cgo_benchmark_test.go
+++ b/usb/libusb_cgo_benchmark_test.go
@@ -0,0 +1,46 @@
+package usb
+
+import "testing"
+
+func BenchmarkCGo(b *testing.B) {
+	for _, bc := range []struct {
+		name  string
+		bfunc func(*libusbContext, int)
+	}{
+		{
+			name: "simple function",
+			bfunc: func(ctx *libusbContext, N int) {
+				for i := 0; i < N; i++ {
+					libusbSetDebug(ctx, i&1)
+				}
+			},
+		},
+		{
+			name: "method",
+			bfunc: func(ctx *libusbContext, N int) {
+				impl := libusbImpl{}
+				for i := 0; i < N; i++ {
+					impl.setDebug(ctx, i&1)
+				}
+			},
+		},
+		{
+			name: "interface",
+			bfunc: func(ctx *libusbContext, N int) {
+				var intf libusbIntf = libusbImpl{}
+				for i := 0; i < N; i++ {
+					intf.setDebug(ctx, i&1)
+				}
+			},
+		},
+	} {
+		b.Run(bc.name, func(b *testing.B) {
+			ctx, err := libusbImpl{}.init()
+			if err != nil {
+				b.Fatalf("libusb_init() failed: %v", err)
+			}
+			b.ResetTimer()
+			bc.bfunc(ctx, b.N)
+		})
+	}
+}
--- a/usb/transfer.go
+++ b/usb/transfer.go
@@ -14,50 +14,14 @@

 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"
 	"runtime"
 	"sync"
 	"time"
-	"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)
-}
-
 type usbTransfer struct {
 	// mu protects the transfer state.
 	mu sync.Mutex
@@ -83,8 +47,7 @@ func (t *usbTransfer) submit() error {
 		return errors.New("transfer was already submitted and is not finished yet.")
 	}
 	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, t.done); err != nil {
 		return err
 	}
 	t.submitted = true
@@ -108,14 +71,7 @@ func (t *usbTransfer) wait() (n int, err error) {
 	case <-t.done:
 	}
 	t.submitted = false
-	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))))
-	default:
-		n = int(t.xfer.actual_length)
-		status = TransferStatus(t.xfer.status)
-	}
+	n, status := libusb.data(t.xfer)
 	if status != LIBUSB_TRANSFER_COMPLETED {
 		return n, status
 	}
@@ -130,15 +86,12 @@ 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 +103,7 @@ 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 +112,7 @@ 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 {
@@ -169,26 +122,17 @@ 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(dev, ei.Address, tt, timeout, isoPackets, buf)
+	if err != nil {
+		return nil, err
 	}

-	xfer.dev_handle = (*C.struct_libusb_device_handle)(dev)
-	xfer.timeout = C.uint(timeout / time.Millisecond)
-	xfer.endpoint = C.uchar(ei.Address)
-	xfer._type = C.uchar(tt)
-
-	xfer.buffer = (*C.uchar)((unsafe.Pointer)(&buf[0]))
-	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{
-		xfer: (*libusbTransfer)(xfer),
+		xfer: xfer,
 		buf:  buf,
 	}
 	runtime.SetFinalizer(t, func(t *usbTransfer) {
--- a/usb/transfer_fakelibusb_test.go
+++ b/usb/transfer_fakelibusb_test.go
@@ -1,56 +0,0 @@
-// Copyright 2017 the gousb Authors.  All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package usb
-
-import "sync"
-
-type fakeLibusb struct {
-	sync.Mutex
-	ts map[*libusbTransfer]chan struct{}
-}
-
-func (f *fakeLibusb) submit(t *libusbTransfer) usbError {
-	f.Lock()
-	defer f.Unlock()
-	if f.ts[t] == nil {
-		f.ts[t] = make(chan struct{})
-	}
-	close(f.ts[t])
-	return SUCCESS
-}
-
-func (f *fakeLibusb) cancel(t *libusbTransfer) usbError { return SUCCESS }
-
-func (f *fakeLibusb) waitForSubmit(t *usbTransfer) {
-	f.Lock()
-	if f.ts[t.xfer] == nil {
-		f.ts[t.xfer] = make(chan struct{})
-	}
-	ch := f.ts[t.xfer]
-	f.Unlock()
-	<-ch
-}
-
-func (f *fakeLibusb) runCallback(t *usbTransfer, cb func(*usbTransfer)) {
-	f.Lock()
-	defer f.Unlock()
-	delete(f.ts, t.xfer)
-	cb(t)
-	close(t.done)
-}
-
-func newFakeLibusb() *fakeLibusb {
-	return &fakeLibusb{ts: make(map[*libusbTransfer]chan struct{})}
-}
--- a/usb/transfer_test.go
+++ b/usb/transfer_test.go
@@ -17,7 +17,6 @@ package usb
 import (
 	"testing"
 	"time"
-	"unsafe"
 )

 func TestNewTransfer(t *testing.T) {
@@ -87,12 +86,10 @@ 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
@@ -109,24 +106,26 @@ func TestTransferProtocol(t *testing.T) {
 	}

 	go func() {
-		f.waitForSubmit(xfers[0])
-		f.runCallback(xfers[0], func(t *usbTransfer) {
-			t.xfer.actual_length = 5
-			t.xfer.status = uint32(SUCCESS)
-			copy(t.buf, []byte{1, 2, 3, 4, 5})
-		})
-	}()
-	go func() {
-		f.waitForSubmit(xfers[1])
-		f.runCallback(xfers[1], func(t *usbTransfer) {
-			t.xfer.actual_length = 99
-			t.xfer.status = uint32(SUCCESS)
-			copy(t.buf, []byte{12, 12, 12, 12, 12})
-		})
+		ft := f.waitForSubmitted()
+		ft.length = 5
+		ft.status = LIBUSB_TRANSFER_COMPLETED
+		copy(ft.buf, []byte{1, 2, 3, 4, 5})
+		close(ft.done)
+
+		ft = f.waitForSubmitted()
+		ft.length = 99
+		ft.status = LIBUSB_TRANSFER_COMPLETED
+		copy(ft.buf, []byte{12, 12, 12, 12, 12})
+		close(ft.done)
+
+		ft = f.waitForSubmitted()
+		ft.length = 123
+		ft.status = LIBUSB_TRANSFER_CANCELLED
+		close(ft.done)
 	}()

-	xfers[1].submit()
 	xfers[0].submit()
+	xfers[1].submit()
 	got, err := xfers[0].wait()
 	if err != nil {
 		t.Errorf("xfer#0.wait returned error %v, want nil", err)
@@ -142,13 +141,6 @@ func TestTransferProtocol(t *testing.T) {
 		t.Errorf("xfer#0.wait returned %d bytes, want %d", got, want)
 	}

-	go func() {
-		f.waitForSubmit(xfers[1])
-		f.runCallback(xfers[1], func(t *usbTransfer) {
-			t.xfer.actual_length = 123
-			t.xfer.status = uint32(LIBUSB_TRANSFER_CANCELLED)
-		})
-	}()
 	xfers[1].submit()
 	xfers[1].cancel()
 	got, err = xfers[1].wait()
@@ -165,66 +157,3 @@ func TestTransferProtocol(t *testing.T) {
 		x.free()
 	}
 }
-
-func TestIsoPackets(t *testing.T) {
-	origSubmit, origCancel := cSubmit, cCancel
-	defer func() { cSubmit, cCancel = origSubmit, origCancel }()
-
-	f := newFakeLibusb()
-	cSubmit = f.submit
-	cCancel = f.cancel
-
-	xfer, err := newUSBTransfer(nil, EndpointInfo{
-		Address:       0x82,
-		Attributes:    uint8(TRANSFER_TYPE_ISOCHRONOUS),
-		MaxPacketSize: 3<<11 + 1024,
-		MaxIsoPacket:  3 * 1024,
-		PollInterval:  1,
-	}, make([]byte, 15000), time.Second)
-	if err != nil {
-		t.Fatalf("newUSBTransfer: %v", err)
-	}
-
-	// 15000 / (3*1024) = 4.something, rounded up to 5
-	if got, want := int(xfer.xfer.num_iso_packets), 5; got != want {
-		t.Fatalf("newUSBTransfer: got %d iso packets, want %d", got, want)
-	}
-
-	go func() {
-		f.waitForSubmit(xfer)
-		f.runCallback(xfer, func(x *usbTransfer) {
-			x.xfer.actual_length = 1234 // meaningless for iso transfers
-			x.xfer.status = uint32(LIBUSB_TRANSFER_TIMED_OUT)
-			for i := 0; i < int(xfer.xfer.num_iso_packets); i++ {
-				// this is a horrible calculation.
-				// libusb_transfer uses a flexible array for the iso packet
-				// descriptors at the end of the transfer struct.
-				// The only way to get access to the elements of that array
-				// is to use pointer arithmetic.
-				// Calculate the offset of the first descriptor in the struct,
-				// then move by sizeof(iso descriptor) for num_iso_packets.
-				desc := (*libusbIso)(unsafe.Pointer(uintptr(unsafe.Pointer(x.xfer)) + libusbIsoOffset + uintptr(i*libusbIsoSize)))
-				// max iso packet = 3 * 1024
-				if desc.length != 3*1024 {
-					t.Errorf("iso pkt length: got %d, want %d", desc.length, 3*1024)
-				}
-				desc.actual_length = 100
-				// packets 0..2 are successful, packet 3 is timed out
-				if i != 4 {
-					desc.status = uint32(LIBUSB_TRANSFER_COMPLETED)
-				} else {
-					desc.status = uint32(LIBUSB_TRANSFER_TIMED_OUT)
-				}
-			}
-		})
-	}()
-
-	xfer.submit()
-	got, err := xfer.wait()
-	if err == nil {
-		t.Error("Iso transfer: got nil error, want non-nil")
-	}
-	if want := 4 * 100; got != want {
-		t.Errorf("Iso transfer: got %d bytes, want %d", got, want)
-	}
-}
--- a/usb/usb.go
+++ b/usb/usb.go
@@ -16,54 +16,26 @@
 // Package usb provides a wrapper around libusb-1.0.
 package usb

-// #cgo pkg-config: libusb-1.0
-// #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 +44,30 @@ 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 +76,14 @@ 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 +94,7 @@ func (c *Context) OpenDeviceWithVidPid(vid, pid int) (*Device, error) {
 func (c *Context) Close() error {
 	c.done <- struct{}{}
 	if c.ctx != nil {
-		C.libusb_exit(c.ctx)
+		libusb.exit(c.ctx)
 	}
 	c.ctx = nil
 	return nil