Hotplug

constants.go

@@ -256,3 +256,15 @@ const (
 
 // Milliamperes is a unit of electric current consumption.
 type Milliamperes uint
+
+// HotplugEventType identifies the type of the hotplug event.
+type HotplugEventType uint
+
+// Hotplug events.
+const (
+	HotplugEventDeviceArrived HotplugEventType = C.LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED
+	HotplugEventDeviceLeft    HotplugEventType = C.LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT
+	HotplugEventAny           HotplugEventType = HotplugEventDeviceArrived | HotplugEventDeviceLeft
+)
+
+const hotplugMatchAny = C.LIBUSB_HOTPLUG_MATCH_ANY

fakelibusb_test.go

@@ -209,6 +209,12 @@ func (f *fakeLibusb) empty() bool {
 	return len(f.submitted) == 0
 }
 
+func (f *fakeLibusb) registerHotplugCallback(ctx *libusbContext, events HotplugEventType, enumerate bool, vendorId int32, productId int32, devClass int32, fn libusbHotplugCallback) (func(), error) {
+	// TODO: implement
+	return func() {
+	}, nil
+}
+
 func newFakeLibusb() *fakeLibusb {
 	fl := &fakeLibusb{
 		fakeDevices: make(map[*libusbDevice]*fakeDevice),

hotplug.c

@@ -0,0 +1,32 @@
+// Copyright 2013 Google Inc.  All rights reserved.
+// Copyright 2016 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.
+
+#include <libusb.h>
+#include "_cgo_export.h"
+
+int gousb_hotplug_register_callback(
+	libusb_context* ctx,
+	libusb_hotplug_event events,
+	libusb_hotplug_flag flags,
+	int vid,
+	int pid,
+	int dev_class,
+	void *user_data,
+	libusb_hotplug_callback_handle *handle
+) {
+	return libusb_hotplug_register_callback(
+		ctx, events, flags, vid, pid, dev_class, (libusb_hotplug_callback_fn)(goHotplugCallback), user_data, handle
+	);
+}

hotplug.go

@@ -0,0 +1,121 @@
+// Copyright 2013 Google Inc.  All rights reserved.
+// Copyright 2016 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 gousb
+
+type HotplugEvent interface {
+	// Type returns the event's type (HotplugEventDeviceArrived or HotplugEventDeviceLeft).
+	Type() HotplugEventType
+	// IsEnumerated returns true if the device was already plugged in when the callback was registered.
+	IsEnumerated() bool
+	// DeviceDesc returns the device's descriptor.
+	DeviceDesc() (*DeviceDesc, error)
+	// Open opens the device.
+	Open() (*Device, error)
+	// Deregister deregisters the callback registration after the callback function returns.
+	Deregister()
+}
+
+// RegisterHotplug registers a hotplug callback function.
+// The callback will receive arrive events for all currently plugged in devices.
+// These events will return true from IsEnumerated().
+// Note that events are delivered concurrently. You may receive arrive and leave events
+// concurrently with enumerated arrive events. You may also receive arrive events twice
+// for the same device, and you may receive a leave event for a device for which
+// you never received an arrive event.
+func (c *Context) RegisterHotplug(fn func(HotplugEvent)) (func(), error) {
+	dereg, err := c.libusb.registerHotplugCallback(c.ctx, HotplugEventAny, false, hotplugMatchAny, hotplugMatchAny, hotplugMatchAny, func(ctx *libusbContext, dev *libusbDevice, eventType HotplugEventType) bool {
+		desc, err := c.libusb.getDeviceDesc(dev)
+		e := &hotplugEvent{
+			eventType:  eventType,
+			ctx:        c,
+			dev:        dev,
+			desc:       desc,
+			err:        err,
+			enumerated: false,
+		}
+		fn(e)
+		return e.deregister
+	})
+	if err != nil {
+		return nil, err
+	}
+	// enumerate devices
+	// this is done in gousb to properly support cancellation and to distinguish enumerated devices
+	list, err := c.libusb.getDevices(c.ctx)
+	if err != nil {
+		dereg()
+		return nil, err
+	}
+	for _, dev := range list {
+		desc, err := c.libusb.getDeviceDesc(dev)
+		e := &hotplugEvent{
+			eventType:  HotplugEventDeviceArrived,
+			ctx:        c,
+			dev:        dev,
+			desc:       desc,
+			err:        err,
+			enumerated: true,
+		}
+		fn(e)
+		if e.deregister {
+			dereg()
+			break
+		}
+	}
+	return dereg, nil
+}
+
+type hotplugEvent struct {
+	eventType  HotplugEventType
+	ctx        *Context
+	dev        *libusbDevice
+	desc       *DeviceDesc
+	err        error
+	enumerated bool
+	deregister bool
+}
+
+// Type returns the event's type (HotplugEventDeviceArrived or HotplugEventDeviceLeft).
+func (e *hotplugEvent) Type() HotplugEventType {
+	return e.eventType
+}
+
+// DeviceDesc returns the device's descriptor.
+func (e *hotplugEvent) DeviceDesc() (*DeviceDesc, error) {
+	return e.desc, e.err
+}
+
+// IsEnumerated returns true if the device was already plugged in when the callback was registered.
+func (e *hotplugEvent) IsEnumerated() bool {
+	return e.enumerated
+}
+
+// Open opens the device.
+func (e *hotplugEvent) Open() (*Device, error) {
+	if e.err != nil {
+		return nil, e.err
+	}
+	handle, err := e.ctx.libusb.open(e.dev)
+	if err != nil {
+		return nil, err
+	}
+	return &Device{handle: handle, ctx: e.ctx, Desc: e.desc}, nil
+}
+
+// Deregister deregisters the callback registration after the callback function returns.
+func (e *hotplugEvent) Deregister() {
+	e.deregister = true
+}

libusb.go

@@ -15,6 +15,7 @@
 package gousb
 
 import (
+	"errors"
 	"fmt"
 	"log"
 	"reflect"
@@ -26,11 +27,22 @@ import (
 /*
 #cgo pkg-config: libusb-1.0
 #include <libusb.h>
+#include <stdlib.h>
 
 int gousb_compact_iso_data(struct libusb_transfer *xfer, unsigned char *status);
 struct libusb_transfer *gousb_alloc_transfer_and_buffer(int bufLen, int numIsoPackets);
 void gousb_free_transfer_and_buffer(struct libusb_transfer *xfer);
 int submit(struct libusb_transfer *xfer);
+int gousb_hotplug_register_callback(
+	libusb_context* ctx,
+	libusb_hotplug_event events,
+	libusb_hotplug_flag flags,
+	int vid,
+	int pid,
+	int dev_class,
+	void *user_data,
+	libusb_hotplug_callback_handle *handle
+);
 */
 import "C"
 
@@ -124,6 +136,8 @@ func (ep libusbEndpoint) endpointDesc(dev *DeviceDesc) EndpointDesc {
 	return ei
 }
 
+type libusbHotplugCallback func(*libusbContext, *libusbDevice, HotplugEventType) bool
+
 // 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.
@@ -165,6 +179,9 @@ type libusbIntf interface {
 	data(*libusbTransfer) (int, TransferStatus)
 	free(*libusbTransfer)
 	setIsoPacketLengths(*libusbTransfer, uint32)
+
+	// hotplug
+	registerHotplugCallback(ctx *libusbContext, events HotplugEventType, enumerate bool, vendorID int32, productID int32, devClass int32, fn libusbHotplugCallback) (func(), error)
 }
 
 // libusbImpl is an implementation of libusbIntf using real CGo-wrapped libusb.
@@ -215,6 +232,17 @@ func (libusbImpl) getDevices(ctx *libusbContext) ([]*libusbDevice, error) {
 
 func (libusbImpl) exit(c *libusbContext) error {
 	C.libusb_exit((*C.libusb_context)(c))
+	// libusb_exit automatically deregisters hotplug callbacks,
+	// but we need to free the callback map.
+	hotplugCallbackMap.Lock()
+	if m, ok := hotplugCallbackMap.m[c]; ok {
+		for id := range m {
+			delete(m, id)
+			C.free(id)
+		}
+	}
+	delete(hotplugCallbackMap.m, c)
+	hotplugCallbackMap.Unlock()
 	return nil
 }
 
@@ -509,3 +537,90 @@ func newDevicePointer() *libusbDevice {
 func newFakeTransferPointer() *libusbTransfer {
 	return (*libusbTransfer)(unsafe.Pointer(C.malloc(1)))
 }
+
+// hotplugCallbackMap keeps a map of go callback functions for libusb hotplug callbacks
+// for each context.
+// When a context is closed with libusb_exit, its callbacks are automatically deregistered
+// by libusb, and they are removed from this map too.
+var hotplugCallbackMap = struct {
+	m map[*libusbContext]map[unsafe.Pointer]libusbHotplugCallback
+	sync.RWMutex
+}{
+	m: make(map[*libusbContext]map[unsafe.Pointer]libusbHotplugCallback),
+}
+
+//export goHotplugCallback
+func goHotplugCallback(ctx *C.libusb_context, device *C.libusb_device, event C.libusb_hotplug_event, userData unsafe.Pointer) C.int {
+	var fn libusbHotplugCallback
+	hotplugCallbackMap.RLock()
+	m, ok := hotplugCallbackMap.m[(*libusbContext)(ctx)]
+	if ok {
+		fn, ok = m[userData]
+	}
+	hotplugCallbackMap.RUnlock()
+	if !ok {
+		// This shouldn't happen. Deregister the callback.
+		return 1
+	}
+	dereg := fn((*libusbContext)(ctx), (*libusbDevice)(device), HotplugEventType(event))
+
+	if dereg {
+		hotplugCallbackMap.Lock()
+		m, ok := hotplugCallbackMap.m[(*libusbContext)(ctx)]
+		if ok {
+			delete(m, userData)
+			C.free(userData)
+		}
+		hotplugCallbackMap.Unlock()
+		return 1
+	}
+	return 0
+}
+
+func (libusbImpl) registerHotplugCallback(ctx *libusbContext, events HotplugEventType, enumerate bool, vendorID int32, productID int32, devClass int32, fn libusbHotplugCallback) (func(), error) {
+	// We must allocate memory to pass to C, since we can't pass a go pointer.
+	// We can use the resulting pointer as a map key instead of
+	// storing the map key inside the memory allocated.
+	id := C.malloc(1)
+	if id == nil {
+		panic(errors.New("Failed to allocate memory during callback registration"))
+	}
+	hotplugCallbackMap.Lock()
+	m, ok := hotplugCallbackMap.m[ctx]
+	if !ok {
+		hotplugCallbackMap.m[ctx] = make(map[unsafe.Pointer]libusbHotplugCallback)
+		m = hotplugCallbackMap.m[ctx]
+	}
+	m[id] = fn
+	hotplugCallbackMap.Unlock()
+
+	var flags C.libusb_hotplug_flag
+	if enumerate {
+		flags = C.LIBUSB_HOTPLUG_ENUMERATE
+	}
+	var handle C.libusb_hotplug_callback_handle
+
+	// TODO: figure out how to run deregister in callback.
+	// There's a race condition here, because the callback may be called before
+	// gousb_hotplug_register_callback returns, depending on libusb's implementation.
+	res := C.gousb_hotplug_register_callback((*C.libusb_context)(ctx), C.libusb_hotplug_event(events), flags, C.int(vendorID), C.int(productID), C.int(devClass), id, &handle)
+	err := fromErrNo(res)
+	if err != nil {
+		hotplugCallbackMap.Lock()
+		delete(hotplugCallbackMap.m[ctx], id)
+		hotplugCallbackMap.Unlock()
+		C.free(id)
+		return nil, err
+	}
+
+	return func() {
+		C.libusb_hotplug_deregister_callback((*C.libusb_context)(ctx), handle)
+		hotplugCallbackMap.Lock()
+		m, ok := hotplugCallbackMap.m[ctx]
+		if ok {
+			delete(m, id)
+			C.free(id)
+		}
+		hotplugCallbackMap.Unlock()
+	}, nil
+}