Fail operations if Close was called before.

usb/config.go

@@ -69,6 +69,7 @@ func (c *Config) Close() error {
 	c.dev.mu.Lock()
 	defer c.dev.mu.Unlock()
 	c.dev.claimed = nil
+	c.dev = nil
 	return nil
 }
 
@@ -78,11 +79,17 @@ func (c *Config) String() string {
 
 // Control sends a control request to the device.
 func (c *Config) Control(rType, request uint8, val, idx uint16, data []byte) (int, error) {
+	if c.dev == nil {
+		return 0, fmt.Errorf("Control() called on %s after Close", c)
+	}
 	return libusb.control(c.dev.handle, c.ControlTimeout, rType, request, val, idx, data)
 }
 
 // Interface claims and returns an interface on a USB device.
 func (c *Config) Interface(intf, alt int) (*Interface, error) {
+	if c.dev == nil {
+		return nil, fmt.Errorf("Interface(%d, %d) called on %s after Close", intf, alt, c)
+	}
 	if intf < 0 || intf >= len(c.Info.Interfaces) {
 		return nil, fmt.Errorf("interface %d not found in %s. Interface number needs to be a 0-based index into the interface table, which has %d elements.", intf, c, len(c.Info.Interfaces))
 	}

usb/device.go

@@ -34,10 +34,13 @@ type Device struct {
 
 // Reset performs a USB port reset to reinitialize a device.
 func (d *Device) Reset() error {
+	if d.handle == nil {
+		return fmt.Errorf("Reset() called on %s after Close", d)
+	}
 	d.mu.Lock()
 	defer d.mu.Unlock()
 	if d.claimed != nil {
-		return fmt.Errorf("can't reset a device with an open configuration")
+		return fmt.Errorf("can't reset device %s while it has an active configuration %s", d, d.claimed)
 	}
 	return libusb.reset(d.handle)
 }
@@ -45,6 +48,9 @@ func (d *Device) Reset() error {
 // ActiveConfig returns the config id (not the index) of the active configuration.
 // This corresponds to the ConfigInfo.Config field.
 func (d *Device) ActiveConfig() (int, error) {
+	if d.handle == nil {
+		return 0, fmt.Errorf("ActiveConfig() called on %s after Close", d)
+	}
 	ret, err := libusb.getConfig(d.handle)
 	return int(ret), err
 }
@@ -55,6 +61,9 @@ func (d *Device) ActiveConfig() (int, error) {
 // USB supports only one active config per device at a time. Config claims the
 // device before setting the desired config and keeps it locked until Close is called.
 func (d *Device) Config(cfgNum int) (*Config, error) {
+	if d.handle == nil {
+		return nil, fmt.Errorf("Config(%d) called on %s after Close", cfgNum, d)
+	}
 	cfg := &Config{
 		dev:     d,
 		claimed: make(map[int]bool),
@@ -82,7 +91,7 @@ func (d *Device) Config(cfgNum int) (*Config, error) {
 // Close closes the device.
 func (d *Device) Close() error {
 	if d.handle == nil {
-		return fmt.Errorf("double close on device %s", d)
+		return nil
 	}
 	d.mu.Lock()
 	defer d.mu.Unlock()
@@ -99,6 +108,9 @@ func (d *Device) Close() error {
 // descriptor string is converted to ASCII (non-ASCII characters are replaced
 // with "?").
 func (d *Device) GetStringDescriptor(descIndex int) (string, error) {
+	if d.handle == nil {
+		return "", fmt.Errorf("GetStringDescriptor(%d) called on %s after Close", descIndex, d)
+	}
 	return libusb.getStringDesc(d.handle, descIndex)
 }
 
@@ -107,6 +119,9 @@ func (d *Device) GetStringDescriptor(descIndex 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 {
+	if d.handle == nil {
+		return fmt.Errorf("SetAutoDetach(%v) called on %s after Close", autodetach, d)
+	}
 	var autodetachInt int
 	switch autodetach {
 	case true:

usb/device_test.go

@@ -50,4 +50,12 @@ func TestOpenEndpoint(t *testing.T) {
 	if want := fakeDevices[1].Configs[0].Interfaces[1].AltSettings[1].Endpoints[1]; !reflect.DeepEqual(got.Info, want) {
 		t.Errorf("InEndpoint(cfg=1, if=1, alt=1, ep=6IN): got %+v, want %+v", got, want)
 	}
+
+	if err := cfg.Close(); err == nil {
+		t.Fatalf("cfg.Close(): returned nil, want non nil, because the Interface was not release.")
+	}
+	if err := dev.Close(); err == nil {
+		t.Fatalf("dev.Close(): returned nil, want non nil, because the Config was not released.")
+	}
+	intf.Close()
 }

usb/interface.go

@@ -71,10 +71,14 @@ func (i *Interface) String() string {
 
 // Close releases the interface.
 func (i *Interface) Close() {
+	if i.config == nil {
+		return
+	}
 	libusb.release(i.config.dev.handle, uint8(i.Setting.Number))
 	i.config.mu.Lock()
 	defer i.config.mu.Unlock()
 	delete(i.config.claimed, i.Setting.Number)
+	i.config = nil
 }
 
 func (i *Interface) openEndpoint(epNum int) (*endpoint, error) {
@@ -100,6 +104,9 @@ func (i *Interface) openEndpoint(epNum int) (*endpoint, error) {
 
 // InEndpoint prepares an IN endpoint for transfer.
 func (i *Interface) InEndpoint(epNum int) (*InEndpoint, error) {
+	if i.config == nil {
+		return nil, fmt.Errorf("InEndpoint(%d) called on %s after Close", epNum, i)
+	}
 	ep, err := i.openEndpoint(epNum)
 	if err != nil {
 		return nil, err
@@ -114,6 +121,9 @@ func (i *Interface) InEndpoint(epNum int) (*InEndpoint, error) {
 
 // OutEndpoint prepares an OUT endpoint for transfer.
 func (i *Interface) OutEndpoint(epNum int) (*OutEndpoint, error) {
+	if i.config == nil {
+		return nil, fmt.Errorf("OutEndpoint(%d) called on %s after Close", epNum, i)
+	}
 	ep, err := i.openEndpoint(epNum)
 	if err != nil {
 		return nil, err