From 9623c1ba8d7f03d6e9ce83b40a1abb3da809bd2f Mon Sep 17 00:00:00 2001
From: Sebastian Zagrodzki <sebek@zagrodzki.net>
Date: Sat, 6 May 2017 00:20:43 +0200
Subject: [PATCH] replace ActiveConfig with ActiveConfigNum. Add a Default()
 helper that simplifies setup for uncomplicated USB devices.

---
 device.go      | 33 +++++++++++++++++++++++++++------
 device_test.go |  6 +++---
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/device.go b/device.go
index 203371c..2dd1283 100644
--- a/device.go
+++ b/device.go
@@ -88,9 +88,10 @@ func (d *Device) Reset() error {
 	return libusb.reset(d.handle)
 }
 
-// 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) {
+// ActiveConfigNum returns the config id of the active configuration.
+// The value corresponds to the ConfigInfo.Config field of one of the
+// ConfigInfos of this Device.
+func (d *Device) ActiveConfigNum() (int, error) {
 	if d.handle == nil {
 		return 0, fmt.Errorf("ActiveConfig() called on %s after Close", d)
 	}
@@ -99,10 +100,11 @@ func (d *Device) ActiveConfig() (int, error) {
 }
 
 // Config returns a USB device set to use a particular config.
-// The cfg provided is the config id (not the index) of the configuration to set,
-// which corresponds to the ConfigInfo.Config field.
+// The cfgNum provided is the config id (not the index) of the configuration to
+// set, which corresponds to the ConfigInfo.Config field.
 // 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.
+// 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)
@@ -125,6 +127,25 @@ func (d *Device) Config(cfgNum int) (*Config, error) {
 	return cfg, nil
 }
 
+// Default opens interface #0 with alternate setting #0 of the currently active
+// config. It's intended as a shortcut for devices that have the simplest
+// interface of a single config, interface and alternate setting.
+func (d *Device) Default() (*Interface, error) {
+	cfgNum, err := d.ActiveConfigNum()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get active config number of device %s: %v", d, err)
+	}
+	cfg, err := d.Config(cfgNum)
+	if err != nil {
+		return nil, fmt.Errorf("failed to claim config %d of device %s: %v", cfgNum, d, err)
+	}
+	intf, err := cfg.Interface(0, 0)
+	if err != nil {
+		return nil, fmt.Errorf("failed to select interface #%d alternate setting %d of config %d of device %s: %v", 0, 0, cfgNum, d, err)
+	}
+	return intf, nil
+}
+
 // Close closes the device.
 func (d *Device) Close() error {
 	if d.handle == nil {
diff --git a/device_test.go b/device_test.go
index a157dfd..a6b9777 100644
--- a/device_test.go
+++ b/device_test.go
@@ -47,10 +47,10 @@ func TestClaimAndRelease(t *testing.T) {
 		t.Fatalf("%s.Config(1): %v", dev, err)
 	}
 	defer cfg.Close()
-	if got, err := dev.ActiveConfig(); err != nil {
-		t.Errorf("%s.ActiveConfig(): got error %v, want nil", dev, err)
+	if got, err := dev.ActiveConfigNum(); err != nil {
+		t.Errorf("%s.ActiveConfigNum(): got error %v, want nil", dev, err)
 	} else if got != cfgNum {
-		t.Errorf("%s.ActiveConfig(): got %d, want %d", dev, got, cfgNum)
+		t.Errorf("%s.ActiveConfigNum(): got %d, want %d", dev, got, cfgNum)
 	}
 
 	intf, err := cfg.Interface(if1Num, alt1Num)