From 80f3c60b2b452203919da1d36d98f48994fbaff8 Mon Sep 17 00:00:00 2001
From: Sebastian Zagrodzki <sebek@zagrodzki.net>
Date: Sat, 29 Apr 2017 00:41:26 +0200
Subject: [PATCH] Better error messages. Update rawread to use the new endpoint
 interface.

---
 rawread/main.go  | 15 +++++++++++++--
 usb/config.go    |  4 ++--
 usb/device.go    |  6 +++++-
 usb/interface.go |  2 +-
 4 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/rawread/main.go b/rawread/main.go
index c697e03..676ebdc 100644
--- a/rawread/main.go
+++ b/rawread/main.go
@@ -140,8 +140,19 @@ func main() {
 	}
 	dev := devs[0]
 
-	log.Printf("Connecting to endpoint %d...", *endpoint)
-	ep, err := dev.InEndpoint(*config, *iface, *alternate, *endpoint)
+	log.Printf("Setting configuration %d...", *config)
+	cfg, err := dev.Config(*config)
+	if err != nil {
+		log.Fatalf("dev.Config(%d): %v", *config, err)
+	}
+	log.Printf("Claiming interface %d (alt setting %d)...", *iface, *alternate)
+	intf, err := cfg.Interface(*iface, *alternate)
+	if err != nil {
+		log.Fatalf("cfg.Interface(%d, %d): %v", *iface, *alternate, err)
+	}
+
+	log.Printf("Using endpoint %d...", *endpoint)
+	ep, err := intf.InEndpoint(*endpoint)
 	if err != nil {
 		log.Fatalf("dev.InEndpoint(): %s", err)
 	}
diff --git a/usb/config.go b/usb/config.go
index ffb3f5c..37be692 100644
--- a/usb/config.go
+++ b/usb/config.go
@@ -94,11 +94,11 @@ func (c *Config) Interface(intf, alt int) (*Interface, error) {
 		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))
+		return nil, fmt.Errorf("interface %d not found in %s, available interfaces 0..%d", intf, c, len(c.Info.Interfaces)-1)
 	}
 	ifInfo := c.Info.Interfaces[intf]
 	if alt < 0 || alt >= len(ifInfo.AltSettings) {
-		return nil, fmt.Errorf("Inteface %d does not have alternate setting %d. Alt setting needs to be a 0-based index into the settings table, which has %d elements.", ifInfo, alt, len(ifInfo.AltSettings))
+		return nil, fmt.Errorf("alternate setting %d not found for %s in %s, available alt settings 0..%d", alt, ifInfo, c, len(ifInfo.AltSettings)-1)
 	}
 
 	c.mu.Lock()
diff --git a/usb/device.go b/usb/device.go
index bce1544..82889a3 100644
--- a/usb/device.go
+++ b/usb/device.go
@@ -77,7 +77,11 @@ func (d *Device) Config(cfgNum int) (*Config, error) {
 		}
 	}
 	if !found {
-		return nil, fmt.Errorf("configuration id %d not found in the descriptor of the device %s", cfg, d)
+		var cfgs []int
+		for _, c := range d.Descriptor.Configs {
+			cfgs = append(cfgs, c.Config)
+		}
+		return nil, fmt.Errorf("configuration id %d not found in the descriptor of the device %s. Available config ids: %v", cfgNum, d, cfgs)
 	}
 	if err := libusb.setConfig(d.handle, uint8(cfgNum)); err != nil {
 		return nil, fmt.Errorf("failed to set active config %d for the device %s: %v", cfgNum, d, err)
diff --git a/usb/interface.go b/usb/interface.go
index c956f60..3757c1e 100644
--- a/usb/interface.go
+++ b/usb/interface.go
@@ -93,7 +93,7 @@ func (i *Interface) openEndpoint(epNum int) (*endpoint, error) {
 		}
 	}
 	if !found {
-		return nil, fmt.Errorf("%s does not have endpoint number %d. Available endpoints: %v", epNum, i.Setting.Endpoints)
+		return nil, fmt.Errorf("%s does not have endpoint number %d. Available endpoints: %v", i, epNum, i.Setting.Endpoints)
 	}
 	return &endpoint{
 		InterfaceSetting: i.Setting,