Better error messages.

Update rawread to use the new endpoint interface.

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()

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)

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,