Start decoding descriptor in Go, rather than relying on libusb helper

functions. Descriptor format is defined explicitly by the USB spec.

descriptors_test.go

@@ -0,0 +1,76 @@
+// Copyright 2017 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
+
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"reflect"
+	"testing"
+)
+
+func bytesFromHexFile(path string) ([]byte, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("Open(): %v", err)
+	}
+	defer f.Close()
+	hexData, err := ioutil.ReadAll(f)
+	if err != nil {
+		return nil, fmt.Errorf("ReadAll(): %v", err)
+	}
+	hexData = bytes.TrimSpace(hexData)
+	if len(hexData)%2 == 1 {
+		return nil, fmt.Errorf("hex data file has %d characters, expected an even number", len(hexData))
+	}
+	data := make([]byte, len(hexData)/2)
+	_, err = hex.Decode(data, hexData)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode hex data: %v", err)
+	}
+	return data, nil
+}
+
+func TestDeviceDescriptor(t *testing.T) {
+	path := "testdata/mouse_device_desc.hex"
+	descData, err := bytesFromHexFile(path)
+	if err != nil {
+		t.Fatalf("loading data from %q failed: %v", path, err)
+	}
+
+	got, err := deviceDescFromBytes(descData)
+	if err != nil {
+		t.Fatalf("failed to decode device descriptor from %q: %v", path, err)
+	}
+
+	// based on device descriptor as presented in mouse_lsusb.txt
+	want := &DeviceDesc{
+		Spec:                 Version(2, 0),
+		Class:                ClassPerInterface,
+		SubClass:             ClassPerInterface,
+		Protocol:             Protocol(0),
+		MaxControlPacketSize: 32,
+		Vendor:               ID(0x046d),
+		Product:              ID(0xc526),
+		Device:               Version(5, 0),
+		Configs:              make(map[int]ConfigDesc),
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("Got descriptor: %+v\nwant: %+v", got, want)
+	}
+}