guid: Improve version and variant handling

Signed-off-by: Kevin Parsons <kevpar@microsoft.com>

pkg/guid/guid.go

@@ -52,10 +52,11 @@ func NewV4() (GUID, error) {
 		return GUID{}, err
 	}
 
-	b[6] = (b[6] & 0x0f) | 0x40 // Version 4 (randomly generated)
-	b[8] = (b[8] & 0x3f) | 0x80 // RFC4122 variant
+	g := FromArray(b)
+	g.setVersion(4) // Version 4 means randomly generated.
+	g.setVariant(VariantRFC4122)
 
-	return FromArray(b), nil
+	return g, nil
 }
 
 func fromArray(b [16]byte, order binary.ByteOrder) GUID {
@@ -150,6 +151,25 @@ func FromString(s string) (GUID, error) {
 	return g, nil
 }
 
+func (g *GUID) setVariant(v Variant) {
+	d := g.Data4[0]
+	switch v {
+	case VariantNCS:
+		d = (d & 0x7f)
+	case VariantRFC4122:
+		d = (d & 0x3f) | 0x80
+	case VariantMicrosoft:
+		d = (d & 0x1f) | 0xc0
+	case VariantFuture:
+		d = (d & 0x0f) | 0xe0
+	case VariantUnknown:
+		fallthrough
+	default:
+		panic(fmt.Sprintf("invalid variant: %d", v))
+	}
+	g.Data4[0] = d
+}
+
 // Variant returns the GUID variant, as defined in RFC 4122.
 func (g GUID) Variant() Variant {
 	b := g.Data4[0]
@@ -165,6 +185,10 @@ func (g GUID) Variant() Variant {
 	return VariantUnknown
 }
 
+func (g *GUID) setVersion(v Version) {
+	g.Data3 = (g.Data3 & 0x0fff) | (uint16(v) << 12)
+}
+
 // Version returns the GUID version, as defined in RFC 4122.
 func (g GUID) Version() Version {
 	return Version((g.Data3 & 0xF000) >> 12)

pkg/guid/guid_test.go

@@ -22,6 +22,78 @@ func mustFromString(t *testing.T, s string) GUID {
 	return g
 }
 
+func Test_Variant(t *testing.T) {
+	type testCase struct {
+		g GUID
+		v Variant
+	}
+	testCases := []testCase{
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-0fdd-b6761fc7dcc0"), VariantNCS},
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-7fdd-b6761fc7dcc0"), VariantNCS},
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-bfdd-b6761fc7dcc0"), VariantRFC4122},
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-9fdd-b6761fc7dcc0"), VariantRFC4122},
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-cfdd-b6761fc7dcc0"), VariantMicrosoft},
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-dfdd-b6761fc7dcc0"), VariantMicrosoft},
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-efdd-b6761fc7dcc0"), VariantFuture},
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-ffdd-b6761fc7dcc0"), VariantFuture},
+	}
+	for _, tc := range testCases {
+		actualVariant := tc.g.Variant()
+		if actualVariant != tc.v {
+			t.Fatalf("Variant is not correct.\nExpected: %d\nActual: %d\nGUID: %s", tc.v, actualVariant, tc.g)
+		}
+	}
+}
+
+func Test_SetVariant(t *testing.T) {
+	testCases := []Variant{
+		VariantNCS,
+		VariantRFC4122,
+		VariantMicrosoft,
+		VariantFuture,
+	}
+	g := mustFromString(t, "f5cbc1a9-4cba-45a0-bfdd-b6761fc7dcc0")
+	for _, tc := range testCases {
+		t.Logf("Test case: %d", tc)
+		g.setVariant(tc)
+		if g.Variant() != tc {
+			t.Fatalf("Variant is incorrect.\nExpected: %d\nActual: %d", tc, g.Variant())
+		}
+	}
+}
+
+func Test_Version(t *testing.T) {
+	type testCase struct {
+		g GUID
+		v Version
+	}
+	testCases := []testCase{
+		{mustFromString(t, "f5cbc1a9-4cba-15a0-0fdd-b6761fc7dcc0"), 1},
+		{mustFromString(t, "f5cbc1a9-4cba-25a0-0fdd-b6761fc7dcc0"), 2},
+		{mustFromString(t, "f5cbc1a9-4cba-35a0-0fdd-b6761fc7dcc0"), 3},
+		{mustFromString(t, "f5cbc1a9-4cba-45a0-0fdd-b6761fc7dcc0"), 4},
+		{mustFromString(t, "f5cbc1a9-4cba-55a0-0fdd-b6761fc7dcc0"), 5},
+	}
+	for _, tc := range testCases {
+		actualVersion := tc.g.Version()
+		if actualVersion != tc.v {
+			t.Fatalf("Version is not correct.\nExpected: %d\nActual: %d\nGUID: %s", tc.v, actualVersion, tc.g)
+		}
+	}
+}
+
+func Test_SetVersion(t *testing.T) {
+	g := mustFromString(t, "f5cbc1a9-4cba-45a0-bfdd-b6761fc7dcc0")
+	for tc := 0; tc < 16; tc++ {
+		t.Logf("Test case: %d", tc)
+		v := Version(tc)
+		g.setVersion(v)
+		if g.Version() != v {
+			t.Fatalf("Version is incorrect.\nExpected: %d\nActual: %d", v, g.Version())
+		}
+	}
+}
+
 func Test_NewV4IsUnique(t *testing.T) {
 	g := mustNewV4(t)
 	g2 := mustNewV4(t)