fix: return UUID in middle endian only on SMBIOS >= 2.6

Changes the conversion logic used to return the UUID. Now only
converts to middle endian on smbios >= 2.6.

Signed-off-by: Brandon Nason <brandon.nason@gmail.com>

smbios/smbios.go

@@ -14,7 +14,11 @@ import (
 
 // SMBIOS represents the Sysytem Management BIOS.
 type SMBIOS struct {
-	Version    string
+	Version struct {
+		Major    int
+		Minor    int
+		Revision int
+	}
 	Structures []*smbios.Structure
 
 	BIOSInformationStructure            BIOSInformationStructure
@@ -47,8 +51,7 @@ func New() (*SMBIOS, error) {
 
 	s := &SMBIOS{}
 
-	major, minor, rev := ep.Version()
-	s.Version = fmt.Sprintf("%d.%d.%d", major, minor, rev)
+	s.Version.Major, s.Version.Minor, s.Version.Revision = ep.Version()
 
 	d := smbios.NewDecoder(rc)
 

smbios/system_information.go

@@ -16,6 +16,7 @@ import (
 // SystemInformationStructure represents the SMBIOS system information structure.
 type SystemInformationStructure struct {
 	smbios.Structure
+	smbios *SMBIOS
 }
 
 // WakeUp defines the Wake-up Type enum.
@@ -70,6 +71,8 @@ func (w WakeUp) String() string {
 
 // SystemInformation returns a `SystemInformationStructure`.
 func (s SMBIOS) SystemInformation() SystemInformationStructure {
+	s.SystemInformationStructure.smbios = &s
+
 	return s.SystemInformationStructure
 }
 
@@ -110,23 +113,42 @@ func (s SystemInformationStructure) WakeUpType() string {
 }
 
 // UUID returns the system UUID.
+// Return middle endian only if SBIOS version >= 2.6.
+// Reference: http://dnaeon.github.io/convert-big-endian-uuid-to-middle-endian/
 func (s SystemInformationStructure) UUID() (uid uuid.UUID, err error) {
-	b, err := toMiddleEndian(s.Formatted)
-	if err != nil {
-		return uid, fmt.Errorf("failed to convernt to middle endian: %w", err)
+	var b []byte
+	if s.smbios.Version.Major >= 3 || (s.smbios.Version.Major == 2 && s.smbios.Version.Minor >= 6) {
+		b, err = toMiddleEndian(s.Formatted)
+		if err != nil {
+			return uid, fmt.Errorf("failed to convert to middle endian: %w", err)
+		}
+	} else {
+		b, err = toBigEndian(s.Formatted)
+		if err != nil {
+			return uid, fmt.Errorf("failed to convert to big endian: %w", err)
+		}
 	}
 
 	uid, err = uuid.FromBytes(b)
 	if err != nil {
 		return uid, fmt.Errorf("invalid UUID: %w", err)
 	}
 
-	// TODO(andrewrynhard): Return middle endian only if SBIOS version > 2.6.
-	// Reference: http://dnaeon.github.io/convert-big-endian-uuid-to-middle-endian/
-
 	return uid, nil
 }
 
+func toBigEndian(formatted []byte) (b []byte, err error) {
+	buf := bytes.NewBuffer(make([]byte, 0, 16))
+
+	if err := binary.Write(buf, binary.BigEndian, formatted[4:20]); err != nil {
+		return nil, err
+	}
+
+	b = buf.Bytes()
+
+	return b, nil
+}
+
 func toMiddleEndian(formatted []byte) (b []byte, err error) {
 	buf := bytes.NewBuffer(make([]byte, 0, 16))