2 files changed, 37 insertions, 8 deletions
diff --git a/dhcpv4/option_userclass.go b/dhcpv4/option_userclass.go
index 307a128..fc088fa 100644
--- a/dhcpv4/option_userclass.go
+++ b/dhcpv4/option_userclass.go
@@ -66,6 +66,23 @@ func ParseOptUserClass(data []byte) (*OptUserClass, error) {
 			totalLength, len(data))
 	}
 
+	// Check if option is Microsoft style instead of RFC compliant, issue #113
+
+	// User-class options are, according to RFC3004, supposed to contain a set
+	// of strings each with length UC_Len_i. Here we check that this is so,
+	// by seeing if all the UC_Len_i lengths are consistent with the overall
+	// option length. If the lengths don't add up, we assume that the option
+	// is a single string and non RFC3004 compliant
+	var counting int
+	for counting < totalLength {
+		// UC_Len_i does not include itself so add 1
+		counting += int(data[counting]) + 1
+	}
+	if counting != totalLength {
+		opt.UserClasses = append(opt.UserClasses, data[:totalLength])
+		return &opt, nil
+	}
+
 	for i := 0; i < totalLength; {
 		ucLen := int(data[i])
 		if ucLen == 0 {
diff --git a/dhcpv4/option_userclass_test.go b/dhcpv4/option_userclass_test.go
index 492cabd..02b6f94 100644
--- a/dhcpv4/option_userclass_test.go
+++ b/dhcpv4/option_userclass_test.go
@@ -38,6 +38,26 @@ func TestParseOptUserClassNone(t *testing.T) {
 	require.Error(t, err)
 }
 
+func TestParseOptUserClassMicrosoft(t *testing.T) {
+	expected := []byte{
+		77, 9, 'l', 'i', 'n', 'u', 'x', 'b', 'o', 'o', 't',
+	}
+	opt, err := ParseOptUserClass(expected)
+	require.NoError(t, err)
+	require.Equal(t, 1, len(opt.UserClasses))
+	require.Equal(t, []byte("linuxboot"), opt.UserClasses[0])
+}
+
+func TestParseOptUserClassMicrosoftLongerThanLength(t *testing.T) {
+	expected := []byte{
+		77, 9, 'l', 'i', 'n', 'u', 'x', 'b', 'o', 'o', 't', 'X',
+	}
+	opt, err := ParseOptUserClass(expected)
+	require.NoError(t, err)
+	require.Equal(t, 1, len(opt.UserClasses))
+	require.Equal(t, []byte("linuxboot"), opt.UserClasses[0])
+}
+
 func TestParseOptUserClass(t *testing.T) {
 	expected := []byte{
 		77, 10, 9, 'l', 'i', 'n', 'u', 'x', 'b', 'o', 'o', 't',
@@ -75,14 +95,6 @@ func TestParseOptUserClassLongerThanLength(t *testing.T) {
 	require.Equal(t, []byte("linuxboot"), opt.UserClasses[0])
 }
 
-func TestParseOptUserClassShorterThanLength(t *testing.T) {
-	expected := []byte{
-		77, 10, 10, 'l', 'i', 'n', 'u', 'x', 'b', 'o', 'o', 't',
-	}
-	_, err := ParseOptUserClass(expected)
-	require.Error(t, err)
-}
-
 func TestParseOptUserClassShorterTotalLength(t *testing.T) {
 	expected := []byte{
 		77, 11, 10, 'l', 'i', 'n', 'u', 'x', 'b', 'o', 'o', 't',