5 files changed, 114 insertions, 4 deletions
diff --git a/dhcpv4/dhcpv4.go b/dhcpv4/dhcpv4.go
index 2d73003..7965161 100644
--- a/dhcpv4/dhcpv4.go
+++ b/dhcpv4/dhcpv4.go
@@ -690,10 +690,10 @@ func (d *DHCPv4) ToBytes() []byte {
 	ret = append(ret, u16...)
 	binary.BigEndian.PutUint16(u16, d.flags)
 	ret = append(ret, u16...)
-	ret = append(ret, d.clientIPAddr[:4]...)
-	ret = append(ret, d.yourIPAddr[:4]...)
-	ret = append(ret, d.serverIPAddr[:4]...)
-	ret = append(ret, d.gatewayIPAddr[:4]...)
+	ret = append(ret, d.clientIPAddr.To4()...)
+	ret = append(ret, d.yourIPAddr.To4()...)
+	ret = append(ret, d.serverIPAddr.To4()...)
+	ret = append(ret, d.gatewayIPAddr.To4()...)
 	ret = append(ret, d.clientHwAddr[:16]...)
 	ret = append(ret, d.serverHostName[:64]...)
 	ret = append(ret, d.bootFileName[:128]...)
diff --git a/dhcpv4/option_subnet_mask.go b/dhcpv4/option_subnet_mask.go
new file mode 100644
index 0000000..f1ff4a4
--- /dev/null
+++ b/dhcpv4/option_subnet_mask.go
@@ -0,0 +1,56 @@
+package dhcpv4
+
+import (
+	"fmt"
+	"net"
+)
+
+// This option implements the subnet mask option
+// https://tools.ietf.org/html/rfc2132
+
+// OptSubnetMask represents an option encapsulating the subnet mask.
+type OptSubnetMask struct {
+	SubnetMask net.IPMask
+}
+
+// ParseOptSubnetMask returns a new OptSubnetMask from a byte
+// stream, or error if any.
+func ParseOptSubnetMask(data []byte) (*OptSubnetMask, error) {
+	if len(data) < 2 {
+		return nil, ErrShortByteStream
+	}
+	code := OptionCode(data[0])
+	if code != OptionSubnetMask {
+		return nil, fmt.Errorf("expected code %v, got %v", OptionSubnetMask, code)
+	}
+	length := int(data[1])
+	if length != 4 {
+		return nil, fmt.Errorf("unexepcted length: expected 4, got %v", length)
+	}
+	if len(data) < 6 {
+		return nil, ErrShortByteStream
+	}
+	return &OptSubnetMask{SubnetMask: net.IPMask(data[2 : 2+length])}, nil
+}
+
+// Code returns the option code.
+func (o *OptSubnetMask) Code() OptionCode {
+	return OptionSubnetMask
+}
+
+// ToBytes returns a serialized stream of bytes for this option.
+func (o *OptSubnetMask) ToBytes() []byte {
+	ret := []byte{byte(o.Code()), byte(o.Length())}
+	return append(ret, o.SubnetMask[:4]...)
+}
+
+// String returns a human-readable string.
+func (o *OptSubnetMask) String() string {
+	return fmt.Sprintf("Subnet Mask -> %v", o.SubnetMask.String())
+}
+
+// Length returns the length of the data portion (excluding option code an byte
+// length).
+func (o *OptSubnetMask) Length() int {
+	return 4
+}
diff --git a/dhcpv4/option_subnet_mask_test.go b/dhcpv4/option_subnet_mask_test.go
new file mode 100644
index 0000000..4cb8819
--- /dev/null
+++ b/dhcpv4/option_subnet_mask_test.go
@@ -0,0 +1,44 @@
+package dhcpv4
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOptSubnetMaskInterfaceMethods(t *testing.T) {
+	mask := net.IPMask{255, 255, 255, 0}
+	o := OptSubnetMask{SubnetMask: mask}
+
+	require.Equal(t, OptionSubnetMask, o.Code(), "Code")
+
+	expectedBytes := []byte{1, 4, 255, 255, 255, 0}
+	require.Equal(t, expectedBytes, o.ToBytes(), "ToBytes")
+
+	require.Equal(t, 4, o.Length(), "Length")
+
+	require.Equal(t, "Subnet Mask -> ffffff00", o.String(), "String")
+}
+
+func TestParseOptSubnetMask(t *testing.T) {
+	var (
+		o   *OptSubnetMask
+		err error
+	)
+	o, err = ParseOptSubnetMask([]byte{})
+	require.Error(t, err, "empty byte stream")
+
+	o, err = ParseOptSubnetMask([]byte{1, 4, 255})
+	require.Error(t, err, "short byte stream")
+
+	o, err = ParseOptSubnetMask([]byte{1, 3, 255, 255, 255, 0})
+	require.Error(t, err, "wrong IP length")
+
+	o, err = ParseOptSubnetMask([]byte{2, 4, 255, 255, 255})
+	require.Error(t, err, "wrong option code")
+
+	o, err = ParseOptSubnetMask([]byte{1, 4, 255, 255, 255, 0})
+	require.NoError(t, err)
+	require.Equal(t, net.IPMask{255, 255, 255, 0}, o.SubnetMask)
+}
diff --git a/dhcpv4/options.go b/dhcpv4/options.go
index 5e6da80..198fbb0 100644
--- a/dhcpv4/options.go
+++ b/dhcpv4/options.go
@@ -40,6 +40,8 @@ func ParseOption(data []byte) (Option, error) {
 		err error
 	)
 	switch OptionCode(data[0]) {
+	case OptionSubnetMask:
+		opt, err = ParseOptSubnetMask(data)
 	case OptionDHCPMessageType:
 		opt, err = ParseOptMessageType(data)
 	case OptionParameterRequestList:
diff --git a/dhcpv4/options_test.go b/dhcpv4/options_test.go
index 41ef415..01d7427 100644
--- a/dhcpv4/options_test.go
+++ b/dhcpv4/options_test.go
@@ -17,6 +17,14 @@ func TestParseOption(t *testing.T) {
 	require.Equal(t, 4, generic.Length())
 	require.Equal(t, "Name Server -> [192 168 1 254]", generic.String())
 
+	// Option subnet mask
+	option = []byte{1, 4, 255, 255, 255, 0}
+	opt, err = ParseOption(option)
+	require.NoError(t, err)
+	require.Equal(t, OptionSubnetMask, opt.Code(), "Code")
+	require.Equal(t, 4, opt.Length(), "Length")
+	require.Equal(t, option, opt.ToBytes(), "ToBytes")
+
 	// Message type
 	option = []byte{53, 1, 1}
 	opt, err = ParseOption(option)