3 files changed, 139 insertions, 0 deletions
diff --git a/dhcpv4/option_domain_name_server.go b/dhcpv4/option_domain_name_server.go
new file mode 100644
index 0000000..78aaf90
--- /dev/null
+++ b/dhcpv4/option_domain_name_server.go
@@ -0,0 +1,72 @@
+package dhcpv4
+
+import (
+	"fmt"
+	"net"
+)
+
+// This option implements the domain name server option
+// https://tools.ietf.org/html/rfc2132
+
+// OptDomainNameServer represents an option encapsulating the domain name
+// servers.
+type OptDomainNameServer struct {
+	NameServers []net.IP
+}
+
+// ParseOptDomainNameServer returns a new OptDomainNameServer from a byte
+// stream, or error if any.
+func ParseOptDomainNameServer(data []byte) (*OptDomainNameServer, error) {
+	if len(data) < 2 {
+		return nil, ErrShortByteStream
+	}
+	code := OptionCode(data[0])
+	if code != OptionDomainNameServer {
+		return nil, fmt.Errorf("expected code %v, got %v", OptionDomainNameServer, code)
+	}
+	length := int(data[1])
+	if length == 0 || length%4 != 0 {
+		return nil, fmt.Errorf("Invalid length: expected multiple of 4 larger than 4, got %v", length)
+	}
+	if len(data) < 2+length {
+		return nil, ErrShortByteStream
+	}
+	nameservers := make([]net.IP, 0, length%4)
+	for idx := 0; idx < length; idx += 4 {
+		b := data[2+idx : 2+idx+4]
+		nameservers = append(nameservers, net.IPv4(b[0], b[1], b[2], b[3]))
+	}
+	return &OptDomainNameServer{NameServers: nameservers}, nil
+}
+
+// Code returns the option code.
+func (o *OptDomainNameServer) Code() OptionCode {
+	return OptionDomainNameServer
+}
+
+// ToBytes returns a serialized stream of bytes for this option.
+func (o *OptDomainNameServer) ToBytes() []byte {
+	ret := []byte{byte(o.Code()), byte(o.Length())}
+	for _, ns := range o.NameServers {
+		ret = append(ret, ns...)
+	}
+	return ret
+}
+
+// String returns a human-readable string.
+func (o *OptDomainNameServer) String() string {
+	var servers string
+	for idx, ns := range o.NameServers {
+		servers += ns.String()
+		if idx < len(o.NameServers)-1 {
+			servers += ", "
+		}
+	}
+	return fmt.Sprintf("Domain Name Servers -> %v", servers)
+}
+
+// Length returns the length of the data portion (excluding option code an byte
+// length).
+func (o *OptDomainNameServer) Length() int {
+	return len(o.NameServers) * 4
+}
diff --git a/dhcpv4/option_domain_name_server_test.go b/dhcpv4/option_domain_name_server_test.go
new file mode 100644
index 0000000..c801cb6
--- /dev/null
+++ b/dhcpv4/option_domain_name_server_test.go
@@ -0,0 +1,65 @@
+package dhcpv4
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOptDomainNameServerInterfaceMethods(t *testing.T) {
+	servers := []net.IP{
+		net.IPv4(192, 168, 0, 10),
+		net.IPv4(192, 168, 0, 20),
+	}
+	o := OptDomainNameServer{NameServers: servers}
+	require.Equal(t, OptionDomainNameServer, o.Code(), "Code")
+	require.Equal(t, net.IPv4len*len(servers), o.Length(), "Length")
+	require.Equal(t, servers, o.NameServers, "NameServers")
+}
+
+func TestParseOptDomainNameServer(t *testing.T) {
+	data := []byte{
+		byte(OptionDomainNameServer),
+		8,               // Length
+		192, 168, 0, 10, // DNS #1
+		192, 168, 0, 20, // DNS #2
+	}
+	o, err := ParseOptDomainNameServer(data)
+	require.NoError(t, err)
+	servers := []net.IP{
+		net.IPv4(192, 168, 0, 10),
+		net.IPv4(192, 168, 0, 20),
+	}
+	require.Equal(t, &OptDomainNameServer{NameServers: servers}, o)
+
+	// Short byte stream
+	data = []byte{byte(OptionDomainNameServer)}
+	_, err = ParseOptDomainNameServer(data)
+	require.Error(t, err, "should get error from short byte stream")
+
+	// Wrong code
+	data = []byte{54, 2, 1, 1}
+	_, err = ParseOptDomainNameServer(data)
+	require.Error(t, err, "should get error from wrong code")
+
+	// Bad length
+	data = []byte{byte(OptionDomainNameServer), 6, 1, 1, 1}
+	_, err = ParseOptDomainNameServer(data)
+	require.Error(t, err, "should get error from bad length")
+}
+
+func TestParseOptDomainNameServerNoServers(t *testing.T) {
+	// RFC2132 requires that at least one DNS server IP is specified
+	data := []byte{
+		byte(OptionDomainNameServer),
+		0, // Length
+	}
+	_, err := ParseOptDomainNameServer(data)
+	require.Error(t, err)
+}
+
+func TestOptDomainNameServerString(t *testing.T) {
+	o := OptDomainNameServer{NameServers: []net.IP{net.IPv4(192, 168, 0, 1), net.IPv4(192, 168, 0, 10)}}
+	require.Equal(t, "Domain Name Servers -> 192.168.0.1, 192.168.0.10", o.String())
+}
diff --git a/dhcpv4/options.go b/dhcpv4/options.go
index 528c175..2bd26a5 100644
--- a/dhcpv4/options.go
+++ b/dhcpv4/options.go
@@ -56,6 +56,8 @@ func ParseOption(data []byte) (Option, error) {
 		opt, err = ParseOptClassIdentifier(data)
 	case OptionDomainName:
 		opt, err = ParseOptDomainName(data)
+	case OptionDomainNameServer:
+		opt, err = ParseOptDomainNameServer(data)
 	case OptionVendorIdentifyingVendorClass:
 		opt, err = ParseOptVIVC(data)
 	default: