From 1192794ac6a2ce5da220ae92be0c09968944e7e3 Mon Sep 17 00:00:00 2001
From: Brian Candler <b.candler@pobox.com>
Date: Sun, 25 Feb 2024 23:56:18 +0700
Subject: [PATCH] Add helpers for AutoConfigure from RFC 2563

Signed-off-by: Brian Candler <b.candler@pobox.com>
---
 dhcpv4/dhcpv4.go                    |  8 ++++
 dhcpv4/option_autoconfigure.go      | 61 +++++++++++++++++++++++++++++
 dhcpv4/option_autoconfigure_test.go | 46 ++++++++++++++++++++++
 dhcpv4/options.go                   |  4 ++
 dhcpv4/options_test.go              |  5 +++
 5 files changed, 124 insertions(+)
 create mode 100644 dhcpv4/option_autoconfigure.go
 create mode 100644 dhcpv4/option_autoconfigure_test.go

diff --git a/dhcpv4/dhcpv4.go b/dhcpv4/dhcpv4.go
index 6043cd95..686d4ef3 100644
--- a/dhcpv4/dhcpv4.go
+++ b/dhcpv4/dhcpv4.go
@@ -737,6 +737,14 @@ func (d *DHCPv4) MaxMessageSize() (uint16, error) {
 	return GetUint16(OptionMaximumDHCPMessageSize, d.Options)
 }
 
+// AutoConfigure returns the AutoConfigure option if present.
+//
+// The AutoConfigure option is described by RFC 2563, Section 2.
+func (d *DHCPv4) AutoConfigure() (AutoConfiguration, error) {
+	v, err := GetByte(OptionAutoConfigure, d.Options)
+	return AutoConfiguration(v), err
+}
+
 // MessageType returns the DHCPv4 Message Type option.
 func (d *DHCPv4) MessageType() MessageType {
 	v := d.Options.Get(OptionDHCPMessageType)
diff --git a/dhcpv4/option_autoconfigure.go b/dhcpv4/option_autoconfigure.go
new file mode 100644
index 00000000..e2237bfc
--- /dev/null
+++ b/dhcpv4/option_autoconfigure.go
@@ -0,0 +1,61 @@
+package dhcpv4
+
+import (
+	"fmt"
+)
+
+// AutoConfiguration implements encoding and decoding functions for a
+// byte enumeration as used in RFC 2563, Section 2.
+type AutoConfiguration byte
+
+const (
+	DoNotAutoConfigure AutoConfiguration = 0
+	AutoConfigure      AutoConfiguration = 1
+)
+
+var autoConfigureToString = map[AutoConfiguration]string{
+	DoNotAutoConfigure: "DoNotAutoConfigure",
+	AutoConfigure:      "AutoConfigure",
+}
+
+// ToBytes returns a serialized stream of bytes for this option.
+func (o AutoConfiguration) ToBytes() []byte {
+	return []byte{byte(o)}
+}
+
+// String returns a human-readable string for this option.
+func (o AutoConfiguration) String() string {
+	s := autoConfigureToString[o]
+	if s != "" {
+		return s
+	}
+	return fmt.Sprintf("UNKNOWN (%d)", byte(o))
+}
+
+// FromBytes parses a a single byte into AutoConfiguration
+func (o *AutoConfiguration) FromBytes(data []byte) error {
+	if len(data) == 1 {
+		*o = AutoConfiguration(data[0])
+		return nil
+	}
+	return fmt.Errorf("Invalid buffer length (%d)", len(data))
+}
+
+// GetByte parses any single-byte option
+func GetByte(code OptionCode, o Options) (byte, error) {
+	data := o.Get(code)
+	if data == nil {
+		return 0, fmt.Errorf("option not present")
+	}
+	if len(data) != 1 {
+		return 0, fmt.Errorf("Invalid buffer length (%d)", len(data))
+	}
+	return data[0], nil
+}
+
+// OptAutoConfigure returns a new AutoConfigure option.
+//
+// The AutoConfigure option is described by RFC 2563, Section 2.
+func OptAutoConfigure(autoconf AutoConfiguration) Option {
+	return Option{Code: OptionAutoConfigure, Value: autoconf}
+}
diff --git a/dhcpv4/option_autoconfigure_test.go b/dhcpv4/option_autoconfigure_test.go
new file mode 100644
index 00000000..abc3b68f
--- /dev/null
+++ b/dhcpv4/option_autoconfigure_test.go
@@ -0,0 +1,46 @@
+package dhcpv4
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOptAutoConfigure(t *testing.T) {
+	o := OptAutoConfigure(0)
+	require.Equal(t, OptionAutoConfigure, o.Code, "Code")
+	require.Equal(t, []byte{0}, o.Value.ToBytes(), "ToBytes")
+	require.Equal(t, "Auto-Configure: DoNotAutoConfigure", o.String())
+
+	o = OptAutoConfigure(1)
+	require.Equal(t, OptionAutoConfigure, o.Code, "Code")
+	require.Equal(t, []byte{1}, o.Value.ToBytes(), "ToBytes")
+	require.Equal(t, "Auto-Configure: AutoConfigure", o.String())
+
+	o = OptAutoConfigure(2)
+	require.Equal(t, OptionAutoConfigure, o.Code, "Code")
+	require.Equal(t, []byte{2}, o.Value.ToBytes(), "ToBytes")
+	require.Equal(t, "Auto-Configure: UNKNOWN (2)", o.String())
+}
+
+func TestGetAutoConfigure(t *testing.T) {
+	m, _ := New(WithGeneric(OptionAutoConfigure, []byte{1}))
+	o, err := m.AutoConfigure()
+	require.NoError(t, err)
+	require.Equal(t, AutoConfigure, o)
+
+	// Missing
+	m, _ = New()
+	_, err = m.AutoConfigure()
+	require.Error(t, err, "should get error if option missing")
+
+	// Short byte stream
+	m, _ = New(WithGeneric(OptionAutoConfigure, []byte{}))
+	_, err = m.AutoConfigure()
+	require.Error(t, err, "should get error from short byte stream")
+
+	// Bad length
+	m, _ = New(WithGeneric(OptionAutoConfigure, []byte{2, 2}))
+	_, err = m.AutoConfigure()
+	require.Error(t, err, "should get error from bad length")
+}
diff --git a/dhcpv4/options.go b/dhcpv4/options.go
index 9d404b43..9a4cfe85 100644
--- a/dhcpv4/options.go
+++ b/dhcpv4/options.go
@@ -344,6 +344,10 @@ func getOption(code OptionCode, data []byte, vendorDecoder OptionDecoder) fmt.St
 		var u Uint16
 		d = &u
 
+	case OptionAutoConfigure:
+		var a AutoConfiguration
+		d = &a
+
 	case OptionUserClassInformation:
 		var s Strings
 		d = &s
diff --git a/dhcpv4/options_test.go b/dhcpv4/options_test.go
index e918ee3d..331dd1b4 100644
--- a/dhcpv4/options_test.go
+++ b/dhcpv4/options_test.go
@@ -106,6 +106,11 @@ func TestParseOption(t *testing.T) {
 			value: []byte{1, 2},
 			want:  "258",
 		},
+		{
+			code:  OptionAutoConfigure,
+			value: []byte{0},
+			want:  "DoNotAutoConfigure",
+		},
 		{
 			code:  OptionUserClassInformation,
 			value: []byte{4, 't', 'e', 's', 't', 3, 'f', 'o', 'o'},