all: imp code, resolve todos

internal/dhcpsvc/interface.go

@@ -34,7 +34,7 @@ func macToKey(mac net.HardwareAddr) (key macKey) {
 type netInterface struct {
 	// logger logs the events related to the network interface.
 	//
-	// TODO(e.burkov):  Consider removing it and using the valud from context.
+	// TODO(e.burkov):  Consider removing it and using the value from context.
 	logger *slog.Logger
 
 	// leases is the set of DHCP leases assigned to this interface.

internal/dhcpsvc/options4.go

@@ -13,15 +13,12 @@ import (
 	"github.com/google/gopacket/layers"
 )
 
-// options returns the implicit and explicit options for the interface.  The two
-// lists are disjoint and the implicit options are initialized with default
-// values.
-//
-// TODO(e.burkov):  DRY with the IPv6 version.
-func (c *IPv4Config) options(ctx context.Context, l *slog.Logger) (imp, exp layers.DHCPOptions) {
+// implicitOptions returns the implicit options for the interface, sorted by
+// code.
+func (c *IPv4Config) implicitOptions() (opts layers.DHCPOptions) {
 	// Set default values of host configuration parameters listed in Appendix A
 	// of RFC-2131.
-	imp = layers.DHCPOptions{
+	opts = layers.DHCPOptions{
 		// Values From Configuration
 
 		layers.NewDHCPOption(layers.DHCPOptSubnetMask, c.SubnetMask.AsSlice()),
@@ -177,7 +174,20 @@ func (c *IPv4Config) options(ctx context.Context, l *slog.Logger) (imp, exp laye
 		// See https://datatracker.ietf.org/doc/html/rfc1122#section-4.2.3.6.
 		layers.NewDHCPOption(layers.DHCPOptTCPKeepAliveGarbage, []byte{0x1}),
 	}
-	slices.SortFunc(imp, compareV4OptionCodes)
+	slices.SortFunc(opts, compareV4OptionCodes)
+
+	return opts
+}
+
+// options returns the implicit and explicit options for the interface.  The two
+// lists are disjoint and the implicit options are initialized with default
+// values.  All options within exp which have a nil Data field should be treated
+// as instruction to remove those from responses.
+//
+// TODO(e.burkov):  DRY with the IPv6 version.
+func (c *IPv4Config) options(ctx context.Context, l *slog.Logger) (imp, exp layers.DHCPOptions) {
+	// Set values of implicit options.
+	imp = c.implicitOptions()
 
 	// Set values for explicitly configured options.
 	for _, o := range c.Options {
@@ -187,10 +197,10 @@ func (c *IPv4Config) options(ctx context.Context, l *slog.Logger) (imp, exp laye
 		}
 
 		i, found = slices.BinarySearchFunc(exp, o, compareV4OptionCodes)
-		if o.Length > 0 {
+		if found {
+			exp[i].Data, exp[i].Length = o.Data, o.Length
+		} else {
 			exp = slices.Insert(exp, i, o)
-		} else if found {
-			exp = slices.Delete(exp, i, i+1)
 		}
 	}
 
@@ -205,11 +215,44 @@ func compareV4OptionCodes(a, b layers.DHCPOption) (res int) {
 }
 
 // updateOptions updates the options of the response in accordance with the
-// request and RFC 2131.
+// requested parameters.  req and resp must not be nil.
 //
 // See https://datatracker.ietf.org/doc/html/rfc2131#section-4.3.1.
 func (iface *dhcpInterfaceV4) updateOptions(req, resp *layers.DHCPv4) {
-	// TODO(e.burkov):  !! Implement
+	// If the server recognizes the parameter as a parameter defined in the Host
+	// Requirements Document, the server MUST include the default value for that
+	// parameter.
+	optWithCode := layers.DHCPOption{}
+	for _, code := range requestedOptions(req) {
+		optWithCode.Type = code
+		i, has := slices.BinarySearchFunc(iface.implicitOpts, optWithCode, compareV4OptionCodes)
+		if has {
+			// The client MAY list the options in order of preference. The DHCP
+			// server is not required to return the options in the requested
+			// order, but MUST try to insert the requested options in the order
+			// requested by the client.
+			//
+			// See https://datatracker.ietf.org/doc/html/rfc2132#section-9.8.
+			resp.Options = append(resp.Options, iface.implicitOpts[i])
+		}
+	}
+
+	// If the server has been explicitly configured with a default value for the
+	// parameter or the parameter has a non-default value on the client's
+	// subnet, the server MUST include that value in an appropriate option.
+	for _, opt := range iface.explicitOpts {
+		if opt.Data != nil {
+			resp.Options = append(resp.Options, opt)
+
+			continue
+		}
+
+		// Remove options explicitly configured to be removed, in case they are
+		// already set.
+		resp.Options = slices.DeleteFunc(resp.Options, func(o layers.DHCPOption) (ok bool) {
+			return o.Type == opt.Type
+		})
+	}
 }
 
 // appendLeaseTime appends the lease time option to the response.
@@ -268,3 +311,23 @@ func hostname4(msg *layers.DHCPv4) (hostname string) {
 
 	return ""
 }
+
+// requestedOptions returns the list of options requested in DHCPv4 message, if
+// any.
+func requestedOptions(msg *layers.DHCPv4) (opts []layers.DHCPOpt) {
+	for _, opt := range msg.Options {
+		l := len(opt.Data)
+		if opt.Type != layers.DHCPOptParamsRequest || l == 0 {
+			continue
+		}
+
+		opts = make([]layers.DHCPOpt, 0, l)
+		for _, code := range opt.Data {
+			opts = append(opts, layers.DHCPOpt(code))
+		}
+
+		return opts
+	}
+
+	return nil
+}

internal/dhcpsvc/options4_internal_test.go

@@ -49,7 +49,9 @@ func TestIPv4Config_Options(t *testing.T) {
 				layers.NewDHCPOption(layers.DHCPOptBroadcastAddr, nil),
 			},
 		},
-		wantExplicit: nil,
+		wantExplicit: layers.DHCPOptions{
+			layers.NewDHCPOption(layers.DHCPOptBroadcastAddr, nil),
+		},
 	}, {
 		name: "rewritten_del",
 		conf: &IPv4Config{

internal/dhcpsvc/v4.go

@@ -41,9 +41,9 @@ type IPv4Config struct {
 	RangeEnd netip.Addr
 
 	// Options is the list of explicitly configured DHCP options to send to
-	// clients.  The options having a zero value within the Length field are
-	// treated as deletions of the corresponding options, either implicit or
-	// explicit.
+	// clients.  Options with nil Data field are removed from responses.
+	//
+	// TODO(e.burkov):  Validate.
 	Options layers.DHCPOptions
 
 	// LeaseDuration is the TTL of a DHCP lease.  It should be positive.
@@ -146,7 +146,8 @@ type dhcpInterfaceV4 struct {
 	implicitOpts layers.DHCPOptions
 
 	// explicitOpts are the user-configured options.  It must not have
-	// intersections with implicitOpts.
+	// intersections with implicitOpts.  Options with nil Data field are removed
+	// from responses.
 	explicitOpts layers.DHCPOptions
 }