WIP: Fix: make rebind & release compliant with RFC2131 #560

dhcpv4/dhcpv4.go

@@ -289,6 +289,24 @@ func NewRenewFromAck(ack *DHCPv4, modifiers ...Modifier) (*DHCPv4, error) {
 	)...)
 }
 
+func NewRebindFromAck(ack *DHCPv4, modifiers ...Modifier) (*DHCPv4, error) {
+	return New(PrependModifiers(modifiers,
+		WithReply(ack),
+		WithMessageType(MessageTypeRequest),
+		// The client IP must be filled in with the IP offered to the client
+		WithClientIP(ack.YourIPAddr),
+		// The renewal request must use unicast
+		WithBroadcast(true),
+		WithRequestedOptions(
+			OptionSubnetMask,
+			OptionRouter,
+			OptionDomainName,
+			OptionDomainNameServer,
+			OptionServerIdentifier,
+		),
+	)...)
+}
+
 // NewReplyFromRequest builds a DHCPv4 reply from a request.
 func NewReplyFromRequest(request *DHCPv4, modifiers ...Modifier) (*DHCPv4, error) {
 	return New(PrependModifiers(modifiers,

dhcpv4/nclient4/lease.go

@@ -53,11 +53,17 @@ func (c *Client) Renew(ctx context.Context, lease *Lease, modifiers ...dhcpv4.Mo
 		return nil, fmt.Errorf("unable to create a request: %w", err)
 	}
 
+	// Force unicasting to the original DHCP server
+	destAddr := &net.UDPAddr{
+		IP:   lease.ACK.Options.Get(dhcpv4.OptionServerIdentifier),
+		Port: ServerPort,
+	}
+
 	// Servers are supposed to only respond to Requests containing their server identifier,
 	// but sometimes non-compliant servers respond anyway.
 	// Clients are not required to validate this field, but servers are required to
 	// include the server identifier in their Offer per RFC 2131 Section 4.3.1 Table 3.
-	response, err := c.SendAndRead(ctx, c.serverAddr, request, IsAll(
+	response, err := c.SendAndRead(ctx, destAddr, request, IsAll(
 		IsCorrectServer(lease.Offer.ServerIdentifier()),
 		IsMessageType(dhcpv4.MessageTypeAck, dhcpv4.MessageTypeNak)))
 	if err != nil {
@@ -77,3 +83,45 @@ func (c *Client) Renew(ctx context.Context, lease *Lease, modifiers ...dhcpv4.Mo
 		CreationTime: time.Now(),
 	}, nil
 }
+
+func (c *Client) Rebind(ctx context.Context, lease *Lease, modifiers ...dhcpv4.Modifier) (*Lease, error) {
+	if lease == nil {
+		return nil, fmt.Errorf("lease is nil")
+	}
+
+	request, err := dhcpv4.NewRebindFromAck(lease.ACK, dhcpv4.PrependModifiers(modifiers,
+		dhcpv4.WithOption(dhcpv4.OptMaxMessageSize(MaxMessageSize)))...)
+	if err != nil {
+		return nil, fmt.Errorf("unable to create a request: %w", err)
+	}
+
+	// Servers are supposed to only respond to Requests containing their server identifier,
+	// but sometimes non-compliant servers respond anyway.
+	// Clients are not required to validate this field, but servers are required to
+	// include the server identifier in their Offer per RFC 2131 Section 4.3.1 Table 3.
+	// For the matcher, the server identifier should be checked as another DHCP server
+	// could answer instead of the original one. The responding server is defacto the new
+	// authoritative DHCP for our client.
+	response, err := c.SendAndRead(ctx, c.serverAddr, request, IsAll(
+		IsMessageType(dhcpv4.MessageTypeAck, dhcpv4.MessageTypeNak)))
+	if err != nil {
+		return nil, fmt.Errorf("got an error while processing the request: %w", err)
+	}
+	if response.MessageType() == dhcpv4.MessageTypeNak {
+		return nil, &ErrNak{
+			Offer: lease.Offer,
+			Nak:   response,
+		}
+	}
+
+	// Modify the initial offer, as we switched to another DHCP server.
+	// This allow further Renew or request to succeed with the new DHCP server.
+	lease.Offer.UpdateOption(dhcpv4.OptServerIdentifier(response.ServerIdentifier()))
+
+	// Return a new lease with the latest ACK and updated creation time
+	return &Lease{
+		Offer:        lease.Offer,
+		ACK:          response,
+		CreationTime: time.Now(),
+	}, nil
+}

dhcpv4/server4/server_test.go

@@ -1,3 +1,4 @@
+//go:build go1.12
 // +build go1.12
 
 package server4
@@ -109,7 +110,7 @@ func TestServer(t *testing.T) {
 		require.Equal(t, ifaces[0].HardwareAddr, p.ClientHWAddr)
 	}
 
-	lease, err = c.Renew(context.Background(), lease, modifiers...)
+	lease, err = c.Rebind(context.Background(), lease, modifiers...)
 	require.NoError(t, err)
 	require.NotNil(t, lease.Offer)
 	require.NotNil(t, lease.ACK)