nclient4: respect NAKs

Signed-off-by: Chris Koch <chrisko@google.com>

3 files changed, 56 insertions, 19 deletions

diff --git a/dhcpv4/dhcpv4.go b/dhcpv4/dhcpv4.go
index 4316c5e..c09e76a 100644
--- a/dhcpv4/dhcpv4.go
+++ b/dhcpv4/dhcpv4.go
@@ -735,6 +735,13 @@ func (d *DHCPv4) MessageType() MessageType {
 	return m
 }
 
+// Message returns the DHCPv4 (Error) Message option.
+//
+// The message options is described in RFC 2132, Section 9.9.
+func (d *DHCPv4) Message() string {
+	return GetString(OptionMessage, d.Options)
+}
+
 // ParameterRequestList returns the DHCPv4 Parameter Request List.
 //
 // The parameter request list option is described by RFC 2132, Section 9.8.
diff --git a/dhcpv4/nclient4/client.go b/dhcpv4/nclient4/client.go
index 83ed065..41c7a73 100644
--- a/dhcpv4/nclient4/client.go
+++ b/dhcpv4/nclient4/client.go
@@ -399,12 +399,18 @@ func WithServerAddr(n *net.UDPAddr) ClientOpt {
 // Matcher matches DHCP packets.
 type Matcher func(*dhcpv4.DHCPv4) bool
 
-// IsMessageType returns a matcher that checks for the message type.
-//
-// If t is MessageTypeNone, all packets are matched.
-func IsMessageType(t dhcpv4.MessageType) Matcher {
+// IsMessageType returns a matcher that checks for the message types.
+func IsMessageType(t dhcpv4.MessageType, tt ...dhcpv4.MessageType) Matcher {
 	return func(p *dhcpv4.DHCPv4) bool {
-		return p.MessageType() == t || t == dhcpv4.MessageTypeNone
+		if p.MessageType() == t {
+			return true
+		}
+		for _, mt := range tt {
+			if p.MessageType() == mt {
+				return true
+			}
+		}
+		return false
 	}
 }
 
@@ -416,17 +422,14 @@ func (c *Client) DiscoverOffer(ctx context.Context, modifiers ...dhcpv4.Modifier
 	discover, err := dhcpv4.NewDiscovery(c.ifaceHWAddr, dhcpv4.PrependModifiers(modifiers,
 		dhcpv4.WithOption(dhcpv4.OptMaxMessageSize(MaxMessageSize)))...)
 	if err != nil {
-		err = fmt.Errorf("unable to create a discovery request: %w", err)
-		return
+		return nil, fmt.Errorf("unable to create a discovery request: %w", err)
 	}
 
 	offer, err = c.SendAndRead(ctx, c.serverAddr, discover, IsMessageType(dhcpv4.MessageTypeOffer))
 	if err != nil {
-		err = fmt.Errorf("got an error while the discovery request: %w", err)
-		return
+		return nil, fmt.Errorf("got an error while the discovery request: %w", err)
 	}
-
-	return
+	return offer, nil
 }
 
 // Request completes the 4-way Discover-Offer-Request-Ack handshake.
@@ -438,25 +441,47 @@ func (c *Client) Request(ctx context.Context, modifiers ...dhcpv4.Modifier) (lea
 		err = fmt.Errorf("unable to receive an offer: %w", err)
 		return
 	}
+	return c.RequestFromOffer(ctx, offer, modifiers...)
+}
 
+// ErrNak is returned if a DHCP server rejected our Request.
+type ErrNak struct {
+	Offer *dhcpv4.DHCPv4
+	Nak   *dhcpv4.DHCPv4
+}
+
+// Error implements error.Error.
+func (e *ErrNak) Error() string {
+	if msg := e.Nak.Message(); len(msg) > 0 {
+		return fmt.Sprintf("server rejected request with Nak (msg: %s)", msg)
+	}
+	return "server rejected request with Nak"
+}
+
+// RequestFromOffer sends a Request message and waits for an response.
+func (c *Client) RequestFromOffer(ctx context.Context, offer *dhcpv4.DHCPv4, modifiers ...dhcpv4.Modifier) (*Lease, error) {
 	// TODO(chrisko): should this be unicast to the server?
 	request, err := dhcpv4.NewRequestFromOffer(offer, dhcpv4.PrependModifiers(modifiers,
 		dhcpv4.WithOption(dhcpv4.OptMaxMessageSize(MaxMessageSize)))...)
 	if err != nil {
-		err = fmt.Errorf("unable to create a request: %w", err)
-		return
+		return nil, fmt.Errorf("unable to create a request: %w", err)
 	}
 
-	ack, err := c.SendAndRead(ctx, c.serverAddr, request, nil)
+	response, err := c.SendAndRead(ctx, c.serverAddr, request, IsMessageType(dhcpv4.MessageTypeAck, dhcpv4.MessageTypeNak))
 	if err != nil {
-		err = fmt.Errorf("got an error while processing the request: %w", err)
-		return
+		return nil, fmt.Errorf("got an error while processing the request: %w", err)
+	}
+	if response.MessageType() == dhcpv4.MessageTypeNak {
+		return nil, &ErrNak{
+			Offer: offer,
+			Nak:   response,
+		}
 	}
-	lease = &Lease{}
-	lease.ACK = ack
+	lease := &Lease{}
+	lease.ACK = response
 	lease.Offer = offer
 	lease.CreationTime = time.Now()
-	return
+	return lease, nil
 }
 
 // ErrTransactionIDInUse is returned if there were an attempt to send a message
diff --git a/dhcpv4/option_string.go b/dhcpv4/option_string.go
index 289319b..eb0cc2b 100644
--- a/dhcpv4/option_string.go
+++ b/dhcpv4/option_string.go
@@ -77,3 +77,8 @@ func OptClassIdentifier(name string) Option {
 func OptUserClass(name string) Option {
 	return Option{Code: OptionUserClassInformation, Value: String(name)}
 }
+
+// OptMessage returns a new DHCPv4 (Error) Message option.
+func OptMessage(msg string) Option {
+	return Option{Code: OptionMessage, Value: String(msg)}
+}