Asynchronous client for DHCPv6 (#80)

1 files changed, 235 insertions, 0 deletions

diff --git a/dhcpv6/async.go b/dhcpv6/async.go
new file mode 100644
index 0000000..e9930bf
--- /dev/null
+++ b/dhcpv6/async.go
@@ -0,0 +1,235 @@
+package dhcpv6
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"sync"
+	"time"
+)
+
+// AsyncClient implements an asynchronous DHCPv6 client
+type AsyncClient struct {
+	ReadTimeout  time.Duration
+	WriteTimeout time.Duration
+	LocalAddr    net.Addr
+	RemoteAddr   net.Addr
+	IgnoreErrors bool
+
+	connection   *net.UDPConn
+	cancel       context.CancelFunc
+	stopping     *sync.WaitGroup
+	receiveQueue chan DHCPv6
+	sendQueue    chan DHCPv6
+	packetsLock  sync.Mutex
+	packets      map[uint32](chan Response)
+	errors       chan error
+}
+
+// NewAsyncClient creates an asynchronous client
+func NewAsyncClient() *AsyncClient {
+	return &AsyncClient{
+		ReadTimeout:  DefaultReadTimeout,
+		WriteTimeout: DefaultWriteTimeout,
+	}
+}
+
+// OpenForInterface starts the client on the specified interface, replacing
+// client LocalAddr with a link-local address of the given interface and
+// standard DHCP port (546).
+func (c *AsyncClient) OpenForInterface(ifname string, bufferSize int) error {
+	addr, err := GetLinkLocalAddr(ifname)
+	if err != nil {
+		return err
+	}
+	c.LocalAddr = &net.UDPAddr{IP: *addr, Port: DefaultClientPort, Zone: ifname}
+	return c.Open(bufferSize)
+}
+
+// Open starts the client
+func (c *AsyncClient) Open(bufferSize int) error {
+	var (
+		addr *net.UDPAddr
+		ok   bool
+		err  error
+	)
+
+	if addr, ok = c.LocalAddr.(*net.UDPAddr); !ok {
+		return fmt.Errorf("Invalid local address: %v not a net.UDPAddr", c.LocalAddr)
+	}
+
+	// prepare the socket to listen on for replies
+	c.connection, err = net.ListenUDP("udp6", addr)
+	if err != nil {
+		return err
+	}
+	c.stopping = new(sync.WaitGroup)
+	c.sendQueue = make(chan DHCPv6, bufferSize)
+	c.receiveQueue = make(chan DHCPv6, bufferSize)
+	c.packets = make(map[uint32](chan Response))
+	c.packetsLock = sync.Mutex{}
+	c.errors = make(chan error)
+
+	var ctx context.Context
+	ctx, c.cancel = context.WithCancel(context.Background())
+	go c.receiverLoop(ctx)
+	go c.senderLoop(ctx)
+
+	return nil
+}
+
+// Close stops the client
+func (c *AsyncClient) Close() {
+	// Wait for sender and receiver loops
+	c.stopping.Add(2)
+	c.cancel()
+	c.stopping.Wait()
+
+	close(c.sendQueue)
+	close(c.receiveQueue)
+	close(c.errors)
+
+	c.connection.Close()
+}
+
+// Errors returns a channel where runtime errors are posted
+func (c *AsyncClient) Errors() <-chan error {
+	return c.errors
+}
+
+func (c *AsyncClient) addError(err error) {
+	if !c.IgnoreErrors {
+		c.errors <- err
+	}
+}
+
+func (c *AsyncClient) receiverLoop(ctx context.Context) {
+	defer func() { c.stopping.Done() }()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case packet := <-c.receiveQueue:
+			c.receive(packet)
+		}
+	}
+}
+
+func (c *AsyncClient) senderLoop(ctx context.Context) {
+	defer func() { c.stopping.Done() }()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case packet := <-c.sendQueue:
+			c.send(packet)
+		}
+	}
+}
+
+func (c *AsyncClient) send(packet DHCPv6) {
+	transactionID, err := GetTransactionID(packet)
+	if err != nil {
+		c.addError(fmt.Errorf("Warning: This should never happen, there is no transaction ID on %s", packet))
+		return
+	}
+	c.packetsLock.Lock()
+	f := c.packets[transactionID]
+	c.packetsLock.Unlock()
+
+	raddr, err := c.remoteAddr()
+	if err != nil {
+		f <- NewResponse(nil, err)
+		return
+	}
+
+	c.connection.SetWriteDeadline(time.Now().Add(c.WriteTimeout))
+	_, err = c.connection.WriteTo(packet.ToBytes(), raddr)
+	if err != nil {
+		f <- NewResponse(nil, err)
+		return
+	}
+
+	c.receiveQueue <- packet
+}
+
+func (c *AsyncClient) receive(_ DHCPv6) {
+	var (
+		oobdata  = []byte{}
+		received DHCPv6
+	)
+
+	c.connection.SetReadDeadline(time.Now().Add(c.ReadTimeout))
+	for {
+		buffer := make([]byte, maxUDPReceivedPacketSize)
+		n, _, _, _, err := c.connection.ReadMsgUDP(buffer, oobdata)
+		if err != nil {
+			if err, ok := err.(net.Error); !ok || !err.Timeout() {
+				c.addError(fmt.Errorf("Error receiving the message: %s", err))
+			}
+			return
+		}
+		received, err = FromBytes(buffer[:n])
+		if err != nil {
+			// skip non-DHCP packets
+			continue
+		}
+		break
+	}
+
+	transactionID, err := GetTransactionID(received)
+	if err != nil {
+		c.addError(fmt.Errorf("Unable to get a transactionID for %s: %s", received, err))
+		return
+	}
+
+	c.packetsLock.Lock()
+	if f, ok := c.packets[transactionID]; ok {
+		delete(c.packets, transactionID)
+		f <- NewResponse(received, nil)
+	}
+	c.packetsLock.Unlock()
+}
+
+func (c *AsyncClient) remoteAddr() (*net.UDPAddr, error) {
+	if c.RemoteAddr == nil {
+		return &net.UDPAddr{IP: AllDHCPRelayAgentsAndServers, Port: DefaultServerPort}, nil
+	}
+
+	if addr, ok := c.RemoteAddr.(*net.UDPAddr); ok {
+		return addr, nil
+	}
+	return nil, fmt.Errorf("Invalid remote address: %v not a net.UDPAddr", c.RemoteAddr)
+}
+
+// Send inserts a message to the queue to be sent asynchronously.
+// Returns a future which resolves to response and error.
+func (c *AsyncClient) Send(message DHCPv6, modifiers ...Modifier) Future {
+	for _, mod := range modifiers {
+		message = mod(message)
+	}
+
+	transactionID, err := GetTransactionID(message)
+	if err != nil {
+		return NewFailureFuture(err)
+	}
+
+	f := NewFuture()
+	c.packetsLock.Lock()
+	c.packets[transactionID] = f
+	c.packetsLock.Unlock()
+	c.sendQueue <- message
+	return f
+}
+
+// Exchange executes asynchronously a 4-way DHCPv6 request (SOLICIT,
+// ADVERTISE, REQUEST, REPLY).
+func (c *AsyncClient) Exchange(solicit DHCPv6, modifiers ...Modifier) Future {
+	return c.Send(solicit).OnSuccess(func(advertise DHCPv6) Future {
+		request, err := NewRequestFromAdvertise(advertise)
+		if err != nil {
+			return NewFailureFuture(err)
+		}
+		return c.Send(request, modifiers...)
+	})
+}