gbn: split out config values into a config struct

gbn/config.go

@@ -0,0 +1,62 @@
+package gbn
+
+import "time"
+
+// config holds the configuration values for an instance of GoBackNConn.
+type config struct {
+	// n is the window size. The sender can send a maximum of n packets
+	// before requiring an ack from the receiver for the first packet in
+	// the window. The value of n is chosen by the client during the
+	// GoBN handshake.
+	n uint8
+
+	// s is the maximum sequence number used to label packets. Packets
+	// are labelled with incrementing sequence numbers modulo s.
+	// s must be strictly larger than the window size, n. This
+	// is so that the receiver can tell if the sender is resending the
+	// previous window (maybe the sender did not receive the acks) or if
+	// they are sending the next window. If s <= n then there would be
+	// no way to tell.
+	s uint8
+
+	// maxChunkSize is the maximum payload size in bytes allowed per
+	// message. If the payload to be sent is larger than maxChunkSize then
+	// the payload will be split between multiple packets.
+	// If maxChunkSize is zero then it is disabled and data won't be split
+	// between packets.
+	maxChunkSize int
+
+	// resendTimeout is the duration that will be waited before resending
+	// the packets in the current queue.
+	resendTimeout time.Duration
+
+	// recvFromStream is the function that will be used to acquire the next
+	// available packet.
+	recvFromStream recvBytesFunc
+
+	// sendToStream is the function that will be used to send over our next
+	// packet.
+	sendToStream sendBytesFunc
+
+	// handshakeTimeout is the time after which the server or client
+	// will abort and restart the handshake if the expected response is
+	// not received from the peer.
+	handshakeTimeout time.Duration
+
+	pingTime time.Duration
+	pongTime time.Duration
+}
+
+// newConfig constructs a new config struct.
+func newConfig(sendFunc sendBytesFunc, recvFunc recvBytesFunc,
+	n uint8) *config {
+
+	return &config{
+		n:                n,
+		s:                n + 1,
+		recvFromStream:   recvFunc,
+		sendToStream:     sendFunc,
+		resendTimeout:    defaultResendTimeout,
+		handshakeTimeout: defaultHandshakeTimeout,
+	}
+}

gbn/gbn_client.go

@@ -21,13 +21,15 @@ func NewClientConn(ctx context.Context, n uint8, sendFunc sendBytesFunc,
 			math.MaxUint8)
 	}
 
-	conn := newGoBackNConn(ctx, sendFunc, receiveFunc, false, n)
+	cfg := newConfig(sendFunc, receiveFunc, n)
 
 	// Apply functional options
 	for _, o := range opts {
-		o(conn)
+		o(cfg)
 	}
 
+	conn := newGoBackNConn(ctx, cfg, "client")
+
 	if err := conn.clientHandshake(); err != nil {
 		if err := conn.Close(); err != nil {
 			log.Errorf("error closing gbn ClientConn: %v", err)
@@ -76,7 +78,7 @@ func (g *GoBackNConn) clientHandshake() error {
 			case <-recvNext:
 			}
 
-			b, err := g.recvFromStream(g.ctx)
+			b, err := g.cfg.recvFromStream(g.ctx)
 			if err != nil {
 				errChan <- err
 				return
@@ -101,15 +103,15 @@ func (g *GoBackNConn) clientHandshake() error {
 handshake:
 	for {
 		// start Handshake
-		msg := &PacketSYN{N: g.n}
+		msg := &PacketSYN{N: g.cfg.n}
 		msgBytes, err := msg.Serialize()
 		if err != nil {
 			return err
 		}
 
 		// Send SYN
 		g.log.Debugf("Sending SYN")
-		if err := g.sendToStream(g.ctx, msgBytes); err != nil {
+		if err := g.cfg.sendToStream(g.ctx, msgBytes); err != nil {
 			return err
 		}
 
@@ -128,7 +130,7 @@ handshake:
 
 			var b []byte
 			select {
-			case <-time.After(g.handshakeTimeout):
+			case <-time.After(g.cfg.handshakeTimeout):
 				g.log.Debugf("SYN resendTimeout. Resending " +
 					"SYN.")
 
@@ -165,7 +167,7 @@ handshake:
 
 	g.log.Debugf("Got SYN")
 
-	if respSYN.N != g.n {
+	if respSYN.N != g.cfg.n {
 		return io.EOF
 	}
 
@@ -176,7 +178,7 @@ handshake:
 		return err
 	}
 
-	if err := g.sendToStream(g.ctx, synack); err != nil {
+	if err := g.cfg.sendToStream(g.ctx, synack); err != nil {
 		return err
 	}