gbn: modularise

Author: ellemouton

gbn/config.go

@@ -10,15 +10,6 @@ type config struct {
 	// 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.
@@ -53,7 +44,6 @@ func newConfig(sendFunc sendBytesFunc, recvFunc recvBytesFunc,
 
 	return &config{
 		n:                n,
-		s:                n + 1,
 		recvFromStream:   recvFunc,
 		sendToStream:     sendFunc,
 		resendTimeout:    defaultResendTimeout,

gbn/gbn_client.go

@@ -14,7 +14,7 @@ import (
 // The resendTimeout parameter defines the duration to wait before resending data
 // if the corresponding ACK for the data is not received.
 func NewClientConn(ctx context.Context, n uint8, sendFunc sendBytesFunc,
-	receiveFunc recvBytesFunc, opts ...Option) (*GoBackNConn, error) {
+	receiveFunc recvBytesFunc, opts ...Option) (GBN, error) {
 
 	if n == math.MaxUint8 {
 		return nil, fmt.Errorf("n must be smaller than %d",
@@ -28,14 +28,15 @@ func NewClientConn(ctx context.Context, n uint8, sendFunc sendBytesFunc,
 		o(cfg)
 	}
 
-	conn := newGoBackNConn(ctx, cfg, "client")
+	conn := newGBN(ctx, cfg, "client")
 
 	if err := conn.clientHandshake(); err != nil {
 		if err := conn.Close(); err != nil {
 			conn.log.Errorf("error closing gbn ClientConn: %v", err)
 		}
 		return nil, err
 	}
+
 	conn.start()
 
 	return conn, nil
@@ -50,7 +51,7 @@ func NewClientConn(ctx context.Context, n uint8, sendFunc sendBytesFunc,
 // SYNACK.
 // 3b. If the client does not receive SYN from the server within a given
 // timeout, then the client restarts the handshake from step 1.
-func (g *GoBackNConn) clientHandshake() error {
+func (g *gbn) clientHandshake() error {
 	// Spin off the recv function in a goroutine so that we can use
 	// a select to choose to timeout waiting for data from the receive
 	// stream. This is needed instead of a context timeout because the