fix: check if writer is nil when closing client rpc

Signed-off-by: Christian Stewart <christian@aperture.us>

srpc/client-rpc.go

@@ -26,6 +26,10 @@ func NewClientRPC(ctx context.Context, service, method string) *ClientRPC {
 // Start sets the writer and writes the MsgSend message.
 // must only be called once!
 func (r *ClientRPC) Start(writer PacketWriter, writeFirstMsg bool, firstMsg []byte) error {
+	if writer == nil {
+		return ErrNilWriter
+	}
+
 	if err := r.ctx.Err(); err != nil {
 		r.ctxCancel()
 		_ = writer.Close()
@@ -104,9 +108,11 @@ func (r *ClientRPC) HandleCallStart(pkt *CallStart) error {
 
 // Close releases any resources held by the ClientRPC.
 func (r *ClientRPC) Close() {
-	_ = r.WriteCallCancel()
-
 	r.bcast.HoldLock(func(broadcast func(), getWaitCh func() <-chan struct{}) {
-		r.closeLocked(broadcast)
+		// call did not start yet if writer is nil.
+		if r.writer != nil {
+			_ = r.WriteCallCancel()
+			r.closeLocked(broadcast)
+		}
 	})
 }

srpc/client.go

@@ -51,6 +51,7 @@ func (c *client) ExecCall(ctx context.Context, service, method string, in, out M
 	if err != nil {
 		return err
 	}
+
 	if err := clientRPC.Start(writer, true, firstMsg); err != nil {
 		return err
 	}
@@ -63,6 +64,7 @@ func (c *client) ExecCall(ctx context.Context, service, method string, in, out M
 	if err := out.UnmarshalVT(msg); err != nil {
 		return errors.Wrap(ErrInvalidMessage, err.Error())
 	}
+
 	return nil
 }
 
@@ -83,6 +85,7 @@ func (c *client) NewStream(ctx context.Context, service, method string, firstMsg
 	if err != nil {
 		return nil, err
 	}
+
 	if err := clientRPC.Start(writer, firstMsg != nil, firstMsgData); err != nil {
 		return nil, err
 	}

srpc/errors.go

@@ -19,4 +19,6 @@ var (
 	ErrEmptyServiceID = errors.New("service id empty")
 	// ErrNoAvailableClients is returned if no clients were available.
 	ErrNoAvailableClients = errors.New("no available rpc clients")
+	// ErrNilWriter is returned if the rpc writer is nil.
+	ErrNilWriter = errors.New("writer cannot be nil")
 )