Rework client interface

client/rpc_request.go

@@ -8,13 +8,18 @@ type rpcRequest struct {
 	opts        RequestOptions
 }
 
-func newRpcRequest(service, method string, request interface{}, contentType string, reqOpts ...RequestOption) Request {
+func newRequest(service, method string, request interface{}, contentType string, reqOpts ...RequestOption) Request {
 	var opts RequestOptions
 
 	for _, o := range reqOpts {
 		o(&opts)
 	}
 
+	// set the content-type specified
+	if len(opts.ContentType) > 0 {
+		contentType = opts.ContentType
+	}
+
 	return &rpcRequest{
 		service:     service,
 		method:      method,