Rework client interface

client/options.go

@@ -68,7 +68,8 @@ type PublishOptions struct {
 }
 
 type RequestOptions struct {
-	Stream bool
+	ContentType string
+	Stream      bool
 
 	// Other options for implementations of the interface
 	// can be stored in a context
@@ -290,6 +291,12 @@ func WithDialTimeout(d time.Duration) CallOption {
 
 // Request Options
 
+func WithContentType(ct string) RequestOption {
+	return func(o *RequestOptions) {
+		o.ContentType = ct
+	}
+}
+
 func StreamingRequest() RequestOption {
 	return func(o *RequestOptions) {
 		o.Stream = true