call_opt.go
func Meta(meta interface{}) CallOption {
	return callOptionFunc(func(r *Request) error {
		return r.SetMeta(meta)
	})
}
func Meta(meta interface{}) CallOption {
	return callOptionFunc(func(r *Request) error {
		return r.SetMeta(meta)
	})
}
// Meta returns a call option which attaches the given meta object to
// the JSON-RPC 2.0 request (this is a Sourcegraph extension to JSON
// RPC 2.0 for carrying metadata).