json rendering without pretty option (compact)

Hello,

I want to minimize postgresql json size when I fetch them.
I translate columnar table to json thought json_build_object/array or even
row_to_jeon.

While row_to_json do have a "pretty_bool" option, the latter do not. Each
json object/array I build contains spaces.

Is there a workaround ?
Is there a plan to add this feature on future version ?

(PG 9.6)

Thank you by advance,