Stability of JSON textual representation

[David Evans <david.evans@xxxxxxxxxx>]

I've noticed that when representing lists as JSON, Postgres 9.4 sometimes outputs spaces after commas, and other times does not.

# SELECT array_to_json(array[1, 2, 3]), json_build_array(1, 2, 3);

 array_to_json | json_build_array 

---------------+------------------

 [1,2,3]       | [1, 2, 3]

This matters to me because I'm intending the hash the JSON text and use the hash for change detection.

This difference in behaviour doesn't seem to be documented anywhere. Does anyone know whether it is likely to be stable?

Many thanks,

Dave