Reduce bandwidth when using preferRest

[brettwillis]

I recently discovered that the Firestore REST API serves JSON responses in a "pretty printed" format with newlines, indentation etc. I also discovered that the REST API also has a prettyPrint query parameter that can opt in to non-pretty printing format, see https://firestore.googleapis.com/$discovery/rest?version=v1.

I found that using ?prettyprint=0 can save up to 50% of the JSON response size (probably less when considering compression) due to the highly nested (and therefore indented) nature of Firestore response data structures.

However this may affect how the underlying libraries (gax?) do streaming parsing (if they do so?). I don't know enough about how the underlying I/O libraries are structured to know the impact or complexity, or even if you're not disabling pretty print already... I just did a quick search and couldn't find any reference to it.

I'll just leave this here for consideration.

[MarkDuckworth]

Nice find. I did some testing an it looks like pretty print is used in the JSON responses. When setting $prettyPrint=0, the nodejs-firestore system tests pass. I haven't quantified the impact on response size and performance.

This should be controlled in the gax fallback implementation, so I'll get in touch with that team.