Given a view relation OID, how to construct a Query?

I'm doing some extension development (in C) and have a situation where I
need to examine the target list of a view, but all I have is the view's oid.

An approach that works is (pseudocode):
SPI_connect();
"SELECT ev_action FROM pg_catalog.pg_rewrite WHERE rulename = '_RETURN'
and ev_class=?oid";
Query *query = linitial(stringToNode(ev_action));
...
SPI_finish();

I backed into this by tracing through pg_getviewdef(). Is there a more
direct way to do this without going through SPI?

I also looked at using postgres.c#pg_analyze_and_rewrite() against a query
like "SELECT * FROM viewname" but the target list of the actual query
wasn't what I was expecting (individual entry tags don't match those of the
SPI approach above).

Thanks for your time!

eric