Duplicate the comment from astreamer_plain_writer_new instead of just
referring to it. Add a further note to mention that there are dangers
if anything else is written to the same FILE. Also add a comment where
we dup() the filehandle, referring to the existing comment in
astreamer_gzip_writer_finalize(), because the dup() looks wrong on
first glance without that comment to clarify.
Per concerns expressed by Tom Lane on pgsql-security, and using
some wording suggested by him.
Discussion: http://postgr.es/m/CA+TgmoYTFAD0YTh4HC1Nuhn0YEyoQi0_CENFgVzAY_YReiSksQ@mail.gmail.com
Make it clear that "astreamer" stands for "archive streamer".
Generalize comments that still believe this code can only be used
by pg_basebackup. Add some comments explaining the asymmetry
between the gzip, lz4, and zstd astreamers, in the hopes of making
life easier for anyone who hacks on this code in the future.
Robert Haas, reviewed by Amul Sul.
Discussion: http://postgr.es/m/CAAJ_b97O2kkKVTWxt8MxDN1o-cDfbgokqtiN2yqFf48=gXpcxQ@mail.gmail.com
