BackgroundPsql needs to wait for all the output from an interactive
psql command to come back. To make sure that's happened, it issues
the command, then issues \echo and \warn psql commands that echo
a "banner" string (which we assume won't appear in the command's
output), then waits for the banner strings to appear. The hazard
in this approach is that the banner will also appear in the echoed
psql commands themselves, so we need to distinguish those echoes from
the desired output. Commit 8b886a4e3 tried to do that by positing
that the desired output would be directly preceded and followed by
newlines, but it turns out that that assumption is timing-sensitive.
In particular, it tends to fail in builds made --without-readline,
wherein the command echoes will be made by the pty driver and may
be interspersed with prompts issued by psql proper.
It does seem safe to assume that the banner output we want will be
followed by a newline, since that should be the last output before
things quiesce. Therefore, we can improve matters by putting quotes
around the banner strings in the \echo and \warn psql commands, so
that their echoes cannot include banner directly followed by newline,
and then checking for just banner-and-newline in the match pattern.
While at it, spruce up the pump() call in sub query() to look like
the neater version in wait_connect(), and don't die on timeout
until after printing whatever we got.
Reported-by: Oleg Tselebrovskiy <o.tselebrovskiy@postgrespro.ru>
Diagnosed-by: Oleg Tselebrovskiy <o.tselebrovskiy@postgrespro.ru>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Soumya S Murali <soumyamurali.work@gmail.com>
Discussion: https://postgr.es/m/db6fdb35a8665ad3c18be01181d44b31@postgrespro.ru
Backpatch-through: 14
6548e4a10d