Up to now, you couldn't escape out of psql's \password command
by typing control-C (or other local spelling of SIGINT). This
is pretty user-unfriendly, so improve it. To do so, we have to
modify the functions provided by pg_get_line.c; but we don't
want to mess with psql's SIGINT handler setup, so provide an
API that lets that handler cause the cancel to occur.
This relies on the assumption that we won't do any major harm by
longjmp'ing out of fgets(). While that's obviously a little shaky,
we've long had the same assumption in the main input loop, and few
issues have been reported.
psql has some other simple_prompt() calls that could usefully
be improved the same way; for now, just deal with \password.
Nathan Bossart, minor tweaks by me
Discussion: https://postgr.es/m/747443.1635536754@sss.pgh.pa.us
Further experience says that the appending behavior offered by
pg_get_line_append is useful to only a very small minority of callers.
For most, the requirement to reset the buffer after each line is just
an error-prone nuisance. Hence, invent another alternative call
pg_get_line_buf, which takes care of that detail.
Noted while reviewing a patch from Daniel Gustafsson.
Discussion: https://postgr.es/m/48A4FA71-524E-41B9-953A-FD04EF36E2E7@yesql.se
Letting the caller provide a StringInfo to read into is helpful when
the caller needs to merge lines or otherwise modify the data after
it's been read. Notably, now the code added by commit 8f8154a50
can use pg_get_line_append() instead of having its own copy of that
logic. A follow-on commit will also make use of this.
Also, since StringInfo buffers are a minimum of 1KB long, blindly
using pg_get_line() in a loop can eat a lot more memory than one would
expect. I discovered for instance that commit e0f05cd5b caused initdb
to consume circa 10MB to read postgres.bki, even though that's under
1MB worth of data. A less memory-hungry alternative is to re-use the
same StringInfo for all lines and pg_strdup the results.
Discussion: https://postgr.es/m/1315832.1599345736@sss.pgh.pa.us
This patch started out with the goal of harmonizing various arbitrary
limits on password length, but after awhile a better idea emerged:
let's just get rid of those fixed limits.
recv_password_packet() has an arbitrary limit on the packet size,
which we don't really need, so just drop it. (Note that this doesn't
really affect anything for MD5 or SCRAM password verification, since
those will hash the user's password to something shorter anyway.
It does matter for auth methods that require a cleartext password.)
Likewise remove the arbitrary error condition in pg_saslprep().
The remaining limits are mostly in client-side code that prompts
for passwords. To improve those, refactor simple_prompt() so that
it allocates its own result buffer that can be made as big as
necessary. Actually, it proves best to make a separate routine
pg_get_line() that has essentially the semantics of fgets(), except
that it allocates a suitable result buffer and hence will never
return a truncated line. (pg_get_line has a lot of potential
applications to replace randomly-sized fgets buffers elsewhere,
but I'll leave that for another patch.)
I built pg_get_line() atop stringinfo.c, which requires moving
that code to src/common/; but that seems fine since it was a poor
fit for src/port/ anyway.
This patch is mostly mine, but it owes a good deal to Nathan Bossart
who pressed for a solution to the password length problem and
created a predecessor patch. Also thanks to Peter Eisentraut and
Stephen Frost for ideas and discussion.
Discussion: https://postgr.es/m/09512C4F-8CB9-4021-B455-EF4C4F0D55A0@amazon.com
Bruce Momjian
Tom Lane