pg_dump: fix crash on error

If pg_dump fails to connect to Postgres, it attempts to print an error
message in ConnectDatabase():

/* check to see that the backend connection was successfully made */
if (PQstatus(AH->connection) == CONNECTION_BAD)
die_horribly(AH, modulename,
"connection to database \"%s\" failed: %s",
dbname, PQerrorMessage(AH->connection));

But if no database is explicitly specified, `dbname' is NULL, and libc
is entitled to crash if you pass a NULL pointer to it for a %s
formatting sequence (it actually does crash on Solaris, for example --
per report from Omar Kilani).

Attached is a patch that fixes this by just removing `dbname' from the
error message, as PQerrorMessage() should provide enough information.

Barring any objections, I'll apply this to HEAD and back branches within
24 hours.

-Neil

Neil Conway <neilc(at)samurai(dot)com> writes:
> If pg_dump fails to connect to Postgres, it attempts to print an error
> message in ConnectDatabase():
> ...
> But if no database is explicitly specified, `dbname' is NULL, and libc
> is entitled to crash if you pass a NULL pointer to it for a %s
> formatting sequence (it actually does crash on Solaris, for example --
> per report from Omar Kilani).

[ scratches head... ] Did this code change recently? It's a tad hard
to believe that such a thing could have gone unnoticed for long.

regards, tom lane

Tom Lane wrote:
> [ scratches head... ] Did this code change recently? It's a tad hard
> to believe that such a thing could have gone unnoticed for long.

Seems the problem was introduced here:

http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_db.c.diff?r1=1.58;r2=1.59

(I could just revert the code to using PQdb(), but I don't think there's
a need to mention the database in the error message ourselves --
PQerrorMessage() should include that information if appropriate.)

-Neil

Neil Conway <neilc(at)samurai(dot)com> writes:
> Tom Lane wrote:
>> [ scratches head... ] Did this code change recently? It's a tad hard
>> to believe that such a thing could have gone unnoticed for long.

> Seems the problem was introduced here:
> http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_db.c.diff?r1=1.58;r2=1.59

Oh dear, that makes it my fault :-(

> (I could just revert the code to using PQdb(), but I don't think there's
> a need to mention the database in the error message ourselves --
> PQerrorMessage() should include that information if appropriate.)

I'd go with reverting it to using PQdb, myself. Looks like I got bit by
the perennial mantra: premature optimization is the root of all evil.

regards, tom lane

Tom Lane wrote:
> I'd go with reverting it to using PQdb, myself.

Fair enough; reverted to using PQdb(), and applied to HEAD and
REL8_0_STABLE.

-Neil