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Allow psql to re-use connection parameters after a connection loss.

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Instead of immediately PQfinish'ing a dead connection, save it aside
so that we can still extract its parameters for \connect attempts.
(This works because PQconninfo doesn't care whether the PGconn is in
CONNECTION_BAD state.)  This allows developers to reconnect with
just \c after a database crash and restart.

It's tempting to use the same approach instead of closing the old
connection after a failed non-interactive \connect command.  However,
that would not be very safe: consider a script containing
	\c db1 user1 live_server
	\c db2 user2 dead_server
	\c db3
The script would be expecting to connect to db3 at dead_server, but
if we re-use parameters from the first connection then it might
successfully connect to db3 at live_server.  This'd defeat the goal
of not letting a script accidentally execute commands against the
wrong database.

Discussion: https://postgr.es/m/38464.1603394584@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2020-10-23 17:07:15 -04:00
parent 860593ec3b
commit 1b62d0fb3e
6 changed files with 73 additions and 26 deletions
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57
src/bin/psql/command.c
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@@ -3060,26 +3060,28 @@ do_connect(enum trivalue reuse_previous_specification,
break;
}
/*
* If we are to re-use parameters, there'd better be an old connection to
* get them from.
*/
if (reuse_previous && !o_conn)
{
pg_log_error("No database connection exists to re-use parameters from");
return false;
}
/*
* If we intend to re-use connection parameters, collect them out of the
* old connection, then replace individual values as necessary. Otherwise,
* obtain a PQconninfoOption array containing libpq's defaults, and modify
* that. Note this function assumes that PQconninfo, PQconndefaults, and
* PQconninfoParse will all produce arrays containing the same options in
* the same order.
* old connection, then replace individual values as necessary. (We may
* need to resort to looking at pset.dead_conn, if the connection died
* previously.) Otherwise, obtain a PQconninfoOption array containing
* libpq's defaults, and modify that. Note this function assumes that
* PQconninfo, PQconndefaults, and PQconninfoParse will all produce arrays
* containing the same options in the same order.
*/
if (reuse_previous)
cinfo = PQconninfo(o_conn);
{
if (o_conn)
cinfo = PQconninfo(o_conn);
else if (pset.dead_conn)
cinfo = PQconninfo(pset.dead_conn);
else
{
/* This is reachable after a non-interactive \connect failure */
pg_log_error("No database connection exists to re-use parameters from");
return false;
}
}
else
cinfo = PQconndefaults();
@@ -3360,14 +3362,26 @@ do_connect(enum trivalue reuse_previous_specification,
if (o_conn)
{
/*
* Transition to having no connection. Keep this bit in sync
* with CheckConnection().
* Transition to having no connection.
*
* Unlike CheckConnection(), we close the old connection
* immediately to prevent its parameters from being re-used.
* This is so that a script cannot accidentally reuse
* parameters it did not expect to. Otherwise, the state
* cleanup should be the same as in CheckConnection().
*/
PQfinish(o_conn);
pset.db = NULL;
ResetCancelConn();
UnsyncVariables();
}
/* On the same reasoning, release any dead_conn to prevent reuse */
if (pset.dead_conn)
{
PQfinish(pset.dead_conn);
pset.dead_conn = NULL;
}
}
return false;
@@ -3421,8 +3435,15 @@ do_connect(enum trivalue reuse_previous_specification,
PQdb(pset.db), PQuser(pset.db));
}
/* Drop no-longer-needed connection(s) */
if (o_conn)
PQfinish(o_conn);
if (pset.dead_conn)
{
PQfinish(pset.dead_conn);
pset.dead_conn = NULL;
}
return true;
}