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Request #34906 mysql: no way to get errno for a failed secondary connection attempt
Submitted: 2005-10-18 13:19 UTC Modified: 2012-05-04 16:01 UTC
Avg. Score:4.7 ± 0.7
Reproduced:6 of 6 (100.0%)
Same Version:0 (0.0%)
Same OS:4 (66.7%)
From: feldgendler at mail dot ru Assigned: mysql (profile)
Status: Wont fix Package: MySQL related
PHP Version: 5CVS-2005-10-19 (cvs) OS: *
Private report: No CVE-ID: None
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 [2005-10-18 13:19 UTC] feldgendler at mail dot ru
This is actually a bug in the well-defined and documented API, so there is no reproduce code here.

After successfully establishing a connection, when an attempt to create another connection fails, there is no way to find out the errno. This is because mysql_errno() always uses an established link, either the one passed as the argument or the default one. There is just no way to find out why the second connection failed.

// assume this one succeeds
$first_connection = mysql_connect($host1, $u1, $p1);

// at this point, $first_connection is the default link

// assume this one fails
$second_connection = mysql_connect($host2, $u2, $p2);

// $second_connection is false,
// $first_connection is still the default link

echo mysql_errno();
// 0 is printed because there is no error
// on $first_connection

Before stamping "Bogus" on this bug, please note the following:

1. I have read the manual about mysql_errno() and mysql_connect(). Every word of it. Even more, I think that PHP currently behaves as documented. But it's just wrong because there is no way to find out why a connection has failed.

2. I have read other bug reports about mysql_errno(). They are actually about other issues, or they don't state this problem clearly enough, so I'm filing this bug report to make it clear what the problem is.

3. I have read the source code of the mysql extension. From the source, I've found out that the error code and message from a failed connection attempt is really stored in mysql_globals (connect_errno and connect_error), but mysql_errno() PHP function only returns MySG(connect_errno) when the function is invoked without arguments AND there is no default link. If there is a default link, and an attempt to establish a second one has failed, there isn't a way to have MySG(connect_errno) returned to the PHP program.

It is not obvious how to fix this bug, because it isn't a deviation from the documented behavior, but rather an incompleteness of the API. Two of the possible approaches are proposed here:


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 [2005-10-18 13:43 UTC]
Assigned to the maintainer.
Georg, please check the patch:
 [2005-10-18 13:51 UTC] feldgendler at mail dot ru
About the patch: I think it's not enough. Once a connection attempt has failed, conect_errno will be nonzero, and mysql_errno() without arguments always will return this value. This will be too much deviation from the current behavior -- in fact, many always call mysql_errno() without arguments. Here is a typical script which will be broken:

if (!mysql_connect('dbhost', 'user', 'pass')) {
    mysql_connect('backup-dbhost', 'user', 'pass');
// ...
if (!mysql_query("...")) {
    echo mysql_errno(); // This will print connect_errno!

I think that connect_errno should be reset to zero somewhere, but I don't know where it would be appropriate. mysql_errno() shouldn't reset connect_errno because mysql_error() and mysql_errno() are expected to be idempotent.
 [2010-12-20 14:14 UTC]
-Package: Feature/Change Request +Package: MySQL related
 [2011-02-16 11:43 UTC]
-Assigned To: georg +Assigned To: johannes
 [2011-02-16 11:43 UTC]
Reassigned to Johannes.
The patch is still available here:
 [2011-02-16 12:07 UTC]
-Assigned To: johannes +Assigned To: mysql
 [2011-02-16 12:07 UTC]
The "easy" solution is to use mysqli without this default connection magic.

Making this work doesn't look trivial as these two cases have to work:

mysql_connect('localhost', 'valid', 'password');
mysql_connect('localhost', 'invalid', 'something');
mysql_query('invalid query');
echo mysql_error(); // should report the query error

as well as

mysql_connect('localhost', 'valid', 'password');
mysql_query('invalid query');
mysql_connect('localhost', 'invalid', 'something');
echo mysql_error(); // Should report the connect error

Assigning to mysql team
 [2012-05-04 16:01 UTC]
-Status: Assigned +Status: Wont fix
 [2012-05-04 16:01 UTC]
It may be a valid feature request but meanwhile ext/mysql is in the process of being softly deprecated. So, no feature additions for ext/mysql any more. Security fixes, sure, feature additions, sorry, migrate to ext/mysqli.
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