Friday, November 25, 2005

Hiding connection parameters with Perl/DBI

In a Perl application, using the widely known DBI module, a database connection is fired up by an instruction such as this one:
my $dbh = DBI->connect("DBI:mysql:test",
"user_name", "my_secret_password", { RaiseError => 1 })
or die "something went wrong ($DBI::errstr)";
The first parameter is compulsory, and it's made of "dbi", which is the same for all connections, the database driver, which in our case is "mysql", and the database name, in our case "test". For a self respecting database, we should also specify the user name and password.
Nothing to complain about if this script is safely stored in your home directory, screened from prying eyes by the OS permissions.
But what happens when you need to distribute this script to somebody? You need to remember to change username and password to some dummy text, to avoid the burden of having to change our real credentials if by dumb chance we sent away our script with the password for everybody to see it.

Luckily, there is an easy solution to hide connection variables from others. You just need to store them in a configuration file, which can be kept in a guarded location and never distributed. So it will be visible to your script as long as it is within the boundaries of your system, but it will be invisible to others, and moreover it won't follow the script if you need to send it away.

It works like this. In your home directory (or the home directory of the user that will execute the script, for example, for a cron job) you create afile named ".my.cnf", containing the following:
[client]
user=user_name
password=my_secret_password
The file needs to be protected with the right privileges (chmod 600 .my.cnf) so that it can't be accessed by other users. Then, you change the connection statement like this:
my $dbh = DBI->connect("DBI:mysql:test"
. ";mysql_read_default_file=$ENV{HOME}/.my.cnf",
undef, undef) or die "something went wrong ($DBI::errstr)";
The "mysql_read_default_file" option will point to the file with the connection variables. Notice that instead of username and password there are two null values (undef). The file name, in this case, is built from the environment variable "$HOME" (in Unix like systems). You can also state it literally, but this trick will make the script usable from different users without modifications. The only thing each of them needs is a configuration file.
For more stuff on Perl/DBI, see DBI recipes.

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