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DPS are New Zealand’s biggest player in the payments gateway business. They’ve been around for as long as I’ve been building E-Commerce sites which must be at least 6 or 7 years now.

Their main service for handling card processing on sites is Payment Express, or PX. It’s been through a number of different incarnations over time, from requiring a proxy daemon (running on the hosting server itself) in the old days to now having a clean web service interface.

DPS have always provided excellent documentation, but their example code for PHP only covered the most basic situations and wasn’t easily reusable. I had always intended to publish some interface code ‘once it was good enough’ and since this class is being used on a dozen or so sites now, it must be the right time.

There are still some features to come like handling refunds and Auth/Completion transactions, and sometime soon I’ll remove the dependency on PEAR::HTTP_Request. I might even backport it to PHP4 if anyone needs it.

Billing a Credit Card

In it’s simplest form, billing a credit card requires very little code:

$dps = new DPSPXPost(DPS_USERNAME, DPS_PASSWORD);
$dps->chargeCard($name, $number, $exp_month, $exp_year, $amount);

You’ll certainly want to check that the transaction was a success though, and record the DPS transaction ID somewhere:

try {
  $txn_ref = $dps->chargeCard($name, $number, $exp_month, $exp_year, $amount);
  // Success!
  printf('Transaction OK: DPS Reference %s', $txn_ref);
} catch (Exception $e) {
  printf('Transaction Failed: %s', $e->getMessage());
}

That was easy and probably covers the vast majority of E-Commerce implementations. How about if we want to get a bit more clever and store our user’s card details (securely) with DPS, for billing again later? Maybe we’re checking their card is valid first, or planning to rebill at the end of each month.

Rebilling a Loaded Card

First we load the card details into the DPS system. Be aware that you’ll need tipping to be enabled on your merchant facility, and activated by DPS for your account.

try {
  $id = $dps->loadCard($name, $number, $exp_month, $exp_year);
} catch (Exception $e) {
  printf("Couldn't load card: %s", $e->getMessage());
}

Now that we’ve sent the credit card details to DPS, we can remove all trace of them from our system. That means there’s no security risk to your customers if anything should happen to your server.

We can then initiate a charge to the card any time by providing the Billing ID we were given when we loaded the card. Again this is just a single line of code, along with some error checking:

try {
  $txn_ref = $dps->chargeLoadedCard($id, $amount);
} catch (Exception $e) {
  printf('Transaction Failed: %s', $e->getMessage());
}

Show me the Code

There are a lot of options for the interface that I haven’t covered here, not least of which is a debugging log. Browse through the API docs at your leisure to see what else you can do.

Hopefully this will be useful to other developers - feel free to send me questions / comments / bug fixes / improvements / beer.

» Download DPSPXPost.zip

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