Transaction amount for bitcoin payment gateway

Question

I'm trying to add bitcoin payment for my ecommerce website. I have installed bitcoind on the server and i've set the notify wallet parameter in bitcoin.conf. the issue i have now is how to know that the client have sent the exact needed amount for products they bought.

Actually, the client can send a lower amount to my wallet and notify wallet will be generated. Please help to handle this issue.

Answer 1

If you insist on using bitcoind directly, you could always use the gettransaction rpc call to get transaction info on that transaction.

Hopefully you're using xpubs or at least a list of pre-imported addresses, and not using that bitcoind to manage your wallet/generate new addresses itself though. You shouldn't keep your private key on the live bitcoind node connected to your public ecommerce site.

Answer 2

Walletnotify needs to be defined in your bitcoin.conf file, example:

walletnotify = /usr/bin/php some/path/newdeposit.php?tx=%s    

In the above example every time there is a new transaction on your wallet, the newdeposit.php script will run and the transaction ID will be stored in a GET named "tx".

Then we can pull the transaction id from the tx GET and put it through a gettransaction command.

$tx = $_GET['tx'];
$getTrans = $bitcoin->gettransaction($tx);

From there we need to look through the API response, see if it has at least once confirmation, and how much was sent. We'll do this by running a loop, checking for the "receive" category. If there is a match you can do whatever you want in your database.

$confirmations = $getTrans["confirmations"];

if($confirmations < 1){
die();

} else {
 $countDetails = count($getTrans['details']);
 for($i=0;$i<$countDetails;$i++){
   $getAddress = $getTrans['details'][$i]['address'];
   $getReceive = $getTrans['details'][$i]['category'];
  
   if($getAddress == $myAddress && $getReceive == "receive"){
    $amount = $getTrans['details'][$i]['amount'];
    $amount = $amount * 100000000;
    //do something with $amount
   }

 }
 
}

Walletnotify only fires twice. Once when the transaction first appears on the network, and a second time after it has been included in a block(one confirmation).

Don't forget to multiply the amount by 100 million to turn it into satoshis so you're not working with floats.