Welcome, developer!
As you may have seen, we are moving to utilising a minimum fee per byte at block 2,200,000. For more information on the reasons behind this decision, please check out this article from the core team: https://blog.turtlecoin.lol/archives/the-turtlecoin-journey-2-years-and-counting/
If you have an application which sends transactions on the TurtleCoin network, you will likely have to update your code to work correctly with fee per byte.
Step one is ensuring you have the latest code. This can currently be found here, but once fully tested will be made into a published release.
Once you are running version 0.22.0 of the software, you will need to update your code to work with it correctly.
Since we charge a fee per byte of 5.00 TRTL (Or 500 atomic units) per 256 bytes of transaction, and transactions are limited at 124400 bytes if you're using the core software, you can just set a fixed fee of 2430 TRTL, or 243000 atomic units.
This fee will always be large enough to cover the biggest transactions, so you can just update your fee parameter in your sendTransaction JSON, both with turtle-service and wallet-api, and you're done.
However, this is not the cheapest way. In addition, if the minimum fee per byte is increased in a later fork, you will have to update your code again. Booooo!
Read on if you want to make your users like you more. Don't worry, it's not hard!
If you just want to use the minimum fee per byte allowed, all you have to do is not specify the fee parameter in your sendTransaction or JSON. The wallet application, be it turtle-service, or wallet-api, will then automatically calculate the minimum fee for the transaction.
Once the transaction is sent, the actual fee paid will be returned along with the transaction hash. This way you can update your database, display the fee to the user, and so on, as needed.
"Hang On!" - I hear you shout. How do you know how much the fee will be before sending the transaction? Not to fear - we've thought of that.
With turtle-service, instead of using sendTransaction, you can use createDelayedTransaction. This method works exactly the same as sendTransaction, except it does not relay the transaction to the network - so no funds are sent. It will return the transaction hash, and the fee of the transaction.
If the fee is fine, and you want to send the transaction, you can use the sendDelayedTransaction method.
If you're not happy with the fee, or want to cancel the transaction for some other reason, use the deleteDelayedTransaction method to cancel the transaction. If you do not delete the delayed transaction, the funds will remain unspendable, so don't forget this step!
With wallet-api, the process is very similar. Instead of using /transactions/send/basic or /transactions/send/advanced, you can use /transactions/prepare/basic or /transactions/prepare/advanced.
As will turtle-service, these methods are identical to the standard ones, and take all the same parameters.
Again, like turtle-service, these methods will return the fee of the prepared transaction, and the transaction hash.
You can then use /transactions/send/prepared to send your prepared transaction if you are happy with the fee. If you want to cancel a prepared transaction, use the /transactions/prepared/{transaction hash}/ DELETE method.
Unlike turtle-service, a prepared transaction does not lock your funds for spending, and therefore cancelling a prepared transaction is not mandatory. It will, however, save a little bit of RAM usage from not having to store the transaction data.
Due to the funds not being locked, this can result in a previously prepared transaction no longer being possible to be sent - If you sent another transaction meanwhile, it could include inputs that the prepared transaction also included.
Finally, due to a deterministic input selection algorithm, even if your prepared transaction is no longer valid, the fee for sending the same transaction again is likely to be very similar. This means you can essentially use the prepare transaction methods as a means to estimate the fee of a subsequent transaction with the same data.
If you desire to pay a higher than minimum fee per byte, we have you covered. Simply include the feePerByte argument in your transaction JSON, in replacement of the fee parameter. This value can be a floating point value, and should be greater or equal to the minimum fee per byte of 1.953125.
If you are a pool operator, you may want to consider upping the default payout thresholds. This will result in you paying less fees, and will also mean your users pay less fees when they come to spend their funds - they will have less resulting inputs in their wallet, so will create smaller, cheaper, transactions.
Confused? Want some more help?
Start by checking out the documentation of the API you are using.
For wallet-api, head to https://turtlecoin.github.io/wallet-api-docs/
For turtle-service, head to https://docs.turtlecoin.lol/developer/api/legacy-wallet-rpc-api
Finally, if you just can't get the hang of it, or want some clarification on how it all works, stop by the #dev_learning or #dev_general channels in our discord, and we'll happily help you out. If you're not in discord already, you can find the invite at chat.turtlecoin.lol.
Happy Hacking!