How to estimate mining fee for raw transaction?

0

In our application we are generating a trasaction hex using the createrawtransaction call to "handcraft" a transaction. The problem we are facing is that we would like to estimate the mining fee for this transaction. I realize that we could call estimatefee x to estimate the mining fee per byte. But the problem is we are generating the transaction, so we don't know the size of the transaction yet! Chicken or egg?! I realize that we can generate a transaction and then account for the mining fee based on the hex, but this sounds like a hack to me.

So the question is: what's the best way to estimate the optimal mining fee while using createrawtransaction ?

motatoes

Posted 2017-02-07T08:18:39.080

Reputation: 133

Answers

1

Have a look at fundrawtransaction (if you are okay using the internal wallet). fundrawtransaction will give you back the used fee (next to the hex byte-array of the funded transaction) before signing or broadcasting the transaction.

The ideal workflow is:

  • createrawtransaction '[]' '{"<addr>": <amount>}' //set no inputs
  • fundrawtransaction <hex>
  • you'll get back {"hex":<tx>, "fee": <amount>, "changepos": <pos of the change output>}
  • Check the fee, maybe increase it (requires Bitcoin Core 0.14, use the feeRate of fundrawtransaction.
  • signrawtransaction <hex>
  • sendrawtransaction <hex>

Jonas Schnelli

Posted 2017-02-07T08:18:39.080

Reputation: 5 465

This is a great suggestion! But we want to spend from a particular address in the wallet which we retrieve from listunspent .. so it won't work for us as there is no way to do this filtering in fundrawtransaction – motatoes – 2017-02-07T10:21:34.607

In that case you need to calculate the transaction size by yourself by assume 72byte per EC sig. But it depends what types of inputs you support (P2PKH, etc.). – Jonas Schnelli – 2017-02-07T19:40:16.447

Well they are all multisig addresses .. So P2SH – motatoes – 2017-02-07T21:05:34.373

Asked: 2017-02-07T08:18:39.080

Viewed: 736 times

Active: 2017-02-07T08:43:57.727