A Fool's Errand or should I try?

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Fractal Encrypt

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May 4, 2024, 11:40:24 AMMay 4
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TLDR: I'd like to investigate the possibilities of extending decoderawtransaction to include the fee (and maybe even sats per v/b).

I'm hoping it will be a good project for me to work on and build at least a tiny understanding of bitcoin development.

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I use the createrawtransaction function to create transactions, and before broadcasting, I always like to use decoderawtransaction to see if I made any mistakes.

I've sometimes messed up on the fee calculation, as I do that myself with a calculator.

Unfortunately decoderawtransaction doesn't give me the fee information (for a very good reason, it is not aware of the value of the inputs in the tx).

So to double check the fees, instead of using createrawtransaction, I'll use createpsbt and then go through the process of finalizing it so I can run decodepsbt, which does give the fee along with all the other relevant data.

But the createpsbt process is more work for a simple transaction where all UTXOs are in the wallet I am creating the rawtx in.

My goal would be to modify decoderawtransaction to perform these additional steps:
  1. Fetch UTXO details for each input.
  2. Calculate the total input value.
  3. Subtract the total output value to determine the fee.
Additionally there are the considerations about whether the inputs in the transaction are in your wallet or not.

If I run listunspent it gives me the info I need to create the raw tx or psbt, and it has the values of the UTXOs that will be used as inputs in my tx.

But I understand decoderawtransaction is meant to be used whether or not the keys are in your wallet (so I was thinking to make a command argument T/F to show the fee value only if keys are in your wallet).

Alternatively if you are running the command in a node with txindex, then you have the full chainstate to look up txids (whether unspent or not) - so this needs to be addressed too.

Doing this within my own node would be cool enough and I don't necessarily need it to go farther than that. However if I do get it working, I'd certainly try to submit a PR.

I have no idea if any of this is possible, so I wanted to ask here for some guidance and maybe mentorship in this self-interest driven project. Also looking for this to be shot down mercilessly if it's just ridiculous.

My abilities and skills are very low. My interest and persistence are high.

Any help or ridicule invited ;)

Ali Sherief

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May 5, 2024, 9:30:48 AMMay 5
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Currently the only way you can fetch the previous input addresses and amounts is if you use the getblock RPC call with a verbosity of 3. This will obviously cause it to print a lot of raw transactions. But since decoderawtrasnsaction is independent of the blocks that are actually stored on your disk, you'd have to modify it to locate each input inside the blocks.dat folder, and then assemble an equivalent "prevout" structure as in getblock.

There is also the issue of the txo not actually existing in the blockchain, which means that such a prevout structure would not exist in the first place.

I think it would be better to create a separate RPC for this, maybe 'getfulltransaction' or something like that since gettransaction for in-walet txs already exists, to implement such functionality.

-Ali

bitcoin-dev...@slmail.me

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May 6, 2024, 5:47:42 AMMay 6
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Are you aware of getrawtransaction verbosity=2? Refer to
https://bitcoincore.org/en/doc/27.0.0/rpc/rawtransactions/getrawtransaction/
for the RPC documentation.

Fractal Encrypt

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May 6, 2024, 6:57:26 AMMay 6
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Thanks Ali, I will investigate these avenues you've pointed out. Most appreciated!

Fractal Encrypt

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May 6, 2024, 8:00:04 PMMay 6
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I am/was not until now) aware of getrawtransaction verbosity=2.

It appears to be for transactions already in the mempool or confirmed in a block. Can it also be used prior to broadcasting a transaction?

I saw the documentation referenced gettransaction but that doesn't seem to fit either.

But it's also possible I am totally missing what you are trying to point out to me...

bitcoin-dev...@slmail.me

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May 7, 2024, 4:43:31 AMMay 7
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> It appears to be for transactions already in the mempool or confirmed in a block. Can it also be used prior to broadcasting a transaction?

To get the fee of a transaction prior to broadcast, you can use
testmempoolaccept. The documentation is at
https://bitcoincore.org/en/doc/27.0.0/rpc/rawtransactions/testmempoolaccept/

Best,
void867

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