estimatefee: tx fee estimate for selected inputs

[hieblmi]

EstimateFee now takes optional inputs to give a fee estimate. If --show_outpoints is provided the auto-selected inputs are returned.

Examples:

reg_zane estimatefee '{"bcrt1q7dnuwzl87hunndngmgzs9s8t279jjkrdgkjp4t" : 500600001}' --conf_target 1 --utxo ca1c4fc61331b35adc8032e8b61461986f40c7f97c1e83c27a181defe5a08ee4:1 --utxo d9665f3fe1190098b2bc0836e25e7a1019e2532b2cca4b5acfb974de5d01b90c:0 --utxo 734d2c21da9e95b412bef63c036b7d72f8c365abab05cc1e5973b292a5d976a2:0 --utxo f766ae254d150cd2556efa096503fba86b29674e606b44a8bbf44b504bdd31d0:1
{
    "fee_sat": "8950",
    "feerate_sat_per_byte": "25",
    "sat_per_vbyte": "25"
}

reg_zane estimatefee '{"bcrt1q7dnuwzl87hunndngmgzs9s8t279jjkrdgkjp4t" : 300001}' --conf_target 2 --show_outpoints
{
    "fee_sat": "3825",
    "feerate_sat_per_byte": "25",
    "sat_per_vbyte": "25",
    "outpoints": [
        "ca1c4fc61331b35adc8032e8b61461986f40c7f97c1e83c27a181defe5a08ee4:1"
    ]
}

[gemini-code-assist]

Summary of Changes

Hello @hieblmi, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the estimatefee RPC by introducing the ability for users to explicitly define which unspent transaction outputs (UTXOs) should be considered when estimating transaction fees. Additionally, it provides an option to return the exact outpoints used in the estimation, enhancing transparency and control for users who need precise fee calculations based on specific inputs.

Highlights

• Enhanced estimatefee command: The estimatefee command now supports specifying custom UTXOs for fee estimation using a new --utxo flag.
• Outpoint visibility: A new --show_outpoints flag has been introduced, allowing users to view the specific outpoints (UTXOs) that were used in the fee estimation process.
• API and Protocol Updates: The EstimateFeeRequest and EstimateFeeResponse protobuf messages have been extended to accommodate the new outpoints input and show_outpoints output.
• RPC Server Logic: The RPC server's EstimateFee handler has been updated to parse and validate user-provided outpoints, pass them to the wallet's transaction creation logic, and return the selected outpoints in the response when requested.

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[gemini-code-assist]

Code Review

This pull request enhances the estimatefee command by allowing users to specify UTXOs for fee estimation and to view the selected outpoints. The implementation is solid, with appropriate changes to the RPC interface, command-line flags, and server-side logic, including validation for duplicate UTXOs. My feedback includes a couple of minor suggestions to improve error messages for better clarity and to align with the repository's style guide.

[gemini-code-assist]

The error message "can't create outpoints" is a bit vague. A more descriptive message would be helpful for debugging, indicating that the failure occurred during the conversion of outpoints. Also, the style guide suggests minimizing lines for error messages.¹

if err != nil {
			return nil, fmt.Errorf("failed to convert rpc outpoints to wire outpoints: %w", err)
		}

Style Guide References

Footnotes

1. Minimize lines for log and error messages, while adhering to the 80-character limit. ↩

[gemini-code-assist]

This error message can be simplified to a single line to improve readability, which is preferred by the style guide when the line length allows.¹

if fn.HasDuplicates(wireOutpoints) {
			return nil, fmt.Errorf("selected outpoints contain duplicate values")
		}

Style Guide References

Footnotes

1. Minimize lines for log and error messages, while adhering to the 80-character limit. ↩

[sputn1ck]

is there a reason to not show them?

[hieblmi]

Thanks for your review! In case we provide a list of outpoints manually I thought they don't have to be displayed again in the output. Only if we estimate for an amount would it make sense to show them imo.

[sputn1ck]

There is already an Outpoint message defined. that would make it easier to pass it over to the next call right?

[hieblmi]

that's a good one, I will change that.