estimatefee: tx fee estimate for selected inputs #10296

hieblmi · 2025-10-15T14:05:21Z

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": [
        {
            "txid_bytes": "",
            "txid_str": "ba88c81dd1456de4714a2c09d38355374362d3e5d97daf00c76f4b918a280b3b",
            "output_index": 0
        }
    ]
}

gemini-code-assist · 2025-10-15T14:05:39Z

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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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.

rpcserver.go

sputn1ck · 2025-10-16T08:45:39Z

lnrpc/lightning.proto

+    repeated OutPoint outpoints = 6;
+
+    // Whether to include the selected outpoints in the response.
+    bool show_outpoints = 7;


is there a reason to not show them?

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.

@gemini-code-assist I think it would make sense to acutally return them as well instead of having this clumsy boolean in the API

I agree with @ziggie1984. From an API design perspective, it's generally beneficial to have predictable responses. Always returning the outpoints in the EstimateFeeResponse, regardless of whether they were provided as input or auto-selected, would simplify client-side logic and provide a more consistent and complete view of the transaction being estimated. This removes the need for the show_outpoints boolean flag in the request, making the API cleaner and easier to use.

I agree with the LLM here as well, let's always show the inputs

lnrpc/lightning.proto

lightninglabs-deploy · 2025-12-23T10:44:59Z

@sputn1ck: review reminder
@ziggie1984: review reminder
@hieblmi, remember to re-request review from reviewers when ready

hieblmi · 2025-12-23T11:16:00Z

Rebased

ziggie1984

Small change, I wonder when this is useful without being able to finally force this transaction to happen via sendcoins, or is this already possible ?

lnrpc/lightning.proto

ziggie1984 · 2025-12-23T11:22:26Z

cmd/commands/commands.go

 		AddrToAmount:          amountToAddr,
 		TargetConf:            int32(ctx.Int64("conf_target")),
 		CoinSelectionStrategy: coinSelectionStrategy,
+		Outpoints:             outpoints,


what if the outpoints (inputs) are not enough what is the behaviour ?

In that case CreateSimpleTx inside EstimateFee will return an error, see

lnd/rpcserver.go

Line 1291 in 013f5c9

tx, err = wallet.CreateSimpleTx(

can you add a comment how it behaves in that case

docs/release-notes/release-notes-0.21.0.md

ziggie1984 · 2025-12-23T14:18:56Z

rpcserver.go

-			nil, outputs, feePerKw, minConfs, coinSelectionStrategy,
-			true,
+			selectOutpoints, outputs, feePerKw, minConfs,
+			coinSelectionStrategy, true,


does the coinselection strategy still have an effedt if we select inputs ?

The selectOutpoints end up as inputs in CreateSimpleTx:

lnd/lnwallet/btcwallet/btcwallet.go

Line 951 in 9a83b38

func (b *BtcWallet) CreateSimpleTx(inputs fn.Set[wire.OutPoint],

The strategy is then ignored in the wallet code if selectOutpoints is set, see: https://github.com/btcsuite/btcwallet/blob/0418e81774bdca20c5b34172e64ab26735de5008/wallet/createtx.go#L194

ziggie1984 · 2025-12-23T14:19:18Z

rpcserver.go


+	// Return the outpoints the estimate is for if the client requested so.
+	outpoints := make([]*lnrpc.OutPoint, 0, len(tx.Tx.TxIn))
+	if in.ShowOutpoints {


always return the outpoints

I thought if the client specifically states the inputs they don't need to be shown to them again. But for consistency of the output I think that's ok.
I removed this option and always show them.

hieblmi · 2025-12-24T08:34:08Z

lnrpc/lightning.proto

    uint64 sat_per_vbyte = 3;
+
+    // A list of selected outpoints as inputs for the transaction.
+    repeated OutPoint outpoints = 4;


Changed this to inputs as well.

hieblmi marked this pull request as draft October 15, 2025 14:05

gemini-code-assist bot reviewed Oct 15, 2025

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saubyk assigned hieblmi Oct 15, 2025

saubyk added this to the v0.21.0 milestone Oct 15, 2025

saubyk added this to v0.21 Oct 15, 2025

saubyk moved this to In progress in v0.21 Oct 15, 2025

sputn1ck reviewed Oct 16, 2025

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hieblmi mentioned this pull request Oct 20, 2025

feature: outpoint based EstimateFee API #10304

Open

hieblmi force-pushed the estimate-inputs branch 2 times, most recently from 6d12c75 to 04bfef2 Compare November 25, 2025 10:31

hieblmi requested a review from sputn1ck November 25, 2025 10:32

hieblmi marked this pull request as ready for review November 25, 2025 10:32

hieblmi force-pushed the estimate-inputs branch 2 times, most recently from 716fd8b to 3a24364 Compare November 25, 2025 10:45

hieblmi requested a review from ziggie1984 December 2, 2025 10:39

hieblmi force-pushed the estimate-inputs branch from 3a24364 to 658f073 Compare December 23, 2025 11:15

ziggie1984 reviewed Dec 23, 2025

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hieblmi force-pushed the estimate-inputs branch from 658f073 to f639036 Compare December 23, 2025 12:47

hieblmi requested a review from ziggie1984 December 23, 2025 13:53

ziggie1984 reviewed Dec 23, 2025

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hieblmi force-pushed the estimate-inputs branch from f639036 to 2319f1a Compare December 24, 2025 08:29

hieblmi added 5 commits December 24, 2025 09:31

lnrpc: transaction inputs in EstimateFeeRequest

29d807e

cmd: make types.go accessible in lnd package

7d574fc

rpcserver: return inputs in EstimateFeeResponse

4002c29

cmd: EstimateFee for explicit inputs

686313b

docs: update release notes

fee5d40

hieblmi force-pushed the estimate-inputs branch from 2319f1a to fee5d40 Compare December 24, 2025 08:33

hieblmi commented Dec 24, 2025

View reviewed changes

estimatefee: tx fee estimate for selected inputs #10296

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estimatefee: tx fee estimate for selected inputs #10296

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