estimatefee: tx fee estimate for selected inputs #10296

hieblmi · 2025-10-15T14:05:21Z

EstimateFee now takes optional inputs to give a fee estimate.

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
{
    "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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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.

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

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

rpcserver.go

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.

types.go

ziggie1984

LGTM, I think you could also add an itest to at least verify that this new feature works.

rpcserver.go

lightninglabs-deploy · 2026-01-01T10:45:22Z

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

hieblmi · 2026-01-05T08:37:21Z

Thank for the review @ziggie1984. I've added itests in 1bbdb21.

They ensure that a fee estimation for selected inputs matches the actual fee produced by SendCoins for the same inputs.

ziggie1984 · 2026-01-05T19:53:29Z

itest/lnd_estimate_on_chain_fee_test.go

+	feeDiff := actualFee - estimateResp.FeeSat
+	if feeDiff < 0 {
+		feeDiff = -feeDiff
+	}
+
+	// Allow up to 1% difference or 100 sats, whichever is larger.
+	maxDiff := actualFee / 100
+	if maxDiff < 100 {
+		maxDiff = 100
+	}


if you use the fee-service and taproot inputs there shouldn't be a error tho, normally we don't need this.

ziggie1984 · 2026-01-05T19:54:12Z

itest/lnd_estimate_on_chain_fee_test.go

+	}
+
+	// Allow up to 1% difference or 100 sats, whichever is larger.
+	maxDiff := actualFee / 100


same here can we avoid this ?

ziggie1984 · 2026-01-05T19:57:32Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces the ability to specify inputs for fee estimation in the EstimateFee RPC and its corresponding estimatefee lncli command. This is a useful feature for users who want more control over coin selection for fee estimation. The implementation involves extending the RPC interface, updating the server-side logic to handle these inputs, and adding new integration tests to validate the functionality. A significant portion of the changes also involves refactoring helper types and functions into a more central package for better code reuse across the application. My review identified a bug in the new integration tests where outpoint indices were being incorrectly converted to strings, which could lead to test failures. I've also included some minor suggestions to improve error message formatting for better readability and consistency with the style guide. Overall, the changes are well-structured and the new feature is a valuable addition.

gemini-code-assist · 2026-01-05T20:00:08Z

itest/lnd_estimate_on_chain_fee_test.go

+	// Create a map of input outpoints from the estimate for easy lookup.
+	estimateInputs := make(map[string]bool)
+	for _, input := range estimateResp.Inputs {
+		key := input.TxidStr + ":" + string(rune(input.OutputIndex))


The conversion of input.OutputIndex to a string is incorrect. string(rune(input.OutputIndex)) converts the integer to its UTF-8 character representation, which is not the desired decimal representation for an outpoint index. This can lead to incorrect map keys and test failures. You should use fmt.Sprintf or strconv.Itoa for a correct conversion.

Suggested change

key := input.TxidStr + ":" + string(rune(input.OutputIndex))

key := fmt.Sprintf("%s:%d", input.TxidStr, input.OutputIndex)

gemini-code-assist · 2026-01-05T20:00:08Z

itest/lnd_estimate_on_chain_fee_test.go

+		key := outpoint.TxidStr + ":" +
+			string(rune(outpoint.OutputIndex))


Similar to the previous loop, the conversion of outpoint.OutputIndex to a string is incorrect. string(rune(outpoint.OutputIndex)) converts the integer to its UTF-8 character representation. This should be converted to its decimal string representation to form a correct outpoint string.

Suggested change

key := outpoint.TxidStr + ":" +

string(rune(outpoint.OutputIndex))

key := fmt.Sprintf("%s:%d", outpoint.TxidStr, outpoint.OutputIndex)

gemini-code-assist · 2026-01-05T20:00:08Z

rpcserver.go

+			return nil, fmt.Errorf("can't create outpoints "+
+				"%w", err)


The error message formatting can be improved for clarity. Instead of concatenating a space before the format verb, it's cleaner to include the colon and space within the format string itself. This improves readability and aligns with the style guide's goal of clear error messages.

return nil, fmt.Errorf("can't create outpoints: %w", err)

References

The style guide recommends minimizing lines for log and error messages and provides examples for clear formatting. Using string concatenation for short error messages like this is unnecessary and less readable than a single format string. ^(link)

gemini-code-assist · 2026-01-05T20:00:09Z

rpcserver.go

+			return nil, fmt.Errorf("selected outpoints contain " +
+				"duplicate values")


The error message can be simplified by removing the string concatenation for better readability.

return nil, fmt.Errorf("selected outpoints contain duplicate values")

References

The style guide recommends minimizing lines for log and error messages. While this isn't a long line, avoiding unnecessary string concatenation improves readability. ^(link)

This is a long line.

gemini-code-assist · 2026-01-05T20:00:09Z

rpcserver.go

+		return nil, fmt.Errorf("can't convert outpoints "+
+			"%w", err)


The error message formatting can be improved for clarity. Instead of concatenating a space before the format verb, it's cleaner to include the colon and space within the format string itself. This improves readability and aligns with the style guide's goal of clear error messages.

return nil, fmt.Errorf("can't convert outpoints: %w", err)

References

The style guide recommends minimizing lines for log and error messages and provides examples for clear formatting. Using string concatenation for short error messages like this is unnecessary and less readable than a single format string. ^(link)

sputn1ck

LGTM!

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

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hieblmi mentioned this pull request Oct 20, 2025

feature: outpoint based EstimateFee API #10304

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hieblmi force-pushed the estimate-inputs branch from 8b70b79 to 52815a0 Compare January 6, 2026 07:30

hieblmi added 6 commits January 7, 2026 10:25

lnrpc: transaction inputs in EstimateFeeRequest

049f2c7

cmd: make types.go accessible in lnd package

e5456d3

rpcserver: return inputs in EstimateFeeResponse

280929b

cmd: EstimateFee for explicit inputs

44aa5ef

itest: estimate on-chain fee with selected inputs

422aa7d

docs: update release notes

202e473

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	key := input.TxidStr + ":" + string(rune(input.OutputIndex))
	key := fmt.Sprintf("%s:%d", input.TxidStr, input.OutputIndex)

		key := outpoint.TxidStr + ":" +
		string(rune(outpoint.OutputIndex))

	key := outpoint.TxidStr + ":" +
	string(rune(outpoint.OutputIndex))
	key := fmt.Sprintf("%s:%d", outpoint.TxidStr, outpoint.OutputIndex)

		return nil, fmt.Errorf("selected outpoints contain " +
		"duplicate values")

		return nil, fmt.Errorf("can't convert outpoints "+
		"%w", err)

estimatefee: tx fee estimate for selected inputs #10296

estimatefee: tx fee estimate for selected inputs #10296

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hieblmi commented Oct 15, 2025 •

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