selector!: Swap ChangePolicyType for bdk_coin_select::ChangePolicy#32
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ValuedMammal merged 6 commits intobitcoindevkit:masterfrom Dec 17, 2025
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The spend weight now accounts for both the weight of a default `TxIn` as well as the expected satisfaction weight.
This is redundant now that SelectorParams holds the ChangePolicy directly.
The name "strategy" is better suited for the enum, as it implies different strategies can be used, and helps to disambiguate from other similarly named types `Target` and `TargetFee`, etc.
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ChangePolicyType for bdk_coin_select::ChangePolicy
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Rebased on #31. |
evanlinjin
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| TargetFee { | ||
| rate: bdk_coin_select::FeeRate::ZERO, | ||
| replace: self.replace.as_ref().map(|r| r.to_cs_replace()), | ||
| } |
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This looks like abusing the API. The underlying crate bdk_coin_select does not support coin selection purely with an absolute fee target.
This may result in unexpected behavior if paired with RBF. The Replace struct would still enforce incremental relay fee requirements, but the zero feerate means the selector wouldn't try to meet the original tx's feerate floor (feerate_lb is ignored). So you could end up with a replacement that satisfies BIP125 rule 4 (absolute fee) but not rule 6 (feerate), or vice versa.
If this feature is needed, we should upstream the changes.
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… SelectorParams 8189b03 refactor!: inline ChangePolicy fields into SelectorParams (志宇) ffd1211 feat: add constructor methods for ChangeScript and ChangePolicy (志宇) b9e7b42 refactor!: eliminate redundant satisfaction weight in SelectorParams (志宇) Pull request description: Fixes #40 Fixes #42 ## Summary This PR fixes two issues with `SelectorParams`: **1. Redundant satisfaction weight (invalid representation)** `SelectorParams` previously had two independent fields that could both specify the change output's satisfaction weight: - `change_script: ScriptSource` — when this is the `Descriptor` variant, the satisfaction weight is derivable from the descriptor via `max_weight_to_satisfy`. - `change_policy: ChangePolicy` — also encodes the satisfaction weight (the spend cost of the change output). Nothing enforced that these agreed with each other, so callers could silently provide inconsistent values. Fixed by introducing **`ChangeScript`**, which bundles a raw script with an optional `satisfaction_weight`, or holds a `DefiniteDescriptor` from which it is derived automatically. `DrainWeights` is now computed internally from `ChangeScript` — there is a single source of truth. `ChangeScript::Descriptor` also accepts optional `satisfaction_assets` — when provided, the satisfaction weight is computed via `Plan` for a tighter estimate (useful for multisig/complex descriptors). Otherwise it falls back to `max_weight_to_satisfy`. The raw `bdk_coin_select::ChangePolicy` is also replaced with a **`ChangePolicy` enum** (`NoDust`, `NoDustLeastWaste`) that is converted to the `bdk_coin_select` type internally. This is `Debug + Clone + PartialEq + Eq`. Both `ChangeScript` and `ChangePolicy` have constructor methods to reduce boilerplate: - `ChangeScript::from_descriptor(desc)`, `from_descriptor_with_assets(desc, assets)`, `from_script(script, weight)` - `ChangePolicy::no_dust()`, `no_dust_least_waste(rate)`, with a builder-style `.min_value(amt)` **2. Hacky `AbsoluteFee` implementation** `FeeStrategy::AbsoluteFee` was implemented by smuggling the fee into `value_sum` and setting the feerate to zero. This meant the coin selector had no awareness of the fee, which interacted poorly with RBF logic (the zero feerate bypasses the original tx's feerate floor). Removed in favor of a direct `target_feerate: FeeRate` field. ### Design rationale The satisfaction weight is a physical property of the script — it describes how much it costs to spend a particular output. It is not a policy choice. When `change_script` is a descriptor, the satisfaction weight is literally derived from it. The fact that it *affects* coin selection doesn't make it *part of* the change policy, any more than the dust threshold is (and dust is already derived from the script). For the raw script case (e.g. silent payments), the satisfaction weight can't be derived and must be provided externally — but it's still a property of the script, not a policy decision. Bundling it into `ChangeScript::Script` makes this explicit. ## Context * #18 (comment) * #32 (comment) ACKs for top commit: aagbotemi: ACK 8189b03 ValuedMammal: ACK 8189b03 Tree-SHA512: c3bd9af598ec55c60ab04656d7907ec3882bd50bbd0783add94057bd2603bc1d0cbe134a3a2d601988e73c57d4c83c91538060e4091e3a150005489c293d9b21
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Description
Fix #29 by removing
ChangePolicyTypefromSelectorParamsin favor ofbdk_coin_select::ChangePolicy. The idea is that this affords maximum flexibility when defining the change policy.Builds on #31 which implements absolute fee targeting. h/t aagbotemi. A test
test_absolute_fee_vs_feerate_target_valueis added that checks the expectedTargetis constructed based on the chosenFeeStrategy.Changelog
Added
FeeStrategyenum which defines the fee target as either a feerate or fee amount.Changed
BREAKING
SelectorParams::target_feeratefield is changed tofee_strategy.SelectorParams::change_policyfield is changed to have typebdk_coin_select::ChangePolicy.SelectorParams::newis changed to accept thefee_strategyandchange_policyas inputs.Removed
SelectorParams::change_weightfield is removed now that the change weights are represented in the actual change policy.SelectorParams::to_cs_change_policyas the conversion is no longer necessary.ChangePolicyTypeenum to allow the user to construct the intendedChangePolicy.