refactor: replace ChangeDescriptor by ScriptSource

Author: nymius

examples/synopsis.rs

@@ -60,7 +60,7 @@ fn main() -> anyhow::Result<()> {
                     recipient_addr.script_pubkey(),
                     Amount::from_sat(21_000_000),
                 )],
-                bdk_tx::ChangeDescriptor::Definite(internal.at_derivation_index(0)?),
+                bdk_tx::ScriptSource::Descriptor(Box::new(internal.at_derivation_index(0)?)),
                 bdk_tx::ChangePolicyType::NoDustAndLeastWaste { longterm_feerate },
             ),
         )?;
@@ -134,9 +134,9 @@ fn main() -> anyhow::Result<()> {
                     // be less wasteful to have no output, however that will not be a valid tx).
                     // If you only want to fee bump, put the original txs' recipients here.
                     target_outputs: vec![],
-                    change_descriptor: bdk_tx::ChangeDescriptor::Definite(
+                    change_source: bdk_tx::ScriptSource::Descriptor(Box::new(
                         internal.at_derivation_index(1)?,
-                    ),
+                    )),
                     change_policy: ChangePolicyType::NoDustAndLeastWaste { longterm_feerate },
                     // This ensures that we satisfy mempool-replacement policy rules 4 and 6.
                     replace: Some(rbf_params),

src/selector.rs

@@ -1,10 +1,10 @@
 use bdk_coin_select::{
     ChangePolicy, DrainWeights, InsufficientFunds, Replace, Target, TargetFee, TargetOutputs,
 };
-use bitcoin::{Amount, FeeRate, ScriptBuf, Transaction, TxOut, Weight};
+use bitcoin::{Amount, FeeRate, Transaction, TxOut, Weight};
 use miniscript::bitcoin;
 
-use crate::{cs_feerate, DefiniteDescriptor, InputCandidates, InputGroup, Output, Selection};
+use crate::{cs_feerate, InputCandidates, InputGroup, Output, ScriptSource, Selection};
 use alloc::vec::Vec;
 use core::fmt;
 
@@ -15,51 +15,10 @@ pub struct Selector<'c> {
     target_outputs: Vec<Output>,
     target: Target,
     change_policy: bdk_coin_select::ChangePolicy,
-    change_descriptor: ChangeDescriptor,
+    change_source: ScriptSource,
     inner: bdk_coin_select::CoinSelector<'c>,
 }
 
-/// Data source to create a change output if needed
-#[derive(Debug, Clone)]
-pub enum ChangeDescriptor {
-    /// Build change output from descriptor
-    Definite(DefiniteDescriptor),
-    /// Build change output without descriptor
-    Manual {
-        /// The final script pubkey the change output should have
-        script_pubkey: ScriptBuf,
-        /// The maximum weight to satisfy the script pubkey
-        max_weight_to_satisfy_wu: u64,
-    },
-}
-
-/// Wrapper methods to unify interface for change outputs
-impl ChangeDescriptor {
-    /// Get the maximum weight to satisfy the script pubkey of the resultant output
-    pub fn get_max_weight_to_satisfy_wu(&self) -> Result<u64, miniscript::Error> {
-        use ChangeDescriptor::*;
-
-        match self {
-            Definite(definite_descriptor) => definite_descriptor
-                .max_weight_to_satisfy()
-                .map(|weight| weight.to_wu()),
-            Manual {
-                max_weight_to_satisfy_wu,
-                ..
-            } => Ok(*max_weight_to_satisfy_wu),
-        }
-    }
-
-    /// Get the script pubkey the change output should have
-    pub fn get_script_pubkey(&self) -> ScriptBuf {
-        use ChangeDescriptor::*;
-        match self {
-            Definite(definite_descriptor) => definite_descriptor.script_pubkey(),
-            Manual { script_pubkey, .. } => script_pubkey.clone(),
-        }
-    }
-}
-
 /// Parameters for creating tx.
 ///
 /// TODO: Create a builder interface on this that does checks. I.e.
@@ -83,7 +42,7 @@ pub struct SelectorParams {
     /// To derive change output.
     ///
     /// Will error if this is unsatisfiable descriptor.
-    pub change_descriptor: ChangeDescriptor,
+    pub change_source: ScriptSource,
 
     /// The policy to determine whether we create a change output.
     pub change_policy: ChangePolicyType,
@@ -181,11 +140,11 @@ impl SelectorParams {
     pub fn new(
         target_feerate: bitcoin::FeeRate,
         target_outputs: Vec<Output>,
-        change_descriptor: ChangeDescriptor,
+        change_source: ScriptSource,
         change_policy: ChangePolicyType,
     ) -> Self {
         Self {
-            change_descriptor,
+            change_source,
             change_policy,
             target_feerate,
             target_outputs,
@@ -216,32 +175,49 @@ impl SelectorParams {
     ///
     /// # Error
     ///
-    /// Fails if `change_descriptor` cannot be satisfied.
-    pub fn to_cs_change_weights(&self) -> Result<bdk_coin_select::DrainWeights, miniscript::Error> {
-        Ok(DrainWeights {
+    /// Fails if `change_source` cannot be satisfied.
+    pub fn to_cs_change_weights(&self) -> Result<bdk_coin_select::DrainWeights, SelectorError> {
+        let (script_pubkey, spend_weight) = match &self.change_source {
+            ScriptSource::Script {
+                script_pubkey,
+                max_weight_to_satisfy,
+            } => {
+                if let Some(weight) = max_weight_to_satisfy {
+                    (script_pubkey.clone(), weight.to_wu())
+                } else {
+                    return Err(SelectorError::MissingChangeSatisfactionWeight);
+                }
+            }
+            ScriptSource::Descriptor(definite_descriptor) => {
+                let script_pubkey = definite_descriptor.script_pubkey();
+                let weight = definite_descriptor
+                    .max_weight_to_satisfy()
+                    .map(|weight| weight.to_wu())
+                    .map_err(SelectorError::Miniscript)?;
+                (script_pubkey, weight)
+            }
+        };
+        let drain_weight = DrainWeights {
             output_weight: (TxOut {
-                script_pubkey: self.change_descriptor.get_script_pubkey(),
+                script_pubkey,
                 value: Amount::ZERO,
             })
             .weight()
             .to_wu(),
-            spend_weight: self.change_descriptor.get_max_weight_to_satisfy_wu()?,
+            spend_weight,
             n_outputs: 1,
-        })
+        };
+        Ok(drain_weight)
     }
 
     /// To change policy.
     ///
     /// # Error
     ///
-    /// Fails if `change_descriptor` cannot be satisfied.
-    pub fn to_cs_change_policy(&self) -> Result<bdk_coin_select::ChangePolicy, miniscript::Error> {
+    /// Fails if `change_source` cannot be satisfied.
+    pub fn to_cs_change_policy(&self) -> Result<bdk_coin_select::ChangePolicy, SelectorError> {
         let change_weights = self.to_cs_change_weights()?;
-        let dust_value = self
-            .change_descriptor
-            .get_script_pubkey()
-            .minimal_non_dust()
-            .to_sat();
+        let dust_value = self.change_source.script().minimal_non_dust().to_sat();
         Ok(match self.change_policy {
             ChangePolicyType::NoDust => ChangePolicy::min_value(change_weights, dust_value),
             ChangePolicyType::NoDustAndLeastWaste { longterm_feerate } => {
@@ -311,11 +287,9 @@ impl<'c> Selector<'c> {
         params: SelectorParams,
     ) -> Result<Self, SelectorError> {
         let target = params.to_cs_target();
-        let change_policy = params
-            .to_cs_change_policy()
-            .map_err(SelectorError::Miniscript)?;
+        let change_policy = params.to_cs_change_policy()?;
         let target_outputs = params.target_outputs;
-        let change_descriptor = params.change_descriptor;
+        let change_source = params.change_source;
         if target.value() > candidates.groups().map(|grp| grp.value().to_sat()).sum() {
             return Err(SelectorError::CannotMeetTarget(CannotMeetTarget));
         }
@@ -328,7 +302,7 @@ impl<'c> Selector<'c> {
             target,
             target_outputs,
             change_policy,
-            change_descriptor,
+            change_source,
             inner,
         })
     }
@@ -405,10 +379,16 @@ impl<'c> Selector<'c> {
             outputs: {
                 let mut outputs = self.target_outputs.clone();
                 if maybe_change.is_some() {
-                    outputs.push(Output::with_script(
-                        self.change_descriptor.get_script_pubkey(),
-                        Amount::from_sat(maybe_change.value),
-                    ));
+                    let change_amount = Amount::from_sat(maybe_change.value);
+                    let change_output = match &self.change_source {
+                        ScriptSource::Descriptor(definite_descriptor) => {
+                            Output::with_descriptor(*definite_descriptor.clone(), change_amount)
+                        }
+                        ScriptSource::Script { script_pubkey, .. } => {
+                            Output::with_script(script_pubkey.clone(), change_amount)
+                        }
+                    };
+                    outputs.push(change_output);
                 }
                 outputs
             },