sweep: make sweeper aware of unconfirmed parent transactions.

Extend the fee estimator to take into account parent transactions with
their weights and fees.

Do not try to cpfp parent transactions that have a higher fee rate than
the sweep tx fee rate.

input/input.go

@@ -3,6 +3,7 @@ package input
 import (
 	"github.com/btcsuite/btcd/txscript"
 	"github.com/btcsuite/btcd/wire"
+	"github.com/btcsuite/btcutil"
 )
 
 // Input represents an abstract UTXO which is to be spent using a sweeping
@@ -41,6 +42,19 @@ type Input interface {
 	// HeightHint returns the minimum height at which a confirmed spending
 	// tx can occur.
 	HeightHint() uint32
+
+	// UnconfParent returns information about a possibly unconfirmed parent
+	// tx.
+	UnconfParent() *TxInfo
+}
+
+// TxInfo describes properties of a parent tx that are relevant for CPFP.
+type TxInfo struct {
+	// Fee is the fee of the tx.
+	Fee btcutil.Amount
+
+	// Weight is the weight of the tx.
+	Weight int64
 }
 
 type inputKit struct {
@@ -49,6 +63,10 @@ type inputKit struct {
 	signDesc        SignDescriptor
 	heightHint      uint32
 	blockToMaturity uint32
+
+	// unconfParent contains information about a potential unconfirmed
+	// parent transaction.
+	unconfParent *TxInfo
 }
 
 // OutPoint returns the breached output's identifier that is to be included as
@@ -82,6 +100,11 @@ func (i *inputKit) BlocksToMaturity() uint32 {
 	return i.blockToMaturity
 }
 
+// Cpfp returns information about a possibly unconfirmed parent tx.
+func (i *inputKit) UnconfParent() *TxInfo {
+	return i.unconfParent
+}
+
 // BaseInput contains all the information needed to sweep a basic output
 // (CSV/CLTV/no time lock)
 type BaseInput struct {
@@ -91,14 +114,16 @@ type BaseInput struct {
 // MakeBaseInput assembles a new BaseInput that can be used to construct a
 // sweep transaction.
 func MakeBaseInput(outpoint *wire.OutPoint, witnessType WitnessType,
-	signDescriptor *SignDescriptor, heightHint uint32) BaseInput {
+	signDescriptor *SignDescriptor, heightHint uint32,
+	unconfParent *TxInfo) BaseInput {
 
 	return BaseInput{
 		inputKit{
-			outpoint:    *outpoint,
-			witnessType: witnessType,
-			signDesc:    *signDescriptor,
-			heightHint:  heightHint,
+			outpoint:     *outpoint,
+			witnessType:  witnessType,
+			signDesc:     *signDescriptor,
+			heightHint:   heightHint,
+			unconfParent: unconfParent,
 		},
 	}
 }
@@ -109,7 +134,7 @@ func NewBaseInput(outpoint *wire.OutPoint, witnessType WitnessType,
 	signDescriptor *SignDescriptor, heightHint uint32) *BaseInput {
 
 	input := MakeBaseInput(
-		outpoint, witnessType, signDescriptor, heightHint,
+		outpoint, witnessType, signDescriptor, heightHint, nil,
 	)
 
 	return &input