Added CoinSelector interface and a few simple algos as a sub-package

This commit contains a basic definition for CoinSelector along with some utility classes and some basic algos to make creating transactions from a set of available unspent outpoints easier. Thanks to @dajohi, @davec, @jrick for all the feedback and suggestions regarding interfaces, organization, optimization, comments and documentation.
2014-03-16 17:02:46 -04:00 · 2014-03-16 17:02:46 -04:00 · 02a1584784
commit 02a1584784
parent 60d4bed78f
6 changed files with 812 additions and 22 deletions
--- a/coinset/README.md
+++ b/coinset/README.md
@ -0,0 +1,96 @@
+coinset
+=======
+
+Package coinset provides bitcoin-specific convenience functions for selecting 
+from and managing sets of unspent transaction outpoints (UTXOs).
+
+A comprehensive suite of tests is provided to ensure proper functionality.  See
+`test_coverage.txt` for the gocov coverage report.  Alternatively, if you are
+running a POSIX OS, you can run the `cov_report.sh` script for a real-time
+report.  Package coinset is licensed under the liberal ISC license.
+
+## Documentation
+
+Full `go doc` style documentation for the project can be viewed online without
+installing this package by using the GoDoc site here:
+http://godoc.org/github.com/conformal/btcutil/coinset
+
+You can also view the documentation locally once the package is installed with
+the `godoc` tool by running `godoc -http=":6060"` and pointing your browser to
+http://localhost:6060/pkg/github.com/conformal/btcutil/coinset
+
+## Installation
+
+```bash
+$ go get github.com/conformal/btcutil/coinset
+```
+
+## Usage
+
+Each unspent transaction outpoint is represented by the Coin interface.  An 
+example of a concrete type that implements Coin is coinset.SimpleCoin.
+
+The typical use case for this library is for creating raw bitcoin transactions
+given a set of Coins that may be spent by the user, for example as below:
+
+```Go
+var unspentCoins = []coinset.Coin{ ... }
+```
+
+When the user needs to spend a certain amount, they will need to select a 
+subset of these coins which contain at least that value.  CoinSelector is 
+an interface that represents types that implement coin selection algos,
+subject to various criteria.  There are a few examples of CoinSelector's:
+
+- MinIndexCoinSelector
+
+- MinNumberCoinSelector
+
+- MaxValueAgeCoinSelector
+
+- MinPriorityCoinSelector
+
+For example, if the user wishes to maximize the probability that their 
+transaction is mined quickly, they could use the MaxValueAgeCoinSelector to
+select high priority coins, then also attach a relatively high fee.
+
+```Go
+selector := &coinset.MaxValueAgeCoinSelector{
+    MaxInputs: 10, 
+    MinAmountChange: 10000,
+}
+selectedCoins, err := selector.CoinSelect(targetAmount + bigFee, unspentCoins)
+if err != nil {
+	return err
+}
+msgTx := coinset.NewMsgTxWithInputCoins(selectedCoins)
+...
+
+```
+
+The user can then create the msgTx.TxOut's as required, then sign the 
+transaction and transmit it to the network.
+
+## GPG Verification Key
+
+All official release tags are signed by Conformal so users can ensure the code
+has not been tampered with and is coming from Conformal.  To verify the
+signature perform the following:
+
+- Download the public key from the Conformal website at
+  https://opensource.conformal.com/GIT-GPG-KEY-conformal.txt
+
+- Import the public key into your GPG keyring:
+  ```bash
+  gpg --import GIT-GPG-KEY-conformal.txt
+  ```
+
+- Verify the release tag with the following command where `TAG_NAME` is a
+  placeholder for the specific tag:
+  ```bash
+  git tag -v TAG_NAME
+  ```
+
+## License
+
+Package coinset is licensed under the liberal ISC License.
--- a/coinset/coins.go
+++ b/coinset/coins.go
@ -0,0 +1,394 @@
+package coinset
+
+import (
+	"container/list"
+	"errors"
+	"github.com/conformal/btcutil"
+	"github.com/conformal/btcwire"
+	"sort"
+)
+
+// Coin represents a spendable transaction outpoint
+type Coin interface {
+	Hash() *btcwire.ShaHash
+	Index() uint32
+	Value() int64
+	PkScript() []byte
+	NumConfs() int64
+	ValueAge() int64
+}
+
+// Coins represents a set of Coins
+type Coins interface {
+	Coins() []Coin
+}
+
+// CoinSet is a utility struct for the modifications of a set of
+// Coins that implements the Coins interface.  To create a CoinSet,
+// you must call NewCoinSet with nil for an empty set or a slice of
+// coins as the initial contents.
+//
+// It is important to note that the all the Coins being added or removed
+// from a CoinSet must have a constant ValueAge() during the use of
+// the CoinSet, otherwise the cached values will be incorrect.
+type CoinSet struct {
+	coinList      *list.List
+	totalValue    int64
+	totalValueAge int64
+}
+
+// Ensure that CoinSet is a Coins
+var _ Coins = NewCoinSet(nil)
+
+// NewCoinSet creates a CoinSet containing the coins provided.
+// To create an empty CoinSet, you may pass null as the coins input parameter.
+func NewCoinSet(coins []Coin) *CoinSet {
+	newCoinSet := &CoinSet{
+		coinList:      list.New(),
+		totalValue:    0,
+		totalValueAge: 0,
+	}
+	for _, coin := range coins {
+		newCoinSet.PushCoin(coin)
+	}
+	return newCoinSet
+}
+
+// Coins returns a new slice of the coins contained in the set.
+func (cs *CoinSet) Coins() []Coin {
+	coins := make([]Coin, cs.coinList.Len())
+	for i, e := 0, cs.coinList.Front(); e != nil; i, e = i+1, e.Next() {
+		coins[i] = e.Value.(Coin)
+	}
+	return coins
+}
+
+// TotalValue returns the total value of the coins in the set.
+func (cs *CoinSet) TotalValue() (value int64) {
+	return cs.totalValue
+}
+
+// TotalValueAge returns the total value * number of confirmations
+//  of the coins in the set.
+func (cs *CoinSet) TotalValueAge() (valueAge int64) {
+	return cs.totalValueAge
+}
+
+// Num returns the number of coins in the set
+func (cs *CoinSet) Num() int {
+	return cs.coinList.Len()
+}
+
+// PushCoin adds a coin to the end of the list and updates
+// the cached value amounts.
+func (cs *CoinSet) PushCoin(c Coin) {
+	cs.coinList.PushBack(c)
+	cs.totalValue += c.Value()
+	cs.totalValueAge += c.ValueAge()
+}
+
+// PopCoin removes the last coin on the list and returns it.
+func (cs *CoinSet) PopCoin() Coin {
+	back := cs.coinList.Back()
+	if back == nil {
+		return nil
+	}
+	return cs.removeElement(back)
+}
+
+// ShiftCoin removes the first coin on the list and returns it.
+func (cs *CoinSet) ShiftCoin() Coin {
+	front := cs.coinList.Front()
+	if front == nil {
+		return nil
+	}
+	return cs.removeElement(front)
+}
+
+// removeElement updates the cached value amounts in the CoinSet,
+// removes the element from the list, then returns the Coin that
+// was removed to the caller.
+func (cs *CoinSet) removeElement(e *list.Element) Coin {
+	c := e.Value.(Coin)
+	cs.coinList.Remove(e)
+	cs.totalValue -= c.Value()
+	cs.totalValueAge -= c.ValueAge()
+	return c
+}
+
+// NewMsgTxWithInputCoins takes the coins in the CoinSet and makes them
+// the inputs to a new btcwire.MsgTx which is returned.
+func NewMsgTxWithInputCoins(inputCoins Coins) *btcwire.MsgTx {
+	msgTx := btcwire.NewMsgTx()
+	coins := inputCoins.Coins()
+	msgTx.TxIn = make([]*btcwire.TxIn, len(coins))
+	for i, coin := range coins {
+		msgTx.TxIn[i] = &btcwire.TxIn{
+			PreviousOutpoint: btcwire.OutPoint{
+				Hash:  *coin.Hash(),
+				Index: coin.Index(),
+			},
+			SignatureScript: nil,
+			Sequence:        btcwire.MaxTxInSequenceNum,
+		}
+	}
+	return msgTx
+}
+
+var (
+	// ErrCoinsNoSelectionAvailable is returned when a CoinSelector believes there is no
+	// possible combination of coins which can meet the requirements provided to the selector.
+	ErrCoinsNoSelectionAvailable = errors.New("no coin selection possible")
+)
+
+// satisfiesTargetValue checks that the totalValue is either exactly the targetValue
+// or is greater than the targetValue by at least the minChange amount.
+func satisfiesTargetValue(targetValue, minChange, totalValue int64) bool {
+	return (totalValue == targetValue || totalValue >= targetValue+minChange)
+}
+
+// CoinSelector is an interface that wraps the CoinSelect method.
+//
+// CoinSelect will attempt to select a subset of the coins which has at
+// least the targetValue amount.  CoinSelect is not guaranteed to return a
+// selection of coins even if the total value of coins given is greater
+// than the target value.
+//
+// The exact choice of coins in the subset will be implementation specific.
+//
+// It is important to note that the Coins being used as inputs need to have
+// a constant ValueAge() during the execution of CoinSelect.
+type CoinSelector interface {
+	CoinSelect(targetValue int64, coins []Coin) (Coins, error)
+}
+
+// MinIndexCoinSelector is a CoinSelector that attempts to construct a
+// selection of coins whose total value is at least targetValue and prefers
+// any number of lower indexes (as in the ordered array) over higher ones.
+type MinIndexCoinSelector struct {
+	MaxInputs       int
+	MinChangeAmount int64
+}
+
+// CoinSelect will attempt to select coins using the algorithm described
+// in the MinIndexCoinSelector struct.
+func (s MinIndexCoinSelector) CoinSelect(targetValue int64, coins []Coin) (Coins, error) {
+	cs := NewCoinSet(nil)
+	for n := 0; n < len(coins) && n < s.MaxInputs; n++ {
+		cs.PushCoin(coins[n])
+		if satisfiesTargetValue(targetValue, s.MinChangeAmount, cs.TotalValue()) {
+			return cs, nil
+		}
+	}
+	return nil, ErrCoinsNoSelectionAvailable
+}
+
+// MinNumberCoinSelector is a CoinSelector that attempts to construct
+// a selection of coins whose total value is at least targetValue
+// that uses as few of the inputs as possible.
+type MinNumberCoinSelector struct {
+	MaxInputs       int
+	MinChangeAmount int64
+}
+
+// CoinSelect will attempt to select coins using the algorithm described
+// in the MinNumberCoinSelector struct.
+func (s MinNumberCoinSelector) CoinSelect(targetValue int64, coins []Coin) (Coins, error) {
+	sortedCoins := make([]Coin, 0, len(coins))
+	sortedCoins = append(sortedCoins, coins...)
+	sort.Sort(sort.Reverse(byAmount(sortedCoins)))
+	return (&MinIndexCoinSelector{
+		MaxInputs:       s.MaxInputs,
+		MinChangeAmount: s.MinChangeAmount,
+	}).CoinSelect(targetValue, sortedCoins)
+}
+
+// MaxValueAgeCoinSelector is a CoinSelector that attempts to construct
+// a selection of coins whose total value is at least targetValue
+// that has as much input value-age as possible.
+//
+// This would be useful in the case where you want to maximize
+// likelihood of the inclusion of your transaction in the next mined
+// block.
+type MaxValueAgeCoinSelector struct {
+	MaxInputs       int
+	MinChangeAmount int64
+}
+
+// CoinSelect will attempt to select coins using the algorithm described
+// in the MaxValueAgeSelector struct.
+func (s MaxValueAgeCoinSelector) CoinSelect(targetValue int64, coins []Coin) (Coins, error) {
+	sortedCoins := make([]Coin, 0, len(coins))
+	sortedCoins = append(sortedCoins, coins...)
+	sort.Sort(sort.Reverse(byValueAge(sortedCoins)))
+	return (&MinIndexCoinSelector{
+		MaxInputs:       s.MaxInputs,
+		MinChangeAmount: s.MinChangeAmount,
+	}).CoinSelect(targetValue, sortedCoins)
+}
+
+// MinPriorityCoinSelector is a CoinSelector that attempts to construct
+// a selection of coins whose total value is at least targetValue and
+// whose average value-age per input is greater than MinAvgValueAgePerInput.
+// If there is change, it must exceed MinChangeAmount to be a valid selection.
+//
+// When possible, MinPriorityCoinSelector will attempt to reduce the average
+// input priority over the threshold, but no guarantees will be made as to
+// minimality of the selection.  The selection below is almost certainly
+// suboptimal.
+//
+type MinPriorityCoinSelector struct {
+	MaxInputs              int
+	MinChangeAmount        int64
+	MinAvgValueAgePerInput int64
+}
+
+// CoinSelect will attempt to select coins using the algorithm described
+// in the MinPriorityCoinSelector struct.
+func (s MinPriorityCoinSelector) CoinSelect(targetValue int64, coins []Coin) (Coins, error) {
+	possibleCoins := make([]Coin, 0, len(coins))
+	possibleCoins = append(possibleCoins, coins...)
+
+	sort.Sort(byValueAge(possibleCoins))
+
+	// find the first coin with sufficient valueAge
+	cutoffIndex := -1
+	for i := 0; i < len(possibleCoins); i++ {
+		if possibleCoins[i].ValueAge() >= s.MinAvgValueAgePerInput {
+			cutoffIndex = i
+			break
+		}
+	}
+	if cutoffIndex < 0 {
+		return nil, ErrCoinsNoSelectionAvailable
+	}
+
+	// create sets of input coins that will obey minimum average valueAge
+	for i := cutoffIndex; i < len(possibleCoins); i++ {
+		possibleHighCoins := possibleCoins[cutoffIndex : i+1]
+
+		// choose a set of high-enough valueAge coins
+		highSelect, err := (&MinNumberCoinSelector{
+			MaxInputs:       s.MaxInputs,
+			MinChangeAmount: s.MinChangeAmount,
+		}).CoinSelect(targetValue, possibleHighCoins)
+
+		if err != nil {
+			// attempt to add available low priority to make a solution
+
+			for numLow := 1; numLow <= cutoffIndex && numLow+(i-cutoffIndex) <= s.MaxInputs; numLow++ {
+				allHigh := NewCoinSet(possibleCoins[cutoffIndex : i+1])
+				newTargetValue := targetValue - allHigh.TotalValue()
+				newMaxInputs := allHigh.Num() + numLow
+				if newMaxInputs > numLow {
+					newMaxInputs = numLow
+				}
+				newMinAvgValueAge := ((s.MinAvgValueAgePerInput * int64(allHigh.Num()+numLow)) - allHigh.TotalValueAge()) / int64(numLow)
+
+				// find the minimum priority that can be added to set
+				lowSelect, err := (&MinPriorityCoinSelector{
+					MaxInputs:              newMaxInputs,
+					MinChangeAmount:        s.MinChangeAmount,
+					MinAvgValueAgePerInput: newMinAvgValueAge,
+				}).CoinSelect(newTargetValue, possibleCoins[0:cutoffIndex])
+
+				if err != nil {
+					continue
+				}
+
+				for _, coin := range lowSelect.Coins() {
+					allHigh.PushCoin(coin)
+				}
+
+				return allHigh, nil
+			}
+			// oh well, couldn't fix, try to add more high priority to the set.
+		} else {
+			extendedCoins := NewCoinSet(highSelect.Coins())
+
+			// attempt to lower priority towards target with lowest ones first
+			for n := 0; n < cutoffIndex; n++ {
+				if extendedCoins.Num() >= s.MaxInputs {
+					break
+				}
+				if possibleCoins[n].ValueAge() == 0 {
+					continue
+				}
+
+				extendedCoins.PushCoin(possibleCoins[n])
+				if extendedCoins.TotalValueAge()/int64(extendedCoins.Num()) < s.MinAvgValueAgePerInput {
+					extendedCoins.PopCoin()
+					continue
+				}
+			}
+			return extendedCoins, nil
+		}
+	}
+
+	return nil, ErrCoinsNoSelectionAvailable
+}
+
+type byValueAge []Coin
+
+func (a byValueAge) Len() int           { return len(a) }
+func (a byValueAge) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a byValueAge) Less(i, j int) bool { return a[i].ValueAge() < a[j].ValueAge() }
+
+type byAmount []Coin
+
+func (a byAmount) Len() int           { return len(a) }
+func (a byAmount) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a byAmount) Less(i, j int) bool { return a[i].Value() < a[j].Value() }
+
+// SimpleCoin defines a concrete instance of Coin that is backed by a
+// btcutil.Tx, a specific outpoint index, and the number of confirmations
+// that transaction has had.
+type SimpleCoin struct {
+	Tx         *btcutil.Tx
+	TxIndex    uint32
+	TxNumConfs int64
+}
+
+// Ensure that SimpleCoin is a Coin
+var _ Coin = &SimpleCoin{}
+
+// Hash returns the hash value of the transaction on which the Coin is an output
+func (c *SimpleCoin) Hash() *btcwire.ShaHash {
+	return c.Tx.Sha()
+}
+
+// Index returns the index of the output on the transaction which the Coin represents
+func (c *SimpleCoin) Index() uint32 {
+	return c.TxIndex
+}
+
+// txOut returns the TxOut of the transaction the Coin represents
+func (c *SimpleCoin) txOut() *btcwire.TxOut {
+	return c.Tx.MsgTx().TxOut[c.TxIndex]
+}
+
+// Value returns the value of the Coin
+func (c *SimpleCoin) Value() int64 {
+	return c.txOut().Value
+}
+
+// PkScript returns the outpoint script of the Coin.
+//
+// This can be used to determine what type of script the Coin uses
+// and extract standard addresses if possible using
+// btcscript.ExtractPkScriptAddrs for example.
+func (c *SimpleCoin) PkScript() []byte {
+	return c.txOut().PkScript
+}
+
+// NumConfs returns the number of confirmations that the transaction the Coin references
+// has had.
+func (c *SimpleCoin) NumConfs() int64 {
+	return c.TxNumConfs
+}
+
+// ValueAge returns the product of the value and the number of confirmations.  This is
+// used as an input to calculate the priority of the transaction.
+func (c *SimpleCoin) ValueAge() int64 {
+	return c.TxNumConfs * c.Value()
+}
--- a/coinset/coins_test.go
+++ b/coinset/coins_test.go
@ -0,0 +1,252 @@
+package coinset_test
+
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"github.com/conformal/btcutil"
+	"github.com/conformal/btcutil/coinset"
+	"github.com/conformal/btcwire"
+	"github.com/conformal/fastsha256"
+	"testing"
+)
+
+type TestCoin struct {
+	TxHash     *btcwire.ShaHash
+	TxIndex    uint32
+	TxValue    int64
+	TxNumConfs int64
+}
+
+func (c *TestCoin) Hash() *btcwire.ShaHash { return c.TxHash }
+func (c *TestCoin) Index() uint32          { return c.TxIndex }
+func (c *TestCoin) Value() int64           { return c.TxValue }
+func (c *TestCoin) PkScript() []byte       { return nil }
+func (c *TestCoin) NumConfs() int64        { return c.TxNumConfs }
+func (c *TestCoin) ValueAge() int64        { return c.TxValue * c.TxNumConfs }
+
+func NewCoin(index, value, numConfs int64) coinset.Coin {
+	h := fastsha256.New()
+	h.Write([]byte(fmt.Sprintf("%d", index)))
+	hash, _ := btcwire.NewShaHash(h.Sum(nil))
+	c := &TestCoin{
+		TxHash:     hash,
+		TxIndex:    0,
+		TxValue:    value,
+		TxNumConfs: numConfs,
+	}
+	return coinset.Coin(c)
+}
+
+type coinSelectTest struct {
+	selector      coinset.CoinSelector
+	inputCoins    []coinset.Coin
+	targetValue   int64
+	expectedCoins []coinset.Coin
+	expectedError error
+}
+
+func testCoinSelector(tests []coinSelectTest, t *testing.T) {
+	for testIndex, test := range tests {
+		cs, err := test.selector.CoinSelect(test.targetValue, test.inputCoins)
+		if err != test.expectedError {
+			t.Errorf("[%d] expected a different error: got=%v, expected=%v", testIndex, err, test.expectedError)
+			continue
+		}
+		if test.expectedCoins != nil {
+			if cs == nil {
+				t.Errorf("[%d] expected non-nil coinset", testIndex)
+				continue
+			}
+			coins := cs.Coins()
+			if len(coins) != len(test.expectedCoins) {
+				t.Errorf("[%d] expected different number of coins: got=%d, expected=%d", testIndex, len(coins), len(test.expectedCoins))
+				continue
+			}
+			for n := 0; n < len(test.expectedCoins); n++ {
+				if coins[n] != test.expectedCoins[n] {
+					t.Errorf("[%d] expected different coins at coin index %d: got=%#v, expected=%#v", testIndex, n, coins[n], test.expectedCoins[n])
+					continue
+				}
+			}
+			coinSet := coinset.NewCoinSet(coins)
+			if coinSet.TotalValue() < test.targetValue {
+				t.Errorf("[%d] targetValue not satistifed", testIndex)
+				continue
+			}
+		}
+	}
+}
+
+var coins = []coinset.Coin{
+	NewCoin(1, 100000000, 1),
+	NewCoin(2, 10000000, 20),
+	NewCoin(3, 50000000, 0),
+	NewCoin(4, 25000000, 6),
+}
+
+func TestCoinSet(t *testing.T) {
+	cs := coinset.NewCoinSet(nil)
+	if cs.PopCoin() != nil {
+		t.Error("Expected popCoin of empty to be nil")
+	}
+	if cs.ShiftCoin() != nil {
+		t.Error("Expected shiftCoin of empty to be nil")
+	}
+
+	cs.PushCoin(coins[0])
+	cs.PushCoin(coins[1])
+	cs.PushCoin(coins[2])
+	if cs.PopCoin() != coins[2] {
+		t.Error("Expected third coin")
+	}
+	if cs.ShiftCoin() != coins[0] {
+		t.Error("Expected first coin")
+	}
+
+	mtx := coinset.NewMsgTxWithInputCoins(cs)
+	if len(mtx.TxIn) != 1 {
+		t.Errorf("Expected only 1 TxIn, got %d", len(mtx.TxIn))
+	}
+	op := mtx.TxIn[0].PreviousOutpoint
+	if !op.Hash.IsEqual(coins[1].Hash()) || op.Index != coins[1].Index() {
+		t.Errorf("Expected the second coin to be added as input to mtx")
+	}
+}
+
+var minIndexSelectors = []coinset.MinIndexCoinSelector{
+	coinset.MinIndexCoinSelector{MaxInputs: 10, MinChangeAmount: 10000},
+	coinset.MinIndexCoinSelector{MaxInputs: 2, MinChangeAmount: 10000},
+}
+
+var minIndexTests = []coinSelectTest{
+	{minIndexSelectors[0], coins, coins[0].Value() - minIndexSelectors[0].MinChangeAmount, []coinset.Coin{coins[0]}, nil},
+	{minIndexSelectors[0], coins, coins[0].Value() - minIndexSelectors[0].MinChangeAmount + 1, []coinset.Coin{coins[0], coins[1]}, nil},
+	{minIndexSelectors[0], coins, 100000000, []coinset.Coin{coins[0]}, nil},
+	{minIndexSelectors[0], coins, 110000000, []coinset.Coin{coins[0], coins[1]}, nil},
+	{minIndexSelectors[0], coins, 140000000, []coinset.Coin{coins[0], coins[1], coins[2]}, nil},
+	{minIndexSelectors[0], coins, 200000000, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{minIndexSelectors[1], coins, 10000000, []coinset.Coin{coins[0]}, nil},
+	{minIndexSelectors[1], coins, 110000000, []coinset.Coin{coins[0], coins[1]}, nil},
+	{minIndexSelectors[1], coins, 140000000, nil, coinset.ErrCoinsNoSelectionAvailable},
+}
+
+func TestMinIndexSelector(t *testing.T) {
+	testCoinSelector(minIndexTests, t)
+}
+
+var minNumberSelectors = []coinset.MinNumberCoinSelector{
+	coinset.MinNumberCoinSelector{MaxInputs: 10, MinChangeAmount: 10000},
+	coinset.MinNumberCoinSelector{MaxInputs: 2, MinChangeAmount: 10000},
+}
+
+var minNumberTests = []coinSelectTest{
+	{minNumberSelectors[0], coins, coins[0].Value() - minNumberSelectors[0].MinChangeAmount, []coinset.Coin{coins[0]}, nil},
+	{minNumberSelectors[0], coins, coins[0].Value() - minNumberSelectors[0].MinChangeAmount + 1, []coinset.Coin{coins[0], coins[2]}, nil},
+	{minNumberSelectors[0], coins, 100000000, []coinset.Coin{coins[0]}, nil},
+	{minNumberSelectors[0], coins, 110000000, []coinset.Coin{coins[0], coins[2]}, nil},
+	{minNumberSelectors[0], coins, 160000000, []coinset.Coin{coins[0], coins[2], coins[3]}, nil},
+	{minNumberSelectors[0], coins, 184990000, []coinset.Coin{coins[0], coins[2], coins[3], coins[1]}, nil},
+	{minNumberSelectors[0], coins, 184990001, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{minNumberSelectors[0], coins, 200000000, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{minNumberSelectors[1], coins, 10000000, []coinset.Coin{coins[0]}, nil},
+	{minNumberSelectors[1], coins, 110000000, []coinset.Coin{coins[0], coins[2]}, nil},
+	{minNumberSelectors[1], coins, 140000000, []coinset.Coin{coins[0], coins[2]}, nil},
+}
+
+func TestMinNumberSelector(t *testing.T) {
+	testCoinSelector(minNumberTests, t)
+}
+
+var maxValueAgeSelectors = []coinset.MaxValueAgeCoinSelector{
+	coinset.MaxValueAgeCoinSelector{MaxInputs: 10, MinChangeAmount: 10000},
+	coinset.MaxValueAgeCoinSelector{MaxInputs: 2, MinChangeAmount: 10000},
+}
+
+var maxValueAgeTests = []coinSelectTest{
+	{maxValueAgeSelectors[0], coins, 100000, []coinset.Coin{coins[1]}, nil},
+	{maxValueAgeSelectors[0], coins, 10000000, []coinset.Coin{coins[1]}, nil},
+	{maxValueAgeSelectors[0], coins, 10000001, []coinset.Coin{coins[1], coins[3]}, nil},
+	{maxValueAgeSelectors[0], coins, 35000000, []coinset.Coin{coins[1], coins[3]}, nil},
+	{maxValueAgeSelectors[0], coins, 135000000, []coinset.Coin{coins[1], coins[3], coins[0]}, nil},
+	{maxValueAgeSelectors[0], coins, 185000000, []coinset.Coin{coins[1], coins[3], coins[0], coins[2]}, nil},
+	{maxValueAgeSelectors[0], coins, 200000000, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{maxValueAgeSelectors[1], coins, 40000000, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{maxValueAgeSelectors[1], coins, 35000000, []coinset.Coin{coins[1], coins[3]}, nil},
+	{maxValueAgeSelectors[1], coins, 34990001, nil, coinset.ErrCoinsNoSelectionAvailable},
+}
+
+func TestMaxValueAgeSelector(t *testing.T) {
+	testCoinSelector(maxValueAgeTests, t)
+}
+
+var minPrioritySelectors = []coinset.MinPriorityCoinSelector{
+	coinset.MinPriorityCoinSelector{MaxInputs: 10, MinChangeAmount: 10000, MinAvgValueAgePerInput: 100000000},
+	coinset.MinPriorityCoinSelector{MaxInputs: 02, MinChangeAmount: 10000, MinAvgValueAgePerInput: 200000000},
+	coinset.MinPriorityCoinSelector{MaxInputs: 02, MinChangeAmount: 10000, MinAvgValueAgePerInput: 150000000},
+	coinset.MinPriorityCoinSelector{MaxInputs: 03, MinChangeAmount: 10000, MinAvgValueAgePerInput: 150000000},
+	coinset.MinPriorityCoinSelector{MaxInputs: 10, MinChangeAmount: 10000, MinAvgValueAgePerInput: 1000000000},
+	coinset.MinPriorityCoinSelector{MaxInputs: 10, MinChangeAmount: 10000, MinAvgValueAgePerInput: 175000000},
+	coinset.MinPriorityCoinSelector{MaxInputs: 02, MinChangeAmount: 10000, MinAvgValueAgePerInput: 125000000},
+}
+
+var connectedCoins = []coinset.Coin{coins[0], coins[1], coins[3]}
+
+var minPriorityTests = []coinSelectTest{
+	{minPrioritySelectors[0], connectedCoins, 100000000, []coinset.Coin{coins[0]}, nil},
+	{minPrioritySelectors[0], connectedCoins, 125000000, []coinset.Coin{coins[0], coins[3]}, nil},
+	{minPrioritySelectors[0], connectedCoins, 135000000, []coinset.Coin{coins[0], coins[3], coins[1]}, nil},
+	{minPrioritySelectors[0], connectedCoins, 140000000, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{minPrioritySelectors[1], connectedCoins, 100000000, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{minPrioritySelectors[1], connectedCoins, 10000000, []coinset.Coin{coins[1]}, nil},
+	{minPrioritySelectors[1], connectedCoins, 100000000, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{minPrioritySelectors[2], connectedCoins, 11000000, []coinset.Coin{coins[3]}, nil},
+	{minPrioritySelectors[2], connectedCoins, 25000001, []coinset.Coin{coins[3], coins[1]}, nil},
+	{minPrioritySelectors[3], connectedCoins, 25000001, []coinset.Coin{coins[3], coins[1], coins[0]}, nil},
+	{minPrioritySelectors[3], connectedCoins, 100000000, []coinset.Coin{coins[3], coins[1], coins[0]}, nil},
+	{minPrioritySelectors[3], []coinset.Coin{coins[1], coins[2]}, 10000000, []coinset.Coin{coins[1]}, nil},
+	{minPrioritySelectors[4], connectedCoins, 1, nil, coinset.ErrCoinsNoSelectionAvailable},
+	{minPrioritySelectors[5], connectedCoins, 20000000, []coinset.Coin{coins[1], coins[3]}, nil},
+	{minPrioritySelectors[6], connectedCoins, 25000000, []coinset.Coin{coins[3], coins[0]}, nil},
+}
+
+func TestMinPrioritySelector(t *testing.T) {
+	testCoinSelector(minPriorityTests, t)
+}
+
+var (
+	// should be two outpoints, with 1st one having 0.035BTC value.
+	testSimpleCoinTxHash              = "9b5965c86de51d5dc824e179a05cf232db78c80ae86ca9d7cb2a655b5e19c1e2"
+	testSimpleCoinTxHex               = "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"
+	testSimpleCoinTxValue0            = int64(3500000)
+	testSimpleCoinTxPkScript0Hex      = "76a914686dd149a79b4a559d561fbc396d3e3c6628b98d88ac"
+	testSimpleCoinTxPkScript0Bytes, _ = hex.DecodeString(testSimpleCoinTxPkScript0Hex)
+	testSimpleCoinTxBytes, _          = hex.DecodeString(testSimpleCoinTxHex)
+	testSimpleCoinTx, _               = btcutil.NewTxFromBytes(testSimpleCoinTxBytes)
+	testSimpleCoin                    = &coinset.SimpleCoin{
+		Tx:         testSimpleCoinTx,
+		TxIndex:    0,
+		TxNumConfs: 1,
+	}
+)
+
+func TestSimpleCoin(t *testing.T) {
+	if testSimpleCoin.Hash().String() != testSimpleCoinTxHash {
+		t.Error("Different value for tx hash than expected")
+	}
+	if testSimpleCoin.Index() != 0 {
+		t.Error("Different value for index of outpoint than expected")
+	}
+	if testSimpleCoin.Value() != testSimpleCoinTxValue0 {
+		t.Error("Different value of coin value than expected")
+	}
+	if !bytes.Equal(testSimpleCoin.PkScript(), testSimpleCoinTxPkScript0Bytes) {
+		t.Error("Different value of coin pkScript than expected")
+	}
+	if testSimpleCoin.NumConfs() != 1 {
+		t.Error("Differet value of num confs than expected")
+	}
+	if testSimpleCoin.ValueAge() != testSimpleCoinTxValue0 {
+		t.Error("Different value of coin value * age than expected")
+	}
+}
--- a/coinset/cov_report.sh
+++ b/coinset/cov_report.sh
@ -0,0 +1,17 @@
+#!/bin/sh
+
+# This script uses gocov to generate a test coverage report.
+# The gocov tool my be obtained with the following command:
+#   go get github.com/axw/gocov/gocov
+#
+# It will be installed to $GOPATH/bin, so ensure that location is in your $PATH.
+
+# Check for gocov.
+type gocov >/dev/null 2>&1
+if [ $? -ne 0 ]; then
+	echo >&2 "This script requires the gocov tool."
+	echo >&2 "You may obtain it with the following command:"
+	echo >&2 "go get github.com/axw/gocov/gocov"
+	exit 1
+fi
+gocov test | gocov report
--- a/coinset/test_coverage.txt
+++ b/coinset/test_coverage.txt
@ -0,0 +1,31 @@
+
+github.com/conformal/btcutil/coinset/coins.go	 MinPriorityCoinSelector.CoinSelect	 100.00% (39/39)
+github.com/conformal/btcutil/coinset/coins.go	 NewMsgTxWithInputCoins			 100.00% (6/6)
+github.com/conformal/btcutil/coinset/coins.go	 MinIndexCoinSelector.CoinSelect	 100.00% (6/6)
+github.com/conformal/btcutil/coinset/coins.go	 CoinSet.removeElement			 100.00% (5/5)
+github.com/conformal/btcutil/coinset/coins.go	 NewCoinSet				 100.00% (4/4)
+github.com/conformal/btcutil/coinset/coins.go	 CoinSet.Coins				 100.00% (4/4)
+github.com/conformal/btcutil/coinset/coins.go	 CoinSet.PopCoin			 100.00% (4/4)
+github.com/conformal/btcutil/coinset/coins.go	 CoinSet.ShiftCoin			 100.00% (4/4)
+github.com/conformal/btcutil/coinset/coins.go	 MinNumberCoinSelector.CoinSelect	 100.00% (4/4)
+github.com/conformal/btcutil/coinset/coins.go	 MaxValueAgeCoinSelector.CoinSelect	 100.00% (4/4)
+github.com/conformal/btcutil/coinset/coins.go	 CoinSet.PushCoin			 100.00% (3/3)
+github.com/conformal/btcutil/coinset/coins.go	 CoinSet.TotalValueAge			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 SimpleCoin.NumConfs			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 SimpleCoin.ValueAge			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 CoinSet.TotalValue			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 byValueAge.Len				 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 byValueAge.Swap			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 byValueAge.Less			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 byAmount.Len				 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 byAmount.Swap				 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 byAmount.Less				 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 SimpleCoin.Hash			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 SimpleCoin.Index			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 SimpleCoin.txOut			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 SimpleCoin.Value			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 SimpleCoin.PkScript			 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 CoinSet.Num				 100.00% (1/1)
+github.com/conformal/btcutil/coinset/coins.go	 satisfiesTargetValue			 100.00% (1/1)
+github.com/conformal/btcutil/coinset		 ----------------------------------	 100.00% (100/100)
+
--- a/test_coverage.txt
+++ b/test_coverage.txt
@ -1,59 +1,59 @@

 github.com/conformal/btcutil/base58.go		 Base58Decode			 100.00% (20/20)
+github.com/conformal/btcutil/address.go		 DecodeAddr			 100.00% (18/18)
 github.com/conformal/btcutil/base58.go		 Base58Encode			 100.00% (15/15)
 github.com/conformal/btcutil/addrconvs.go	 DecodeAddress			 100.00% (14/14)
 github.com/conformal/btcutil/block.go		 Block.Tx			 100.00% (12/12)
 github.com/conformal/btcutil/block.go		 Block.Transactions		 100.00% (11/11)
 github.com/conformal/btcutil/block.go		 Block.TxShas			 100.00% (10/10)
 github.com/conformal/btcutil/address.go		 encodeAddress			 100.00% (9/9)
-github.com/conformal/btcutil/addrconvs.go	 EncodeAddress			 100.00% (8/8)
 github.com/conformal/btcutil/addrconvs.go	 EncodeScriptHash		 100.00% (8/8)
-github.com/conformal/btcutil/addrconvs.go	 encodeHashWithNetId		 100.00% (7/7)
+github.com/conformal/btcutil/addrconvs.go	 EncodeAddress			 100.00% (8/8)
 github.com/conformal/btcutil/tx.go		 NewTxFromBytes			 100.00% (7/7)
 github.com/conformal/btcutil/block.go		 NewBlockFromBytes		 100.00% (7/7)
+github.com/conformal/btcutil/addrconvs.go	 encodeHashWithNetId		 100.00% (7/7)
 github.com/conformal/btcutil/block.go		 Block.Sha			 100.00% (5/5)
 github.com/conformal/btcutil/tx.go		 Tx.Sha				 100.00% (5/5)
 github.com/conformal/btcutil/block.go		 Block.TxSha			 100.00% (4/4)
 github.com/conformal/btcutil/hash160.go		 calcHash			 100.00% (2/2)
 github.com/conformal/btcutil/address.go		 NewAddressScriptHash		 100.00% (2/2)
-github.com/conformal/btcutil/block.go		 NewBlock			 100.00% (1/1)
-github.com/conformal/btcutil/tx.go		 NewTx				 100.00% (1/1)
-github.com/conformal/btcutil/address.go		 AddressScriptHash.String	 100.00% (1/1)
-github.com/conformal/btcutil/tx.go		 Tx.SetIndex			 100.00% (1/1)
-github.com/conformal/btcutil/block.go		 Block.MsgBlock			 100.00% (1/1)
-github.com/conformal/btcutil/block.go		 NewBlockFromBlockAndBytes	 100.00% (1/1)
-github.com/conformal/btcutil/address.go		 AddressScriptHash.ScriptAddress 100.00% (1/1)
 github.com/conformal/btcutil/address.go		 AddressPubKeyHash.ScriptAddress 100.00% (1/1)
-github.com/conformal/btcutil/address.go		 AddressPubKeyHash.EncodeAddress 100.00% (1/1)
-github.com/conformal/btcutil/block.go		 Block.Height			 100.00% (1/1)
+github.com/conformal/btcutil/block.go		 NewBlock			 100.00% (1/1)
 github.com/conformal/btcutil/block.go		 Block.SetHeight		 100.00% (1/1)
+github.com/conformal/btcutil/block.go		 Block.Height			 100.00% (1/1)
 github.com/conformal/btcutil/address.go		 AddressPubKey.EncodeAddress	 100.00% (1/1)
 github.com/conformal/btcutil/address.go		 AddressPubKey.ScriptAddress	 100.00% (1/1)
-github.com/conformal/btcutil/tx.go		 Tx.Index			 100.00% (1/1)
+github.com/conformal/btcutil/tx.go		 NewTx				 100.00% (1/1)
 github.com/conformal/btcutil/address.go		 AddressPubKey.String		 100.00% (1/1)
-github.com/conformal/btcutil/tx.go		 Tx.MsgTx			 100.00% (1/1)
-github.com/conformal/btcutil/address.go		 AddressScriptHash.EncodeAddress 100.00% (1/1)
+github.com/conformal/btcutil/tx.go		 Tx.SetIndex			 100.00% (1/1)
+github.com/conformal/btcutil/tx.go		 Tx.Index			 100.00% (1/1)
+github.com/conformal/btcutil/address.go		 AddressScriptHash.ScriptAddress 100.00% (1/1)
 github.com/conformal/btcutil/hash160.go		 Hash160			 100.00% (1/1)
-github.com/conformal/btcutil/address.go		 AddressPubKeyHash.String	 100.00% (1/1)
+github.com/conformal/btcutil/address.go		 AddressPubKeyHash.EncodeAddress 100.00% (1/1)
+github.com/conformal/btcutil/address.go		 AddressScriptHash.EncodeAddress 100.00% (1/1)
+github.com/conformal/btcutil/block.go		 NewBlockFromBlockAndBytes	 100.00% (1/1)
 github.com/conformal/btcutil/block.go		 OutOfRangeError.Error		 100.00% (1/1)
-github.com/conformal/btcutil/address.go		 DecodeAddr			 95.65% (22/23)
+github.com/conformal/btcutil/block.go		 Block.MsgBlock			 100.00% (1/1)
+github.com/conformal/btcutil/tx.go		 Tx.MsgTx			 100.00% (1/1)
 github.com/conformal/btcutil/appdata.go		 appDataDir			 92.00% (23/25)
-github.com/conformal/btcutil/address.go		 NewAddressPubKeyHash		 91.67% (11/12)
 github.com/conformal/btcutil/address.go		 NewAddressScriptHashFromHash	 91.67% (11/12)
+github.com/conformal/btcutil/address.go		 NewAddressPubKeyHash		 91.67% (11/12)
 github.com/conformal/btcutil/addrconvs.go	 EncodePrivateKey		 90.91% (20/22)
-github.com/conformal/btcutil/block.go		 Block.Bytes			 88.89% (8/9)
 github.com/conformal/btcutil/block.go		 Block.TxLoc			 88.89% (8/9)
+github.com/conformal/btcutil/block.go		 Block.Bytes			 88.89% (8/9)
 github.com/conformal/btcutil/address.go		 AddressPubKey.serialize	 85.71% (6/7)
+github.com/conformal/btcutil/addrconvs.go	 DecodePrivateKey		 83.33% (20/24)
 github.com/conformal/btcutil/address.go		 NewAddressPubKey		 83.33% (15/18)
 github.com/conformal/btcutil/address.go		 checkBitcoinNet		 83.33% (5/6)
-github.com/conformal/btcutil/addrconvs.go	 DecodePrivateKey		 82.61% (19/23)
 github.com/conformal/btcutil/address.go		 AddressPubKeyHash.IsForNet	 60.00% (3/5)
 github.com/conformal/btcutil/address.go		 AddressPubKey.IsForNet		 60.00% (3/5)
 github.com/conformal/btcutil/address.go		 AddressScriptHash.IsForNet	 60.00% (3/5)
 github.com/conformal/btcutil/certgen.go		 NewTLSCertPair			 0.00% (0/50)
 github.com/conformal/btcutil/address.go		 AddressPubKey.AddressPubKeyHash 0.00% (0/3)
-github.com/conformal/btcutil/address.go		 AddressPubKey.Format		 0.00% (0/1)
-github.com/conformal/btcutil/address.go		 AddressPubKey.SetFormat	 0.00% (0/1)
+github.com/conformal/btcutil/address.go		 AddressPubKeyHash.String	 0.00% (0/1)
 github.com/conformal/btcutil/appdata.go		 AppDataDir			 0.00% (0/1)
-github.com/conformal/btcutil			 ------------------------------- 80.15% (323/403)
+github.com/conformal/btcutil/address.go		 AddressPubKey.SetFormat	 0.00% (0/1)
+github.com/conformal/btcutil/address.go		 AddressPubKey.Format		 0.00% (0/1)
+github.com/conformal/btcutil/address.go		 AddressScriptHash.String	 0.00% (0/1)
+github.com/conformal/btcutil			 ------------------------------- 79.70% (318/399)