From 106a4a829f92a07ef852a1eb8fc5afdbeed4bc65 Mon Sep 17 00:00:00 2001
From: Hans Moog <hm@mkjc.net>
Date: Thu, 8 Aug 2019 01:21:12 +0200
Subject: [PATCH] Feat: added balance - to allow nodes to reach consensus on
mana balances
---
packages/errors/errors.go | 2 +-
packages/mana/balance.go | 122 ++++++++++++++++++-------
packages/mana/balance_history_entry.go | 7 ++
packages/mana/balance_test.go | 19 ++--
packages/mana/calculator.go | 6 +-
packages/mana/transfer.go | 15 +++
6 files changed, 127 insertions(+), 44 deletions(-)
create mode 100644 packages/mana/balance_history_entry.go
create mode 100644 packages/mana/transfer.go
diff --git a/packages/errors/errors.go b/packages/errors/errors.go
index 738ed629..5ad2f9cc 100644
--- a/packages/errors/errors.go
+++ b/packages/errors/errors.go
@@ -142,7 +142,7 @@ func (f *fundamental) Derive(msg string) *fundamental {
func (f *fundamental) Error() string { return f.msg }
func (f *fundamental) Equals(err IdentifiableError) bool {
- return f.id == err.Id()
+ return err != nil && f.id == err.Id()
}
func (f *fundamental) Id() int {
diff --git a/packages/mana/balance.go b/packages/mana/balance.go
index 1c407ff9..95e6e857 100644
--- a/packages/mana/balance.go
+++ b/packages/mana/balance.go
@@ -1,59 +1,115 @@
package mana
import (
- "fmt"
+ "github.com/iotaledger/goshimmer/packages/datastructure"
)
type Balance struct {
- calculator *Calculator
- currentBalance uint64
- lastErosion uint64
- accumulatedRoundingError float64
+ calculator *Calculator
+ transferHistory *datastructure.DoublyLinkedList
}
func NewBalance(calculator *Calculator) *Balance {
return &Balance{
- calculator: calculator,
- currentBalance: 0,
- lastErosion: 0,
- accumulatedRoundingError: 0,
+ calculator: calculator,
+ transferHistory: &datastructure.DoublyLinkedList{},
}
}
+// Returns the current mana balance.
func (balance *Balance) GetValue() uint64 {
- return balance.currentBalance
+ if lastBalanceHistoryEntry, err := balance.transferHistory.GetLast(); datastructure.ErrNoSuchElement.Equals(err) {
+ return 0
+ } else {
+ return lastBalanceHistoryEntry.(*BalanceHistoryEntry).balance
+ }
}
-func (balance *Balance) AddTransfer(movedCoins uint64, receivedTime uint64, spentTime uint64) {
- gainedMana, roundingError := balance.calculator.GenerateMana(movedCoins, spentTime-receivedTime)
-
- if balance.currentBalance != 0 {
- if spentTime >= balance.lastErosion {
- balance.Erode(spentTime)
- } else {
- fmt.Println("empty")
- // revert old actions
- // apply new
- // replay old
- }
+// Returns the timestamp of the last mana erosion.
+func (balance *Balance) GetLastErosion() uint64 {
+ if lastBalanceHistoryEntry, err := balance.transferHistory.GetLast(); datastructure.ErrNoSuchElement.Equals(err) {
+ return 0
+ } else {
+ return lastBalanceHistoryEntry.(*BalanceHistoryEntry).transfer.spentTime
}
+}
+
+// Books a new transfer to the balance.
+func (balance *Balance) AddTransfer(transfer *Transfer) {
+ // check if we need to rollback transfers (to prevent rounding errors)
+ rolledBackTransactions := balance.rollbackTransfers(transfer.spentTime)
- balance.currentBalance += gainedMana
- balance.accumulatedRoundingError += roundingError
- balance.lastErosion = spentTime
+ // apply new transfer
+ balance.applyTransfer(transfer)
- fmt.Println("GENERATE: ", spentTime-receivedTime, movedCoins, gainedMana)
+ // replay rolled back transfers (in reverse order)
+ for i := len(rolledBackTransactions) - 1; i >= 0; i-- {
+ balance.applyTransfer(rolledBackTransactions[i])
+ }
}
-func (balance *Balance) Erode(erosionTime uint64) {
- if balance.lastErosion <= erosionTime {
- erodedMana, _ := balance.calculator.ErodeMana(balance.currentBalance, erosionTime-balance.lastErosion)
+// Rolls back transfers that have their spentTime after the given referenceTime and returns a slice containing the
+// rolled back transfers.
+//
+// Since the mana calculations use floats, we will see rounding errors. To allow all nodes to have consensus on the
+// current mana balance, we need to make nodes use the exact same formulas and apply them in the exact same order.
+// Because of the asynchronous nature of the tangle, nodes will see different transactions at different times and will
+// therefore process their mana gains in a different order. This could lead to discrepancies in the balance due to
+// accumulated rounding errors. To work around this problem, we keep a history of the latest transfers (up till a
+// certain age), that can be rolled back. This allows us to apply all mana changes in the exact same order which will
+// lead to a network wide consensus on the mana balances.
+func (balance *Balance) rollbackTransfers(referenceTime uint64) (result []*Transfer) {
+ result = make([]*Transfer, 0)
+
+ for {
+ if lastListEntry, err := balance.transferHistory.GetLast(); err != nil {
+ if !datastructure.ErrNoSuchElement.Equals(err) {
+ panic(err)
+ }
+
+ return
+ } else if lastTransfer := lastListEntry.(*BalanceHistoryEntry).transfer; lastTransfer.spentTime < referenceTime {
+ return
+ } else {
+ result = append(result, lastTransfer)
+
+ if _, err := balance.transferHistory.RemoveLast(); err != nil {
+ panic(err)
+ }
+ }
+ }
+}
- fmt.Println("ERODE: ", erosionTime-balance.lastErosion, balance.currentBalance, erodedMana)
+// Applies the balance changes of the given transfer.
+func (balance *Balance) applyTransfer(transfer *Transfer) {
+ // retrieve current values
+ var currentBalance, lastErosion uint64
+ if lastListEntry, err := balance.transferHistory.GetLastEntry(); err != nil {
+ if !datastructure.ErrNoSuchElement.Equals(err) {
+ panic(err)
+ }
- balance.currentBalance = erodedMana
+ currentBalance = 0
+ lastErosion = 0
} else {
- fmt.Println("empty")
- // revert old erosions
+ lastBalanceHistoryEntry := lastListEntry.GetValue().(*BalanceHistoryEntry)
+
+ currentBalance = lastBalanceHistoryEntry.balance
+ lastErosion = lastBalanceHistoryEntry.transfer.spentTime
+ }
+
+ // erode if we have a balance
+ if currentBalance != 0 {
+ currentBalance, _ = balance.calculator.ErodeMana(currentBalance, transfer.spentTime-lastErosion)
}
+
+ // calculate mana gains
+ gainedMana, roundingError := balance.calculator.GenerateMana(transfer.movedCoins, transfer.spentTime-transfer.receivedTime)
+
+ // store results
+ balance.transferHistory.AddLast(&BalanceHistoryEntry{
+ transfer: transfer,
+ balance: currentBalance + gainedMana,
+ accumulatedRoundingError: roundingError,
+ })
}
diff --git a/packages/mana/balance_history_entry.go b/packages/mana/balance_history_entry.go
new file mode 100644
index 00000000..7d4d6d43
--- /dev/null
+++ b/packages/mana/balance_history_entry.go
@@ -0,0 +1,7 @@
+package mana
+
+type BalanceHistoryEntry struct {
+ transfer *Transfer
+ balance uint64
+ accumulatedRoundingError float64
+}
diff --git a/packages/mana/balance_test.go b/packages/mana/balance_test.go
index 23345898..5aa0b3f1 100644
--- a/packages/mana/balance_test.go
+++ b/packages/mana/balance_test.go
@@ -1,20 +1,25 @@
package mana
import (
- "fmt"
"testing"
+
+ "github.com/magiconair/properties/assert"
)
func TestBalance_AddTransfer(t *testing.T) {
calculator := NewCalculator(500, 0.1)
+ // spend coins multiple times
balance1 := NewBalance(calculator)
- balance1.AddTransfer(1000, 0, 500)
- balance1.AddTransfer(1000, 500, 1000)
- balance1.AddTransfer(1000, 1000, 1700)
- fmt.Println(balance1.GetValue())
+ balance1.AddTransfer(NewTransfer(1000, 1000, 1700))
+ balance1.AddTransfer(NewTransfer(1000, 700, 1000))
+ balance1.AddTransfer(NewTransfer(1000, 0, 700))
+ // hold coins for the full time
balance2 := NewBalance(calculator)
- balance2.AddTransfer(1000, 0, 1700)
- fmt.Println(balance2.GetValue())
+ balance2.AddTransfer(NewTransfer(1000, 0, 1700))
+
+ // check result
+ assert.Equal(t, balance1.GetValue(), uint64(301))
+ assert.Equal(t, balance2.GetValue(), uint64(301))
}
diff --git a/packages/mana/calculator.go b/packages/mana/calculator.go
index 46aa3c53..38b3135a 100644
--- a/packages/mana/calculator.go
+++ b/packages/mana/calculator.go
@@ -18,13 +18,13 @@ func NewCalculator(decayInterval float64, decayRate float64, optionalOptions ...
// store key settings
decayInterval: decayInterval,
- // configure optional parameters
- options: DEFAULT_OPTIONS.Override(optionalOptions...),
-
// derive important factors ...
// ... make mana reach exactly the token supply as it's max value (n coins => n mana)
decayFactor: 1 - decayRate,
tokenSupplyScalefactor: decayRate / (1 - decayRate),
+
+ // configure optional parameters
+ options: DEFAULT_OPTIONS.Override(optionalOptions...),
}
}
diff --git a/packages/mana/transfer.go b/packages/mana/transfer.go
new file mode 100644
index 00000000..eae37e0d
--- /dev/null
+++ b/packages/mana/transfer.go
@@ -0,0 +1,15 @@
+package mana
+
+type Transfer struct {
+ movedCoins uint64
+ receivedTime uint64
+ spentTime uint64
+}
+
+func NewTransfer(movedCoins uint64, receivedTime uint64, spentTime uint64) *Transfer {
+ return &Transfer{
+ movedCoins: movedCoins,
+ receivedTime: receivedTime,
+ spentTime: spentTime,
+ }
+}
--
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