[payments] disperser client local metering

api/clients/accountant.go

@@ -0,0 +1,154 @@
+package clients
+
+import (
+	"context"
+	"fmt"
+	"math/big"
+	"sync"
+	"time"
+
+	commonpb "github.com/Layr-Labs/eigenda/api/grpc/common"
+	"github.com/Layr-Labs/eigenda/core"
+	"github.com/Layr-Labs/eigenda/core/meterer"
+)
+
+type IAccountant interface {
+	AccountBlob(ctx context.Context, data []byte, quorums []uint8) (uint32, uint64, error)
+}
+
+type Accountant struct {
+	// on-chain states
+	reservation       core.ActiveReservation
+	onDemand          core.OnDemandPayment
+	reservationWindow uint32
+	pricePerSymbol    uint32
+	minNumSymbols     uint32
+
+	// local accounting
+	// contains 3 bins; index 0 for current bin, 1 for next bin, 2 for overflowed bin
+	binUsages         []uint64
+	usageLock         sync.Mutex
+	cumulativePayment *big.Int
+	stopRotation      chan struct{}
+
+	paymentSigner core.PaymentSigner
+}
+
+func NewAccountant(reservation core.ActiveReservation, onDemand core.OnDemandPayment, reservationWindow uint32, pricePerSymbol uint32, minNumSymbols uint32, paymentSigner core.PaymentSigner) *Accountant {
+	//TODO: client storage; currently every instance starts fresh but on-chain or a small store makes more sense
+	// Also client is currently responsible for supplying network params, we need to add RPC in order to be automatic
+	// There's a subsequent PR that handles populating the accountant with on-chain state from the disperser
+	a := Accountant{
+		reservation:       reservation,
+		onDemand:          onDemand,
+		reservationWindow: reservationWindow,
+		pricePerSymbol:    pricePerSymbol,
+		minNumSymbols:     minNumSymbols,
+		binUsages:         []uint64{0, 0, 0},
+		cumulativePayment: big.NewInt(0),
+		stopRotation:      make(chan struct{}),
+		paymentSigner:     paymentSigner,
+	}
+	go a.startBinRotation()
+	// TODO: add a routine to refresh the on-chain state occasionally?
+	return &a
+}
+
+func (a *Accountant) startBinRotation() {
+	ticker := time.NewTicker(time.Duration(a.reservationWindow) * time.Second)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			a.rotateBins()
+		case <-a.stopRotation:
+			return
+		}
+	}
+}
+
+func (a *Accountant) rotateBins() {
+	a.usageLock.Lock()
+	defer a.usageLock.Unlock()
+	// Shift bins: bin_i to bin_{i-1}, set 0 to bin2
+	a.binUsages[0] = a.binUsages[1]
+	a.binUsages[1] = a.binUsages[2]
+	a.binUsages[2] = 0
+}
+
+func (a *Accountant) Stop() {
+	close(a.stopRotation)
+}
+
+// accountant calculates and records payment information
+func (a *Accountant) BlobPaymentInfo(ctx context.Context, dataLength uint64) (uint32, *big.Int, error) {
+	//TODO: do we need to lock the binUsages here in case the blob rotation happens in the middle of the function?
+	// binUsage := a.binUsages[0] + dataLength
+	a.usageLock.Lock()
+	defer a.usageLock.Unlock()
+	a.binUsages[0] += dataLength
+	now := time.Now().Unix()
+	currentBinIndex := meterer.GetBinIndex(uint64(now), a.reservationWindow)
+
+	// first attempt to use the active reservation
+	binLimit := a.reservation.SymbolsPerSec * uint64(a.reservationWindow)
+	if a.binUsages[0] <= binLimit {
+		return currentBinIndex, big.NewInt(0), nil
+	}
+
+	// Allow one overflow when the overflow bin is empty, the current usage and new length are both less than the limit
+	if a.binUsages[2] == 0 && a.binUsages[0]-dataLength < binLimit && dataLength <= binLimit {
+		a.binUsages[2] += a.binUsages[0] - binLimit
+		return currentBinIndex, big.NewInt(0), nil
+	}
+
+	// reservation not available, attempt on-demand
+	//todo: rollback if disperser respond with some type of rejection?
+	a.binUsages[0] -= dataLength
+	incrementRequired := big.NewInt(int64(a.PaymentCharged(uint(dataLength))))
+	a.cumulativePayment.Add(a.cumulativePayment, incrementRequired)
+	if a.cumulativePayment.Cmp(a.onDemand.CumulativePayment) <= 0 {
+		return 0, a.cumulativePayment, nil
+	}
+	return 0, big.NewInt(0), fmt.Errorf("Accountant cannot approve payment for this blob")
+}
+
+// accountant provides and records payment information
+func (a *Accountant) AccountBlob(ctx context.Context, dataLength uint64, quorums []uint8) (*commonpb.PaymentHeader, []byte, error) {
+	binIndex, cumulativePayment, err := a.BlobPaymentInfo(ctx, dataLength)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	accountID := a.paymentSigner.GetAccountID()
+	pm := &core.PaymentMetadata{
+		AccountID:         accountID,
+		BinIndex:          binIndex,
+		CumulativePayment: cumulativePayment,
+	}
+	protoPaymentHeader := pm.ConvertToProtoPaymentHeader()
+
+	signature, err := a.paymentSigner.SignBlobPayment(protoPaymentHeader)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return protoPaymentHeader, signature, nil
+}
+
+// TODO: PaymentCharged and SymbolsCharged copied from meterer, should be refactored
+// PaymentCharged returns the chargeable price for a given data length
+func (a *Accountant) PaymentCharged(dataLength uint) uint64 {
+	return uint64(a.SymbolsCharged(dataLength)) * uint64(a.pricePerSymbol)
+}
+
+// SymbolsCharged returns the number of symbols charged for a given data length
+// being at least MinNumSymbols or the nearest rounded-up multiple of MinNumSymbols.
+func (a *Accountant) SymbolsCharged(dataLength uint) uint32 {
+	if dataLength <= uint(a.minNumSymbols) {
+		return a.minNumSymbols
+	}
+	// Round up to the nearest multiple of MinNumSymbols
+	return uint32(core.RoundUpDivide(uint(dataLength), uint(a.minNumSymbols))) * a.minNumSymbols
+}