payment updates

sdk/go.mod

@@ -5,6 +5,7 @@ go 1.16
 replace github.com/stellar/go => github.com/leighmcculloch/stellar--go v0.0.0-20210528222607-c2e3ef441a5d
 
 require (
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/stellar/go v0.0.0-00010101000000-000000000000
 	github.com/stretchr/testify v1.5.1
 )

sdk/go.sum

@@ -117,8 +117,9 @@ github.com/openzipkin/zipkin-go v0.1.6/go.mod h1:QgAqvLzwWbR/WpD4A3cGpPtJrZXNIiJ
 github.com/pelletier/go-toml v1.9.0/go.mod h1:u1nR/EPcESfeI/szUZKdtJ0xRNbUoANCkoOuaOx1Y+c=
 github.com/pierrec/lz4 v2.0.5+incompatible/go.mod h1:pdkljMzZIN41W+lC3N2tnIh5sFi+IEE17M5jbnwPHcY=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
-github.com/pkg/errors v0.8.1 h1:iURUrRGxPUNPdy5/HRSm+Yj6okJ6UtLINN0Q9M4+h3I=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/prometheus/client_golang v0.9.1/go.mod h1:7SWBe2y4D6OKWSNQJUaRYU/AaXPKyh/dDVn+NZz0KFw=

sdk/state/state.go

@@ -32,7 +32,14 @@ type Channel struct {
 	observationPeriodLedgerGap int64
 
 	startingSequence int64
-	// TODO: balances         []Amount
+	iterationNumber  int64
+	// TODO - leave execution out for now
+	// iterationNumberExecuted int64
+
+	// The balance owing from the initiator to the responder, if positive, or
+	// the balance owing from the responder to the initiator, if negative.
+	// TODO - use Balance struct
+	amount Amount
 
 	initiator           bool
 	localEscrowAccount  *EscrowAccount
@@ -46,6 +53,7 @@ type Config struct {
 	NetworkPassphrase          string
 	ObservationPeriodTime      time.Duration
 	ObservationPeriodLedgerGap int64
+	StartingSequence           int64
 
 	Initiator bool
 
@@ -61,6 +69,7 @@ func NewChannel(c Config) *Channel {
 		networkPassphrase:          c.NetworkPassphrase,
 		observationPeriodTime:      c.ObservationPeriodTime,
 		observationPeriodLedgerGap: c.ObservationPeriodLedgerGap,
+		startingSequence:           c.StartingSequence,
 		initiator:                  c.Initiator,
 		localEscrowAccount:         c.LocalEscrowAccount,
 		remoteEscrowAccount:        c.RemoteEscrowAccount,
@@ -150,10 +159,6 @@ func (c *Channel) verifySigned(tx *txnbuild.Transaction, sigs []xdr.DecoratedSig
 	}
 }
 
-func (c *Channel) Payment(sendAmount int) error {
-	return nil
-}
-
 func (c *Channel) CloseStart(iterationNumber int) error {
 	return nil
 }

sdk/state/update.go

@@ -0,0 +1,124 @@
+package state
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/stellar/experimental-payment-channels/sdk/txbuild"
+	"github.com/stellar/go/xdr"
+)
+
+type Payment struct {
+	IterationNumber       int64
+	Amount                int64
+	CloseSignatures       []xdr.DecoratedSignature
+	DeclarationSignatures []xdr.DecoratedSignature
+	FromInitiator         bool
+}
+
+func (c *Channel) NewPayment(amount int64) (*Payment, error) {
+	if amount <= 0 {
+		return nil, errors.New("payment amount must be greater than 0")
+	}
+	newBalance := int64(0)
+	if c.initiator {
+		newBalance = c.amount.Amount + amount
+	} else {
+		newBalance = c.amount.Amount - amount
+	}
+	txC, err := txbuild.Close(txbuild.CloseParams{
+		ObservationPeriodTime:      c.observationPeriodTime,
+		ObservationPeriodLedgerGap: c.observationPeriodLedgerGap,
+		InitiatorSigner:            c.initiatorSigner(),
+		ResponderSigner:            c.responderSigner(),
+		InitiatorEscrow:            c.initiatorEscrowAccount().Address,
+		ResponderEscrow:            c.responderEscrowAccount().Address,
+		StartSequence:              c.startingSequence,
+		IterationNumber:            c.iterationNumber,
+		AmountToInitiator:          maxInt64(0, newBalance*-1),
+		AmountToResponder:          maxInt64(0, newBalance),
+	})
+	if err != nil {
+		return nil, err
+	}
+	txC, err = txC.Sign(c.networkPassphrase, c.localSigner)
+	if err != nil {
+		return nil, err
+	}
+	return &Payment{
+		Amount:          amount,
+		CloseSignatures: txC.Signatures(),
+		FromInitiator:   c.initiator,
+	}, nil
+}
+
+func (c *Channel) ConfirmPayment(p *Payment) (*Payment, error) {
+	var newCloseSignatures, newDeclarationSignatures []xdr.DecoratedSignature
+	var amountFromInitiator, amountFromResponder int64
+	if p.FromInitiator {
+		amountFromInitiator = p.Amount
+	} else {
+		amountFromResponder = p.Amount
+	}
+	newBalance := c.amount.Amount + amountFromInitiator - amountFromResponder
+
+	// validate txC, should always be signed correctly
+	txC, err := txbuild.Close(txbuild.CloseParams{
+		ObservationPeriodTime:      c.observationPeriodTime,
+		ObservationPeriodLedgerGap: c.observationPeriodLedgerGap,
+		InitiatorSigner:            c.initiatorSigner(),
+		ResponderSigner:            c.responderSigner(),
+		InitiatorEscrow:            c.initiatorEscrowAccount().Address,
+		ResponderEscrow:            c.responderEscrowAccount().Address,
+		StartSequence:              c.startingSequence,
+		IterationNumber:            c.iterationNumber,
+		AmountToInitiator:          maxInt64(0, newBalance*-1),
+		AmountToResponder:          maxInt64(0, newBalance),
+	})
+	if err != nil {
+		return nil, err
+	}
+	if err := c.verifySigned(txC, p.CloseSignatures, c.remoteSigner); err != nil {
+		return nil, fmt.Errorf("incorrect closing transaction, the one given may have different data: %w", err)
+	}
+	// validate txD, may or may not be signed depending where in the payment step we are
+	signedTxD := false
+	txD, err := txbuild.Declaration(txbuild.DeclarationParams{
+		InitiatorEscrow:         c.initiatorEscrowAccount().Address,
+		StartSequence:           c.startingSequence,
+		IterationNumber:         c.iterationNumber,
+		IterationNumberExecuted: 0,
+	})
+	if err != nil {
+		return nil, err
+	}
+	if err := c.verifySigned(txD, p.DeclarationSignatures, c.remoteSigner); err == nil {
+		signedTxD = true
+	}
+	// sign C_i if given a signed C_i with no D_i
+	if !signedTxD {
+		txC, err = txC.Sign(c.networkPassphrase, c.localSigner)
+		if err != nil {
+			return nil, err
+		}
+		newCloseSignatures = txC.Signatures()
+	}
+	// sign D_i always if above passes
+	txD, err = txD.Sign(c.networkPassphrase, c.localSigner)
+	if err != nil {
+		return nil, err
+	}
+	newDeclarationSignatures = txD.Signatures()
+
+	p.CloseSignatures = append(p.CloseSignatures, newCloseSignatures...)
+	p.DeclarationSignatures = append(p.DeclarationSignatures, newDeclarationSignatures...)
+	c.amount.Amount = newBalance
+	return p, nil
+}
+
+func maxInt64(x int64, y int64) int64 {
+	if x > y {
+		return x
+	}
+	return y
+}