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twoparty.go
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twoparty.go
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package protocol
import (
"bytes"
"errors"
"fmt"
"sync"
"github.com/fxamacker/cbor/v2"
"github.com/taurusgroup/multi-party-sig/internal/round"
)
// TwoPartyHandler represents a restriction of the Handler for 2 party protocols.
type TwoPartyHandler struct {
round round.Session
leader bool
err error
result interface{}
messages map[round.Number]*Message
out chan *Message
mtx sync.Mutex
}
func NewTwoPartyHandler(create StartFunc, sessionID []byte, leader bool) (*TwoPartyHandler, error) {
r, err := create(sessionID)
if err != nil {
return nil, fmt.Errorf("protocol: failed to create round: %w", err)
}
handler := &TwoPartyHandler{
round: r,
leader: leader,
err: nil,
result: nil,
messages: map[round.Number]*Message{},
out: make(chan *Message, 2),
mtx: sync.Mutex{},
}
if leader {
handler.advance()
}
return handler, nil
}
func (h *TwoPartyHandler) Result() (interface{}, error) {
h.mtx.Lock()
defer h.mtx.Unlock()
if h.result != nil {
return h.result, nil
}
if h.err != nil {
return nil, h.err
}
return nil, errors.New("protocol: not finished")
}
func (h *TwoPartyHandler) Listen() <-chan *Message {
h.mtx.Lock()
defer h.mtx.Unlock()
return h.out
}
func (h *TwoPartyHandler) Stop() {
if h.err != nil || h.result != nil {
h.abort(errors.New("aborted by user"))
}
}
func (h *TwoPartyHandler) String() string {
return fmt.Sprintf("party: %s, protocol: %s", h.round.SelfID(), h.round.ProtocolID())
}
func (h *TwoPartyHandler) abort(err error) {
if err != nil {
h.err = err
select {
case h.out <- &Message{
SSID: h.round.SSID(),
From: h.round.SelfID(),
Protocol: h.round.ProtocolID(),
Data: []byte(h.err.Error()),
}:
default:
}
}
close(h.out)
}
func (h *TwoPartyHandler) canAdvance() bool {
if h.round.MessageContent() == nil {
return true
}
if h.messages[h.round.Number()] != nil {
return true
}
return false
}
func extractRoundMessage(r round.Session, msg *Message) (round.Message, error) {
content := r.MessageContent()
if err := cbor.Unmarshal(msg.Data, content); err != nil {
return round.Message{}, fmt.Errorf("failed to unmarshal message: %w", err)
}
roundMsg := round.Message{
From: msg.From,
To: msg.To,
Content: content,
Broadcast: msg.Broadcast,
}
return roundMsg, nil
}
func (h *TwoPartyHandler) verifyMessage(msg *Message) error {
if msg == nil {
return nil
}
r := h.round
roundMsg, err := extractRoundMessage(r, msg)
if err != nil {
return err
}
if err = r.VerifyMessage(roundMsg); err != nil {
return fmt.Errorf("round %d: %w", r.Number(), err)
}
if err = r.StoreMessage(roundMsg); err != nil {
return fmt.Errorf("round %d: %w", r.Number(), err)
}
return nil
}
func (h *TwoPartyHandler) advance() {
for h.canAdvance() {
msg := h.messages[h.round.Number()]
if err := h.verifyMessage(msg); err != nil {
h.abort(err)
return
}
out := make(chan *round.Message, 1)
newRound, err := h.round.Finalize(out)
if err != nil || newRound == nil {
h.abort(err)
return
}
close(out)
for roundMsg := range out {
data, err := cbor.Marshal(roundMsg.Content)
if err != nil {
panic(fmt.Errorf("failed to marshal round message: %w", err))
}
msg := &Message{
SSID: newRound.SSID(),
From: newRound.SelfID(),
To: roundMsg.To,
Protocol: newRound.ProtocolID(),
RoundNumber: roundMsg.Content.RoundNumber(),
Data: data,
Broadcast: roundMsg.Broadcast,
BroadcastVerification: nil,
}
h.out <- msg
}
h.round = newRound
switch R := newRound.(type) {
// An abort happened
case *round.Abort:
h.abort(R.Err)
return
// We have the result
case *round.Output:
h.result = R.Result
h.abort(nil)
return
default:
}
}
}
func (h *TwoPartyHandler) CanAccept(msg *Message) bool {
r := h.round
if msg == nil {
return false
}
if !msg.IsFor(r.SelfID()) {
return false
}
if msg.Protocol != r.ProtocolID() {
return false
}
if !bytes.Equal(msg.SSID, r.SSID()) {
return false
}
if !r.PartyIDs().Contains(msg.From) {
return false
}
if msg.Data == nil {
return false
}
if msg.RoundNumber > r.FinalRoundNumber() {
return false
}
return true
}
func (h *TwoPartyHandler) Accept(msg *Message) {
h.mtx.Lock()
defer h.mtx.Unlock()
if !h.CanAccept(msg) || h.err != nil || h.result != nil {
return
}
if msg.RoundNumber == 0 {
h.abort(fmt.Errorf("aborted by other party with error: \"%s\"", msg.Data))
return
}
h.messages[msg.RoundNumber] = msg
h.advance()
}