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broker.go
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broker.go
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package dkg
import (
"context"
"fmt"
"sync"
"time"
"github.com/rs/zerolog"
"github.com/sethvargo/go-retry"
"github.com/onflow/flow-go/crypto"
"github.com/onflow/flow-go/engine"
"github.com/onflow/flow-go/model/fingerprint"
"github.com/onflow/flow-go/model/flow"
"github.com/onflow/flow-go/model/messages"
"github.com/onflow/flow-go/module"
"github.com/onflow/flow-go/module/retrymiddleware"
)
// BrokerOpt is a functional option which modifies the DKG Broker config.
type BrokerOpt func(*BrokerConfig)
// BrokerConfig is configuration for the DKG Broker component.
type BrokerConfig struct {
// PublishMaxRetries is the maximum number of times the broker will attempt
// to broadcast a message or publish a result.
PublishMaxRetries uint64
// ReadMaxRetries is the max number of times the broker will attempt to
// read messages before giving up.
ReadMaxRetries uint64
// RetryMaxConsecutiveFailures is the number of consecutive failures allowed
// before we switch to a different Access client for subsequent attempts.
RetryMaxConsecutiveFailures int
// RetryInitialWait is the initial duration to wait between retries for all
// retryable requests - increases exponentially for subsequent retries.
RetryInitialWait time.Duration
// RetryJitterPct is the percentage jitter to introduce to each retry interval
// for all retryable requests.
RetryJitterPct uint64
}
// DefaultBrokerConfig returns the default config for the DKG Broker component.
func DefaultBrokerConfig() BrokerConfig {
return BrokerConfig{
PublishMaxRetries: 10,
ReadMaxRetries: 3,
RetryMaxConsecutiveFailures: 2,
RetryInitialWait: time.Second,
RetryJitterPct: 25,
}
}
// Broker is an implementation of the DKGBroker interface which is intended to
// be used in conjunction with the DKG MessagingEngine for private messages, and
// with the DKG smart-contract for broadcast messages.
type Broker struct {
config BrokerConfig
log zerolog.Logger
unit *engine.Unit
dkgInstanceID string // unique identifier of the current dkg run (prevent replay attacks)
committee flow.IdentityList // identities of DKG members
me module.Local // used for signing broadcast messages
myIndex int // index of this instance in the committee
dkgContractClients []module.DKGContractClient // array of clients to communicate with the DKG smart contract in priority order for fallbacks during retries
lastSuccessfulClientIndex int // index of the contract client that was last successful during retries
tunnel *BrokerTunnel // channels through which the broker communicates with the network engine
privateMsgCh chan messages.PrivDKGMessageIn // channel to forward incoming private messages to consumers
broadcastMsgCh chan messages.BroadcastDKGMessage // channel to forward incoming broadcast messages to consumers
messageOffset uint // offset for next broadcast messages to fetch
shutdownCh chan struct{} // channel to stop the broker from listening
broadcasts uint // broadcasts counts the number of attempted broadcasts
clientLock sync.Mutex // lock around updates to current client
broadcastLock sync.Mutex // lock around outbound broadcasts
pollLock sync.Mutex // lock around polls to read inbound broadcasts
}
var _ module.DKGBroker = (*Broker)(nil)
// NewBroker instantiates a new epoch-specific broker capable of communicating
// with other nodes via a network engine and dkg smart-contract.
func NewBroker(
log zerolog.Logger,
dkgInstanceID string,
committee flow.IdentityList,
me module.Local,
myIndex int,
dkgContractClients []module.DKGContractClient,
tunnel *BrokerTunnel,
opts ...BrokerOpt,
) *Broker {
config := DefaultBrokerConfig()
for _, apply := range opts {
apply(&config)
}
b := &Broker{
config: config,
log: log.With().Str("component", "broker").Str("dkg_instance_id", dkgInstanceID).Logger(),
unit: engine.NewUnit(),
dkgInstanceID: dkgInstanceID,
committee: committee,
me: me,
myIndex: myIndex,
dkgContractClients: dkgContractClients,
tunnel: tunnel,
privateMsgCh: make(chan messages.PrivDKGMessageIn),
broadcastMsgCh: make(chan messages.BroadcastDKGMessage),
shutdownCh: make(chan struct{}),
}
go b.listen()
return b
}
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Implement DKGBroker
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
// GetIndex returns the index of this node in the committee list.
func (b *Broker) GetIndex() int {
return b.myIndex
}
// PrivateSend sends a DKGMessage to a destination over a private channel. It
// appends the current DKG instance ID to the message.
func (b *Broker) PrivateSend(dest int, data []byte) {
if dest >= len(b.committee) || dest < 0 {
b.log.Error().Msgf("destination id out of range: %d", dest)
return
}
dkgMessageOut := messages.PrivDKGMessageOut{
DKGMessage: messages.NewDKGMessage(data, b.dkgInstanceID),
DestID: b.committee[dest].NodeID,
}
b.tunnel.SendOut(dkgMessageOut)
}
// Broadcast signs and broadcasts a message to all participants.
func (b *Broker) Broadcast(data []byte) {
b.unit.Launch(func() {
// NOTE: We're counting the number of times the underlying DKG requested
// a broadcast so that we can detect an unhappy path (any time there is
// more than 1 broadcast message per DKG) Thus incrementing broadcasts
// before we perform the broadcasts is okay.
b.broadcastLock.Lock()
if b.broadcasts > 0 {
// The warn-level log is used by the integration tests to check if this
// func is called more than once within one epoch (unhappy path).
b.log.Warn().Msgf("preparing to send DKG broadcast number %d with header %d", b.broadcasts+1, data[0])
} else {
b.log.Info().Msgf("preparing to send DKG message broadcast with header %d", data[0])
}
b.broadcasts++
log := b.log.With().Uint("broadcast_number", b.broadcasts).Logger()
b.broadcastLock.Unlock()
bcastMsg, err := b.prepareBroadcastMessage(data)
if err != nil {
log.Fatal().Err(err).Msg("failed to create broadcast message")
}
backoff := retry.NewExponential(b.config.RetryInitialWait)
backoff = retry.WithMaxRetries(b.config.PublishMaxRetries, backoff)
backoff = retry.WithJitterPercent(b.config.RetryJitterPct, backoff)
clientIndex, dkgContractClient := b.getInitialContractClient()
onMaxConsecutiveRetries := func(totalAttempts int) {
clientIndex, dkgContractClient = b.updateContractClient(clientIndex)
log.Warn().Msgf("broadcast: retrying on attempt (%d) with fallback access node at index (%d)", totalAttempts, clientIndex)
}
backoff = retrymiddleware.AfterConsecutiveFailures(b.config.RetryMaxConsecutiveFailures, backoff, onMaxConsecutiveRetries)
b.broadcastLock.Lock()
attempts := 1
err = retry.Do(b.unit.Ctx(), backoff, func(ctx context.Context) error {
err := dkgContractClient.Broadcast(bcastMsg)
if err != nil {
log.Error().Err(err).Msgf("error broadcasting, retrying (attempt %d)", attempts)
attempts++
return retry.RetryableError(err)
}
// update our last successful client index for future calls
b.updateLastSuccessfulClient(clientIndex)
return nil
})
b.broadcastLock.Unlock()
// Various network conditions can result in errors while broadcasting DKG messages.
// Because the overall DKG is resilient to individual message failures,
// it is acceptable to log the error and move on.
if err != nil {
log.Error().Err(err).Msgf("failed to broadcast message after %d attempts", attempts)
return
}
log.Info().Msgf("dkg broadcast successfully on attempt %d", attempts)
})
}
// SubmitResult publishes the result of the DKG protocol to the smart contract.
func (b *Broker) SubmitResult(groupKey crypto.PublicKey, pubKeys []crypto.PublicKey) error {
// If the DKG failed locally, we will get a nil key vector here. We need to convert
// the nil slice to a slice of nil keys before submission.
//
// In general, if pubKeys does not have one key per participant, we cannot submit
// a valid result - therefore we submit a nil vector (indicating that we have
// completed the process, but we know that we don't have a valid result).
if len(pubKeys) != len(b.committee) {
b.log.Warn().Msgf("submitting dkg result with incomplete key vector (len=%d, expected=%d)", len(pubKeys), len(b.committee))
// create a key vector with one nil entry for each committee member
pubKeys = make([]crypto.PublicKey, len(b.committee))
}
backoff := retry.NewExponential(b.config.RetryInitialWait)
backoff = retry.WithMaxRetries(b.config.PublishMaxRetries, backoff)
backoff = retry.WithJitterPercent(b.config.RetryJitterPct, backoff)
clientIndex, dkgContractClient := b.getInitialContractClient()
onMaxConsecutiveRetries := func(totalAttempts int) {
clientIndex, dkgContractClient = b.updateContractClient(clientIndex)
b.log.Warn().Msgf("submit result: retrying on attempt (%d) with fallback access node at index (%d)", totalAttempts, clientIndex)
}
backoff = retrymiddleware.AfterConsecutiveFailures(b.config.RetryMaxConsecutiveFailures, backoff, onMaxConsecutiveRetries)
attempts := 1
err := retry.Do(b.unit.Ctx(), backoff, func(ctx context.Context) error {
err := dkgContractClient.SubmitResult(groupKey, pubKeys)
if err != nil {
b.log.Error().Err(err).Msgf("error submitting DKG result, retrying (attempt %d)", attempts)
attempts++
return retry.RetryableError(err)
}
// update our last successful client index for future calls
b.updateLastSuccessfulClient(clientIndex)
return nil
})
if err != nil {
return fmt.Errorf("failed to submit dkg result after %d attempts: %w", attempts, err)
}
b.log.Info().Msgf("dkg result submitted successfully on attempt %d", attempts)
return nil
}
// Disqualify flags that a node is misbehaving and got disqualified
func (b *Broker) Disqualify(node int, log string) {
var nodeID flow.Identifier
if node < len(b.committee) {
nodeID = b.committee[node].NodeID
}
// The warn-level log is used by the integration tests to check if this method is called.
b.log.Warn().Msgf("participant %d (this node) is disqualifying participant (index=%d, node_id=%s) because: %s",
b.myIndex, node, nodeID, log)
}
// FlagMisbehavior warns that a node is misbehaving.
func (b *Broker) FlagMisbehavior(node int, log string) {
var nodeID flow.Identifier
if node < len(b.committee) {
nodeID = b.committee[node].NodeID
}
// The warn-level log is used by the integration tests to check if this method is called.
b.log.Warn().Msgf("participant %d (this node) is flagging participant (index=%d, node_id=%s) because: %s",
b.myIndex, node, nodeID, log)
}
// GetPrivateMsgCh returns the channel through which consumers can receive
// incoming private DKG messages.
func (b *Broker) GetPrivateMsgCh() <-chan messages.PrivDKGMessageIn {
return b.privateMsgCh
}
// GetBroadcastMsgCh returns the channel through which consumers can receive
// incoming broadcast DKG messages.
func (b *Broker) GetBroadcastMsgCh() <-chan messages.BroadcastDKGMessage {
return b.broadcastMsgCh
}
// Poll calls the DKG smart contract to get missing DKG messages for the current
// epoch, and forwards them to the msgCh. It should be called with the ID of a
// block whose seal is finalized. The function doesn't return until the received
// messages are processed by the consumer because b.msgCh is not buffered.
func (b *Broker) Poll(referenceBlock flow.Identifier) error {
// We only issue one poll at a time to avoid delivering duplicate broadcast messages.
// The messageOffset determines which messages are retrieved by a Poll,
// and is not updated until the end of this function.
b.pollLock.Lock()
defer b.pollLock.Unlock()
backoff := retry.NewExponential(b.config.RetryInitialWait)
backoff = retry.WithMaxRetries(b.config.ReadMaxRetries, backoff)
backoff = retry.WithJitterPercent(b.config.RetryJitterPct, backoff)
clientIndex, dkgContractClient := b.getInitialContractClient()
onMaxConsecutiveRetries := func(totalAttempts int) {
clientIndex, dkgContractClient = b.updateContractClient(clientIndex)
b.log.Warn().Msgf("poll: retrying on attempt (%d) with fallback access node at index (%d)", totalAttempts, clientIndex)
}
backoff = retrymiddleware.AfterConsecutiveFailures(b.config.RetryMaxConsecutiveFailures, backoff, onMaxConsecutiveRetries)
var msgs []messages.BroadcastDKGMessage
var err error
attempt := 1
err = retry.Do(b.unit.Ctx(), backoff, func(ctx context.Context) error {
msgs, err = dkgContractClient.ReadBroadcast(b.messageOffset, referenceBlock)
if err != nil {
err = fmt.Errorf("could not read broadcast messages (attempt: %d, offset: %d, ref: %v): %w", attempt, b.messageOffset, referenceBlock, err)
attempt++
return retry.RetryableError(err)
}
// update our last successful client index for future calls
b.updateLastSuccessfulClient(clientIndex)
return nil
})
// Various network conditions can result in errors while reading DKG messages
// We will read any missed messages during the next poll because messageOffset is not increased
if err != nil {
b.log.Error().Err(err).Msgf("failed to read messages after %d attempts", attempt)
return nil
}
for _, msg := range msgs {
// set the CommitteeMemberIndex field for the message
memberIndex, ok := b.committee.GetIndex(msg.NodeID)
if !ok {
b.log.Error().Msgf("broadcast message from node with id (%v) does not match the ID of any committee member", msg.NodeID)
continue
}
msg.CommitteeMemberIndex = uint64(memberIndex)
ok, err := b.verifyBroadcastMessage(msg)
if err != nil {
b.log.Error().Err(err).Msg("unable to verify broadcast message")
continue
}
if !ok {
b.log.Error().Msg("invalid signature on broadcast dkg message")
continue
}
b.log.Debug().Msgf("forwarding broadcast message to controller")
b.broadcastMsgCh <- msg
}
// update message offset to use for future polls, this avoids forwarding the
// same message more than once
b.messageOffset += uint(len(msgs))
return nil
}
// Shutdown stop the goroutine that listens to incoming private messages.
func (b *Broker) Shutdown() {
close(b.shutdownCh)
}
/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
// updateContractClient will return the last successful client index by default for all initial operations or else
// it will return the appropriate client index with respect to last successful and number of client.
func (b *Broker) updateContractClient(clientIndex int) (int, module.DKGContractClient) {
b.clientLock.Lock()
defer b.clientLock.Unlock()
if clientIndex == b.lastSuccessfulClientIndex {
if clientIndex == len(b.dkgContractClients)-1 {
clientIndex = 0
} else {
clientIndex++
}
} else {
clientIndex = b.lastSuccessfulClientIndex
}
return clientIndex, b.dkgContractClients[clientIndex]
}
// getInitialContractClient will return the last successful contract client or the initial
func (b *Broker) getInitialContractClient() (int, module.DKGContractClient) {
b.clientLock.Lock()
defer b.clientLock.Unlock()
return b.lastSuccessfulClientIndex, b.dkgContractClients[b.lastSuccessfulClientIndex]
}
// updateLastSuccessfulClient set lastSuccessfulClientIndex in concurrency safe way
func (b *Broker) updateLastSuccessfulClient(clientIndex int) {
b.clientLock.Lock()
defer b.clientLock.Unlock()
b.lastSuccessfulClientIndex = clientIndex
}
// listen is a blocking call that processes incoming messages from the network
// engine.
func (b *Broker) listen() {
for {
select {
case msg := <-b.tunnel.MsgChIn:
b.onPrivateMessage(msg.OriginID, msg.DKGMessage)
case <-b.shutdownCh:
return
}
}
}
// onPrivateMessage verifies the integrity of an incoming message, sets the CommitteeMemberIndex and forwards
// it to consumers via the msgCh.
func (b *Broker) onPrivateMessage(originID flow.Identifier, msg messages.DKGMessage) {
memberIndex, ok := b.committee.GetIndex(originID)
if !ok {
b.log.Error().Msgf("bad message: OriginID (%v) does not match the NodeID of any committee member", originID)
return
}
err := b.hasValidDKGInstanceID(msg)
if err != nil {
b.log.Err(err).Msg("bad message")
return
}
b.privateMsgCh <- messages.PrivDKGMessageIn{DKGMessage: msg, OriginID: originID, CommitteeMemberIndex: uint64(memberIndex)}
}
// hasValidDKGInstanceID returns an error if msg.DKGInstanceID does not match Broker.DKGInstanceID
func (b *Broker) hasValidDKGInstanceID(msg messages.DKGMessage) error {
// check that the message corresponds to the current epoch
if b.dkgInstanceID != msg.DKGInstanceID {
return fmt.Errorf("wrong DKG instance. Got %s, want %s", msg.DKGInstanceID, b.dkgInstanceID)
}
return nil
}
// prepareBroadcastMessage creates BroadcastDKGMessage with a signature from the
// node's staking key.
func (b *Broker) prepareBroadcastMessage(data []byte) (messages.BroadcastDKGMessage, error) {
dkgMessage := messages.NewDKGMessage(
data,
b.dkgInstanceID,
)
sigData := fingerprint.Fingerprint(dkgMessage)
signature, err := b.me.Sign(sigData[:], NewDKGMessageHasher())
if err != nil {
return messages.BroadcastDKGMessage{}, err
}
bcastMsg := messages.BroadcastDKGMessage{
DKGMessage: dkgMessage,
Signature: signature,
}
return bcastMsg, nil
}
// verifyBroadcastMessage checks the DKG instance of a broadcast
// message, as well as the signature against the staking key of the sender.
// Returns:
// - true, nil if the message contents are valid and have a valid signature
// - false, nil if the message contents are valid but have an invalid signature
// - false, err if the message contents are invalid, or could not be checked,
// or the signature could not be checked
//
// TODO differentiate errors
func (b *Broker) verifyBroadcastMessage(bcastMsg messages.BroadcastDKGMessage) (bool, error) {
err := b.hasValidDKGInstanceID(bcastMsg.DKGMessage)
if err != nil {
return false, err
}
origin := b.committee[bcastMsg.CommitteeMemberIndex]
signData := fingerprint.Fingerprint(bcastMsg.DKGMessage)
return origin.StakingPubKey.Verify(
bcastMsg.Signature,
signData[:],
NewDKGMessageHasher(),
)
}