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package evidence
import (
"fmt"
"runtime/debug"
"sync"
"time"
clist "github.com/tendermint/tendermint/internal/libs/clist"
tmsync "github.com/tendermint/tendermint/internal/libs/sync"
"github.com/tendermint/tendermint/internal/p2p"
"github.com/tendermint/tendermint/libs/log"
"github.com/tendermint/tendermint/libs/service"
tmproto "github.com/tendermint/tendermint/proto/tendermint/types"
"github.com/tendermint/tendermint/types"
)
var _ service.Service = (*Reactor)(nil)
const (
EvidenceChannel = p2p.ChannelID(0x38)
maxMsgSize = 1048576 // 1MB TODO make it configurable
// broadcast all uncommitted evidence this often. This sets when the reactor
// goes back to the start of the list and begins sending the evidence again.
// Most evidence should be committed in the very next block that is why we wait
// just over the block production rate before sending evidence again.
broadcastEvidenceIntervalS = 10
)
// GetChannelDescriptor produces an instance of a descriptor for this
// package's required channels.
func GetChannelDescriptor() *p2p.ChannelDescriptor {
return &p2p.ChannelDescriptor{
ID: EvidenceChannel,
MessageType: new(tmproto.EvidenceList),
Priority: 6,
RecvMessageCapacity: maxMsgSize,
RecvBufferCapacity: 32,
}
}
// Reactor handles evpool evidence broadcasting amongst peers.
type Reactor struct {
service.BaseService
evpool *Pool
evidenceCh *p2p.Channel
peerUpdates *p2p.PeerUpdates
closeCh chan struct{}
peerWG sync.WaitGroup
mtx tmsync.Mutex
peerRoutines map[types.NodeID]*tmsync.Closer
}
// NewReactor returns a reference to a new evidence reactor, which implements the
// service.Service interface. It accepts a p2p Channel dedicated for handling
// envelopes with EvidenceList messages.
func NewReactor(
logger log.Logger,
evidenceCh *p2p.Channel,
peerUpdates *p2p.PeerUpdates,
evpool *Pool,
) *Reactor {
r := &Reactor{
evpool: evpool,
evidenceCh: evidenceCh,
peerUpdates: peerUpdates,
closeCh: make(chan struct{}),
peerRoutines: make(map[types.NodeID]*tmsync.Closer),
}
r.BaseService = *service.NewBaseService(logger, "Evidence", r)
return r
}
// OnStart starts separate go routines for each p2p Channel and listens for
// envelopes on each. In addition, it also listens for peer updates and handles
// messages on that p2p channel accordingly. The caller must be sure to execute
// OnStop to ensure the outbound p2p Channels are closed. No error is returned.
func (r *Reactor) OnStart() error {
go r.processEvidenceCh()
go r.processPeerUpdates()
return nil
}
// OnStop stops the reactor by signaling to all spawned goroutines to exit and
// blocking until they all exit.
func (r *Reactor) OnStop() {
r.mtx.Lock()
for _, c := range r.peerRoutines {
c.Close()
}
r.mtx.Unlock()
// Wait for all spawned peer evidence broadcasting goroutines to gracefully
// exit.
r.peerWG.Wait()
// Close closeCh to signal to all spawned goroutines to gracefully exit. All
// p2p Channels should execute Close().
close(r.closeCh)
// Wait for all p2p Channels to be closed before returning. This ensures we
// can easily reason about synchronization of all p2p Channels and ensure no
// panics will occur.
<-r.evidenceCh.Done()
<-r.peerUpdates.Done()
}
// handleEvidenceMessage handles envelopes sent from peers on the EvidenceChannel.
// It returns an error only if the Envelope.Message is unknown for this channel
// or if the given evidence is invalid. This should never be called outside of
// handleMessage.
func (r *Reactor) handleEvidenceMessage(envelope p2p.Envelope) error {
logger := r.Logger.With("peer", envelope.From)
switch msg := envelope.Message.(type) {
case *tmproto.EvidenceList:
// TODO: Refactor the Evidence type to not contain a list since we only ever
// send and receive one piece of evidence at a time. Or potentially consider
// batching evidence.
//
// see: https://github.com/tendermint/tendermint/issues/4729
for i := 0; i < len(msg.Evidence); i++ {
ev, err := types.EvidenceFromProto(&msg.Evidence[i])
if err != nil {
logger.Error("failed to convert evidence", "err", err)
continue
}
if err := r.evpool.AddEvidence(ev); err != nil {
// If we're given invalid evidence by the peer, notify the router that
// we should remove this peer by returning an error.
if _, ok := err.(*types.ErrInvalidEvidence); ok {
return err
}
}
}
default:
return fmt.Errorf("received unknown message: %T", msg)
}
return nil
}
// handleMessage handles an Envelope sent from a peer on a specific p2p Channel.
// It will handle errors and any possible panics gracefully. A caller can handle
// any error returned by sending a PeerError on the respective channel.
func (r *Reactor) handleMessage(chID p2p.ChannelID, envelope p2p.Envelope) (err error) {
defer func() {
if e := recover(); e != nil {
err = fmt.Errorf("panic in processing message: %v", e)
r.Logger.Error(
"recovering from processing message panic",
"err", err,
"stack", string(debug.Stack()),
)
}
}()
r.Logger.Debug("received message", "message", envelope.Message, "peer", envelope.From)
switch chID {
case EvidenceChannel:
err = r.handleEvidenceMessage(envelope)
default:
err = fmt.Errorf("unknown channel ID (%d) for envelope (%v)", chID, envelope)
}
return err
}
// processEvidenceCh implements a blocking event loop where we listen for p2p
// Envelope messages from the evidenceCh.
func (r *Reactor) processEvidenceCh() {
defer r.evidenceCh.Close()
for {
select {
case envelope := <-r.evidenceCh.In:
if err := r.handleMessage(r.evidenceCh.ID, envelope); err != nil {
r.Logger.Error("failed to process message", "ch_id", r.evidenceCh.ID, "envelope", envelope, "err", err)
r.evidenceCh.Error <- p2p.PeerError{
NodeID: envelope.From,
Err: err,
}
}
case <-r.closeCh:
r.Logger.Debug("stopped listening on evidence channel; closing...")
return
}
}
}
// processPeerUpdate processes a PeerUpdate. For new or live peers it will check
// if an evidence broadcasting goroutine needs to be started. For down or
// removed peers, it will check if an evidence broadcasting goroutine
// exists and signal that it should exit.
//
// FIXME: The peer may be behind in which case it would simply ignore the
// evidence and treat it as invalid. This would cause the peer to disconnect.
// The peer may also receive the same piece of evidence multiple times if it
// connects/disconnects frequently from the broadcasting peer(s).
//
// REF: https://github.com/tendermint/tendermint/issues/4727
func (r *Reactor) processPeerUpdate(peerUpdate p2p.PeerUpdate) {
r.Logger.Debug("received peer update", "peer", peerUpdate.NodeID, "status", peerUpdate.Status)
r.mtx.Lock()
defer r.mtx.Unlock()
switch peerUpdate.Status {
case p2p.PeerStatusUp:
// Do not allow starting new evidence broadcast loops after reactor shutdown
// has been initiated. This can happen after we've manually closed all
// peer broadcast loops and closed r.closeCh, but the router still sends
// in-flight peer updates.
if !r.IsRunning() {
return
}
// Check if we've already started a goroutine for this peer, if not we create
// a new done channel so we can explicitly close the goroutine if the peer
// is later removed, we increment the waitgroup so the reactor can stop
// safely, and finally start the goroutine to broadcast evidence to that peer.
_, ok := r.peerRoutines[peerUpdate.NodeID]
if !ok {
closer := tmsync.NewCloser()
r.peerRoutines[peerUpdate.NodeID] = closer
r.peerWG.Add(1)
go r.broadcastEvidenceLoop(peerUpdate.NodeID, closer)
}
case p2p.PeerStatusDown:
// Check if we've started an evidence broadcasting goroutine for this peer.
// If we have, we signal to terminate the goroutine via the channel's closure.
// This will internally decrement the peer waitgroup and remove the peer
// from the map of peer evidence broadcasting goroutines.
closer, ok := r.peerRoutines[peerUpdate.NodeID]
if ok {
closer.Close()
}
}
}
// processPeerUpdates initiates a blocking process where we listen for and handle
// PeerUpdate messages. When the reactor is stopped, we will catch the signal and
// close the p2p PeerUpdatesCh gracefully.
func (r *Reactor) processPeerUpdates() {
defer r.peerUpdates.Close()
for {
select {
case peerUpdate := <-r.peerUpdates.Updates():
r.processPeerUpdate(peerUpdate)
case <-r.closeCh:
r.Logger.Debug("stopped listening on peer updates channel; closing...")
return
}
}
}
// broadcastEvidenceLoop starts a blocking process that continuously reads pieces
// of evidence off of a linked-list and sends the evidence in a p2p Envelope to
// the given peer by ID. This should be invoked in a goroutine per unique peer
// ID via an appropriate PeerUpdate. The goroutine can be signaled to gracefully
// exit by either explicitly closing the provided doneCh or by the reactor
// signaling to stop.
//
// TODO: This should be refactored so that we do not blindly gossip evidence
// that the peer has already received or may not be ready for.
//
// REF: https://github.com/tendermint/tendermint/issues/4727
func (r *Reactor) broadcastEvidenceLoop(peerID types.NodeID, closer *tmsync.Closer) {
var next *clist.CElement
defer func() {
r.mtx.Lock()
delete(r.peerRoutines, peerID)
r.mtx.Unlock()
r.peerWG.Done()
if e := recover(); e != nil {
r.Logger.Error(
"recovering from broadcasting evidence loop",
"err", e,
"stack", string(debug.Stack()),
)
}
}()
for {
// This happens because the CElement we were looking at got garbage
// collected (removed). That is, .NextWaitChan() returned nil. So we can go
// ahead and start from the beginning.
if next == nil {
select {
case <-r.evpool.EvidenceWaitChan(): // wait until next evidence is available
if next = r.evpool.EvidenceFront(); next == nil {
continue
}
case <-closer.Done():
// The peer is marked for removal via a PeerUpdate as the doneCh was
// explicitly closed to signal we should exit.
return
case <-r.closeCh:
// The reactor has signaled that we are stopped and thus we should
// implicitly exit this peer's goroutine.
return
}
}
ev := next.Value.(types.Evidence)
evProto, err := types.EvidenceToProto(ev)
if err != nil {
panic(fmt.Errorf("failed to convert evidence: %w", err))
}
// Send the evidence to the corresponding peer. Note, the peer may be behind
// and thus would not be able to process the evidence correctly. Also, the
// peer may receive this piece of evidence multiple times if it added and
// removed frequently from the broadcasting peer.
r.evidenceCh.Out <- p2p.Envelope{
To: peerID,
Message: &tmproto.EvidenceList{
Evidence: []tmproto.Evidence{*evProto},
},
}
r.Logger.Debug("gossiped evidence to peer", "evidence", ev, "peer", peerID)
select {
case <-time.After(time.Second * broadcastEvidenceIntervalS):
// start from the beginning after broadcastEvidenceIntervalS seconds
next = nil
case <-next.NextWaitChan():
next = next.Next()
case <-closer.Done():
// The peer is marked for removal via a PeerUpdate as the doneCh was
// explicitly closed to signal we should exit.
return
case <-r.closeCh:
// The reactor has signaled that we are stopped and thus we should
// implicitly exit this peer's goroutine.
return
}
}
}