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package statesync
import (
"context"
"errors"
"fmt"
"sync"
"time"
"github.com/tendermint/tendermint/internal/p2p"
"github.com/tendermint/tendermint/light/provider"
ssproto "github.com/tendermint/tendermint/proto/tendermint/statesync"
proto "github.com/tendermint/tendermint/proto/tendermint/types"
"github.com/tendermint/tendermint/types"
)
var (
errNoConnectedPeers = errors.New("no available peers to dispatch request to")
errUnsolicitedResponse = errors.New("unsolicited light block response")
errNoResponse = errors.New("peer failed to respond within timeout")
errPeerAlreadyBusy = errors.New("peer is already processing a request")
errDisconnected = errors.New("dispatcher has been disconnected")
)
// dispatcher keeps a list of peers and allows concurrent requests for light
// blocks. NOTE: It is not the responsibility of the dispatcher to verify the
// light blocks.
type dispatcher struct {
availablePeers *peerlist
requestCh chan<- p2p.Envelope
timeout time.Duration
mtx sync.Mutex
calls map[types.NodeID]chan *types.LightBlock
running bool
}
func newDispatcher(requestCh chan<- p2p.Envelope, timeout time.Duration) *dispatcher {
return &dispatcher{
availablePeers: newPeerList(),
timeout: timeout,
requestCh: requestCh,
calls: make(map[types.NodeID]chan *types.LightBlock),
running: true,
}
}
// LightBlock uses the request channel to fetch a light block from the next peer
// in a list, tracks the call and waits for the reactor to pass along the response
func (d *dispatcher) LightBlock(ctx context.Context, height int64) (*types.LightBlock, types.NodeID, error) {
d.mtx.Lock()
// check to see that the dispatcher is connected to at least one peer
if d.availablePeers.Len() == 0 && len(d.calls) == 0 {
d.mtx.Unlock()
return nil, "", errNoConnectedPeers
}
d.mtx.Unlock()
// fetch the next peer id in the list and request a light block from that
// peer
peer := d.availablePeers.Pop(ctx)
lb, err := d.lightBlock(ctx, height, peer)
return lb, peer, err
}
// Providers turns the dispatcher into a set of providers (per peer) which can
// be used by a light client
func (d *dispatcher) Providers(chainID string, timeout time.Duration) []provider.Provider {
d.mtx.Lock()
defer d.mtx.Unlock()
providers := make([]provider.Provider, d.availablePeers.Len())
peers := d.availablePeers.Peers()
for index, peer := range peers {
providers[index] = &blockProvider{
peer: peer,
dispatcher: d,
chainID: chainID,
timeout: timeout,
}
}
return providers
}
func (d *dispatcher) stop() {
d.mtx.Lock()
defer d.mtx.Unlock()
d.running = false
for peer, call := range d.calls {
close(call)
delete(d.calls, peer)
}
}
func (d *dispatcher) start() {
d.mtx.Lock()
defer d.mtx.Unlock()
d.running = true
}
func (d *dispatcher) lightBlock(ctx context.Context, height int64, peer types.NodeID) (*types.LightBlock, error) {
// dispatch the request to the peer
callCh, err := d.dispatch(peer, height)
if err != nil {
return nil, err
}
// wait for a response, cancel or timeout
select {
case resp := <-callCh:
return resp, nil
case <-ctx.Done():
d.release(peer)
return nil, nil
case <-time.After(d.timeout):
d.release(peer)
return nil, errNoResponse
}
}
// respond allows the underlying process which receives requests on the
// requestCh to respond with the respective light block
func (d *dispatcher) respond(lb *proto.LightBlock, peer types.NodeID) error {
d.mtx.Lock()
defer d.mtx.Unlock()
// check that the response came from a request
answerCh, ok := d.calls[peer]
if !ok {
// this can also happen if the response came in after the timeout
return errUnsolicitedResponse
}
// release the peer after returning the response
defer d.availablePeers.Append(peer)
defer close(answerCh)
defer delete(d.calls, peer)
if lb == nil {
answerCh <- nil
return nil
}
block, err := types.LightBlockFromProto(lb)
if err != nil {
fmt.Println("error with converting light block")
return err
}
answerCh <- block
return nil
}
func (d *dispatcher) addPeer(peer types.NodeID) {
d.availablePeers.Append(peer)
}
func (d *dispatcher) removePeer(peer types.NodeID) {
d.mtx.Lock()
defer d.mtx.Unlock()
if _, ok := d.calls[peer]; ok {
delete(d.calls, peer)
} else {
d.availablePeers.Remove(peer)
}
}
// dispatch takes a peer and allocates it a channel so long as it's not already
// busy and the receiving channel is still running. It then dispatches the message
func (d *dispatcher) dispatch(peer types.NodeID, height int64) (chan *types.LightBlock, error) {
d.mtx.Lock()
defer d.mtx.Unlock()
ch := make(chan *types.LightBlock, 1)
// check if the dispatcher is running or not
if !d.running {
close(ch)
return ch, errDisconnected
}
// this should happen only if we add the same peer twice (somehow)
if _, ok := d.calls[peer]; ok {
close(ch)
return ch, errPeerAlreadyBusy
}
d.calls[peer] = ch
// send request
d.requestCh <- p2p.Envelope{
To: peer,
Message: &ssproto.LightBlockRequest{
Height: uint64(height),
},
}
return ch, nil
}
// release appends the peer back to the list and deletes the allocated call so
// that a new call can be made to that peer
func (d *dispatcher) release(peer types.NodeID) {
d.mtx.Lock()
defer d.mtx.Unlock()
if call, ok := d.calls[peer]; ok {
close(call)
delete(d.calls, peer)
}
d.availablePeers.Append(peer)
}
//----------------------------------------------------------------
// blockProvider is a p2p based light provider which uses a dispatcher connected
// to the state sync reactor to serve light blocks to the light client
//
// TODO: This should probably be moved over to the light package but as we're
// not yet officially supporting p2p light clients we'll leave this here for now.
type blockProvider struct {
peer types.NodeID
chainID string
timeout time.Duration
dispatcher *dispatcher
}
func (p *blockProvider) LightBlock(ctx context.Context, height int64) (*types.LightBlock, error) {
// FIXME: The provider doesn't know if the dispatcher is still connected to
// that peer. If the connection is dropped for whatever reason the
// dispatcher needs to be able to relay this back to the provider so it can
// return ErrConnectionClosed instead of ErrNoResponse
ctx, cancel := context.WithTimeout(ctx, p.timeout)
defer cancel()
lb, _ := p.dispatcher.lightBlock(ctx, height, p.peer)
if lb == nil {
return nil, provider.ErrNoResponse
}
if err := lb.ValidateBasic(p.chainID); err != nil {
return nil, provider.ErrBadLightBlock{Reason: err}
}
return lb, nil
}
// ReportEvidence should allow for the light client to report any light client
// attacks. This is a no op as there currently isn't a way to wire this up to
// the evidence reactor (we should endeavor to do this in the future but for now
// it's not critical for backwards verification)
func (p *blockProvider) ReportEvidence(ctx context.Context, ev types.Evidence) error {
return nil
}
// String implements stringer interface
func (p *blockProvider) String() string { return string(p.peer) }
//----------------------------------------------------------------
// peerList is a rolling list of peers. This is used to distribute the load of
// retrieving blocks over all the peers the reactor is connected to
type peerlist struct {
mtx sync.Mutex
peers []types.NodeID
waiting []chan types.NodeID
}
func newPeerList() *peerlist {
return &peerlist{
peers: make([]types.NodeID, 0),
waiting: make([]chan types.NodeID, 0),
}
}
func (l *peerlist) Len() int {
l.mtx.Lock()
defer l.mtx.Unlock()
return len(l.peers)
}
func (l *peerlist) Pop(ctx context.Context) types.NodeID {
l.mtx.Lock()
if len(l.peers) == 0 {
// if we don't have any peers in the list we block until a peer is
// appended
wait := make(chan types.NodeID, 1)
l.waiting = append(l.waiting, wait)
// unlock whilst waiting so that the list can be appended to
l.mtx.Unlock()
select {
case peer := <-wait:
return peer
case <-ctx.Done():
return ""
}
}
peer := l.peers[0]
l.peers = l.peers[1:]
l.mtx.Unlock()
return peer
}
func (l *peerlist) Append(peer types.NodeID) {
l.mtx.Lock()
defer l.mtx.Unlock()
if len(l.waiting) > 0 {
wait := l.waiting[0]
l.waiting = l.waiting[1:]
wait <- peer
close(wait)
} else {
l.peers = append(l.peers, peer)
}
}
func (l *peerlist) Remove(peer types.NodeID) {
l.mtx.Lock()
defer l.mtx.Unlock()
for i, p := range l.peers {
if p == peer {
l.peers = append(l.peers[:i], l.peers[i+1:]...)
return
}
}
}
func (l *peerlist) Peers() []types.NodeID {
l.mtx.Lock()
defer l.mtx.Unlock()
return l.peers
}