// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
// Package light implements on-demand retrieval capable state and chain objects
// for the Ethereum Light Client.
package les
import (
"context"
"crypto/rand"
"encoding/binary"
"fmt"
"sync"
"time"
"github.com/ethereum/go-ethereum/common/mclock"
)
var (
retryQueue = time.Millisecond * 100
softRequestTimeout = time.Millisecond * 500
hardRequestTimeout = time.Second * 10
)
// retrieveManager is a layer on top of requestDistributor which takes care of
// matching replies by request ID and handles timeouts and resends if necessary.
type retrieveManager struct {
dist *requestDistributor
peers *peerSet
serverPool peerSelector
lock sync.RWMutex
sentReqs map[uint64]*sentReq
}
// validatorFunc is a function that processes a reply message
type validatorFunc func(distPeer, *Msg) error
// peerSelector receives feedback info about response times and timeouts
type peerSelector interface {
adjustResponseTime(*poolEntry, time.Duration, bool)
}
// sentReq represents a request sent and tracked by retrieveManager
type sentReq struct {
rm *retrieveManager
req *distReq
id uint64
validate validatorFunc
eventsCh chan reqPeerEvent
stopCh chan struct{}
stopped bool
err error
lock sync.RWMutex // protect access to sentTo map
sentTo map[distPeer]sentReqToPeer
reqQueued bool // a request has been queued but not sent
reqSent bool // a request has been sent but not timed out
reqSrtoCount int // number of requests that reached soft (but not hard) timeout
}
// sentReqToPeer notifies the request-from-peer goroutine (tryRequest) about a response
// delivered by the given peer. Only one delivery is allowed per request per peer,
// after which delivered is set to true, the validity of the response is sent on the
// valid channel and no more responses are accepted.
type sentReqToPeer struct {
delivered bool
valid chan bool
}
// reqPeerEvent is sent by the request-from-peer goroutine (tryRequest) to the
// request state machine (retrieveLoop) through the eventsCh channel.
type reqPeerEvent struct {
event int
peer distPeer
}
const (
rpSent = iota // if peer == nil, not sent (no suitable peers)
rpSoftTimeout
rpHardTimeout
rpDeliveredValid
rpDeliveredInvalid
)
// newRetrieveManager creates the retrieve manager
func newRetrieveManager(peers *peerSet, dist *requestDistributor, serverPool peerSelector) *retrieveManager {
return &retrieveManager{
peers: peers,
dist: dist,
serverPool: serverPool,
sentReqs: make(map[uint64]*sentReq),
}
}
// retrieve sends a request (to multiple peers if necessary) and waits for an answer
// that is delivered through the deliver function and successfully validated by the
// validator callback. It returns when a valid answer is delivered or the context is
// cancelled.
func (rm *retrieveManager) retrieve(ctx context.Context, reqID uint64, req *distReq, val validatorFunc, shutdown chan struct{}) error {
sentReq := rm.sendReq(reqID, req, val)
select {
case <-sentReq.stopCh:
case <-ctx.Done():
sentReq.stop(ctx.Err())
case <-shutdown:
sentReq.stop(fmt.Errorf("Client is shutting down"))
}
return sentReq.getError()
}
// sendReq starts a process that keeps trying to retrieve a valid answer for a
// request from any suitable peers until stopped or succeeded.
func (rm *retrieveManager) sendReq(reqID uint64, req *distReq, val validatorFunc) *sentReq {
r := &sentReq{
rm: rm,
req: req,
id: reqID,
sentTo: make(map[distPeer]sentReqToPeer),
stopCh: make(chan struct{}),
eventsCh: make(chan reqPeerEvent, 10),
validate: val,
}
canSend := req.canSend
req.canSend = func(p distPeer) bool {
// add an extra check to canSend: the request has not been sent to the same peer before
r.lock.RLock()
_, sent := r.sentTo[p]
r.lock.RUnlock()
return !sent && canSend(p)
}
request := req.request
req.request = func(p distPeer) func() {
// before actually sending the request, put an entry into the sentTo map
r.lock.Lock()
r.sentTo[p] = sentReqToPeer{false, make(chan bool, 1)}
r.lock.Unlock()
return request(p)
}
rm.lock.Lock()
rm.sentReqs[reqID] = r
rm.lock.Unlock()
go r.retrieveLoop()
return r
}
// deliver is called by the LES protocol manager to deliver reply messages to waiting requests
func (rm *retrieveManager) deliver(peer distPeer, msg *Msg) error {
rm.lock.RLock()
req, ok := rm.sentReqs[msg.ReqID]
rm.lock.RUnlock()
if ok {
return req.deliver(peer, msg)
}
return errResp(ErrUnexpectedResponse, "reqID = %v", msg.ReqID)
}
// reqStateFn represents a state of the retrieve loop state machine
type reqStateFn func() reqStateFn
// retrieveLoop is the retrieval state machine event loop
func (r *sentReq) retrieveLoop() {
go r.tryRequest()
r.reqQueued = true
state := r.stateRequesting
for state != nil {
state = state()
}
r.rm.lock.Lock()
delete(r.rm.sentReqs, r.id)
r.rm.lock.Unlock()
}
// stateRequesting: a request has been queued or sent recently; when it reaches soft timeout,
// a new request is sent to a new peer
func (r *sentReq) stateRequesting() reqStateFn {
select {
case ev := <-r.eventsCh:
r.update(ev)
switch ev.event {
case rpSent:
if ev.peer == nil {
// request send failed, no more suitable peers
if r.waiting() {
// we are already waiting for sent requests which may succeed so keep waiting
return r.stateNoMorePeers
}
// nothing to wait for, no more peers to ask, return with error
r.stop(ErrNoPeers)
// no need to go to stopped state because waiting() already returned false
return nil
}
case rpSoftTimeout:
// last request timed out, try asking a new peer
go r.tryRequest()
r.reqQueued = true
return r.stateRequesting
case rpDeliveredValid:
r.stop(nil)
return r.stateStopped
}
return r.stateRequesting
case <-r.stopCh:
return r.stateStopped
}
}
// stateNoMorePeers: could not send more requests because no suitable peers are available.
// Peers may become suitable for a certain request later or new peers may appear so we
// keep trying.
func (r *sentReq) stateNoMorePeers() reqStateFn {
select {
case <-time.After(retryQueue):
go r.tryRequest()
r.reqQueued = true
return r.stateRequesting
case ev := <-r.eventsCh:
r.update(ev)
if ev.event == rpDeliveredValid {
r.stop(nil)
return r.stateStopped
}
return r.stateNoMorePeers
case <-r.stopCh:
return r.stateStopped
}
}
// stateStopped: request succeeded or cancelled, just waiting for some peers
// to either answer or time out hard
func (r *sentReq) stateStopped() reqStateFn {
for r.waiting() {
r.update(<-r.eventsCh)
}
return nil
}
// update updates the queued/sent flags and timed out peers counter according to the event
func (r *sentReq) update(ev reqPeerEvent) {
switch ev.event {
case rpSent:
r.reqQueued = false
if ev.peer != nil {
r.reqSent = true
}
case rpSoftTimeout:
r.reqSent = false
r.reqSrtoCount++
case rpHardTimeout, rpDeliveredValid, rpDeliveredInvalid:
r.reqSrtoCount--
}
}
// waiting returns true if the retrieval mechanism is waiting for an answer from
// any peer
func (r *sentReq) waiting() bool {
return r.reqQueued || r.reqSent || r.reqSrtoCount > 0
}
// tryRequest tries to send the request to a new peer and waits for it to either
// succeed or time out if it has been sent. It also sends the appropriate reqPeerEvent
// messages to the request's event channel.
func (r *sentReq) tryRequest() {
sent := r.rm.dist.queue(r.req)
var p distPeer
select {
case p = <-sent:
case <-r.stopCh:
if r.rm.dist.cancel(r.req) {
p = nil
} else {
p = <-sent
}
}
r.eventsCh <- reqPeerEvent{rpSent, p}
if p == nil {
return
}
reqSent := mclock.Now()
srto, hrto := false, false
r.lock.RLock()
s, ok := r.sentTo[p]
r.lock.RUnlock()
if !ok {
panic(nil)
}
defer func() {
// send feedback to server pool and remove peer if hard timeout happened
pp, ok := p.(*peer)
if ok && r.rm.serverPool != nil {
respTime := time.Duration(mclock.Now() - reqSent)
r.rm.serverPool.adjustResponseTime(pp.poolEntry, respTime, srto)
}
if hrto {
pp.Log().Debug("Request timed out hard")
if r.rm.peers != nil {
r.rm.peers.Unregister(pp.id)
}
}
r.lock.Lock()
delete(r.sentTo, p)
r.lock.Unlock()
}()
select {
case ok := <-s.valid:
if ok {
r.eventsCh <- reqPeerEvent{rpDeliveredValid, p}
} else {
r.eventsCh <- reqPeerEvent{rpDeliveredInvalid, p}
}
return
case <-time.After(softRequestTimeout):
srto = true
r.eventsCh <- reqPeerEvent{rpSoftTimeout, p}
}
select {
case ok := <-s.valid:
if ok {
r.eventsCh <- reqPeerEvent{rpDeliveredValid, p}
} else {
r.eventsCh <- reqPeerEvent{rpDeliveredInvalid, p}
}
case <-time.After(hardRequestTimeout):
hrto = true
r.eventsCh <- reqPeerEvent{rpHardTimeout, p}
}
}
// deliver a reply belonging to this request
func (r *sentReq) deliver(peer distPeer, msg *Msg) error {
r.lock.Lock()
defer r.lock.Unlock()
s, ok := r.sentTo[peer]
if !ok || s.delivered {
return errResp(ErrUnexpectedResponse, "reqID = %v", msg.ReqID)
}
valid := r.validate(peer, msg) == nil
r.sentTo[peer] = sentReqToPeer{true, s.valid}
s.valid <- valid
if !valid {
return errResp(ErrInvalidResponse, "reqID = %v", msg.ReqID)
}
return nil
}
// stop stops the retrieval process and sets an error code that will be returned
// by getError
func (r *sentReq) stop(err error) {
r.lock.Lock()
if !r.stopped {
r.stopped = true
r.err = err
close(r.stopCh)
}
r.lock.Unlock()
}
// getError returns any retrieval error (either internally generated or set by the
// stop function) after stopCh has been closed
func (r *sentReq) getError() error {
return r.err
}
// genReqID generates a new random request ID
func genReqID() uint64 {
var rnd [8]byte
rand.Read(rnd[:])
return binary.BigEndian.Uint64(rnd[:])
}
