go-pulse/les/retrieve.go
Felföldi Zsolt b4a2681120
les, les/lespay: implement new server pool (#20758)
This PR reimplements the light client server pool. It is also a first step
to move certain logic into a new lespay package. This package will contain
the implementation of the lespay token sale functions, the token buying and
selling logic and other components related to peer selection/prioritization
and service quality evaluation. Over the long term this package will be
reusable for incentivizing future protocols.

Since the LES peer logic is now based on enode.Iterator, it can now use
DNS-based fallback discovery to find servers.

This document describes the function of the new components:
https://gist.github.com/zsfelfoldi/3c7ace895234b7b345ab4f71dab102d4
2020-05-22 13:46:34 +02:00

436 lines
12 KiB
Go

// 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 les
import (
"context"
"crypto/rand"
"encoding/binary"
"fmt"
"sync"
"time"
"github.com/ethereum/go-ethereum/light"
)
var (
retryQueue = time.Millisecond * 100
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 *serverPeerSet
softRequestTimeout func() time.Duration
lock sync.RWMutex
sentReqs map[uint64]*sentReq
}
// validatorFunc is a function that processes a reply message
type validatorFunc func(distPeer, *Msg) error
// 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
lastReqQueued bool // last request has been queued but not sent
lastReqSentTo distPeer // if not nil then last request has been sent to given peer 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, frozen bool
event chan int
}
// 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
rpNotDelivered
)
// newRetrieveManager creates the retrieve manager
func newRetrieveManager(peers *serverPeerSet, dist *requestDistributor, srto func() time.Duration) *retrieveManager {
return &retrieveManager{
peers: peers,
dist: dist,
sentReqs: make(map[uint64]*sentReq),
softRequestTimeout: srto,
}
}
// 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{delivered: false, frozen: false, event: make(chan int, 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)
}
// frozen is called by the LES protocol manager when a server has suspended its service and we
// should not expect an answer for the requests already sent there
func (rm *retrieveManager) frozen(peer distPeer) {
rm.lock.RLock()
defer rm.lock.RUnlock()
for _, req := range rm.sentReqs {
req.frozen(peer)
}
}
// 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.lastReqQueued = 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(light.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.lastReqQueued = true
return r.stateRequesting
case rpDeliveredInvalid, rpNotDelivered:
// if it was the last sent request (set to nil by update) then start a new one
if !r.lastReqQueued && r.lastReqSentTo == nil {
go r.tryRequest()
r.lastReqQueued = 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.lastReqQueued = true
return r.stateRequesting
case ev := <-r.eventsCh:
r.update(ev)
if ev.event == rpDeliveredValid {
r.stop(nil)
return r.stateStopped
}
if r.waiting() {
return r.stateNoMorePeers
}
r.stop(light.ErrNoPeers)
return nil
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.lastReqQueued = false
r.lastReqSentTo = ev.peer
case rpSoftTimeout:
r.lastReqSentTo = nil
r.reqSrtoCount++
case rpHardTimeout:
r.reqSrtoCount--
case rpDeliveredValid, rpDeliveredInvalid, rpNotDelivered:
if ev.peer == r.lastReqSentTo {
r.lastReqSentTo = nil
} else {
r.reqSrtoCount--
}
}
}
// waiting returns true if the retrieval mechanism is waiting for an answer from
// any peer
func (r *sentReq) waiting() bool {
return r.lastReqQueued || r.lastReqSentTo != nil || 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
}
hrto := 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.(*serverPeer)
if hrto && ok {
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 event := <-s.event:
if event == rpNotDelivered {
r.lock.Lock()
delete(r.sentTo, p)
r.lock.Unlock()
}
r.eventsCh <- reqPeerEvent{event, p}
return
case <-time.After(r.rm.softRequestTimeout()):
r.eventsCh <- reqPeerEvent{rpSoftTimeout, p}
}
select {
case event := <-s.event:
if event == rpNotDelivered {
r.lock.Lock()
delete(r.sentTo, p)
r.lock.Unlock()
}
r.eventsCh <- reqPeerEvent{event, 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)
}
if s.frozen {
return nil
}
valid := r.validate(peer, msg) == nil
r.sentTo[peer] = sentReqToPeer{delivered: true, frozen: false, event: s.event}
if valid {
s.event <- rpDeliveredValid
} else {
s.event <- rpDeliveredInvalid
}
if !valid {
return errResp(ErrInvalidResponse, "reqID = %v", msg.ReqID)
}
return nil
}
// frozen sends a "not delivered" event to the peer event channel belonging to the
// given peer if the request has been sent there, causing the state machine to not
// expect an answer and potentially even send the request to the same peer again
// when canSend allows it.
func (r *sentReq) frozen(peer distPeer) {
r.lock.Lock()
defer r.lock.Unlock()
s, ok := r.sentTo[peer]
if ok && !s.delivered && !s.frozen {
r.sentTo[peer] = sentReqToPeer{delivered: false, frozen: true, event: s.event}
s.event <- rpNotDelivered
}
}
// 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[:])
}