path: root/p2p/dial.go

// Copyright 2015 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 p2p

import (
    "container/heap"
    "crypto/rand"
    "errors"
    "fmt"
    "net"
    "time"

    "github.com/ethereum/go-ethereum/log"
    "github.com/ethereum/go-ethereum/p2p/discover"
    "github.com/ethereum/go-ethereum/p2p/netutil"
)

const (
    // This is the amount of time spent waiting in between
    // redialing a certain node.
    dialHistoryExpiration = 30 * time.Second

    // Discovery lookups are throttled and can only run
    // once every few seconds.
    lookupInterval = 4 * time.Second

    // Endpoint resolution is throttled with bounded backoff.
    initialResolveDelay = 60 * time.Second
    maxResolveDelay     = time.Hour
)

// dialstate schedules dials and discovery lookups.
// it get's a chance to compute new tasks on every iteration
// of the main loop in Server.run.
type dialstate struct {
    maxDynDials int
    ntab        discoverTable
    netrestrict *netutil.Netlist

    lookupRunning bool
    dialing       map[discover.NodeID]connFlag
    lookupBuf     []*discover.Node // current discovery lookup results
    randomNodes   []*discover.Node // filled from Table
    static        map[discover.NodeID]*dialTask
    hist          *dialHistory
}

type discoverTable interface {
    Self() *discover.Node
    Close()
    Resolve(target discover.NodeID) *discover.Node
    Lookup(target discover.NodeID) []*discover.Node
    ReadRandomNodes([]*discover.Node) int
}

// the dial history remembers recent dials.
type dialHistory []pastDial

// pastDial is an entry in the dial history.
type pastDial struct {
    id  discover.NodeID
    exp time.Time
}

type task interface {
    Do(*Server)
}

// A dialTask is generated for each node that is dialed. Its
// fields cannot be accessed while the task is running.
type dialTask struct {
    flags        connFlag
    dest         *discover.Node
    lastResolved time.Time
    resolveDelay time.Duration
}

// discoverTask runs discovery table operations.
// Only one discoverTask is active at any time.
// discoverTask.Do performs a random lookup.
type discoverTask struct {
    results []*discover.Node
}

// A waitExpireTask is generated if there are no other tasks
// to keep the loop in Server.run ticking.
type waitExpireTask struct {
    time.Duration
}

func newDialState(static []*discover.Node, ntab discoverTable, maxdyn int, netrestrict *netutil.Netlist) *dialstate {
    s := &dialstate{
        maxDynDials: maxdyn,
        ntab:        ntab,
        netrestrict: netrestrict,
        static:      make(map[discover.NodeID]*dialTask),
        dialing:     make(map[discover.NodeID]connFlag),
        randomNodes: make([]*discover.Node, maxdyn/2),
        hist:        new(dialHistory),
    }
    for _, n := range static {
        s.addStatic(n)
    }
    return s
}

func (s *dialstate) addStatic(n *discover.Node) {
    // This overwites the task instead of updating an existing
    // entry, giving users the opportunity to force a resolve operation.
    s.static[n.ID] = &dialTask{flags: staticDialedConn, dest: n}
}

func (s *dialstate) removeStatic(n *discover.Node) {
    // This removes a task so future attempts to connect will not be made.
    delete(s.static, n.ID)
}

func (s *dialstate) newTasks(nRunning int, peers map[discover.NodeID]*Peer, now time.Time) []task {
    var newtasks []task
    addDial := func(flag connFlag, n *discover.Node) bool {
        if err := s.checkDial(n, peers); err != nil {
            log.Debug(fmt.Sprintf("skipping dial candidate %x@%v:%d: %v", n.ID[:8], n.IP, n.TCP, err))
            return false
        }
        s.dialing[n.ID] = flag
        newtasks = append(newtasks, &dialTask{flags: flag, dest: n})
        return true
    }

    // Compute number of dynamic dials necessary at this point.
    needDynDials := s.maxDynDials
    for _, p := range peers {
        if p.rw.is(dynDialedConn) {
            needDynDials--
        }
    }
    for _, flag := range s.dialing {
        if flag&dynDialedConn != 0 {
            needDynDials--
        }
    }

    // Expire the dial history on every invocation.
    s.hist.expire(now)

    // Create dials for static nodes if they are not connected.
    for id, t := range s.static {
        err := s.checkDial(t.dest, peers)
        switch err {
        case errNotWhitelisted, errSelf:
            log.Debug(fmt.Sprintf("removing static dial candidate %x@%v:%d: %v", t.dest.ID[:8], t.dest.IP, t.dest.TCP, err))
            delete(s.static, t.dest.ID)
        case nil:
            s.dialing[id] = t.flags
            newtasks = append(newtasks, t)
        }
    }

    // Use random nodes from the table for half of the necessary
    // dynamic dials.
    randomCandidates := needDynDials / 2
    if randomCandidates > 0 {
        n := s.ntab.ReadRandomNodes(s.randomNodes)
        for i := 0; i < randomCandidates && i < n; i++ {
            if addDial(dynDialedConn, s.randomNodes[i]) {
                needDynDials--
            }
        }
    }
    // Create dynamic dials from random lookup results, removing tried
    // items from the result buffer.
    i := 0
    for ; i < len(s.lookupBuf) && needDynDials > 0; i++ {
        if addDial(dynDialedConn, s.lookupBuf[i]) {
            needDynDials--
        }
    }
    s.lookupBuf = s.lookupBuf[:copy(s.lookupBuf, s.lookupBuf[i:])]
    // Launch a discovery lookup if more candidates are needed.
    if len(s.lookupBuf) < needDynDials && !s.lookupRunning {
        s.lookupRunning = true
        newtasks = append(newtasks, &discoverTask{})
    }

    // Launch a timer to wait for the next node to expire if all
    // candidates have been tried and no task is currently active.
    // This should prevent cases where the dialer logic is not ticked
    // because there are no pending events.
    if nRunning == 0 && len(newtasks) == 0 && s.hist.Len() > 0 {
        t := &waitExpireTask{s.hist.min().exp.Sub(now)}
        newtasks = append(newtasks, t)
    }
    return newtasks
}

var (
    errSelf             = errors.New("is self")
    errAlreadyDialing   = errors.New("already dialing")
    errAlreadyConnected = errors.New("already connected")
    errRecentlyDialed   = errors.New("recently dialed")
    errNotWhitelisted   = errors.New("not contained in netrestrict whitelist")
)

func (s *dialstate) checkDial(n *discover.Node, peers map[discover.NodeID]*Peer) error {
    _, dialing := s.dialing[n.ID]
    switch {
    case dialing:
        return errAlreadyDialing
    case peers[n.ID] != nil:
        return errAlreadyConnected
    case s.ntab != nil && n.ID == s.ntab.Self().ID:
        return errSelf
    case s.netrestrict != nil && !s.netrestrict.Contains(n.IP):
        return errNotWhitelisted
    case s.hist.contains(n.ID):
        return errRecentlyDialed
    }
    return nil
}

func (s *dialstate) taskDone(t task, now time.Time) {
    switch t := t.(type) {
    case *dialTask:
        s.hist.add(t.dest.ID, now.Add(dialHistoryExpiration))
        delete(s.dialing, t.dest.ID)
    case *discoverTask:
        s.lookupRunning = false
        s.lookupBuf = append(s.lookupBuf, t.results...)
    }
}

func (t *dialTask) Do(srv *Server) {
    if t.dest.Incomplete() {
        if !t.resolve(srv) {
            return
        }
    }
    success := t.dial(srv, t.dest)
    // Try resolving the ID of static nodes if dialing failed.
    if !success && t.flags&staticDialedConn != 0 {
        if t.resolve(srv) {
            t.dial(srv, t.dest)
        }
    }
}

// resolve attempts to find the current endpoint for the destination
// using discovery.
//
// Resolve operations are throttled with backoff to avoid flooding the
// discovery network with useless queries for nodes that don't exist.
// The backoff delay resets when the node is found.
func (t *dialTask) resolve(srv *Server) bool {
    if srv.ntab == nil {
        log.Debug(fmt.Sprintf("can't resolve node %x: discovery is disabled", t.dest.ID[:6]))
        return false
    }
    if t.resolveDelay == 0 {
        t.resolveDelay = initialResolveDelay
    }
    if time.Since(t.lastResolved) < t.resolveDelay {
        return false
    }
    resolved := srv.ntab.Resolve(t.dest.ID)
    t.lastResolved = time.Now()
    if resolved == nil {
        t.resolveDelay *= 2
        if t.resolveDelay > maxResolveDelay {
            t.resolveDelay = maxResolveDelay
        }
        log.Debug(fmt.Sprintf("resolving node %x failed (new delay: %v)", t.dest.ID[:6], t.resolveDelay))
        return false
    }
    // The node was found.
    t.resolveDelay = initialResolveDelay
    t.dest = resolved
    log.Debug(fmt.Sprintf("resolved node %x: %v:%d", t.dest.ID[:6], t.dest.IP, t.dest.TCP))
    return true
}

// dial performs the actual connection attempt.
func (t *dialTask) dial(srv *Server, dest *discover.Node) bool {
    addr := &net.TCPAddr{IP: dest.IP, Port: int(dest.TCP)}
    log.Debug(fmt.Sprintf("dial tcp %v (%x)", addr, dest.ID[:6]))
    fd, err := srv.Dialer.Dial("tcp", addr.String())
    if err != nil {
        log.Trace(fmt.Sprintf("%v", err))
        return false
    }
    mfd := newMeteredConn(fd, false)
    srv.setupConn(mfd, t.flags, dest)
    return true
}

func (t *dialTask) String() string {
    return fmt.Sprintf("%v %x %v:%d", t.flags, t.dest.ID[:8], t.dest.IP, t.dest.TCP)
}

func (t *discoverTask) Do(srv *Server) {
    // newTasks generates a lookup task whenever dynamic dials are
    // necessary. Lookups need to take some time, otherwise the
    // event loop spins too fast.
    next := srv.lastLookup.Add(lookupInterval)
    if now := time.Now(); now.Before(next) {
        time.Sleep(next.Sub(now))
    }
    srv.lastLookup = time.Now()
    var target discover.NodeID
    rand.Read(target[:])
    t.results = srv.ntab.Lookup(target)
}

func (t *discoverTask) String() string {
    s := "discovery lookup"
    if len(t.results) > 0 {
        s += fmt.Sprintf(" (%d results)", len(t.results))
    }
    return s
}

func (t waitExpireTask) Do(*Server) {
    time.Sleep(t.Duration)
}
func (t waitExpireTask) String() string {
    return fmt.Sprintf("wait for dial hist expire (%v)", t.Duration)
}

// Use only these methods to access or modify dialHistory.
func (h dialHistory) min() pastDial {
    return h[0]
}
func (h *dialHistory) add(id discover.NodeID, exp time.Time) {
    heap.Push(h, pastDial{id, exp})
}
func (h dialHistory) contains(id discover.NodeID) bool {
    for _, v := range h {
        if v.id == id {
            return true
        }
    }
    return false
}
func (h *dialHistory) expire(now time.Time) {
    for h.Len() > 0 && h.min().exp.Before(now) {
        heap.Pop(h)
    }
}

// heap.Interface boilerplate
func (h dialHistory) Len() int           { return len(h) }
func (h dialHistory) Less(i, j int) bool { return h[i].exp.Before(h[j].exp) }
func (h dialHistory) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
func (h *dialHistory) Push(x interface{}) {
    *h = append(*h, x.(pastDial))
}
func (h *dialHistory) Pop() interface{} {
    old := *h
    n := len(old)
    x := old[n-1]
    *h = old[0 : n-1]
    return x
}