path: root/p2p/protocol.go

package p2p

import (
    "bytes"
    "time"
)

// Protocol represents a P2P subprotocol implementation.
type Protocol struct {
    // Name should contain the official protocol name,
    // often a three-letter word.
    Name string

    // Version should contain the version number of the protocol.
    Version uint

    // Length should contain the number of message codes used
    // by the protocol.
    Length uint64

    // Run is called in a new groutine when the protocol has been
    // negotiated with a peer. It should read and write messages from
    // rw. The Payload for each message must be fully consumed.
    //
    // The peer connection is closed when Start returns. It should return
    // any protocol-level error (such as an I/O error) that is
    // encountered.
    Run func(peer *Peer, rw MsgReadWriter) error
}

func (p Protocol) cap() Cap {
    return Cap{p.Name, p.Version}
}

const (
    baseProtocolVersion    = 2
    baseProtocolLength     = uint64(16)
    baseProtocolMaxMsgSize = 10 * 1024 * 1024
)

const (
    // devp2p message codes
    handshakeMsg = 0x00
    discMsg      = 0x01
    pingMsg      = 0x02
    pongMsg      = 0x03
    getPeersMsg  = 0x04
    peersMsg     = 0x05
)

// handshake is the structure of a handshake list.
type handshake struct {
    Version    uint64
    ID         string
    Caps       []Cap
    ListenPort uint64
    NodeID     []byte
}

func (h *handshake) String() string {
    return h.ID
}
func (h *handshake) Pubkey() []byte {
    return h.NodeID
}

// Cap is the structure of a peer capability.
type Cap struct {
    Name    string
    Version uint
}

func (cap Cap) RlpData() interface{} {
    return []interface{}{cap.Name, cap.Version}
}

type capsByName []Cap

func (cs capsByName) Len() int           { return len(cs) }
func (cs capsByName) Less(i, j int) bool { return cs[i].Name < cs[j].Name }
func (cs capsByName) Swap(i, j int)      { cs[i], cs[j] = cs[j], cs[i] }

type baseProtocol struct {
    rw   MsgReadWriter
    peer *Peer
}

func runBaseProtocol(peer *Peer, rw MsgReadWriter) error {
    bp := &baseProtocol{rw, peer}
    errc := make(chan error, 1)
    go func() { errc <- rw.WriteMsg(bp.handshakeMsg()) }()
    if err := bp.readHandshake(); err != nil {
        return err
    }
    // handle write error
    if err := <-errc; err != nil {
        return err
    }
    // run main loop
    go func() {
        for {
            if err := bp.handle(rw); err != nil {
                errc <- err
                break
            }
        }
    }()
    return bp.loop(errc)
}

var pingTimeout = 2 * time.Second

func (bp *baseProtocol) loop(quit <-chan error) error {
    ping := time.NewTimer(pingTimeout)
    activity := bp.peer.activity.Subscribe(time.Time{})
    lastActive := time.Time{}
    defer ping.Stop()
    defer activity.Unsubscribe()

    getPeersTick := time.NewTicker(10 * time.Second)
    defer getPeersTick.Stop()
    err := bp.rw.EncodeMsg(getPeersMsg)

    for err == nil {
        select {
        case err = <-quit:
            return err
        case <-getPeersTick.C:
            err = bp.rw.EncodeMsg(getPeersMsg)
        case event := <-activity.Chan():
            ping.Reset(pingTimeout)
            lastActive = event.(time.Time)
        case t := <-ping.C:
            if lastActive.Add(pingTimeout * 2).Before(t) {
                err = newPeerError(errPingTimeout, "")
            } else if lastActive.Add(pingTimeout).Before(t) {
                err = bp.rw.EncodeMsg(pingMsg)
            }
        }
    }
    return err
}

func (bp *baseProtocol) handle(rw MsgReadWriter) error {
    msg, err := rw.ReadMsg()
    if err != nil {
        return err
    }
    if msg.Size > baseProtocolMaxMsgSize {
        return newPeerError(errMisc, "message too big")
    }
    // make sure that the payload has been fully consumed
    defer msg.Discard()

    switch msg.Code {
    case handshakeMsg:
        return newPeerError(errProtocolBreach, "extra handshake received")

    case discMsg:
        var reason [1]DiscReason
        if err := msg.Decode(&reason); err != nil {
            return err
        }
        return discRequestedError(reason[0])

    case pingMsg:
        return bp.rw.EncodeMsg(pongMsg)

    case pongMsg:

    case getPeersMsg:
        peers := bp.peer.PeerList()
        // this is dangerous. the spec says that we should _delay_
        // sending the response if no new information is available.
        // this means that would need to send a response later when
        // new peers become available.
        //
        // TODO: add event mechanism to notify baseProtocol for new peers
        if len(peers) > 0 {
            return bp.rw.EncodeMsg(peersMsg, peers...)
        }

    case peersMsg:
        var peers []*peerAddr
        if err := msg.Decode(&peers); err != nil {
            return err
        }
        for _, addr := range peers {
            bp.peer.Debugf("received peer suggestion: %v", addr)
            bp.peer.newPeerAddr <- addr
        }

    default:
        return newPeerError(errInvalidMsgCode, "unknown message code %v", msg.Code)
    }
    return nil
}

func (bp *baseProtocol) readHandshake() error {
    // read and handle remote handshake
    msg, err := bp.rw.ReadMsg()
    if err != nil {
        return err
    }
    if msg.Code != handshakeMsg {
        return newPeerError(errProtocolBreach, "first message must be handshake, got %x", msg.Code)
    }
    if msg.Size > baseProtocolMaxMsgSize {
        return newPeerError(errMisc, "message too big")
    }
    var hs handshake
    if err := msg.Decode(&hs); err != nil {
        return err
    }
    // validate handshake info
    if hs.Version != baseProtocolVersion {
        return newPeerError(errP2PVersionMismatch, "Require protocol %d, received %d\n",
            baseProtocolVersion, hs.Version)
    }
    if len(hs.NodeID) == 0 {
        return newPeerError(errPubkeyMissing, "")
    }
    if len(hs.NodeID) != 64 {
        return newPeerError(errPubkeyInvalid, "require 512 bit, got %v", len(hs.NodeID)*8)
    }
    if da := bp.peer.dialAddr; da != nil {
        // verify that the peer we wanted to connect to
        // actually holds the target public key.
        if da.Pubkey != nil && !bytes.Equal(da.Pubkey, hs.NodeID) {
            return newPeerError(errPubkeyForbidden, "dial address pubkey mismatch")
        }
    }
    pa := newPeerAddr(bp.peer.conn.RemoteAddr(), hs.NodeID)
    if err := bp.peer.pubkeyHook(pa); err != nil {
        return newPeerError(errPubkeyForbidden, "%v", err)
    }
    // TODO: remove Caps with empty name
    var addr *peerAddr
    if hs.ListenPort != 0 {
        addr = newPeerAddr(bp.peer.conn.RemoteAddr(), hs.NodeID)
        addr.Port = hs.ListenPort
    }
    bp.peer.setHandshakeInfo(&hs, addr, hs.Caps)
    bp.peer.startSubprotocols(hs.Caps)
    return nil
}

func (bp *baseProtocol) handshakeMsg() Msg {
    var (
        port uint64
        caps []interface{}
    )
    if bp.peer.ourListenAddr != nil {
        port = bp.peer.ourListenAddr.Port
    }
    for _, proto := range bp.peer.protocols {
        caps = append(caps, proto.cap())
    }
    return NewMsg(handshakeMsg,
        baseProtocolVersion,
        bp.peer.ourID.String(),
        caps,
        port,
        bp.peer.ourID.Pubkey()[1:],
    )
}