path: root/p2p/message.go

package p2p

import (
    "bufio"
    "bytes"
    "encoding/binary"
    "errors"
    "fmt"
    "io"
    "io/ioutil"
    "math/big"
    "net"
    "sync"
    "sync/atomic"
    "time"

    "github.com/ethereum/go-ethereum/ethutil"
    "github.com/ethereum/go-ethereum/rlp"
)

// parameters for frameRW
const (
    // maximum time allowed for reading a message header.
    // this is effectively the amount of time a connection can be idle.
    frameReadTimeout = 1 * time.Minute

    // maximum time allowed for reading the payload data of a message.
    // this is shorter than (and distinct from) frameReadTimeout because
    // the connection is not considered idle while a message is transferred.
    // this also limits the payload size of messages to how much the connection
    // can transfer within the timeout.
    payloadReadTimeout = 5 * time.Second

    // maximum amount of time allowed for writing a complete message.
    msgWriteTimeout = 5 * time.Second

    // messages smaller than this many bytes will be read at
    // once before passing them to a protocol. this increases
    // concurrency in the processing.
    wholePayloadSize = 64 * 1024
)

// Msg defines the structure of a p2p message.
//
// Note that a Msg can only be sent once since the Payload reader is
// consumed during sending. It is not possible to create a Msg and
// send it any number of times. If you want to reuse an encoded
// structure, encode the payload into a byte array and create a
// separate Msg with a bytes.Reader as Payload for each send.
type Msg struct {
    Code    uint64
    Size    uint32 // size of the paylod
    Payload io.Reader
}

// NewMsg creates an RLP-encoded message with the given code.
func NewMsg(code uint64, params ...interface{}) Msg {
    buf := new(bytes.Buffer)
    for _, p := range params {
        buf.Write(ethutil.Encode(p))
    }
    return Msg{Code: code, Size: uint32(buf.Len()), Payload: buf}
}

func encodePayload(params ...interface{}) []byte {
    buf := new(bytes.Buffer)
    for _, p := range params {
        buf.Write(ethutil.Encode(p))
    }
    return buf.Bytes()
}

// Decode parse the RLP content of a message into
// the given value, which must be a pointer.
//
// For the decoding rules, please see package rlp.
func (msg Msg) Decode(val interface{}) error {
    s := rlp.NewListStream(msg.Payload, uint64(msg.Size))
    if err := s.Decode(val); err != nil {
        return newPeerError(errInvalidMsg, "(code %#x) (size %d) %v", msg.Code, msg.Size, err)
    }
    return nil
}

func (msg Msg) String() string {
    return fmt.Sprintf("msg #%v (%v bytes)", msg.Code, msg.Size)
}

// Discard reads any remaining payload data into a black hole.
func (msg Msg) Discard() error {
    _, err := io.Copy(ioutil.Discard, msg.Payload)
    return err
}

type MsgReader interface {
    ReadMsg() (Msg, error)
}

type MsgWriter interface {
    // WriteMsg sends a message. It will block until the message's
    // Payload has been consumed by the other end.
    //
    // Note that messages can be sent only once because their
    // payload reader is drained.
    WriteMsg(Msg) error
}

// MsgReadWriter provides reading and writing of encoded messages.
// Implementations should ensure that ReadMsg and WriteMsg can be
// called simultaneously from multiple goroutines.
type MsgReadWriter interface {
    MsgReader
    MsgWriter
}

// EncodeMsg writes an RLP-encoded message with the given code and
// data elements.
func EncodeMsg(w MsgWriter, code uint64, data ...interface{}) error {
    return w.WriteMsg(NewMsg(code, data...))
}

// frameRW is a MsgReadWriter that reads and writes devp2p message frames.
// As required by the interface, ReadMsg and WriteMsg can be called from
// multiple goroutines.
type frameRW struct {
    net.Conn // make Conn methods available. be careful.
    bufconn  *bufio.ReadWriter

    // this channel is used to 'lend' bufconn to a caller of ReadMsg
    // until the message payload has been consumed. the channel
    // receives a value when EOF is reached on the payload, unblocking
    // a pending call to ReadMsg.
    rsync chan struct{}

    // this mutex guards writes to bufconn.
    writeMu sync.Mutex
}

func newFrameRW(conn net.Conn, timeout time.Duration) *frameRW {
    rsync := make(chan struct{}, 1)
    rsync <- struct{}{}
    return &frameRW{
        Conn:    conn,
        bufconn: bufio.NewReadWriter(bufio.NewReader(conn), bufio.NewWriter(conn)),
        rsync:   rsync,
    }
}

var magicToken = []byte{34, 64, 8, 145}

func (rw *frameRW) WriteMsg(msg Msg) error {
    rw.writeMu.Lock()
    defer rw.writeMu.Unlock()
    rw.SetWriteDeadline(time.Now().Add(msgWriteTimeout))
    if err := writeMsg(rw.bufconn, msg); err != nil {
        return err
    }
    return rw.bufconn.Flush()
}

func writeMsg(w io.Writer, msg Msg) error {
    // TODO: handle case when Size + len(code) + len(listhdr) overflows uint32
    code := ethutil.Encode(uint32(msg.Code))
    listhdr := makeListHeader(msg.Size + uint32(len(code)))
    payloadLen := uint32(len(listhdr)) + uint32(len(code)) + msg.Size

    start := make([]byte, 8)
    copy(start, magicToken)
    binary.BigEndian.PutUint32(start[4:], payloadLen)

    for _, b := range [][]byte{start, listhdr, code} {
        if _, err := w.Write(b); err != nil {
            return err
        }
    }
    _, err := io.CopyN(w, msg.Payload, int64(msg.Size))
    return err
}

func makeListHeader(length uint32) []byte {
    if length < 56 {
        return []byte{byte(length + 0xc0)}
    }
    enc := big.NewInt(int64(length)).Bytes()
    lenb := byte(len(enc)) + 0xf7
    return append([]byte{lenb}, enc...)
}

func (rw *frameRW) ReadMsg() (msg Msg, err error) {
    <-rw.rsync // wait until bufconn is ours

    rw.SetReadDeadline(time.Now().Add(frameReadTimeout))

    // read magic and payload size
    start := make([]byte, 8)
    if _, err = io.ReadFull(rw.bufconn, start); err != nil {
        return msg, err
    }
    if !bytes.HasPrefix(start, magicToken) {
        return msg, fmt.Errorf("bad magic token %x", start[:4], magicToken)
    }
    size := binary.BigEndian.Uint32(start[4:])

    // decode start of RLP message to get the message code
    posr := &postrack{rw.bufconn, 0}
    s := rlp.NewStream(posr)
    if _, err := s.List(); err != nil {
        return msg, err
    }
    msg.Code, err = s.Uint()
    if err != nil {
        return msg, err
    }
    msg.Size = size - posr.p

    rw.SetReadDeadline(time.Now().Add(payloadReadTimeout))

    if msg.Size <= wholePayloadSize {
        // msg is small, read all of it and move on to the next message.
        pbuf := make([]byte, msg.Size)
        if _, err := io.ReadFull(rw.bufconn, pbuf); err != nil {
            return msg, err
        }
        rw.rsync <- struct{}{} // bufconn is available again
        msg.Payload = bytes.NewReader(pbuf)
    } else {
        // lend bufconn to the caller until it has
        // consumed the payload. eofSignal will send a value
        // on rw.rsync when EOF is reached.
        pr := &eofSignal{rw.bufconn, msg.Size, rw.rsync}
        msg.Payload = pr
    }
    return msg, nil
}

// postrack wraps an rlp.ByteReader with a position counter.
type postrack struct {
    r rlp.ByteReader
    p uint32
}

func (r *postrack) Read(buf []byte) (int, error) {
    n, err := r.r.Read(buf)
    r.p += uint32(n)
    return n, err
}

func (r *postrack) ReadByte() (byte, error) {
    b, err := r.r.ReadByte()
    if err == nil {
        r.p++
    }
    return b, err
}

// eofSignal wraps a reader with eof signaling. the eof channel is
// closed when the wrapped reader returns an error or when count bytes
// have been read.
type eofSignal struct {
    wrapped io.Reader
    count   uint32 // number of bytes left
    eof     chan<- struct{}
}

// note: when using eofSignal to detect whether a message payload
// has been read, Read might not be called for zero sized messages.
func (r *eofSignal) Read(buf []byte) (int, error) {
    if r.count == 0 {
        if r.eof != nil {
            r.eof <- struct{}{}
            r.eof = nil
        }
        return 0, io.EOF
    }

    max := len(buf)
    if int(r.count) < len(buf) {
        max = int(r.count)
    }
    n, err := r.wrapped.Read(buf[:max])
    r.count -= uint32(n)
    if (err != nil || r.count == 0) && r.eof != nil {
        r.eof <- struct{}{} // tell Peer that msg has been consumed
        r.eof = nil
    }
    return n, err
}

// MsgPipe creates a message pipe. Reads on one end are matched
// with writes on the other. The pipe is full-duplex, both ends
// implement MsgReadWriter.
func MsgPipe() (*MsgPipeRW, *MsgPipeRW) {
    var (
        c1, c2  = make(chan Msg), make(chan Msg)
        closing = make(chan struct{})
        closed  = new(int32)
        rw1     = &MsgPipeRW{c1, c2, closing, closed}
        rw2     = &MsgPipeRW{c2, c1, closing, closed}
    )
    return rw1, rw2
}

// ErrPipeClosed is returned from pipe operations after the
// pipe has been closed.
var ErrPipeClosed = errors.New("p2p: read or write on closed message pipe")

// MsgPipeRW is an endpoint of a MsgReadWriter pipe.
type MsgPipeRW struct {
    w       chan<- Msg
    r       <-chan Msg
    closing chan struct{}
    closed  *int32
}

// WriteMsg sends a messsage on the pipe.
// It blocks until the receiver has consumed the message payload.
func (p *MsgPipeRW) WriteMsg(msg Msg) error {
    if atomic.LoadInt32(p.closed) == 0 {
        consumed := make(chan struct{}, 1)
        msg.Payload = &eofSignal{msg.Payload, msg.Size, consumed}
        select {
        case p.w <- msg:
            if msg.Size > 0 {
                // wait for payload read or discard
                <-consumed
            }
            return nil
        case <-p.closing:
        }
    }
    return ErrPipeClosed
}

// ReadMsg returns a message sent on the other end of the pipe.
func (p *MsgPipeRW) ReadMsg() (Msg, error) {
    if atomic.LoadInt32(p.closed) == 0 {
        select {
        case msg := <-p.r:
            return msg, nil
        case <-p.closing:
        }
    }
    return Msg{}, ErrPipeClosed
}

// Close unblocks any pending ReadMsg and WriteMsg calls on both ends
// of the pipe. They will return ErrPipeClosed. Note that Close does
// not interrupt any reads from a message payload.
func (p *MsgPipeRW) Close() error {
    if atomic.AddInt32(p.closed, 1) != 1 {
        // someone else is already closing
        atomic.StoreInt32(p.closed, 1) // avoid overflow
        return nil
    }
    close(p.closing)
    return nil
}