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package p2p
import (
"bytes"
"encoding/binary"
"io"
"io/ioutil"
"math/big"
"github.com/ethereum/go-ethereum/ethutil"
"github.com/ethereum/go-ethereum/rlp"
)
// 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))
return s.Decode(val)
}
// 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 an existing message.
// The Payload reader of the message is consumed.
// Note that messages can be sent only once.
WriteMsg(Msg) error
// EncodeMsg writes an RLP-encoded message with the given
// code and data elements.
EncodeMsg(code uint64, data ...interface{}) error
}
// MsgReadWriter provides reading and writing of encoded messages.
type MsgReadWriter interface {
MsgReader
MsgWriter
}
var magicToken = []byte{34, 64, 8, 145}
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...)
}
// readMsg reads a message header from r.
// It takes an rlp.ByteReader to ensure that the decoding doesn't buffer.
func readMsg(r rlp.ByteReader) (msg Msg, err error) {
// read magic and payload size
start := make([]byte, 8)
if _, err = io.ReadFull(r, start); err != nil {
return msg, newPeerError(errRead, "%v", err)
}
if !bytes.HasPrefix(start, magicToken) {
return msg, newPeerError(errMagicTokenMismatch, "got %x, want %x", start[:4], magicToken)
}
size := binary.BigEndian.Uint32(start[4:])
// decode start of RLP message to get the message code
posr := &postrack{r, 0}
s := rlp.NewStream(posr)
if _, err := s.List(); err != nil {
return msg, err
}
code, err := s.Uint()
if err != nil {
return msg, err
}
payloadsize := size - posr.p
return Msg{code, payloadsize, io.LimitReader(r, int64(payloadsize))}, 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
}
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