package p2p import ( "bytes" "encoding/binary" "errors" "fmt" "io" "io/ioutil" "math/big" "sync/atomic" "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)) 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 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 } // 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, int64(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 } // EncodeMsg is a convenient shorthand for sending an RLP-encoded message. func (p *MsgPipeRW) EncodeMsg(code uint64, data ...interface{}) error { return p.WriteMsg(NewMsg(code, data...)) } // 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 }