1 files changed, 232 insertions, 0 deletions
diff --git a/p2p/message.go b/p2p/message.go
new file mode 100644
index 000000000..f5418ff47
--- /dev/null
+++ b/p2p/message.go
@@ -0,0 +1,232 @@
+package p2p
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"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))
+	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
+}
+
+// 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
+}