p2p: rework protocol API

p2p/message.go

@@ -1,75 +1,174 @@
 package p2p
 
 import (
-	// "fmt"
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"math/big"
+
 	"github.com/ethereum/go-ethereum/ethutil"
 )
 
-type MsgCode uint8
+type MsgCode uint64
 
+// 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    MsgCode // this is the raw code as per adaptive msg code scheme
-	data    *ethutil.Value
-	encoded []byte
+	Code    MsgCode
+	Size    uint32 // size of the paylod
+	Payload io.Reader
 }
 
-func (self *Msg) Code() MsgCode {
-	return self.code
+// NewMsg creates an RLP-encoded message with the given code.
+func NewMsg(code MsgCode, 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 (self *Msg) Data() *ethutil.Value {
-	return self.data
+func encodePayload(params ...interface{}) []byte {
+	buf := new(bytes.Buffer)
+	for _, p := range params {
+		buf.Write(ethutil.Encode(p))
+	}
+	return buf.Bytes()
 }
 
-func NewMsg(code MsgCode, params ...interface{}) (msg *Msg, err error) {
+// Data returns the decoded RLP payload items in a message.
+func (msg Msg) Data() (*ethutil.Value, error) {
+	// TODO: avoid copying when we have a better RLP decoder
+	buf := new(bytes.Buffer)
+	var s []interface{}
+	if _, err := buf.ReadFrom(msg.Payload); err != nil {
+		return nil, err
+	}
+	for buf.Len() > 0 {
+		s = append(s, ethutil.DecodeWithReader(buf))
+	}
+	return ethutil.NewValue(s), nil
+}
 
-	// // data := [][]interface{}{}
-	// data := []interface{}{}
-	// for _, value := range params {
-	// 	if encodable, ok := value.(ethutil.RlpEncodeDecode); ok {
-	// 		data = append(data, encodable.RlpValue())
-	// 	} else if raw, ok := value.([]interface{}); ok {
-	// 		data = append(data, raw)
-	// 	} else {
-	// 		// data = append(data, interface{}(raw))
-	// 		err = fmt.Errorf("Unable to encode object of type %T", value)
-	// 		return
-	// 	}
-	// }
-	return &Msg{
-		code: code,
-		data: ethutil.NewValue(interface{}(params)),
+// Discard reads any remaining payload data into a black hole.
+func (msg Msg) Discard() error {
+	_, err := io.Copy(ioutil.Discard, msg.Payload)
+	return err
+}
+
+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...)
+}
+
+type byteReader interface {
+	io.Reader
+	io.ByteReader
+}
+
+// readMsg reads a message header.
+func readMsg(r 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(ReadError, "%v", err)
+	}
+	if !bytes.HasPrefix(start, magicToken) {
+		return msg, NewPeerError(MagicTokenMismatch, "got %x, want %x", start[:4], magicToken)
+	}
+	size := binary.BigEndian.Uint32(start[4:])
+
+	// decode start of RLP message to get the message code
+	_, hdrlen, err := readListHeader(r)
+	if err != nil {
+		return msg, err
+	}
+	code, codelen, err := readMsgCode(r)
+	if err != nil {
+		return msg, err
+	}
+
+	rlpsize := size - hdrlen - codelen
+	return Msg{
+		Code:    code,
+		Size:    rlpsize,
+		Payload: io.LimitReader(r, int64(rlpsize)),
 	}, nil
 }
 
-func NewMsgFromBytes(encoded []byte) (msg *Msg, err error) {
-	value := ethutil.NewValueFromBytes(encoded)
-	// Type of message
-	code := value.Get(0).Uint()
-	// Actual data
-	data := value.SliceFrom(1)
-
-	msg = &Msg{
-		code: MsgCode(code),
-		data: data,
-		// data:    ethutil.NewValue(data),
-		encoded: encoded,
+// readListHeader reads an RLP list header from r.
+func readListHeader(r byteReader) (len uint64, hdrlen uint32, err error) {
+	b, err := r.ReadByte()
+	if err != nil {
+		return 0, 0, err
 	}
-	return
-}
-
-func (self *Msg) Decode(offset MsgCode) {
-	self.code = self.code - offset
-}
-
-// encode takes an offset argument to implement adaptive message coding
-// the encoded message is memoized to make msgs relayed to several peers more efficient
-func (self *Msg) Encode(offset MsgCode) (res []byte) {
-	if len(self.encoded) == 0 {
-		res = ethutil.NewValue(append([]interface{}{byte(self.code + offset)}, self.data.Slice()...)).Encode()
-		self.encoded = res
+	if b < 0xC0 {
+		return 0, 0, fmt.Errorf("expected list start byte >= 0xC0, got %x", b)
+	} else if b < 0xF7 {
+		len = uint64(b - 0xc0)
+		hdrlen = 1
 	} else {
-		res = self.encoded
+		lenlen := b - 0xF7
+		lenbuf := make([]byte, 8)
+		if _, err := io.ReadFull(r, lenbuf[8-lenlen:]); err != nil {
+			return 0, 0, err
+		}
+		len = binary.BigEndian.Uint64(lenbuf)
+		hdrlen = 1 + uint32(lenlen)
 	}
-	return
+	return len, hdrlen, nil
+}
+
+// readUint reads an RLP-encoded unsigned integer from r.
+func readMsgCode(r byteReader) (code MsgCode, codelen uint32, err error) {
+	b, err := r.ReadByte()
+	if err != nil {
+		return 0, 0, err
+	}
+	if b < 0x80 {
+		return MsgCode(b), 1, nil
+	} else if b < 0x89 { // max length for uint64 is 8 bytes
+		codelen = uint32(b - 0x80)
+		if codelen == 0 {
+			return 0, 1, nil
+		}
+		buf := make([]byte, 8)
+		if _, err := io.ReadFull(r, buf[8-codelen:]); err != nil {
+			return 0, 0, err
+		}
+		return MsgCode(binary.BigEndian.Uint64(buf)), codelen, nil
+	}
+	return 0, 0, fmt.Errorf("bad RLP type for message code: %x", b)
 }