// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
/*
Package protocols is an extension to p2p. It offers a user friendly simple way to define
devp2p subprotocols by abstracting away code standardly shared by protocols.
* automate assigments of code indexes to messages
* automate RLP decoding/encoding based on reflecting
* provide the forever loop to read incoming messages
* standardise error handling related to communication
* standardised handshake negotiation
* TODO: automatic generation of wire protocol specification for peers
*/
package protocols
import (
"context"
"fmt"
"reflect"
"sync"
"time"
"github.com/ethereum/go-ethereum/metrics"
"github.com/ethereum/go-ethereum/p2p"
)
// error codes used by this protocol scheme
const (
ErrMsgTooLong = iota
ErrDecode
ErrWrite
ErrInvalidMsgCode
ErrInvalidMsgType
ErrHandshake
ErrNoHandler
ErrHandler
)
// error description strings associated with the codes
var errorToString = map[int]string{
ErrMsgTooLong: "Message too long",
ErrDecode: "Invalid message (RLP error)",
ErrWrite: "Error sending message",
ErrInvalidMsgCode: "Invalid message code",
ErrInvalidMsgType: "Invalid message type",
ErrHandshake: "Handshake error",
ErrNoHandler: "No handler registered error",
ErrHandler: "Message handler error",
}
/*
Error implements the standard go error interface.
Use:
errorf(code, format, params ...interface{})
Prints as:
<description>: <details>
where description is given by code in errorToString
and details is fmt.Sprintf(format, params...)
exported field Code can be checked
*/
type Error struct {
Code int
message string
format string
params []interface{}
}
func (e Error) Error() (message string) {
if len(e.message) == 0 {
name, ok := errorToString[e.Code]
if !ok {
panic("invalid message code")
}
e.message = name
if e.format != "" {
e.message += ": " + fmt.Sprintf(e.format, e.params...)
}
}
return e.message
}
func errorf(code int, format string, params ...interface{}) *Error {
return &Error{
Code: code,
format: format,
params: params,
}
}
// Spec is a protocol specification including its name and version as well as
// the types of messages which are exchanged
type Spec struct {
// Name is the name of the protocol, often a three-letter word
Name string
// Version is the version number of the protocol
Version uint
// MaxMsgSize is the maximum accepted length of the message payload
MaxMsgSize uint32
// Messages is a list of message data types which this protocol uses, with
// each message type being sent with its array index as the code (so
// [&foo{}, &bar{}, &baz{}] would send foo, bar and baz with codes
// 0, 1 and 2 respectively)
// each message must have a single unique data type
Messages []interface{}
initOnce sync.Once
codes map[reflect.Type]uint64
types map[uint64]reflect.Type
}
func (s *Spec) init() {
s.initOnce.Do(func() {
s.codes = make(map[reflect.Type]uint64, len(s.Messages))
s.types = make(map[uint64]reflect.Type, len(s.Messages))
for i, msg := range s.Messages {
code := uint64(i)
typ := reflect.TypeOf(msg)
if typ.Kind() == reflect.Ptr {
typ = typ.Elem()
}
s.codes[typ] = code
s.types[code] = typ
}
})
}
// Length returns the number of message types in the protocol
func (s *Spec) Length() uint64 {
return uint64(len(s.Messages))
}
// GetCode returns the message code of a type, and boolean second argument is
// false if the message type is not found
func (s *Spec) GetCode(msg interface{}) (uint64, bool) {
s.init()
typ := reflect.TypeOf(msg)
if typ.Kind() == reflect.Ptr {
typ = typ.Elem()
}
code, ok := s.codes[typ]
return code, ok
}
// NewMsg construct a new message type given the code
func (s *Spec) NewMsg(code uint64) (interface{}, bool) {
s.init()
typ, ok := s.types[code]
if !ok {
return nil, false
}
return reflect.New(typ).Interface(), true
}
// Peer represents a remote peer or protocol instance that is running on a peer connection with
// a remote peer
type Peer struct {
*p2p.Peer // the p2p.Peer object representing the remote
rw p2p.MsgReadWriter // p2p.MsgReadWriter to send messages to and read messages from
spec *Spec
}
// NewPeer constructs a new peer
// this constructor is called by the p2p.Protocol#Run function
// the first two arguments are the arguments passed to p2p.Protocol.Run function
// the third argument is the Spec describing the protocol
func NewPeer(p *p2p.Peer, rw p2p.MsgReadWriter, spec *Spec) *Peer {
return &Peer{
Peer: p,
rw: rw,
spec: spec,
}
}
// Run starts the forever loop that handles incoming messages
// called within the p2p.Protocol#Run function
// the handler argument is a function which is called for each message received
// from the remote peer, a returned error causes the loop to exit
// resulting in disconnection
func (p *Peer) Run(handler func(msg interface{}) error) error {
for {
if err := p.handleIncoming(handler); err != nil {
return err
}
}
}
// Drop disconnects a peer.
// TODO: may need to implement protocol drop only? don't want to kick off the peer
// if they are useful for other protocols
func (p *Peer) Drop(err error) {
p.Disconnect(p2p.DiscSubprotocolError)
}
// Send takes a message, encodes it in RLP, finds the right message code and sends the
// message off to the peer
// this low level call will be wrapped by libraries providing routed or broadcast sends
// but often just used to forward and push messages to directly connected peers
func (p *Peer) Send(msg interface{}) error {
defer metrics.GetOrRegisterResettingTimer("peer.send_t", nil).UpdateSince(time.Now())
metrics.GetOrRegisterCounter("peer.send", nil).Inc(1)
code, found := p.spec.GetCode(msg)
if !found {
return errorf(ErrInvalidMsgType, "%v", code)
}
return p2p.Send(p.rw, code, msg)
}
// handleIncoming(code)
// is called each cycle of the main forever loop that dispatches incoming messages
// if this returns an error the loop returns and the peer is disconnected with the error
// this generic handler
// * checks message size,
// * checks for out-of-range message codes,
// * handles decoding with reflection,
// * call handlers as callbacks
func (p *Peer) handleIncoming(handle func(msg interface{}) error) error {
msg, err := p.rw.ReadMsg()
if err != nil {
return err
}
// make sure that the payload has been fully consumed
defer msg.Discard()
if msg.Size > p.spec.MaxMsgSize {
return errorf(ErrMsgTooLong, "%v > %v", msg.Size, p.spec.MaxMsgSize)
}
val, ok := p.spec.NewMsg(msg.Code)
if !ok {
return errorf(ErrInvalidMsgCode, "%v", msg.Code)
}
if err := msg.Decode(val); err != nil {
return errorf(ErrDecode, "<= %v: %v", msg, err)
}
// call the registered handler callbacks
// a registered callback take the decoded message as argument as an interface
// which the handler is supposed to cast to the appropriate type
// it is entirely safe not to check the cast in the handler since the handler is
// chosen based on the proper type in the first place
if err := handle(val); err != nil {
return errorf(ErrHandler, "(msg code %v): %v", msg.Code, err)
}
return nil
}
// Handshake negotiates a handshake on the peer connection
// * arguments
// * context
// * the local handshake to be sent to the remote peer
// * funcion to be called on the remote handshake (can be nil)
// * expects a remote handshake back of the same type
// * the dialing peer needs to send the handshake first and then waits for remote
// * the listening peer waits for the remote handshake and then sends it
// returns the remote handshake and an error
func (p *Peer) Handshake(ctx context.Context, hs interface{}, verify func(interface{}) error) (rhs interface{}, err error) {
if _, ok := p.spec.GetCode(hs); !ok {
return nil, errorf(ErrHandshake, "unknown handshake message type: %T", hs)
}
errc := make(chan error, 2)
handle := func(msg interface{}) error {
rhs = msg
if verify != nil {
return verify(rhs)
}
return nil
}
send := func() { errc <- p.Send(hs) }
receive := func() { errc <- p.handleIncoming(handle) }
go func() {
if p.Inbound() {
receive()
send()
} else {
send()
receive()
}
}()
for i := 0; i < 2; i++ {
select {
case err = <-errc:
case <-ctx.Done():
err = ctx.Err()
}
if err != nil {
return nil, errorf(ErrHandshake, err.Error())
}
}
return rhs, nil
}
