ethereum
diff --git a/‎p2p/protocols/protocol.go‎
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+/*
+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.
+The subprotocol architecture is inspired by the node package. Similar to a node
+the standard protocol (class) registers service contructors that are instantiated as service
+instances on the protocol isntance that is launched on a p2p peer connection.
+
+By mounting various protocol modules protocols can encapsulate vertical slices of business logic
+without duplicating code related to protocol communication.
+Standard protocol supports:
+
+* mounting services instantiated with the remote peer when a protocol instance is launched on a newly
+  established peer connection
+* registering module-specific handshakes and offers validation and renegotiation  of handshakes
+* registering multiple handlers for incoming messages
+* 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
+* enables access to sister services of the same peer connection analogous to node.Service
+* TODO: automatic generation of wire protocol specification for peers
+* peerPool abstracting out peer management by defining a peerPool that is called to register/unregister
+  peers as they connect and drop (ideally the peerPool also implements the peerPool interface that the
+  p2p server needs to suggest peers to connect to in server-as-initiator mode of operation
+  see https://github.com/ethereum/go-ethereum/issues/2254 for the peer management/connectivity related
+  aspect
+
+*/
+
+package protocols
+
+import (
+	"fmt"
+	"reflect"
+
+	"github.com/ethereum/go-ethereum/logger"
+	"github.com/ethereum/go-ethereum/logger/glog"
+	"github.com/ethereum/go-ethereum/p2p"
+)
+
+// error codes used by this  protocol scheme
+const (
+	ErrMsgTooLong = iota
+	ErrDecode
+	ErrWrite
+	ErrInvalidMsgCode
+	ErrInvalidMsgType
+	ErrLocalHandshake
+	ErrRemoteHandshake
+	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",
+	ErrLocalHandshake:  "Local handshake error",
+	ErrRemoteHandshake: "Remote handshake 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 (self Error) Error() (message string) {
+	if len(message) == 0 {
+		name, ok := errorToString[self.Code]
+		if !ok {
+			panic("invalid message code")
+		}
+		self.message = name
+		if self.format != "" {
+			self.message += ": " + fmt.Sprintf(self.format, self.params...)
+		}
+	}
+	return self.message
+}
+
+func errorf(code int, format string, params ...interface{}) *Error {
+	self := &Error{
+		Code:   code,
+		format: format,
+		params: params,
+	}
+
+	return self
+}
+
+// implements the code table spec
+// listing the message codes and types etc
+// and further metadata about the protocol
+type CodeMap struct {
+	Name       string                // name of the protocol
+	Version    uint                  // version
+	MaxMsgSize int                   // max length of message payload size
+	codes      []reflect.Type        // index of codes to msg types - to create zero values
+	messages   map[reflect.Type]uint // index of types to codes, for sending by type
+}
+
+func NewCodeMap(name string, version uint, maxMsgSize int, msgs ...interface{}) *CodeMap {
+	self := &CodeMap{
+		Name:       name,
+		Version:    version,
+		MaxMsgSize: maxMsgSize,
+		messages:   make(map[reflect.Type]uint),
+	}
+	self.Register(msgs...)
+	return self
+}
+
+func (self *CodeMap) Length() uint64 {
+	return uint64(len(self.codes))
+}
+
+func (self *CodeMap) Register(msgs ...interface{}) {
+	code := uint(len(self.codes))
+	for _, msg := range msgs {
+		typ := reflect.TypeOf(msg)
+		_, found := self.messages[typ]
+		if found {
+			// ignore duplicates
+			continue
+		}
+		// next code assigned to message type typ
+		self.messages[typ] = code
+		self.codes = append(self.codes, typ)
+		code++
+	}
+}
+
+// A Peer represents a remote peer or protocol instance that is running on a peer connection with
+// a remote peer
+type Peer struct {
+	ct         *CodeMap                                   // CodeMap for the protocol
+	*p2p.Peer                                             // the p2p.Peer object representing the remote
+	rw         p2p.MsgReadWriter                          // p2p.MsgReadWriter to send messages to and read messages from
+	handlers   map[reflect.Type][]func(interface{}) error //  message type -> message handler callback(s) map
+	disconnect func()                                     // Disconnect function set differently for testing
+	// lastActive time.Time                                  // tracking last active state
+}
+
+// NewPeer returns a new peer
+// this constructor is called by the p2p.Protocol#Run function
+// the first two arguments are comming the arguments passed to p2p.Protocol.Run function
+// the third argument is the CodeMap describing the protocol messages and options
+func NewPeer(p *p2p.Peer, rw p2p.MsgReadWriter, ct *CodeMap) *Peer {
+	return newPeer(p, rw, ct, func() {
+		p.Disconnect(p2p.DiscSubprotocolError)
+	})
+}
+
+// the disconnect function needs to be set differently for testing
+func NewTestPeer(p *p2p.Peer, rw p2p.MsgReadWriter, ct *CodeMap) *Peer {
+	return newPeer(p, rw, ct, func() {
+		rw.(*p2p.MsgPipeRW).Close()
+	})
+}
+
+func newPeer(p *p2p.Peer, rw p2p.MsgReadWriter, ct *CodeMap, disconn func()) *Peer {
+	return &Peer{
+		ct:         ct,
+		Peer:       p,
+		rw:         rw,
+		handlers:   make(map[reflect.Type][]func(interface{}) error),
+		disconnect: disconn,
+	}
+}
+
+// Register is called on the peer typically within the constructor of service instances running on peer connections
+// These constructors are called by the p2p.Protocol#Run function
+// It ties handler callbackss for specific message types
+// A message type can have several handlers registered by the same or different protocol services
+// Register is meant to be called once, deregistering is not currently supported therefore
+// handlers are assumed to be static across handshake renegotiations
+// i.e., a service instance either handles a message or not (irrespective of the handshake)
+// it panics if the message type is not defined in the CodeMap
+func (self *Peer) Register(msg interface{}, handler func(interface{}) error) uint {
+	typ := reflect.TypeOf(msg)
+	code, found := self.ct.messages[typ]
+	if !found {
+		panic(fmt.Sprintf("message type '%v' unknown ", typ))
+	}
+	glog.V(logger.Debug).Infof("registered handle for %v %v", msg, typ)
+	self.handlers[typ] = append(self.handlers[typ], handler)
+	return code
+}
+
+// Run starts the forever loop that handles incoming messages
+// called within the p2p.Protocol#Run function
+func (self *Peer) Run() error {
+	var err error
+	for {
+		_, err = self.handleIncoming()
+		if err != nil {
+			return err
+		}
+	}
+}
+
+// Drop disconnects a peer.
+// falls back to self.disconnect which is set as p2p.Peer#Disconnect except
+// for test peers where it calls p2p.MsgPipe#Close so that the readloop can terminate
+// TODO: may need to implement protocol drop only? don't want to kick off the peer
+// if they are useful for other protocols
+// overwrite Disconnect for testing, so that protocol readloop quits
+func (self *Peer) Drop() {
+	self.disconnect()
+}
+
+// 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 (self *Peer) Send(msg interface{}) error {
+	typ := reflect.TypeOf(msg)
+	code, found := self.ct.messages[typ]
+	if !found {
+		return errorf(ErrInvalidMsgType, "%v", typ)
+	}
+	glog.V(logger.Debug).Infof("=> %v %v (%d)", msg, typ, code)
+	err := p2p.Send(self.rw, uint64(code), msg)
+	if err != nil {
+		self.Drop()
+		return errorf(ErrWrite, "(msg code: %v): %v", code, err)
+	}
+	return nil
+}
+
+// handleIncoming(code)
+// is called each cycle of the main forever loop that handles and dispatches incoming messages
+// if this returns an error the loop returns and the peer is disconnected with the error
+// checks message size, out-of-range message codes, handles decoding with reflection,
+// call handlers as callback onside
+func (self *Peer) handleIncoming() (interface{}, error) {
+	msg, err := self.rw.ReadMsg()
+	glog.V(logger.Debug).Infof("<= %v", msg)
+	if err != nil {
+		return nil, err
+	}
+	// make sure that the payload has been fully consumed
+	defer msg.Discard()
+
+	if msg.Size > uint32(self.ct.MaxMsgSize) {
+		return nil, errorf(ErrMsgTooLong, "%v > %v", msg.Size, self.ct.MaxMsgSize)
+	}
+
+	// check if the message code is correct
+	maxMsgCode := uint(len(self.ct.messages))
+	if msg.Code >= uint64(maxMsgCode) {
+		return nil, errorf(ErrInvalidMsgCode, "%v (>=%v)", msg.Code, maxMsgCode)
+	}
+
+	// it is safe to be unsafe here
+	typ := self.ct.codes[msg.Code]
+	val := reflect.New(typ)
+	req := val.Elem()
+	req.Set(reflect.Zero(typ))
+	if err := msg.Decode(val.Interface()); err != nil {
+		return nil, errorf(ErrDecode, "<= %v: %v", msg, err)
+	}
+	glog.V(logger.Debug).Infof("<= %v %v (%d)", req, typ, msg.Code)
+
+	// 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
+	for _, f := range self.handlers[typ] {
+		glog.V(6).Infof("handler for %v", typ)
+		err = f(req.Interface())
+		if err != nil {
+			return nil, errorf(ErrHandler, "(msg code %v): %v", msg.Code, err)
+		}
+	}
+	return req.Interface(), nil
+}
+
+// Handshake initiates a handshake on the peer connection
+// * the argument is the local  handshake 	to be sent to the remote peer
+// * expects a remote handshake back of the same type
+// returns the remote hs and an error
+func (self *Peer) Handshake(hs interface{}) (interface{}, error) {
+	typ := reflect.TypeOf(hs)
+	_, found := self.ct.messages[typ]
+	if !found {
+		return nil, errorf(ErrLocalHandshake, "unknown handshake message type: %v", typ)
+	}
+	err := self.Send(hs)
+	if err != nil {
+		return nil, errorf(ErrLocalHandshake, "cannot send: %v", err)
+	}
+	// receiving and validating remote handshake, expect code
+	rhs, err := self.handleIncoming()
+	if err != nil {
+		return nil, errorf(ErrRemoteHandshake, "'%v': %v", self.ct.Name, err)
+	}
+	return rhs, nil
+}