p2p: new dialer, peer management without locks

The most visible change is event-based dialing, which should be an
improvement over the timer-based system that we have at the moment.
The dialer gets a chance to compute new tasks whenever peers change or
dials complete. This is better than checking peers on a timer because
dials happen faster. The dialer can now make more precise decisions
about whom to dial based on the peer set and we can test those
decisions without actually opening any sockets.

Peer management is easier to test because the tests can inject
connections at checkpoints (after enc handshake, after protocol
handshake).

Most of the handshake stuff is now part of the RLPx code. It could be
exported or move to its own package because it is no longer entangled
with Server logic.

p2p/peer_error.go

@@ -5,39 +5,17 @@ import (
 )
 
 const (
-	errMagicTokenMismatch = iota
-	errRead
-	errWrite
-	errMisc
-	errInvalidMsgCode
+	errInvalidMsgCode = iota
 	errInvalidMsg
-	errP2PVersionMismatch
-	errPubkeyInvalid
-	errPubkeyForbidden
-	errProtocolBreach
-	errPingTimeout
-	errInvalidNetworkId
-	errInvalidProtocolVersion
 )
 
 var errorToString = map[int]string{
-	errMagicTokenMismatch:     "magic token mismatch",
-	errRead:                   "read error",
-	errWrite:                  "write error",
-	errMisc:                   "misc error",
-	errInvalidMsgCode:         "invalid message code",
-	errInvalidMsg:             "invalid message",
-	errP2PVersionMismatch:     "P2P Version Mismatch",
-	errPubkeyInvalid:          "public key invalid",
-	errPubkeyForbidden:        "public key forbidden",
-	errProtocolBreach:         "protocol Breach",
-	errPingTimeout:            "ping timeout",
-	errInvalidNetworkId:       "invalid network id",
-	errInvalidProtocolVersion: "invalid protocol version",
+	errInvalidMsgCode: "invalid message code",
+	errInvalidMsg:     "invalid message",
 }
 
 type peerError struct {
-	Code    int
+	code    int
 	message string
 }
 
@@ -107,23 +85,13 @@ func discReasonForError(err error) DiscReason {
 		return reason
 	}
 	peerError, ok := err.(*peerError)
-	if !ok {
-		return DiscSubprotocolError
-	}
-	switch peerError.Code {
-	case errP2PVersionMismatch:
-		return DiscIncompatibleVersion
-	case errPubkeyInvalid:
-		return DiscInvalidIdentity
-	case errPubkeyForbidden:
-		return DiscUselessPeer
-	case errInvalidMsgCode, errMagicTokenMismatch, errProtocolBreach:
-		return DiscProtocolError
-	case errPingTimeout:
-		return DiscReadTimeout
-	case errRead, errWrite:
-		return DiscNetworkError
-	default:
-		return DiscSubprotocolError
+	if ok {
+		switch peerError.code {
+		case errInvalidMsgCode, errInvalidMsg:
+			return DiscProtocolError
+		default:
+			return DiscSubprotocolError
+		}
 	}
+	return DiscSubprotocolError
 }