p2p: add connectivity docs and protocol-level Prefer channel

p2p/doc.go

@@ -0,0 +1,61 @@
+// Copyright 2015 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 p2p implements the devp2p protocol suite.
+
+The devp2p suite is a framework for the definition of RLP-based
+peer-to-peer protocols.
+
+From Nodes to Peers and Protocols
+
+Devp2p distinguishes nodes and peers. A node is any devp2p-capable
+host participating in the network. Peers are nodes to which a
+connection has been established. Nodes are identified by their Node
+ID, a secp256k1 public key.
+
+On any particular connection, one or more protocols are spoken. The
+protocols understood by the local node are declared when creating the
+local Server. When the connection is established, the sets of
+available protocols are matched against each other and the Run
+function of each protocol present on both sides is launched.
+
+RLPx
+
+Connections between peers use the RLPx wire protocol, which provides
+an encrypted and authenticated communication channel over TCP. RLPx
+supports concurrent transfer of protocol messages, ensuring that all
+protocols get an equal share of the available bandwidth.
+
+Connection Handling
+
+Package p2p establishes peer connections automatically by selecting
+randomly from the pool of all existing nodes in the network. The
+connectivity graph approaches an unstructured network with low
+diameter. If a protocol requires stronger connectivity properties
+(e.g. when building a structured overlay), the protocol implementation
+should provide information about preferred nodes on its Prefer channel.
+
+In order to accomodate new nodes joining the network, non-preferred
+peer connections may be terminated under certain conditions. Protocol
+implementations are free to terminate connections at any time by
+simply returning from the Run function.
+
+Users can configure static connectivity targets through the AddPeer
+method of Server. It will attempt to keep such nodes connected at all
+times.
+*/
+package p2p

p2p/protocol.go

@@ -35,22 +35,30 @@ type Protocol struct {
 	// by the protocol.
 	Length uint64
 
-	// Run is called in a new groutine when the protocol has been
+	// Run is called in a new goroutine when the protocol has been
 	// negotiated with a peer. It should read and write messages from
 	// rw. The Payload for each message must be fully consumed.
 	//
-	// The peer connection is closed when Start returns. It should return
+	// The peer connection is closed when Run returns. It should return
 	// any protocol-level error (such as an I/O error) that is
 	// encountered.
 	Run func(peer *Peer, rw MsgReadWriter) error
 
-	// NodeInfo is an optional helper method to retrieve protocol specific metadata
-	// about the host node.
+	// Prefer, if non-nil, should receive nodes that the protocol
+	// implementation wants to be connected to. If a preferred node is
+	// not connected yet, package p2p will attempt to establish a
+	// connection. A successful send on this channel does not
+	// guarantee that a connection will actually be established.
+	Prefer <-chan *discover.Node
+
+	// NodeInfo is an optional helper method to retrieve protocol
+	// specific metadata about the host node.
 	NodeInfo func() interface{}
 
-	// PeerInfo is an optional helper method to retrieve protocol specific metadata
-	// about a certain peer in the network. If an info retrieval function is set,
-	// but returns nil, it is assumed that the protocol handshake is still running.
+	// PeerInfo is an optional helper method to retrieve protocol
+	// specific metadata about a certain peer in the network. If an
+	// info retrieval function is set, but returns nil, it is assumed
+	// that the protocol handshake is still running.
 	PeerInfo func(id discover.NodeID) interface{}
 }
 

p2p/server.go

@@ -14,7 +14,6 @@
 // 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 p2p implements the Ethereum p2p network protocols.
 package p2p
 
 import (