core/forkid: implement the forkid EIP, announce via ENR (#19738)

* eth: chain config (genesis + fork) ENR entry

* core/forkid, eth: protocol independent fork ID, update to CRC32 spec

* core/forkid, eth: make forkid a struct, next uint64, enr struct, RLP

* core/forkid: change forkhash rlp encoding from int to [4]byte

* eth: fixup eth entry a bit and update it every block

* eth: fix lint

* eth: fix crash in ethclient tests

6 files changed, 123 insertions, 94 deletions

diff --git a/eth/backend.go b/eth/backend.go
index a3275caca..dc4ff8ade 100644
--- a/eth/backend.go
+++ b/eth/backend.go
@@ -47,6 +47,7 @@ import (
 	"github.com/ethereum/go-ethereum/miner"
 	"github.com/ethereum/go-ethereum/node"
 	"github.com/ethereum/go-ethereum/p2p"
+	"github.com/ethereum/go-ethereum/p2p/enr"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/ethereum/go-ethereum/rpc"
@@ -66,7 +67,9 @@ type Ethereum struct {
 	config *Config
 
 	// Channel for shutting down the service
-	shutdownChan chan bool // Channel for shutting down the Ethereum
+	shutdownChan chan bool
+
+	server *p2p.Server
 
 	// Handlers
 	txPool          *core.TxPool
@@ -496,7 +499,7 @@ func (s *Ethereum) EventMux() *event.TypeMux           { return s.eventMux }
 func (s *Ethereum) Engine() consensus.Engine           { return s.engine }
 func (s *Ethereum) ChainDb() ethdb.Database            { return s.chainDb }
 func (s *Ethereum) IsListening() bool                  { return true } // Always listening
-func (s *Ethereum) EthVersion() int                    { return int(s.protocolManager.SubProtocols[0].Version) }
+func (s *Ethereum) EthVersion() int                    { return int(ProtocolVersions[0]) }
 func (s *Ethereum) NetVersion() uint64                 { return s.networkID }
 func (s *Ethereum) Downloader() *downloader.Downloader { return s.protocolManager.downloader }
 func (s *Ethereum) Synced() bool                       { return atomic.LoadUint32(&s.protocolManager.acceptTxs) == 1 }
@@ -505,15 +508,22 @@ func (s *Ethereum) ArchiveMode() bool                  { return s.config.NoPruni
 // Protocols implements node.Service, returning all the currently configured
 // network protocols to start.
 func (s *Ethereum) Protocols() []p2p.Protocol {
-	if s.lesServer == nil {
-		return s.protocolManager.SubProtocols
+	protos := make([]p2p.Protocol, len(ProtocolVersions))
+	for i, vsn := range ProtocolVersions {
+		protos[i] = s.protocolManager.makeProtocol(vsn)
+		protos[i].Attributes = []enr.Entry{s.currentEthEntry()}
+	}
+	if s.lesServer != nil {
+		protos = append(protos, s.lesServer.Protocols()...)
 	}
-	return append(s.protocolManager.SubProtocols, s.lesServer.Protocols()...)
+	return protos
 }
 
 // Start implements node.Service, starting all internal goroutines needed by the
 // Ethereum protocol implementation.
 func (s *Ethereum) Start(srvr *p2p.Server) error {
+	s.startEthEntryUpdate(srvr.LocalNode())
+
 	// Start the bloom bits servicing goroutines
 	s.startBloomHandlers(params.BloomBitsBlocks)
 
diff --git a/eth/enr_entry.go b/eth/enr_entry.go
new file mode 100644
index 000000000..d9e7b9578
--- /dev/null
+++ b/eth/enr_entry.go
@@ -0,0 +1,61 @@
+// Copyright 2019 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 eth
+
+import (
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/core/forkid"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+// ethEntry is the "eth" ENR entry which advertises eth protocol
+// on the discovery network.
+type ethEntry struct {
+	ForkID forkid.ID // Fork identifier per EIP-2124
+
+	// Ignore additional fields (for forward compatibility).
+	Rest []rlp.RawValue `rlp:"tail"`
+}
+
+// ENRKey implements enr.Entry.
+func (e ethEntry) ENRKey() string {
+	return "eth"
+}
+
+func (eth *Ethereum) startEthEntryUpdate(ln *enode.LocalNode) {
+	var newHead = make(chan core.ChainHeadEvent, 10)
+	sub := eth.blockchain.SubscribeChainHeadEvent(newHead)
+
+	go func() {
+		defer sub.Unsubscribe()
+		for {
+			select {
+			case <-newHead:
+				ln.Set(eth.currentEthEntry())
+			case <-sub.Err():
+				// Would be nice to sync with eth.Stop, but there is no
+				// good way to do that.
+				return
+			}
+		}
+	}()
+}
+
+func (eth *Ethereum) currentEthEntry() *ethEntry {
+	return &ethEntry{ForkID: forkid.NewID(eth.blockchain)}
+}
diff --git a/eth/handler.go b/eth/handler.go
index fe9f8b53b..4ce2d1c82 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -58,10 +58,6 @@ var (
 	syncChallengeTimeout = 15 * time.Second // Time allowance for a node to reply to the sync progress challenge
 )
 
-// errIncompatibleConfig is returned if the requested protocols and configs are
-// not compatible (low protocol version restrictions and high requirements).
-var errIncompatibleConfig = errors.New("incompatible configuration")
-
 func errResp(code errCode, format string, v ...interface{}) error {
 	return fmt.Errorf("%v - %v", code, fmt.Sprintf(format, v...))
 }
@@ -75,17 +71,14 @@ type ProtocolManager struct {
 	checkpointNumber uint64      // Block number for the sync progress validator to cross reference
 	checkpointHash   common.Hash // Block hash for the sync progress validator to cross reference
 
-	txpool      txPool
-	blockchain  *core.BlockChain
-	chainconfig *params.ChainConfig
-	maxPeers    int
+	txpool     txPool
+	blockchain *core.BlockChain
+	maxPeers   int
 
 	downloader *downloader.Downloader
 	fetcher    *fetcher.Fetcher
 	peers      *peerSet
 
-	SubProtocols []p2p.Protocol
-
 	eventMux      *event.TypeMux
 	txsCh         chan core.NewTxsEvent
 	txsSub        event.Subscription
@@ -113,7 +106,6 @@ func NewProtocolManager(config *params.ChainConfig, checkpoint *params.TrustedCh
 		eventMux:    mux,
 		txpool:      txpool,
 		blockchain:  blockchain,
-		chainconfig: config,
 		peers:       newPeerSet(),
 		whitelist:   whitelist,
 		newPeerCh:   make(chan *peer),
@@ -149,45 +141,7 @@ func NewProtocolManager(config *params.ChainConfig, checkpoint *params.TrustedCh
 		manager.checkpointNumber = (checkpoint.SectionIndex+1)*params.CHTFrequency - 1
 		manager.checkpointHash = checkpoint.SectionHead
 	}
-	// Initiate a sub-protocol for every implemented version we can handle
-	manager.SubProtocols = make([]p2p.Protocol, 0, len(ProtocolVersions))
-	for i, version := range ProtocolVersions {
-		// Skip protocol version if incompatible with the mode of operation
-		// TODO(karalabe): hard-drop eth/62 from the code base
-		if atomic.LoadUint32(&manager.fastSync) == 1 && version < eth63 {
-			continue
-		}
-		// Compatible; initialise the sub-protocol
-		version := version // Closure for the run
-		manager.SubProtocols = append(manager.SubProtocols, p2p.Protocol{
-			Name:    ProtocolName,
-			Version: version,
-			Length:  ProtocolLengths[i],
-			Run: func(p *p2p.Peer, rw p2p.MsgReadWriter) error {
-				peer := manager.newPeer(int(version), p, rw)
-				select {
-				case manager.newPeerCh <- peer:
-					manager.wg.Add(1)
-					defer manager.wg.Done()
-					return manager.handle(peer)
-				case <-manager.quitSync:
-					return p2p.DiscQuitting
-				}
-			},
-			NodeInfo: func() interface{} {
-				return manager.NodeInfo()
-			},
-			PeerInfo: func(id enode.ID) interface{} {
-				if p := manager.peers.Peer(fmt.Sprintf("%x", id[:8])); p != nil {
-					return p.Info()
-				}
-				return nil
-			},
-		})
-	}
-	if len(manager.SubProtocols) == 0 {
-		return nil, errIncompatibleConfig
-	}
+
 	// Construct the downloader (long sync) and its backing state bloom if fast
 	// sync is requested. The downloader is responsible for deallocating the state
 	// bloom when it's done.
@@ -235,6 +189,39 @@ func NewProtocolManager(config *params.ChainConfig, checkpoint *params.TrustedCh
 	return manager, nil
 }
 
+func (pm *ProtocolManager) makeProtocol(version uint) p2p.Protocol {
+	length, ok := protocolLengths[version]
+	if !ok {
+		panic("makeProtocol for unknown version")
+	}
+
+	return p2p.Protocol{
+		Name:    protocolName,
+		Version: version,
+		Length:  length,
+		Run: func(p *p2p.Peer, rw p2p.MsgReadWriter) error {
+			peer := pm.newPeer(int(version), p, rw)
+			select {
+			case pm.newPeerCh <- peer:
+				pm.wg.Add(1)
+				defer pm.wg.Done()
+				return pm.handle(peer)
+			case <-pm.quitSync:
+				return p2p.DiscQuitting
+			}
+		},
+		NodeInfo: func() interface{} {
+			return pm.NodeInfo()
+		},
+		PeerInfo: func(id enode.ID) interface{} {
+			if p := pm.peers.Peer(fmt.Sprintf("%x", id[:8])); p != nil {
+				return p.Info()
+			}
+			return nil
+		},
+	}
+}
+
 func (pm *ProtocolManager) removePeer(id string) {
 	// Short circuit if the peer was already removed
 	peer := pm.peers.Peer(id)
@@ -381,8 +368,8 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 	if err != nil {
 		return err
 	}
-	if msg.Size > ProtocolMaxMsgSize {
-		return errResp(ErrMsgTooLarge, "%v > %v", msg.Size, ProtocolMaxMsgSize)
+	if msg.Size > protocolMaxMsgSize {
+		return errResp(ErrMsgTooLarge, "%v > %v", msg.Size, protocolMaxMsgSize)
 	}
 	defer msg.Discard()
 
diff --git a/eth/handler_test.go b/eth/handler_test.go
index 445d52afc..0f1672fd4 100644
--- a/eth/handler_test.go
+++ b/eth/handler_test.go
@@ -38,35 +38,6 @@ import (
 	"github.com/ethereum/go-ethereum/params"
 )
 
-// Tests that protocol versions and modes of operations are matched up properly.
-func TestProtocolCompatibility(t *testing.T) {
-	// Define the compatibility chart
-	tests := []struct {
-		version    uint
-		mode       downloader.SyncMode
-		compatible bool
-	}{
-		{61, downloader.FullSync, true}, {62, downloader.FullSync, true}, {63, downloader.FullSync, true},
-		{61, downloader.FastSync, false}, {62, downloader.FastSync, false}, {63, downloader.FastSync, true},
-	}
-	// Make sure anything we screw up is restored
-	backup := ProtocolVersions
-	defer func() { ProtocolVersions = backup }()
-
-	// Try all available compatibility configs and check for errors
-	for i, tt := range tests {
-		ProtocolVersions = []uint{tt.version}
-
-		pm, _, err := newTestProtocolManager(tt.mode, 0, nil, nil)
-		if pm != nil {
-			defer pm.Stop()
-		}
-		if (err == nil && !tt.compatible) || (err != nil && tt.compatible) {
-			t.Errorf("test %d: compatibility mismatch: have error %v, want compatibility %v", i, err, tt.compatible)
-		}
-	}
-}
-
 // Tests that block headers can be retrieved from a remote chain based on user queries.
 func TestGetBlockHeaders62(t *testing.T) { testGetBlockHeaders(t, 62) }
 func TestGetBlockHeaders63(t *testing.T) { testGetBlockHeaders(t, 63) }
diff --git a/eth/peer.go b/eth/peer.go
index 208badc5e..814c787b8 100644
--- a/eth/peer.go
+++ b/eth/peer.go
@@ -394,8 +394,8 @@ func (p *peer) readStatus(network uint64, status *statusData, genesis common.Has
 	if msg.Code != StatusMsg {
 		return errResp(ErrNoStatusMsg, "first msg has code %x (!= %x)", msg.Code, StatusMsg)
 	}
-	if msg.Size > ProtocolMaxMsgSize {
-		return errResp(ErrMsgTooLarge, "%v > %v", msg.Size, ProtocolMaxMsgSize)
+	if msg.Size > protocolMaxMsgSize {
+		return errResp(ErrMsgTooLarge, "%v > %v", msg.Size, protocolMaxMsgSize)
 	}
 	// Decode the handshake and make sure everything matches
 	if err := msg.Decode(&status); err != nil {
diff --git a/eth/protocol.go b/eth/protocol.go
index 5beb562f8..de0c979d8 100644
--- a/eth/protocol.go
+++ b/eth/protocol.go
@@ -34,16 +34,16 @@ const (
 	eth63 = 63
 )
 
-// ProtocolName is the official short name of the protocol used during capability negotiation.
-var ProtocolName = "eth"
+// protocolName is the official short name of the protocol used during capability negotiation.
+const protocolName = "eth"
 
 // ProtocolVersions are the supported versions of the eth protocol (first is primary).
-var ProtocolVersions = []uint{eth63, eth62}
+var ProtocolVersions = []uint{eth63}
 
-// ProtocolLengths are the number of implemented message corresponding to different protocol versions.
-var ProtocolLengths = []uint64{17, 8}
+// protocolLengths are the number of implemented message corresponding to different protocol versions.
+var protocolLengths = map[uint]uint64{eth63: 17, eth62: 8}
 
-const ProtocolMaxMsgSize = 10 * 1024 * 1024 // Maximum cap on the size of a protocol message
+const protocolMaxMsgSize = 10 * 1024 * 1024 // Maximum cap on the size of a protocol message
 
 // eth protocol message codes
 const (