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

3 files changed, 442 insertions, 1 deletions

diff --git a/core/blockchain.go b/core/blockchain.go
index 8b7c2e615..59be35589 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -2146,7 +2146,7 @@ func (bc *BlockChain) GetHeaderByNumber(number uint64) *types.Header {
 	return bc.hc.GetHeaderByNumber(number)
 }
 
-// Config retrieves the blockchain's chain configuration.
+// Config retrieves the chain's fork configuration.
 func (bc *BlockChain) Config() *params.ChainConfig { return bc.chainConfig }
 
 // Engine retrieves the blockchain's consensus engine.
diff --git a/core/forkid/forkid.go b/core/forkid/forkid.go
new file mode 100644
index 000000000..8c1700879
--- /dev/null
+++ b/core/forkid/forkid.go
@@ -0,0 +1,236 @@
+// 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 forkid implements EIP-2124 (https://eips.ethereum.org/EIPS/eip-2124).
+package forkid
+
+import (
+	"encoding/binary"
+	"errors"
+	"hash/crc32"
+	"math"
+	"math/big"
+	"reflect"
+	"strings"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+var (
+	// ErrRemoteStale is returned by the validator if a remote fork checksum is a
+	// subset of our already applied forks, but the announced next fork block is
+	// not on our already passed chain.
+	ErrRemoteStale = errors.New("remote needs update")
+
+	// ErrLocalIncompatibleOrStale is returned by the validator if a remote fork
+	// checksum does not match any local checksum variation, signalling that the
+	// two chains have diverged in the past at some point (possibly at genesis).
+	ErrLocalIncompatibleOrStale = errors.New("local incompatible or needs update")
+)
+
+// ID is a fork identifier as defined by EIP-2124.
+type ID struct {
+	Hash [4]byte // CRC32 checksum of the genesis block and passed fork block numbers
+	Next uint64  // Block number of the next upcoming fork, or 0 if no forks are known
+}
+
+// NewID calculates the Ethereum fork ID from the chain config and head.
+func NewID(chain *core.BlockChain) ID {
+	return newID(
+		chain.Config(),
+		chain.Genesis().Hash(),
+		chain.CurrentHeader().Number.Uint64(),
+	)
+}
+
+// newID is the internal version of NewID, which takes extracted values as its
+// arguments instead of a chain. The reason is to allow testing the IDs without
+// having to simulate an entire blockchain.
+func newID(config *params.ChainConfig, genesis common.Hash, head uint64) ID {
+	// Calculate the starting checksum from the genesis hash
+	hash := crc32.ChecksumIEEE(genesis[:])
+
+	// Calculate the current fork checksum and the next fork block
+	var next uint64
+	for _, fork := range gatherForks(config) {
+		if fork <= head {
+			// Fork already passed, checksum the previous hash and the fork number
+			hash = checksumUpdate(hash, fork)
+			continue
+		}
+		next = fork
+		break
+	}
+	return ID{Hash: checksumToBytes(hash), Next: next}
+}
+
+// NewFilter creates an filter that returns if a fork ID should be rejected or not
+// based on the local chain's status.
+func NewFilter(chain *core.BlockChain) func(id ID) error {
+	return newFilter(
+		chain.Config(),
+		chain.Genesis().Hash(),
+		func() uint64 {
+			return chain.CurrentHeader().Number.Uint64()
+		},
+	)
+}
+
+// newFilter is the internal version of NewFilter, taking closures as its arguments
+// instead of a chain. The reason is to allow testing it without having to simulate
+// an entire blockchain.
+func newFilter(config *params.ChainConfig, genesis common.Hash, headfn func() uint64) func(id ID) error {
+	// Calculate the all the valid fork hash and fork next combos
+	var (
+		forks = gatherForks(config)
+		sums  = make([][4]byte, len(forks)+1) // 0th is the genesis
+	)
+	hash := crc32.ChecksumIEEE(genesis[:])
+	sums[0] = checksumToBytes(hash)
+	for i, fork := range forks {
+		hash = checksumUpdate(hash, fork)
+		sums[i+1] = checksumToBytes(hash)
+	}
+	// Add two sentries to simplify the fork checks and don't require special
+	// casing the last one.
+	forks = append(forks, math.MaxUint64) // Last fork will never be passed
+
+	// Create a validator that will filter out incompatible chains
+	return func(id ID) error {
+		// Run the fork checksum validation ruleset:
+		//   1. If local and remote FORK_CSUM matches, connect.
+		//        The two nodes are in the same fork state currently. They might know
+		//        of differing future forks, but that's not relevant until the fork
+		//        triggers (might be postponed, nodes might be updated to match).
+		//   2. If the remote FORK_CSUM is a subset of the local past forks and the
+		//      remote FORK_NEXT matches with the locally following fork block number,
+		//      connect.
+		//        Remote node is currently syncing. It might eventually diverge from
+		//        us, but at this current point in time we don't have enough information.
+		//   3. If the remote FORK_CSUM is a superset of the local past forks and can
+		//      be completed with locally known future forks, connect.
+		//        Local node is currently syncing. It might eventually diverge from
+		//        the remote, but at this current point in time we don't have enough
+		//        information.
+		//   4. Reject in all other cases.
+		head := headfn()
+		for i, fork := range forks {
+			// If our head is beyond this fork, continue to the next (we have a dummy
+			// fork of maxuint64 as the last item to always fail this check eventually).
+			if head > fork {
+				continue
+			}
+			// Found the first unpassed fork block, check if our current state matches
+			// the remote checksum (rule #1).
+			if sums[i] == id.Hash {
+				// Yay, fork checksum matched, ignore any upcoming fork
+				return nil
+			}
+			// The local and remote nodes are in different forks currently, check if the
+			// remote checksum is a subset of our local forks (rule #2).
+			for j := 0; j < i; j++ {
+				if sums[j] == id.Hash {
+					// Remote checksum is a subset, validate based on the announced next fork
+					if forks[j] != id.Next {
+						return ErrRemoteStale
+					}
+					return nil
+				}
+			}
+			// Remote chain is not a subset of our local one, check if it's a superset by
+			// any chance, signalling that we're simply out of sync (rule #3).
+			for j := i + 1; j < len(sums); j++ {
+				if sums[j] == id.Hash {
+					// Yay, remote checksum is a superset, ignore upcoming forks
+					return nil
+				}
+			}
+			// No exact, subset or superset match. We are on differing chains, reject.
+			return ErrLocalIncompatibleOrStale
+		}
+		log.Error("Impossible fork ID validation", "id", id)
+		return nil // Something's very wrong, accept rather than reject
+	}
+}
+
+// checksum calculates the IEEE CRC32 checksum of a block number.
+func checksum(fork uint64) uint32 {
+	var blob [8]byte
+	binary.BigEndian.PutUint64(blob[:], fork)
+	return crc32.ChecksumIEEE(blob[:])
+}
+
+// checksumUpdate calculates the next IEEE CRC32 checksum based on the previous
+// one and a fork block number (equivalent to CRC32(original-blob || fork)).
+func checksumUpdate(hash uint32, fork uint64) uint32 {
+	var blob [8]byte
+	binary.BigEndian.PutUint64(blob[:], fork)
+	return crc32.Update(hash, crc32.IEEETable, blob[:])
+}
+
+// checksumToBytes converts a uint32 checksum into a [4]byte array.
+func checksumToBytes(hash uint32) [4]byte {
+	var blob [4]byte
+	binary.BigEndian.PutUint32(blob[:], hash)
+	return blob
+}
+
+// gatherForks gathers all the known forks and creates a sorted list out of them.
+func gatherForks(config *params.ChainConfig) []uint64 {
+	// Gather all the fork block numbers via reflection
+	kind := reflect.TypeOf(params.ChainConfig{})
+	conf := reflect.ValueOf(config).Elem()
+
+	var forks []uint64
+	for i := 0; i < kind.NumField(); i++ {
+		// Fetch the next field and skip non-fork rules
+		field := kind.Field(i)
+		if !strings.HasSuffix(field.Name, "Block") {
+			continue
+		}
+		if field.Type != reflect.TypeOf(new(big.Int)) {
+			continue
+		}
+		// Extract the fork rule block number and aggregate it
+		rule := conf.Field(i).Interface().(*big.Int)
+		if rule != nil {
+			forks = append(forks, rule.Uint64())
+		}
+	}
+	// Sort the fork block numbers to permit chronologival XOR
+	for i := 0; i < len(forks); i++ {
+		for j := i + 1; j < len(forks); j++ {
+			if forks[i] > forks[j] {
+				forks[i], forks[j] = forks[j], forks[i]
+			}
+		}
+	}
+	// Deduplicate block numbers applying multiple forks
+	for i := 1; i < len(forks); i++ {
+		if forks[i] == forks[i-1] {
+			forks = append(forks[:i], forks[i+1:]...)
+			i--
+		}
+	}
+	// Skip any forks in block 0, that's the genesis ruleset
+	if len(forks) > 0 && forks[0] == 0 {
+		forks = forks[1:]
+	}
+	return forks
+}
diff --git a/core/forkid/forkid_test.go b/core/forkid/forkid_test.go
new file mode 100644
index 000000000..b33f85bec
--- /dev/null
+++ b/core/forkid/forkid_test.go
@@ -0,0 +1,205 @@
+// 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 forkid
+
+import (
+	"bytes"
+	"math"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/params"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+// TestCreation tests that different genesis and fork rule combinations result in
+// the correct fork ID.
+func TestCreation(t *testing.T) {
+	type testcase struct {
+		head uint64
+		want ID
+	}
+	tests := []struct {
+		config  *params.ChainConfig
+		genesis common.Hash
+		cases   []testcase
+	}{
+		// Mainnet test cases
+		{
+			params.MainnetChainConfig,
+			params.MainnetGenesisHash,
+			[]testcase{
+				{0, ID{Hash: checksumToBytes(0xfc64ec04), Next: 1150000}},       // Unsynced
+				{1149999, ID{Hash: checksumToBytes(0xfc64ec04), Next: 1150000}}, // Last Frontier block
+				{1150000, ID{Hash: checksumToBytes(0x97c2c34c), Next: 1920000}}, // First Homestead block
+				{1919999, ID{Hash: checksumToBytes(0x97c2c34c), Next: 1920000}}, // Last Homestead block
+				{1920000, ID{Hash: checksumToBytes(0x91d1f948), Next: 2463000}}, // First DAO block
+				{2462999, ID{Hash: checksumToBytes(0x91d1f948), Next: 2463000}}, // Last DAO block
+				{2463000, ID{Hash: checksumToBytes(0x7a64da13), Next: 2675000}}, // First Tangerine block
+				{2674999, ID{Hash: checksumToBytes(0x7a64da13), Next: 2675000}}, // Last Tangerine block
+				{2675000, ID{Hash: checksumToBytes(0x3edd5b10), Next: 4370000}}, // First Spurious block
+				{4369999, ID{Hash: checksumToBytes(0x3edd5b10), Next: 4370000}}, // Last Spurious block
+				{4370000, ID{Hash: checksumToBytes(0xa00bc324), Next: 7280000}}, // First Byzantium block
+				{7279999, ID{Hash: checksumToBytes(0xa00bc324), Next: 7280000}}, // Last Byzantium block
+				{7280000, ID{Hash: checksumToBytes(0x668db0af), Next: 0}},       // First and last Constantinople, first Petersburg block
+				{7987396, ID{Hash: checksumToBytes(0x668db0af), Next: 0}},       // Today Petersburg block
+			},
+		},
+		// Ropsten test cases
+		{
+			params.TestnetChainConfig,
+			params.TestnetGenesisHash,
+			[]testcase{
+				{0, ID{Hash: checksumToBytes(0x30c7ddbc), Next: 10}},            // Unsynced, last Frontier, Homestead and first Tangerine block
+				{9, ID{Hash: checksumToBytes(0x30c7ddbc), Next: 10}},            // Last Tangerine block
+				{10, ID{Hash: checksumToBytes(0x63760190), Next: 1700000}},      // First Spurious block
+				{1699999, ID{Hash: checksumToBytes(0x63760190), Next: 1700000}}, // Last Spurious block
+				{1700000, ID{Hash: checksumToBytes(0x3ea159c7), Next: 4230000}}, // First Byzantium block
+				{4229999, ID{Hash: checksumToBytes(0x3ea159c7), Next: 4230000}}, // Last Byzantium block
+				{4230000, ID{Hash: checksumToBytes(0x97b544f3), Next: 4939394}}, // First Constantinople block
+				{4939393, ID{Hash: checksumToBytes(0x97b544f3), Next: 4939394}}, // Last Constantinople block
+				{4939394, ID{Hash: checksumToBytes(0xd6e2149b), Next: 0}},       // First Petersburg block
+				{5822692, ID{Hash: checksumToBytes(0xd6e2149b), Next: 0}},       // Today Petersburg block
+			},
+		},
+		// Rinkeby test cases
+		{
+			params.RinkebyChainConfig,
+			params.RinkebyGenesisHash,
+			[]testcase{
+				{0, ID{Hash: checksumToBytes(0x3b8e0691), Next: 1}},             // Unsynced, last Frontier block
+				{1, ID{Hash: checksumToBytes(0x60949295), Next: 2}},             // First and last Homestead block
+				{2, ID{Hash: checksumToBytes(0x8bde40dd), Next: 3}},             // First and last Tangerine block
+				{3, ID{Hash: checksumToBytes(0xcb3a64bb), Next: 1035301}},       // First Spurious block
+				{1035300, ID{Hash: checksumToBytes(0xcb3a64bb), Next: 1035301}}, // Last Spurious block
+				{1035301, ID{Hash: checksumToBytes(0x8d748b57), Next: 3660663}}, // First Byzantium block
+				{3660662, ID{Hash: checksumToBytes(0x8d748b57), Next: 3660663}}, // Last Byzantium block
+				{3660663, ID{Hash: checksumToBytes(0xe49cab14), Next: 4321234}}, // First Constantinople block
+				{4321233, ID{Hash: checksumToBytes(0xe49cab14), Next: 4321234}}, // Last Constantinople block
+				{4321234, ID{Hash: checksumToBytes(0xafec6b27), Next: 0}},       // First Petersburg block
+				{4586649, ID{Hash: checksumToBytes(0xafec6b27), Next: 0}},       // Today Petersburg block
+			},
+		},
+		// Goerli test cases
+		{
+			params.GoerliChainConfig,
+			params.GoerliGenesisHash,
+			[]testcase{
+				{0, ID{Hash: checksumToBytes(0xa3f5ab08), Next: 0}},      // Unsynced, last Frontier, Homestead, Tangerine, Spurious, Byzantium, Constantinople and first Petersburg block
+				{795329, ID{Hash: checksumToBytes(0xa3f5ab08), Next: 0}}, // Today Petersburg block
+			},
+		},
+	}
+	for i, tt := range tests {
+		for j, ttt := range tt.cases {
+			if have := newID(tt.config, tt.genesis, ttt.head); have != ttt.want {
+				t.Errorf("test %d, case %d: fork ID mismatch: have %x, want %x", i, j, have, ttt.want)
+			}
+		}
+	}
+}
+
+// TestValidation tests that a local peer correctly validates and accepts a remote
+// fork ID.
+func TestValidation(t *testing.T) {
+	tests := []struct {
+		head uint64
+		id   ID
+		err  error
+	}{
+		// Local is mainnet Petersburg, remote announces the same. No future fork is announced.
+		{7987396, ID{Hash: checksumToBytes(0x668db0af), Next: 0}, nil},
+
+		// Local is mainnet Petersburg, remote announces the same. Remote also announces a next fork
+		// at block 0xffffffff, but that is uncertain.
+		{7987396, ID{Hash: checksumToBytes(0x668db0af), Next: math.MaxUint64}, nil},
+
+		// Local is mainnet currently in Byzantium only (so it's aware of Petersburg), remote announces
+		// also Byzantium, but it's not yet aware of Petersburg (e.g. non updated node before the fork).
+		// In this case we don't know if Petersburg passed yet or not.
+		{7279999, ID{Hash: checksumToBytes(0xa00bc324), Next: 0}, nil},
+
+		// Local is mainnet currently in Byzantium only (so it's aware of Petersburg), remote announces
+		// also Byzantium, and it's also aware of Petersburg (e.g. updated node before the fork). We
+		// don't know if Petersburg passed yet (will pass) or not.
+		{7279999, ID{Hash: checksumToBytes(0xa00bc324), Next: 7280000}, nil},
+
+		// Local is mainnet currently in Byzantium only (so it's aware of Petersburg), remote announces
+		// also Byzantium, and it's also aware of some random fork (e.g. misconfigured Petersburg). As
+		// neither forks passed at neither nodes, they may mismatch, but we still connect for now.
+		{7279999, ID{Hash: checksumToBytes(0xa00bc324), Next: math.MaxUint64}, nil},
+
+		// Local is mainnet Petersburg, remote announces Byzantium + knowledge about Petersburg. Remote
+		// is simply out of sync, accept.
+		{7987396, ID{Hash: checksumToBytes(0x668db0af), Next: 7280000}, nil},
+
+		// Local is mainnet Petersburg, remote announces Spurious + knowledge about Byzantium. Remote
+		// is definitely out of sync. It may or may not need the Petersburg update, we don't know yet.
+		{7987396, ID{Hash: checksumToBytes(0x3edd5b10), Next: 4370000}, nil},
+
+		// Local is mainnet Byzantium, remote announces Petersburg. Local is out of sync, accept.
+		{7279999, ID{Hash: checksumToBytes(0x668db0af), Next: 0}, nil},
+
+		// Local is mainnet Spurious, remote announces Byzantium, but is not aware of Petersburg. Local
+		// out of sync. Local also knows about a future fork, but that is uncertain yet.
+		{4369999, ID{Hash: checksumToBytes(0xa00bc324), Next: 0}, nil},
+
+		// Local is mainnet Petersburg. remote announces Byzantium but is not aware of further forks.
+		// Remote needs software update.
+		{7987396, ID{Hash: checksumToBytes(0xa00bc324), Next: 0}, ErrRemoteStale},
+
+		// Local is mainnet Petersburg, and isn't aware of more forks. Remote announces Petersburg +
+		// 0xffffffff. Local needs software update, reject.
+		{7987396, ID{Hash: checksumToBytes(0x5cddc0e1), Next: 0}, ErrLocalIncompatibleOrStale},
+
+		// Local is mainnet Byzantium, and is aware of Petersburg. Remote announces Petersburg +
+		// 0xffffffff. Local needs software update, reject.
+		{7279999, ID{Hash: checksumToBytes(0x5cddc0e1), Next: 0}, ErrLocalIncompatibleOrStale},
+
+		// Local is mainnet Petersburg, remote is Rinkeby Petersburg.
+		{7987396, ID{Hash: checksumToBytes(0xafec6b27), Next: 0}, ErrLocalIncompatibleOrStale},
+	}
+	for i, tt := range tests {
+		filter := newFilter(params.MainnetChainConfig, params.MainnetGenesisHash, func() uint64 { return tt.head })
+		if err := filter(tt.id); err != tt.err {
+			t.Errorf("test %d: validation error mismatch: have %v, want %v", i, err, tt.err)
+		}
+	}
+}
+
+// Tests that IDs are properly RLP encoded (specifically important because we
+// use uint32 to store the hash, but we need to encode it as [4]byte).
+func TestEncoding(t *testing.T) {
+	tests := []struct {
+		id   ID
+		want []byte
+	}{
+		{ID{Hash: checksumToBytes(0), Next: 0}, common.Hex2Bytes("c6840000000080")},
+		{ID{Hash: checksumToBytes(0xdeadbeef), Next: 0xBADDCAFE}, common.Hex2Bytes("ca84deadbeef84baddcafe,")},
+		{ID{Hash: checksumToBytes(math.MaxUint32), Next: math.MaxUint64}, common.Hex2Bytes("ce84ffffffff88ffffffffffffffff")},
+	}
+	for i, tt := range tests {
+		have, err := rlp.EncodeToBytes(tt.id)
+		if err != nil {
+			t.Errorf("test %d: failed to encode forkid: %v", i, err)
+			continue
+		}
+		if !bytes.Equal(have, tt.want) {
+			t.Errorf("test %d: RLP mismatch: have %x, want %x", i, have, tt.want)
+		}
+	}
+}