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-rw-r--r--core/forkid/forkid.go258
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diff --git a/core/forkid/forkid.go b/core/forkid/forkid.go
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+// 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/ava-labs/coreth/core/types"
+ "github.com/ava-labs/coreth/params"
+ "github.com/ethereum/go-ethereum/common"
+ "github.com/ethereum/go-ethereum/log"
+)
+
+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")
+)
+
+// Blockchain defines all necessary method to build a forkID.
+type Blockchain interface {
+ // Config retrieves the chain's fork configuration.
+ Config() *params.ChainConfig
+
+ // Genesis retrieves the chain's genesis block.
+ Genesis() *types.Block
+
+ // CurrentHeader retrieves the current head header of the canonical chain.
+ CurrentHeader() *types.Header
+}
+
+// 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
+}
+
+// Filter is a fork id filter to validate a remotely advertised ID.
+type Filter func(id ID) error
+
+// NewID calculates the Ethereum fork ID from the chain config and head.
+func NewID(chain 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 a filter that returns if a fork ID should be rejected or not
+// based on the local chain's status.
+func NewFilter(chain Blockchain) Filter {
+ return newFilter(
+ chain.Config(),
+ chain.Genesis().Hash(),
+ func() uint64 {
+ return chain.CurrentHeader().Number.Uint64()
+ },
+ )
+}
+
+// NewStaticFilter creates a filter at block zero.
+func NewStaticFilter(config *params.ChainConfig, genesis common.Hash) Filter {
+ head := func() uint64 { return 0 }
+ return newFilter(config, genesis, head)
+}
+
+// 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) Filter {
+ // 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, compare local head to FORK_NEXT.
+ // 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).
+ // 1a. A remotely announced but remotely not passed block is already passed
+ // locally, disconnect, since the chains are incompatible.
+ // 1b. No remotely announced fork; or not yet passed locally, connect.
+ // 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 {
+ // Fork checksum matched, check if a remote future fork block already passed
+ // locally without the local node being aware of it (rule #1a).
+ if id.Next > 0 && head >= id.Next {
+ return ErrLocalIncompatibleOrStale
+ }
+ // Haven't passed locally a remote-only fork, accept the connection (rule #1b).
+ 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
+ }
+}
+
+// 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 chronological 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
+}