Genesis is the content of the genesis block. A blockchain is formed by rules from the same genesis block. Different networks have different genesis blocks, creation networks of the main network and test network. It is different.
This module sets the state of genesis based on the initial value of the incoming genesis and the database. If there is no genesis block, create it in the database.
data structure
// Genesis specifies the header fields, state of a genesis block. It also defines hard
// fork switch-over blocks through the chain configuration.
type Genesis struct {
Config *params.ChainConfig `json:"config"`
Nonce uint64 `json:"nonce"`
Timestamp uint64 `json:"timestamp"`
ExtraData []byte `json:"extraData"`
GasLimit uint64 `json:"gasLimit" gencodec:"required"`
Difficulty *big.Int `json:"difficulty" gencodec:"required"`
Mixhash common.Hash `json:"mixHash"`
Coinbase common.Address `json:"coinbase"`
Alloc GenesisAlloc `json:"alloc" gencodec:"required"`
// These fields are used for consensus tests. Please don't use them
// in actual genesis blocks.
Number uint64 `json:"number"`
GasUsed uint64 `json:"gasUsed"`
ParentHash common.Hash `json:"parentHash"`
}
// GenesisAlloc specifies the initial state that is part of the genesis block.
type GenesisAlloc map[common.Address]GenesisAccountSetupGenesisBlock,
// SetupGenesisBlock writes or updates the genesis block in db.
//
// The block that will be used is:
//
// genesis == nil genesis != nil
// +------------------------------------------
// db has no genesis | main-net default | genesis
// db has genesis | from DB | genesis (if compatible)
//
// The stored chain configuration will be updated if it is compatible (i.e. does not
// specify a fork block below the local head block). In case of a conflict, the
// error is a *params.ConfigCompatError and the new, unwritten config is returned.
// The returned chain configuration is never nil.
// genesis is not nil if it is testnet dev or rinkeby mode.
func SetupGenesisBlock(db ethdb.Database, genesis *Genesis) (*params.ChainConfig, common.Hash, error) {
if genesis != nil && genesis.Config == nil {
return params.AllProtocolChanges, common.Hash{}, errGenesisNoConfig
}
// Just commit the new block if there is no stored genesis block.
stored := GetCanonicalHash(db, 0)
if (stored == common.Hash{}) { // If there is no block, the start of the geth will start here.
if genesis == nil {
log.Info("Writing default main-net genesis block")
genesis = DefaultGenesisBlock()
} else { // custome genesis block
log.Info("Writing custom genesis block")
}
// update blockchain db
block, err := genesis.Commit(db)
return genesis.Config, block.Hash(), err
}
// Check whether the genesis block is already written.
if genesis != nil {
block, _ := genesis.ToBlock()
hash := block.Hash()
if hash != stored {
return genesis.Config, block.Hash(), &GenesisMismatchError{stored, hash}
}
}
// Get the existing chain configuration.
newcfg := genesis.configOrDefault(stored)
// Get the current blockchain configuration
storedcfg, err := GetChainConfig(db, stored)
if err != nil {
if err == ErrChainConfigNotFound {
// This case happens if a genesis write was interrupted.
log.Warn("Found genesis block without chain config")
err = WriteChainConfig(db, stored, newcfg)
}
return newcfg, stored, err
}
// Special case: don't change the existing config of a non-mainnet chain if no new
// config is supplied. These chains would get AllProtocolChanges (and a compat error)
// if we just continued here.
if genesis == nil && stored != params.MainnetGenesisHash {
return storedcfg, stored, nil // If it is a private blockchain, it will exit from here.
}
// Check config compatibility and write the config. Compatibility errors
// are returned to the caller unless we're already at block zero.
height := GetBlockNumber(db, GetHeadHeaderHash(db))
if height == missingNumber {
return newcfg, stored, fmt.Errorf("missing block number for head header hash")
}
compatErr := storedcfg.CheckCompatible(newcfg, height)
// If the block has already written data, then the genesis configuration cannot be changed.
if compatErr != nil && height != 0 && compatErr.RewindTo != 0 {
return newcfg, stored, compatErr
}
// else it is from the main net
return newcfg, stored, WriteChainConfig(db, stored, newcfg)
}ToBlock, this method uses the genesis data, uses a memory-based database, then creates a block and returns.
// ToBlock creates the block and state of a genesis specification.
func (g *Genesis) ToBlock() (*types.Block, *state.StateDB) {
db, _ := ethdb.NewMemDatabase()
statedb, _ := state.New(common.Hash{}, state.NewDatabase(db))
for addr, account := range g.Alloc {
statedb.AddBalance(addr, account.Balance)
statedb.SetCode(addr, account.Code)
statedb.SetNonce(addr, account.Nonce)
for key, value := range account.Storage {
statedb.SetState(addr, key, value)
}
}
root := statedb.IntermediateRoot(false)
head := &types.Header{
Number: new(big.Int).SetUint64(g.Number),
Nonce: types.EncodeNonce(g.Nonce),
Time: new(big.Int).SetUint64(g.Timestamp),
ParentHash: g.ParentHash,
Extra: g.ExtraData,
GasLimit: new(big.Int).SetUint64(g.GasLimit),
GasUsed: new(big.Int).SetUint64(g.GasUsed),
Difficulty: g.Difficulty,
MixDigest: g.Mixhash,
Coinbase: g.Coinbase,
Root: root,
}
if g.GasLimit == 0 {
head.GasLimit = params.GenesisGasLimit
}
if g.Difficulty == nil {
head.Difficulty = params.GenesisDifficulty
}
return types.NewBlock(head, nil, nil, nil), statedb
}The Commit method and the MustCommit method, the Commit method writes the block and state of a given genesis into the database. This block is considered to be the canonical blockchain.
// Commit writes the block and state of a genesis specification to the database.
// The block is committed as the canonical head block.
func (g *Genesis) Commit(db ethdb.Database) (*types.Block, error) {
block, statedb := g.ToBlock()
if block.Number().Sign() != 0 {
return nil, fmt.Errorf("can't commit genesis block with number > 0")
}
if _, err := statedb.CommitTo(db, false); err != nil {
return nil, fmt.Errorf("cannot write state: %v", err)
}
// write the total difficult
if err := WriteTd(db, block.Hash(), block.NumberU64(), g.Difficulty); err != nil {
return nil, err
}
// write block
if err := WriteBlock(db, block); err != nil {
return nil, err
}
// write the receipt
if err := WriteBlockReceipts(db, block.Hash(), block.NumberU64(), nil); err != nil {
return nil, err
}
// headerPrefix + num (uint64 big endian) + numSuffix -> hash
if err := WriteCanonicalHash(db, block.Hash(), block.NumberU64()); err != nil {
return nil, err
}
// "LastBlock" -> hash
if err := WriteHeadBlockHash(db, block.Hash()); err != nil {
return nil, err
}
// "LastHeader" -> hash
if err := WriteHeadHeaderHash(db, block.Hash()); err != nil {
return nil, err
}
config := g.Config
if config == nil {
config = params.AllProtocolChanges
}
// ethereum-config-hash -> config
return block, WriteChainConfig(db, block.Hash(), config)
}
// MustCommit writes the genesis block and state to db, panicking on error.
// The block is committed as the canonical head block.
func (g *Genesis) MustCommit(db ethdb.Database) *types.Block {
block, err := g.Commit(db)
if err != nil {
panic(err)
}
return block
}Return to the default Genesis for various modes
// DefaultGenesisBlock returns the Ethereum main net genesis block.
func DefaultGenesisBlock() *Genesis {
return &Genesis{
Config: params.MainnetChainConfig,
Nonce: 66,
ExtraData: hexutil.MustDecode("0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa"),
GasLimit: 5000,
Difficulty: big.NewInt(17179869184),
Alloc: decodePrealloc(mainnetAllocData),
}
}
// DefaultTestnetGenesisBlock returns the Ropsten network genesis block.
func DefaultTestnetGenesisBlock() *Genesis {
return &Genesis{
Config: params.TestnetChainConfig,
Nonce: 66,
ExtraData: hexutil.MustDecode("0x3535353535353535353535353535353535353535353535353535353535353535"),
GasLimit: 16777216,
Difficulty: big.NewInt(1048576),
Alloc: decodePrealloc(testnetAllocData),
}
}
// DefaultRinkebyGenesisBlock returns the Rinkeby network genesis block.
func DefaultRinkebyGenesisBlock() *Genesis {
return &Genesis{
Config: params.RinkebyChainConfig,
Timestamp: 1492009146,
ExtraData: hexutil.MustDecode("0x52657370656374206d7920617574686f7269746168207e452e436172746d616e42eb768f2244c8811c63729a21a3569731535f067ffc57839b00206d1ad20c69a1981b489f772031b279182d99e65703f0076e4812653aab85fca0f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"),
GasLimit: 4700000,
Difficulty: big.NewInt(1),
Alloc: decodePrealloc(rinkebyAllocData),
}
}
// DevGenesisBlock returns the 'geth --dev' genesis block.
func DevGenesisBlock() *Genesis {
return &Genesis{
Config: params.AllProtocolChanges,
Nonce: 42,
GasLimit: 4712388,
Difficulty: big.NewInt(131072),
Alloc: decodePrealloc(devAllocData),
}
}