兄弟连区块链教程以太坊源码分析core-genesis创世区块源码分析

genesis 是创世区块的意思. 一个区块链就是从同一个创世区块开始,通过规则形成的.不同的网络有不同的创世区块, 主网络和测试网路的创世区块是不同的.

这个模块根据传入的genesis的初始值和database，来设置genesis的状态，如果不存在创世区块，那么在database里面创建它。

数据结构

// Genesis specifies the header fields, state of a genesis block. It also defines hard

// fork switch-over blocks through the chain configuration.

// Genesis指定header的字段，起始块的状态。 它还通过配置来定义硬叉切换块。

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.

// GenesisAlloc 指定了最开始的区块的初始状态.

type GenesisAlloc map[common.Address]GenesisAccount

SetupGenesisBlock,

// 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.

// 如果存储的区块链配置不兼容那么会被更新(). 为了避免发生冲突,会返回一个错误,并且新的配置和原来的配置会返回.

// The returned chain configuration is never nil.

// genesis 如果是 testnet dev 或者是 rinkeby 模式， 那么不为nil。如果是mainnet或者是私有链接。那么为空

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) //获取genesis对应的区块
if (stored == common.Hash{}) { //如果没有区块 最开始启动geth会进入这里。
    if genesis == nil {
        //如果genesis是nil 而且stored也是nil 那么使用主网络
        // 如果是test dev rinkeby 那么genesis不为空 会设置为各自的genesis
        log.Info("Writing default main-net genesis block")
        genesis = DefaultGenesisBlock()
    } else { // 否则使用配置的区块
        log.Info("Writing custom genesis block")
    }
    // 写入数据库
    block, err := genesis.Commit(db)
    return genesis.Config, block.Hash(), err
}
// Check whether the genesis block is already written.
if genesis != nil { //如果genesis存在而且区块也存在 那么对比这两个区块是否相同
    block, _ := genesis.ToBlock()
    hash := block.Hash()
    if hash != stored {
        return genesis.Config, block.Hash(), &GenesisMismatchError{stored, hash}
    }
}
// Get the existing chain configuration.
// 获取当前存在的区块链的genesis配置
newcfg := genesis.configOrDefault(stored)
// 获取当前的区块链的配置
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.
// 特殊情况：如果没有提供新的配置，请不要更改非主网链的现有配置。
// 如果我们继续这里，这些链会得到AllProtocolChanges（和compat错误）。
if genesis == nil && stored != params.MainnetGenesisHash {
    return storedcfg, stored, nil // 如果是私有链接会从这里退出。
}
// Check config compatibility and write the config. Compatibility errors
// are returned to the caller unless we're already at block zero.
// 检查配置的兼容性,除非我们在区块0,否则返回兼容性错误.
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)
// 如果区块已经写入数据了,那么就不能更改genesis配置了
if compatErr != nil && height != 0 && compatErr.RewindTo != 0 {
    return newcfg, stored, compatErr
}
// 如果是主网络会从这里退出。
return newcfg, stored, WriteChainConfig(db, stored, newcfg)

}

ToBlock, 这个方法使用genesis的数据，使用基于内存的数据库，然后创建了一个block并返回。

// 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

}

Commit方法和MustCommit方法, Commit方法把给定的genesis的block和state写入数据库， 这个block被认为是规范的区块链头。

// 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)
}
// 写入总难度
if err := WriteTd(db, block.Hash(), block.NumberU64(), g.Difficulty); err != nil {
    return nil, err
}
// 写入区块
if err := WriteBlock(db, block); err != nil {
    return nil, err
}
// 写入区块收据
if err := WriteBlockReceipts(db, block.Hash(), block.NumberU64(), nil); err != nil {
    return nil, err
}
// 写入 headerPrefix + num (uint64 big endian) + numSuffix -> hash
if err := WriteCanonicalHash(db, block.Hash(), block.NumberU64()); err != nil {
    return nil, err
}
// 写入 "LastBlock" -> hash
if err := WriteHeadBlockHash(db, block.Hash()); err != nil {
    return nil, err
}
// 写入 "LastHeader" -> hash
if err := WriteHeadHeaderHash(db, block.Hash()); err != nil {
    return nil, err
}
config := g.Config
if config == nil {
    config = params.AllProtocolChanges
}
// 写入 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

}

返回各种模式的默认Genesis

// 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),
}

}