以太坊源码分析 genesis处理

1. Genesis struct

// 创世区块类结构，后面的是区块对应json字段名称
type Genesis struct {
    // 配置文件，用于指定链的chainId(network id)
    Config     *params.ChainConfig `json:"config"`
    // 随机数，与Mixhash组合用于满足POW算法要求
    Nonce      uint64              `json:"nonce"`
    // 时间戳
    Timestamp  uint64              `json:"timestamp"`
    // 区块额外信息
    ExtraData  []byte              `json:"extraData"`
    // Gas消耗量限制
    GasLimit   uint64              `json:"gasLimit"   gencodec:"required"`
    // 区块难度值
    Difficulty *big.Int            `json:"difficulty" gencodec:"required"`
    // 由上个区块的一部分生成的Hash，和Nonce组合用于找到满足POW算法的条件
    Mixhash    common.Hash         `json:"mixHash"`
    // 矿工地址
    Coinbase   common.Address      `json:"coinbase"`
    // 创世区块初始状态
    Alloc      GenesisAlloc        `json:"alloc"      gencodec:"required"`

    // These fields are used for consensus tests. Please don't use them
    // in actual genesis blocks.
    /** 下面字段用于共识测试，不要在创世区块中使用
    */
    Number     uint64      `json:"number"`
    GasUsed    uint64      `json:"gasUsed"`
    // 父区块哈希
    ParentHash common.Hash `json:"parentHash"`
}

2. SetupGenesisBlock

SetupGenesisBlock 用于启动以太坊创世区块。

/**如果存储的区块链配置不兼容，将调用该方法更新。为了避免冲突，错误将会被作为参数返回，并且新的配置
和原有配置都会被返回。
*/
func SetupGenesisBlock(db ethdb.Database, genesis *Genesis) (*params.ChainConfig, common.Hash, error) {
    if genesis != nil && genesis.Config == nil {
        return params.AllEthashProtocolChanges, common.Hash{}, errGenesisNoConfig
    }

    // Just commit the new block if there is no stored genesis block.
    // 如果没有存储的genesis块，只需提交新块。
    stored := rawdb.ReadCanonicalHash(db, 0)    // 从数据库中获取genesis对应的区块
    if (stored == common.Hash{}) {
        if genesis == nil {
            // genesis和stored都为空，使用主网
            log.Info("Writing default main-net genesis block")
            genesis = DefaultGenesisBlock()
        } else {
            // 使用自定义的genesis配置
            log.Info("Writing custom genesis block")
        }
        // 创世区块写入数据库
        block, err := genesis.Commit(db)
        return genesis.Config, block.Hash(), err
    }

    // Check whether the genesis block is already written.
    // 检查创世区块是否写入成功
    if genesis != nil {
        // 获取创世区块哈希
        hash := genesis.ToBlock(nil).Hash()
        if hash != stored {
            return genesis.Config, hash, &GenesisMismatchError{stored, hash}
        }
    }

    // Get the existing chain configuration.
    // 获取当前区块链相关配置
    newcfg := genesis.configOrDefault(stored)
    storedcfg := rawdb.ReadChainConfig(db, stored)
    if storedcfg == nil {
        // 读取失败，说明创世区块写入被中断
        log.Warn("Found genesis block without chain config")
        rawdb.WriteChainConfig(db, stored, newcfg)
        return newcfg, stored, nil
    }
    // 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：如果没有新的配置，请勿更改非主网链的相关配置
    // 这些链会得到AllProtocolChanges以及compat error，如果我们继续
    if genesis == nil && stored != params.MainnetGenesisHash {
        return storedcfg, stored, nil
    }

    // Check config compatibility and write the config. Compatibility errors
    // are returned to the caller unless we're already at block zero.
    // 检查配置兼容性并写入配置
    // 兼容性错误将返回给调用者，除非我们已经处于块0
    height := rawdb.ReadHeaderNumber(db, rawdb.ReadHeadHeaderHash(db))
    if height == nil {
        return newcfg, stored, fmt.Errorf("missing block number for head header hash")
    }
    compatErr := storedcfg.CheckCompatible(newcfg, *height)
    // 如果compatErr为空并且非高度为0的区块，那么久不能更改genesis配置了
    if compatErr != nil && *height != 0 && compatErr.RewindTo != 0 {
        return newcfg, stored, compatErr
    }
    rawdb.WriteChainConfig(db, stored, newcfg)
    return newcfg, stored, nil
}

3. ToBlock

ToBlock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, 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。
func (g *Genesis) ToBlock(db ethdb.Database) *types.Block {
    if db == nil {
        db = ethdb.NewMemDatabase()
    }
    // 用genesis的数据给statedb赋值
    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)
    // 填充head值
    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:   g.GasLimit,
        GasUsed:    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
    }

    // 数据库提交
    statedb.Commit(false)
    statedb.Database().TrieDB().Commit(root, true)

    return types.NewBlock(head, nil, nil, nil)
}

4. Commit

上面两个主要函数都用到了Commit 方法，接下来我们就看下该方法到底做了哪些操作。

// Commit writes the block and state of a genesis specification to the database.
// The block is committed as the canonical head block.
// Commit方法调用rawdb.WriteChainConfig(db, block.Hash(), config)函数把给定的genesis的block
// 和state写入数据库，该block被认为是规范的区块链头
func (g *Genesis) Commit(db ethdb.Database) (*types.Block, error) {
    
    // 取到genesis对应的block
    block := g.ToBlock(db)
    if block.Number().Sign() != 0 {
        return nil, fmt.Errorf("can't commit genesis block with number > 0")
    }
    // 写入总难度
    rawdb.WriteTd(db, block.Hash(), block.NumberU64(), g.Difficulty)
    // 写入区块
    rawdb.WriteBlock(db, block)
    // 写入区块数据
    rawdb.WriteReceipts(db, block.Hash(), block.NumberU64(), nil)
    // 写入 headerPrefix + num (uint64 big endian) + numSuffix -> hash
    rawdb.WriteCanonicalHash(db, block.Hash(), block.NumberU64())
    rawdb.WriteHeadBlockHash(db, block.Hash())
    rawdb.WriteHeadHeaderHash(db, block.Hash())

    config := g.Config
    if config == nil {
        config = params.AllEthashProtocolChanges
    }
    // 写入 ethereum-config-hash -> config
    rawdb.WriteChainConfig(db, block.Hash(), config)
    return block, nil
}

5. 各种模式的GenesisBlock

// 各种返回模式的Genesis
// GenesisBlockForTesting creates and writes a block in which addr has the given wei balance.
// GenesisBlockForTesting创建并写入一个块，其中addr具有给定的wei余额。
func GenesisBlockForTesting(db ethdb.Database, addr common.Address, balance *big.Int) *types.Block {
    g := Genesis{Alloc: GenesisAlloc{addr: {Balance: balance}}}
    return g.MustCommit(db)
}

// DefaultGenesisBlock returns the Ethereum main net genesis block.
// DefaultGenesisBlock返回以太坊主网络创世块
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.
// DefaultTestnetGenesisBlock返回Ropsten网络创世块。
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.
// DefaultRinkebyGenesisBlock返回Rinkeby网络创世块。
func DefaultRinkebyGenesisBlock() *Genesis {
    return &Genesis{
        Config:     params.RinkebyChainConfig,
        Timestamp:  1492009146,
        ExtraData:  hexutil.MustDecode("0x52657370656374206d7920617574686f7269746168207e452e436172746d616e42eb768f2244c8811c63729a21a3569731535f067ffc57839b00206d1ad20c69a1981b489f772031b279182d99e65703f0076e4812653aab85fca0f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"),
        GasLimit:   4700000,
        Difficulty: big.NewInt(1),
        Alloc:      decodePrealloc(rinkebyAllocData),
    }
}

// DeveloperGenesisBlock returns the 'geth --dev' genesis block. Note, this must
// be seeded with the
// eveloperGenesisBlock返回'geth --dev'创世块。
func DeveloperGenesisBlock(period uint64, faucet common.Address) *Genesis {
    // Override the default period to the user requested one
    config := *params.AllCliqueProtocolChanges
    config.Clique.Period = period

    // Assemble and return the genesis with the precompiles and faucet pre-funded
    return &Genesis{
        Config:     &config,
        ExtraData:  append(append(make([]byte, 32), faucet[:]...), make([]byte, 65)...),
        GasLimit:   6283185,
        Difficulty: big.NewInt(1),
        Alloc: map[common.Address]GenesisAccount{
            common.BytesToAddress([]byte{1}): {Balance: big.NewInt(1)}, // ECRecover
            common.BytesToAddress([]byte{2}): {Balance: big.NewInt(1)}, // SHA256
            common.BytesToAddress([]byte{3}): {Balance: big.NewInt(1)}, // RIPEMD
            common.BytesToAddress([]byte{4}): {Balance: big.NewInt(1)}, // Identity
            common.BytesToAddress([]byte{5}): {Balance: big.NewInt(1)}, // ModExp
            common.BytesToAddress([]byte{6}): {Balance: big.NewInt(1)}, // ECAdd
            common.BytesToAddress([]byte{7}): {Balance: big.NewInt(1)}, // ECScalarMul
            common.BytesToAddress([]byte{8}): {Balance: big.NewInt(1)}, // ECPairing
            faucet: {Balance: new(big.Int).Sub(new(big.Int).Lsh(big.NewInt(1), 256), big.NewInt(9))},
        },
    }
}

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