以太坊源码分析-同步之Syncing接口

在节点同步的过程中，我们经常需要执行eth.syncing来查看当前的同步情况，本篇博客带领大家看一下syncing api的源代码实现。

Syncing方法源代码

// Syncing returns false in case the node is currently not syncing with the network. It can be up to date or has not
// yet received the latest block headers from its pears. In case it is synchronizing:
// - startingBlock: block number this node started to synchronise from
// - currentBlock:  block number this node is currently importing
// - highestBlock:  block number of the highest block header this node has received from peers
// - pulledStates:  number of state entries processed until now
// - knownStates:   number of known state entries that still need to be pulled
func (s *PublicEthereumAPI) Syncing() (interface{}, error) {
    progress := s.b.Downloader().Progress()

    // Return not syncing if the synchronisation already completed
    if progress.CurrentBlock >= progress.HighestBlock {
        return false, nil
    }
    // Otherwise gather the block sync stats
    return map[string]interface{}{
        "startingBlock": hexutil.Uint64(progress.StartingBlock),
        "currentBlock":  hexutil.Uint64(progress.CurrentBlock),
        "highestBlock":  hexutil.Uint64(progress.HighestBlock),
        "pulledStates":  hexutil.Uint64(progress.PulledStates),
        "knownStates":   hexutil.Uint64(progress.KnownStates),
    }, nil
}

Syncing方法的源代码很简单，注释说明也已经很清楚了。通过这段源代码我们可以得知一下信息：
- 当然CurrentBlock大于等于HighestBlock时返回false，这也正是通常所说的同步完成之后，再执行eth.syncing()函数会返回false的原因。
- startingBlock：开始同步的起始区块编号；
- currentBlock：当前正在导入的区块编号；
- highestBlock：通过所链接的节点获得的当前最高的区块高度；
- pulledStates：当前已经拉取的状态条目数；
- knownStates：当前已知的待拉取的总状态条目数；

对应的结构体代码

下面是同步信息对应的结构体的代码及注释。

// SyncProgress gives progress indications when the node is synchronising with
// the Ethereum network.
type SyncProgress struct {
    StartingBlock uint64 // Block number where sync began
    CurrentBlock  uint64 // Current block number where sync is at
    HighestBlock  uint64 // Highest alleged block number in the chain
    PulledStates  uint64 // Number of state trie entries already downloaded
    KnownStates   uint64 // Total number of state trie entries known about
}

结构体信息计算

上面看到当执行eth.syncing返回结果信息的代码，再延伸一下看看这些数据从哪里来。进入下面Progress方法的内部实现：

progress := s.b.Downloader().Progress()

可以看到如下代码：

// Progress retrieves the synchronisation boundaries, specifically the origin
// block where synchronisation started at (may have failed/suspended); the block
// or header sync is currently at; and the latest known block which the sync targets.
//
// In addition, during the state download phase of fast synchronisation the number
// of processed and the total number of known states are also returned. Otherwise
// these are zero.
func (d *Downloader) Progress() ethereum.SyncProgress {
    // Lock the current stats and return the progress
    d.syncStatsLock.RLock()
    defer d.syncStatsLock.RUnlock()

    current := uint64(0)
    switch d.mode {
    case FullSync:
        current = d.blockchain.CurrentBlock().NumberU64()
    case FastSync:
        current = d.blockchain.CurrentFastBlock().NumberU64()
    case LightSync:
        current = d.lightchain.CurrentHeader().Number.Uint64()
    }
    return ethereum.SyncProgress{
        StartingBlock: d.syncStatsChainOrigin,
        CurrentBlock:  current,
        HighestBlock:  d.syncStatsChainHeight,
        PulledStates:  d.syncStatsState.processed,
        KnownStates:   d.syncStatsState.processed + d.syncStatsState.pending,
    }
}

从这端代码我们可以分析得出，current的值在不同的同步模式下是有所不同的：
- full模式：返回当前区块的高度；
- fast模式：返回fast区块的高度；
- light模式：返回当前的header编号；
- 而KnownStates又是由PulledStates的值加上当前处于pending装的值获得。

总结

通过上面源代码分析，我们已经可以明了的看到当我们执行eth.sycing时返回不同的结果信息所代表的含义。欢迎大家关注微信公众号，获取最新的相关技术分享。

原文链接：http://www.choupangxia.com/topic/detail/13

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