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。
1
Syncing方法源代码
1. `// Syncing returns false in case the node is currently not syncing with the network. It can be up to date or has not`
2. `// yet received the latest block headers from its pears. In case it is synchronizing:`
3. `// - startingBlock: block number this node started to synchronise from`
4. `// - currentBlock: block number this node is currently importing`
5. `// - highestBlock: block number of the highest block header this node has received from peers`
6. `// - pulledStates: number of state entries processed until now`
7. `// - knownStates: number of known state entries that still need to be pulled`
8. `func (s *PublicEthereumAPI) Syncing() (interface{}, error) {`
9. `progress := s.b.Downloader().Progress()`
11. `// Return not syncing if the synchronisation already completed`
12. `if progress.CurrentBlock >= progress.HighestBlock {`
13. `return false, nil`
14. `}`
15. `// Otherwise gather the block sync stats`
16. `return map[string]interface{}{`
17. `"startingBlock": hexutil.Uint64(progress.StartingBlock),`
18. `"currentBlock": hexutil.Uint64(progress.CurrentBlock),`
19. `"highestBlock": hexutil.Uint64(progress.HighestBlock),`
20. `"pulledStates": hexutil.Uint64(progress.PulledStates),`
21. `"knownStates": hexutil.Uint64(progress.KnownStates),`
22. `}, nil`
23. `}`
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：
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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；
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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。
2
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。
1. `// SyncProgress gives progress indications when the node is synchronising with`
2. `// the Ethereum network.`
3. `type SyncProgress struct {`
4. `StartingBlock uint64 // Block number where sync began`
5. `CurrentBlock uint64 // Current block number where sync is at`
6. `HighestBlock uint64 // Highest alleged block number in the chain`
7. `PulledStates uint64 // Number of state trie entries already downloaded`
8. `KnownStates uint64 // Total number of state trie entries known about`
9. `}`
3
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：
1. `progress := s.b.Downloader().Progress()`
可以看到如下代码：
1. `// Progress retrieves the synchronisation boundaries, specifically the origin`
2. `// block where synchronisation started at (may have failed/suspended); the block`
3. `// or header sync is currently at; and the latest known block which the sync targets.`
4. `//`
5. `// In addition, during the state download phase of fast synchronisation the number`
6. `// of processed and the total number of known states are also returned. Otherwise`
7. `// these are zero.`
8. `func (d *Downloader) Progress() ethereum.SyncProgress {`
9. `// Lock the current stats and return the progress`
10. `d.syncStatsLock.RLock()`
11. `defer d.syncStatsLock.RUnlock()`
13. `current := uint64(0)`
14. `switch d.mode {`
15. `case FullSync:`
16. `current = d.blockchain.CurrentBlock().NumberU64()`
17. `case FastSync:`
18. `current = d.blockchain.CurrentFastBlock().NumberU64()`
19. `case LightSync:`
20. `current = d.lightchain.CurrentHeader().Number.Uint64()`
21. `}`
22. `return ethereum.SyncProgress{`
23. `StartingBlock: d.syncStatsChainOrigin,`
24. `CurrentBlock: current,`
25. `HighestBlock: d.syncStatsChainHeight,`
26. `PulledStates: d.syncStatsState.processed,`
27. `KnownStates: d.syncStatsState.processed + d.syncStatsState.pending,`
28. `}`
29. `}`
从这端代码我们可以分析得出，curren
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full模式：返回当前区块的高度；
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fast模式：返回fast区块的高度；
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light模式：返回当前的header编号；
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而KnownStates又是由PulledStates的值加上当前处于pending装的值获得。
4
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。
内容来源：程序新视界
作者：二师兄
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