之前有同事詢問，過去被回滾的區(qū)塊是否還能在全節(jié)點找到？ 當時沒有具體了解bitcoin在forked block上的處理，給他的結(jié)論是全節(jié)點不會保存被forked block信息，如果保留也是短暫時間內(nèi)的。這個結(jié)論的主要依據(jù)是bitcoin源碼中定義了一個BlockIndex的鏈表數(shù)據(jù)，而這個結(jié)構(gòu)只保留主鏈上的block，所以想當然的認為全節(jié)點是不會保留forked block信息的。

另外一種情況是: 歷史上發(fā)生了區(qū)塊回滾的事件，一個新建的bitcoin全節(jié)點，通過區(qū)塊同步的方式下載所有區(qū)塊鏈數(shù)據(jù)，那么可以肯定的是，在下載到最高度的區(qū)間內(nèi)的所有forked block信息，將會全部丟失。因為區(qū)塊同步下載的過程是不會涉及到forked block的。

獲取forked block數(shù)據(jù)

bitcon給出的API getchaintips中能夠獲得相關(guān)信息，具體使用方法如下:

> bitcoin-cli getchaintips
[
  {
    "height": 580618,
    "hash": "00000000000000000021873a6237b6bf299c334925062609b5e91d39d46ca044",
    "branchlen": 0,
    "status": "active"
  },
  {
    "height": 578141,
    "hash": "0000000000000000001253a5f37d3763dbe928d21f7d72a708f05268c044179c",
    "branchlen": 1,
    "status": "valid-fork"
  },
  {
    "height": 573313,
    "hash": "0000000000000000000883f9f6eb9a459426f715ee3895a4dbb6e51e9237eceb",
    "branchlen": 1,
    "status": "valid-fork"
  },
  {
    "height": 570069,
    "hash": "000000000000000000214b7d19ea458da8f8e80bc437587a02eb418b5fd8b3aa",
    "branchlen": 1,
    "status": "valid-headers"
  },
  {
    "height": 478576,
    "hash": "000000000000000001416af072f8989829f4c60a1a9658e1cec08411798e4ffa",
    "branchlen": 18,
    "status": "headers-only"
  }
]

該API返回的是一個json數(shù)組，各個字段的含義如下:

• height: 發(fā)生fork事件的高度
• hash: forked block hash值
• branchlen: 發(fā)生fork的深度
• status: forked block的驗證狀態(tài)

對于status字段，其可能的值，以及具體含義可以查看如下代碼:

std::string status;
if (chainActive.Contains(block)) {
    // This block is part of the currently active chain.
    status = "active";
} else if (block->nStatus & BLOCK_FAILED_MASK) {
    // This block or one of its ancestors is invalid.
    status = "invalid";
} else if (!block->HaveTxsDownloaded()) {
    // This block cannot be connected because full block data for it or one of its parents is   missing.
    status = "headers-only";
} else if (block->IsValid(BLOCK_VALID_SCRIPTS)) {
    // This block is fully validated, but no longer part of the active chain. It was probably   the active block once, but was reorganized.
    status = "valid-fork";
} else if (block->IsValid(BLOCK_VALID_TREE)) {
    // The headers for this block are valid, but it has not been validated. It was probably     never part of the most-work chain.
    status = "valid-headers";
} else {
    // No clue.
    status = "unknown";
}
obj.pushKV("status", status);

分析

之所以bitcoin全節(jié)點保存了這些數(shù)據(jù)，是因為有一個全局的block容器mapBlockIndex，來處理該節(jié)點遇到的所有block，以及header數(shù)據(jù)。上面提到只保留主鏈的容器是:

/** The currently-connected chain of blocks (protected by cs_main). */
extern CChain& chainActive;