通过上篇getBalance和这个getBlock，理论上eth也能变成一个中心化的服务，因为用户和交易最终也都是保存到了数据库，那就和我们平时开发的项目没什么区别。这还蛮有意思的，eth实际上是区块链+传统项目的结合体。

//命令
eth.getBlock(1,true)
//跳过了前面几层
func (bc *BlockChain) GetBlockByNumber(number uint64) *types.Block {
        //用block number换block的hash
    hash := rawdb.ReadCanonicalHash(bc.db, number)
    if hash == (common.Hash{}) {
        return nil
    }
        //根据hash和number获取block
    return bc.GetBlock(hash, number)
}

//获取hash
func ReadCanonicalHash(db ethdb.Reader, number uint64) common.Hash {
  //这个还没弄明白
   data, _ := db.Ancient(freezerHashTable, number)
   if len(data) == 0 {
  //从db中读
      data, _ = db.Get(headerHashKey(number))
      if len(data) == 0 {
         data, _ = db.Ancient(freezerHashTable, number)
      }
   }
   if len(data) == 0 {
      return common.Hash{}
   }
   return common.BytesToHash(data)
}

//获取区块
func (bc *BlockChain) GetBlock(hash common.Hash, number uint64) *types.Block {
   //从缓存中读，这里用到了lur
   if block, ok := bc.blockCache.Get(hash); ok {
      return block.(*types.Block)
   }
//从db中读，内容和getbalance一样，里面是先获取header，再获取body，然后创建区块，将header和body copy到block返回
   block := rawdb.ReadBlock(bc.db, hash, number)
   if block == nil {
      return nil
   }
//缓存区块
   bc.blockCache.Add(block.Hash(), block)
   return block
}

两篇get方法都是大同小异，进一步了解到eth是可以很简单的实现的，那些很牛逼的东西，都是为了满足区块链、性能这些需求。

另外这篇内容的主要代码都在blockchain内，又一次出现了这个，说明很重要，而statedb却没有出现，目前可以猜测statedb和账户有关，和block无关，需要后续验证。

也能知道leveldb里大致存的内容

1. 用户数据

2. header

3. number→hash

4. body,body里存了tx，uncle

5. 可以想象还有receipt

//block的例子
{
  difficulty: 1461115576915,
  extraData: "0x476574682f76312e302e312f6c696e75782f676f312e342e32",
  gasLimit: 22150,
  gasUsed: 21000,
  hash: "0xeecb25ce31fb7a212500443a31d463b663a2c5f65e7838c5364bb8110a0750f1",
  logsBloom: "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  miner: "0x47ff6576639c2e94762ea5443978d7681c0e78dc",
  mixHash: "0xaaad7bf5c87f1b2fc08ed73a1519dae6832b458a112891cd7c5a0a86125a8321",
  nonce: "0x4e164418632effd2",
  number: 46251,
  parentHash: "0x3c93a7ff6fb6f39e63456e9ea6fb069c7783f3c00b1012e36f0a8a02bdae604a",
  receiptsRoot: "0x5add83c7805c02ab079871e3a2379b6a764d34e557d758ddce00b6a1bf5cc79f",
  sha3Uncles: "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347",
  size: 652,
  stateRoot: "0x7692ecfeac33453620701bad9eae23f89c01e845274f0e5adec78a5ea96f5083",
  timestamp: 1438919990,
  totalDifficulty: 42835839136947252,
  transactions: [{
      blockHash: "0xeecb25ce31fb7a212500443a31d463b663a2c5f65e7838c5364bb8110a0750f1",
      blockNumber: 46251,
      from: "0xfd2605a2bf58fdbb90db1da55df61628b47f9e8c",
      gas: 21000,
      gasPrice: 88893746891,
      hash: "0x304346de678ddca5b1311970e7e8d3f26a42d2924aaa2f2d73b8781a9a9a2c73",
      input: "0x",
      nonce: 1,
      r: "0x26f3e5c541f526b549d9f003c8e7de442d3cf4bbf9c66934027672693a88275f",
      s: "0x7bd40d54be85b58444d6f0a28f22591474a84380fc8a6a7515bda42b5ebb0e2b",
      to: "0x073f70b5bfade6409e4951ef72bc8f4157677729",
      transactionIndex: 0,
      v: "0x1c",
      value: 10000000000000000
  }],
  transactionsRoot: "0xf642520ac0ce7008292d2c835b8d2e6eb90822f8a68b8ae368b0774229371b5d",
  uncles: []
}