用 Python 構建一個極小的區塊鏈 | Linux 中國

真棒！現在我們有了一種儲存使用者彼此傳送 SnakeCoin 的記錄的方式。這就是為什麼人們將區塊鏈稱之為公共的、分散式賬本：所有的交易資訊儲存給所有人看，並被儲存在該網路的每個節點上。

但是，有個問題：人們從哪裡得到 SnakeCoin 呢？現在還沒有辦法得到，還沒有一個稱之為 SnakeCoin 這樣的東西，因為我們還沒有建立和分發任何一個幣。要建立新的幣，人們需要“挖”一個新的 SnakeCoin 區塊。當他們成功地挖到了新區塊，就會創建出一個新的 SnakeCoin ，並獎勵給挖出該區塊的人（礦工）。一旦挖礦的礦工將 SnakeCoin 傳送給別人，這個幣就流通起來了。

我們不想讓挖新的 SnakeCoin 區塊太容易，因為這將導致 SnakeCoin 太多了，其價值就變低了；同樣，我們也不想讓它變得太難，因為如果沒有足夠的幣供每個人使用，它們對於我們來說就太昂貴了。為了控制挖新的 SnakeCoin 區塊的難度，我們會實現一個工作量證明Proof-of-Work[3]（PoW）演演算法。工作量證明基本上就是一個生成某個專案比較難，但是容易驗證（其正確性）的演演算法。這個專案被稱之為“證明”，聽起來就像是它證明瞭計算機執行了特定的工作量。

在 SnakeCoin 中，我們建立了一個簡單的 PoW 演演算法。要建立一個新區塊，礦工的計算機需要遞增一個數字，當該數字能被 9 （“SnakeCoin” 這個單詞的字母數）整除時，這就是最後這個區塊的證明數字，就會挖出一個新的 SnakeCoin 區塊，而該礦工就會得到一個新的 SnakeCoin。

# ...blockchain
# ...Block class definition
miner_address = "q3nf394hjg-random-miner-address-34nf3i4nflkn3oi"
def proof_of_work(last_proof):
  # Create a variable that we will use to find
  # our next proof of work
  incrementor = last_proof + 1
  # Keep incrementing the incrementor until
  # it's equal to a number divisible by 9
  # and the proof of work of the previous
  # block in the chain
  while not (incrementor % 9 == 0 and incrementor % last_proof == 0):
    incrementor += 1
  # Once that number is found,
  # we can return it as a proof
  # of our work
  return incrementor
@node.route('/mine', methods = ['GET'])
def mine():
  # Get the last proof of work
  last_block = blockchain[len(blockchain) - 1]
  last_proof = last_block.data['proof-of-work']
  # Find the proof of work for
  # the current block being mined
  # Note: The program will hang here until a new
  #       proof of work is found
  proof = proof_of_work(last_proof)
  # Once we find a valid proof of work,
  # we know we can mine a block so 
  # we reward the miner by adding a transaction
  this_nodes_transactions.append(
    { "from": "network", "to": miner_address, "amount": 1 }
  )
  # Now we can gather the data needed
  # to create the new block
  new_block_data = {
    "proof-of-work": proof,
    "transactions": list(this_nodes_transactions)
  }
  new_block_index = last_block.index + 1
  new_block_timestamp = this_timestamp = date.datetime.now()
  last_block_hash = last_block.hash
  # Empty transaction list
  this_nodes_transactions[:] = []
  # Now create the
  # new block!
  mined_block = Block(
    new_block_index,
    new_block_timestamp,
    new_block_data,
    last_block_hash
  )
  blockchain.append(mined_block)
  # Let the client know we mined a block
  return json.dumps({
      "index": new_block_index,
      "timestamp": str(new_block_timestamp),
      "data": new_block_data,
      "hash": last_block_hash
  }) + "\n"

@node.route('/blocks', methods=['GET'])
def get_blocks():
  chain_to_send = blockchain
  # Convert our blocks into dictionaries
  # so we can send them as json objects later
  for block in chain_to_send:
    block_index = str(block.index)
    block_timestamp = str(block.timestamp)
    block_data = str(block.data)
    block_hash = block.hash
    block = {
      "index": block_index,
      "timestamp": block_timestamp,
      "data": block_data,
      "hash": block_hash
    }
  # Send our chain to whomever requested it
  chain_to_send = json.dumps(chain_to_send)
  return chain_to_send
def find_new_chains():
  # Get the blockchains of every
  # other node
  other_chains = []
  for node_url in peer_nodes:
    # Get their chains using a GET request
    block = requests.get(node_url + "/blocks").content
    # Convert the JSON object to a Python dictionary
    block = json.loads(block)
    # Add it to our list
    other_chains.append(block)
  return other_chains
def consensus():
  # Get the blocks from other nodes
  other_chains = find_new_chains()
  # If our chain isn't longest,
  # then we store the longest chain
  longest_chain = blockchain
  for chain in other_chains:
    if len(longest_chain) < len(chain):
      longest_chain = chain
  # If the longest chain wasn't ours,
  # then we set our chain to the longest
  blockchain = longest_chain

curl "localhost:5000/txion" \
     -H "Content-Type: application/json" \
     -d '{"from": "akjflw", "to":"fjlakdj", "amount": 3}'

curl localhost:5000/mine

{
  "index": 2,
  "data": {
    "transactions": [
      {
        "to": "fjlakdj",
        "amount": 3,
        "from": "akjflw"
      },
      {
        "to": "q3nf394hjg-random-miner-address-34nf3i4nflkn3oi",
        "amount": 1,
        "from": "network"
      }
    ],
    "proof-of-work": 36
  },
  "hash": "151edd3ef6af2e7eb8272245cb8ea91b4ecfc3e60af22d8518ef0bba8b4a6b18",
  "timestamp": "2017-07-23 11:23:10.140996"
}