p2p - 如何在 Bittorrent DHT 中找到具有精确 info_hash 的节点？

Question

在bittorrent的DHT协议(protocol)的文档中，给出了get_peers方法用于查找具有给定info_hash的节点。它说如果响应包含“values”键，则查询的节点已返回有关包含准确info_hash的节点的信息.如果节点返回“nodes”键，它已经返回了最接近结果的 K 个节点。我们是否应该在返回的节点(最近的)上递归调用 get_peers 以到达精确的节点(具有相同的 info_hash)？

Answer 1

Should we recursively call get_peers on returned nodes(closest) in order to reach till exact nodes(with same info_hash)?

是也不是。如果你是 LISP 那种人，你可以使用递归函数。也就是说，一个 while 循环就可以完成这项工作。下面是一些实现 FIND_VALUE 算法的 python 代码，带有一些注释:

async def _get(self, key):
    """Fetch the value associated with KEY from the network"""
    uid = key
    queried = set()
    while True:
        # retrieve the k nearest peers and remove already queried peers
        peers = nearest(k, self.peers)
        # no more peer to query, the key is not found in the dht
        if not peers:
            raise KeyError(uid)
        # query selected peers
        responses = dict()
        for address in peers:
            response = self._protocol.rpc(address, "value", uid)
            responses[address] = response
        # check responses: look for the value or add peers more near KEY
        for (address, response) in responses.items():
            queried.add(address)
            if isinstance(response, Exception):
                continue
            elif response[0] == b"VALUE":
                # value is found, return it
                value = response[1]
                if hash(value) == unpack(uid):
                    # at last!
                    return value
                else:
                    log.warning(
                        "[%r] bad value returned from %r", self._uid, address
                    )
                    await self.blacklist(address)
                    continue
            elif response[0] == b"PEERS":
                # value not found but we got peers that are more near KEY
                await self._welcome_peers(response[1])

此代码基于qadom's peer.py