Freeze on startup due to invalid handshake?

[Navya]

As documented, the client sometimes freezes upon startup; I tried to debug this and managed to root out the cause.

In a nutshell, we're running into an infinite loop trying to parse the handshake response:

  async def _handshake(self):
        """
        Send the initial handshake to the remote peer and wait for the peer
        to respond with its handshake.
        """
        self.writer.write(Handshake(self.info_hash, self.peer_id).encode())
        await self.writer.drain()

        buf = b''
        while len(buf) < Handshake.length:
            buf = await self.reader.read(PeerStreamIterator.CHUNK_SIZE)

When debugging, I noticed that the len(buf) stays at 0 at all times during the occasional freeze, thus creating the infinite loop. I'm not entirely surely if it's a problem with our parsing methods, or if the handshake from that one peer was indeed invalid.

That said, I think we can easily mitigate this issue by hardcoding a retry limit. I've attempted a fix in #2 in conjunction with main feature in that PR, and things seemed to work fine (i.e, we can download a torrent without freezing).