code: func (sp *ServerPeer) OnHeaders(p *peer.Peer, msg *wire.MsgHeaders) {
  	log.Tracef("Got headers with %d items from %s", len(msg.Headers),
  		p.Addr())
  	sp.server.blockManager.QueueHeaders(msg, sp)
  }
docs: // OnHeaders is invoked when a peer receives a headers bitcoin
  // message.  The message is passed down to the block manager.