ahmedas22/COMP3010-Blockchain

Assignment 3

Getting Started

To start your peer, follow these steps:

1. Open a terminal.
2. Run the following command:

python main.py [arguments]

Command Line Arguments

• [ip]: optional ip address in format 192.168.y.x for host, by default it's silicon.cs.umanitoba.ca
• [port]: optional port number, by default it's 8793
• ...

Synchronization

The synchronization process may take approximately 1.5 minutes. During synchronization, you can expect to see on the terminal, all the blocks, gossips and stats that have been requested or responded to.

Consensus Code

The consensus code for choosing which chain to synchronize is located in the file main.py at lines 202-224. It picks chains by doing the following:

• iterating through the chains list, which contains stats of all peers that answered before timeout.
• It identifies the chain with the maximum height (max_height)
  • In the case of a tie, it appends all chains with the same height and matching top hash to the longest_chains list.
• It updates the list of tracked peers (tracked_peers) based on the chosen longest chains and returns the list of longest chains.

Cleaning up Peers

The cleanup process for peers can be found in the file main.py at lines 262-266, 113-116. It cleans up peers by doing the following:

• Every peer has an instance variable of last_message_time that keeps track of the last time a message was received
  • last_message_time changes every time handle_msg is called since it holds tuple of an address which I find the peer associated with, by calling find_peer_by_addr
• The peers finally get cleaned up by comparing every peer's last_message_time to current_time with the constant CLEANUP_INTERVAL added to last_message_time which is false, it kicks out that peer from the peer list