A distributed computing application that builds and validates a blockchain by requesting blocks from peers. This application was built in Python and uses Sockets to send requests and receive responses from peers. It purely builds and validates the blockchain. There is no block mining implemented because other peers on the network mined blocks faster than the local application could.
You can view the full project here.
Joining the Network
On joining the network, a keep_alive() GOSSIP is sent to 3 random peers (or just to wellknown host if there’s less than 3 peers). Any GOSSIPs that have ids that are not in the global list of ids are replied to via GOSSIP_REPLY.
Any peers that have not sent a GOSSIP for at least a minute are assumed to have timed out and are removed from the global list of peers via peerTimeout().
To ensure that the application is not timed out by peers, GOSSIPs are sent every 30 seconds via keep_alive(). GOSSIPs are also sent out if the socket times out.
Consensus
After joining the network and receiving GOSSIP_REPLYs, the consensus process begins.
A STATS request is sent to all known peers. After waiting a timeout amount of time for STAT_REPLYs, the longest chain is identified using max(height,hash) included in the reply and the method longest_chain(). Ties are immediately broken by finding the max number of peers with the max height. After determining the longest chain, blocks are requested round-robin from all peers that have the longest chain via get_blocks(height).
When adding a block to the local chain:
- All blocks are validated before being added
- Blocks are stored in a global list since they might not be received in height order and popped off if they are the next block
- If the next block needed is missing, send another
get_block(height)request to known peers with longest chain - Blocks that are mined and ANNOUNCED are either added to the top of the chain if it is built, or stored in the global list
To be considered valid a block must meet the following criteria:
- Its nonce must be at most 40 characters
- A block must have less than 10 messages
- Each message in the block must be at most 20 characters
- Its hash must respect the order predefined by instructor
To ensure local chain synchronization with the distributed chain:
- Consensus is done every 2 minutes
- Consensus can be requested by peers via CONSENSUS request
- Validate the entire local chain before sending it upon receiving a STATS request from a peer