Proof of work simple example

Sequence diagram

sequenceDiagram
    Client->>Server: ask\n
    Server->>Client: uuid\n
    loop nonce calc
        Client->>Client: 
    end
    Client->>Server: answer:uuid:nonce\n
    Server->>Client: random quote\n

Loading

Description

1. The client wants to get a quote. It sends an "ask" message
2. The server generates a uuid, stores it in the internal storage with a timestamp and sends it to the client.
3. The client tries to find a nonce for this uuid which is suitable for pow algorithm.
4. The client sends answer to the server with uuid and nonce
5. The server checks:
   • if this uuid exists in internal storage;
   • if it has already been used;
   • if it has expired;
   • if it a suitable nonce,
6. If all is ok server sends quote to the client.

PoW algorithm

For this task I took a Hashcash algorithm used by Bitcoin.

The main reason: it was interesting for me personally)

Commands

1. Run tests:
   make test

2. Start client - server interaction in docker:

   docker-run

   and loot at you terminal.

Notes

1. This example uses hardcoded 24 target bits for Hashcash algorithm.
2. If client can't find a proper nonce it fails in 10 seconds
3. Every task expires on 2 seconds

Sources

1. For this task I used a habr article