“Word of Wisdom” TCP-server

Status:

Task description

Design and implement "Word of Wisdom" TCP server.

• TCP server should be protected from DDOS attacks with the Prof of Work, and the challenge-response protocol should be used.
• The choice of the POW algorithm should be explained.
• After Prof Of Work verification, the server should send one of the quotes from the "Word of Wisdom" book or any other collection of the quotes.
• Docker file should be provided both for the server and for the client that solves the POW challenge.

The Proof Of Work algorithm

In this project implemented the Hashcash algorithm. It is a classic, well-documented algorithm that has several advantages:

• well documented
• simple validation
• a client can get all required data via one request
• a wide range of challenge complexity settings In this project, some changes to the hashcash protocol implemented:
• replaced a random number with a UUID-string in the rand field of the challenge data. It should prevent the usage of precomputed challenges
• added issued challenges cache to the service to check that the client solved the real challenge.
  • in this implementation used in-memory local cache, but in production can be used, for example, a Redis cache (Also implemented). Redis can improve the scalability of the service, especially with the async client

Project structure

According to the Go-Layout:

• cmd/client – client entry point
• cmd/service – service entry point
• config/config.yaml – config file
• data/quotes.txt – data file, contains quotes from the Book of Wisdom
• docker – Docker files for service and client
• internal/client – client protocol implementation
• internal/pkg/cache – cache for requested challenges
• internal/pkg/clock – interface for testing purposes
• internal/pkg/config – project configuration. It reads from the config file and env variables. Environment variables have priority and can override settings.
• internal/pkg/pow – hashcash implementation
• internal/pkg/storage – in-memory storage for quotes
• internal/pkg/transport – client-service protocol definition
• internal/service – service protocol implementation

Prerequisites

• Go 1.20+
• Docker

How to run?

make install        # to get dependencies
make test           # to run unit tests
make run-service    # to start service
make run-client     # to start the client
make run-prod       # to start both client and server in
                    # docker containers