Service description

It's example of TCP service to provide Anti-DDOS protection with PoW. Client requests challange from server and calculate token by the following rules: hash_sha256(challenge+token) starts with 000 bytes. If passed token is correct, service will process request to get random quote of wisdom.

Explanation of the choice of the POW algorithm

In this implementation, the client generates random data and computes the SHA-256 hash result by appending a counter in a loop until a hash result with the required prefix (number of leading zeros) is found. This requires a certain amount of computation time which can effectively limit the rate at which requests can be made to the server.

Here PoW algorithm is simple Hashcash, it is high enough to provide sufficient protection against DDoS attacks, but not too high that it causes significant delays or inconvenience for legitimate users.

Build&Run

Prepare server docker

docker build -t word-of-wisdom-server -f Dockerfile.server .

Prepare client docker

docker build -t word-of-wisdom-client -f Dockerfile.client .

Run server

docker run -p 8080:8080 word-of-wisdom-server

Run client

docker run --network="host" word-of-wisdom-client

Contract

Client sends message in format:

<fullCommand> <token:optional>

When command supports versions:

<fullCommand> = <version>.<command>

Versions are implemented in hub-spike approach: each version must call hub methods. So, versions implement mapping under hub.

Client commands

CHG

Client requests "challenge" from server.

v1.CHG

Response:

OK <challenge>

CHGT

Client passes "challenge" token to server.

v1.CHGT <token>

Response:

OK

QTR

Client requests random qoute from server.

v1.QTR

OK <quote>

Server commands

OK

Server responses successful message.

OK
OK <payload>

ERR

Server responses failed error and reason.

ERR <error-message>