About the Project

This is a finished Java implementation for the codecrafters "Build Your Own DNS server" Challenge. This code implements functionality for all stages (and extensions) of the challenge as of 2025-02-13.

What can it do?

1. Respond to multiple questions with a hardcoded A record of 8.8.8.8.
2. Handle compressed label sequences in questions.
3. Forward queries for A records to an upstream resolver specified with --resolver <address> on the command line. That upstream resolver must:
   • Always respond with an answer section for the queries.
   • Generate a response that does not contain other sections like (authority section and additional section)
   • Only respond when there is only one question in the question section (this DNS server handles splitting questions into multiple packets then merges the answers into a single response packet).

Running Locally

You will need Java 23 (or later) and maven installed to run this code. The program can then be run with:

./your_program.sh --resolver <optional-upstream-ressolver>

Test Run Video

A short video of the code being run in the codecrafters test environment:

codecrafters-dns-server-java-test-run-av1.webm