DNS Server in Rust

This is my Rust implementation of the CodeCrafters Build Your Own DNS Server challenge.

The project is intentionally small, but it covers the core pieces of a DNS server: parsing DNS packets from UDP, decoding compressed question names, encoding DNS responses, forwarding queries to an upstream resolver, and generating mock A-record answers for challenge stages that allow synthetic responses.

What It Demonstrates

• DNS wire-format parsing and serialization without a DNS library.
• Rust ownership around borrowed packet buffers and encoded response buffers.
• Typed errors with thiserror and application-level error propagation with anyhow.
• A bounded, standard-library worker pool for concurrent UDP request handling.
• Structured logging with tracing.
• Unit tests for packet encoding/decoding, compressed names, response construction, handler behavior, provider behavior, CLI parsing, and worker configuration.

Running

cargo run -- --local-addr 127.0.0.1:2053 --resolver 8.8.8.8:53

Optional concurrency settings:

cargo run -- --workers 4 --queue-capacity 128

Logging can be controlled with RUST_LOG:

RUST_LOG=debug cargo run

Verification

cargo test
cargo clippy --all-targets --all-features -- -D warnings

Notes

This is a learning project, not a production DNS server. It supports the subset of DNS needed for the CodeCrafters challenge. One challenge-specific behavior is called out in code: when an upstream resolver fails, the handler falls back to synthetic A records because some CodeCrafters stages accept mocked answers.