onionlink: Connect to v3 onion services with C++20 using libsodium and mbedTLS.

Onionlink stands out in the crowded space of Tor clients by adopting a highly focused, minimal engineering approach. Most commercial or large-scale open-source Tor implementations aim to be holistic, bundling features like path-selection algorithms, complex anonymity guardrails, and user-facing features. Onionlink deliberately eschews this breadth. Its goal is strictly one thing: reliable, direct connectivity to Tor v3 onion services, using the minimum necessary code to achieve maximum interoperability with the underlying protocol. Technically, the library is a deep dive into the Tor v3 specification. It handles the complex, multi-stage handshake process: parsing the dynamic microdescriptor consensus, hydrating the required Ed25519 identities, deriving the blinded v3 key material, and navigating the rendezvous establishment. The client's ability to manage guarded `EXTEND2circuit` for descriptor fetching, correctly process the `INTRODUCE1` message, and finally complete the `hs-ntor` handshake, demonstrates a high degree of protocol accuracy. For a developer, this level of detailed, low-level protocol adherence is extremely valuable for educational purposes or building custom tooling on top of the Tor stack. However, this minimalist focus is also its most significant limitation. The documentation is explicit: Onionlink omits critical security features like full consensus validation, directory signature checking, path-bias algorithms, and sophisticated session management. It operates as a proof-of-concept protocol experiment, not a secure, production-ready client. Using it requires a deep understanding of both the Tor v3 protocol and the underlying cryptographic assumptions, as the builder is effectively responsible for the security posture of the resulting application. The command-line interface, which supports raw data streams, simple HTTP GETs, and standard input piping, makes it immediately useful for scripting and automation tasks. In conclusion, Onionlink is not meant to replace the Tor Browser or Arti. It is a sophisticated toolkit for the security-minded developer who needs to rapidly prototype interactions with onion services. While it sacrifices generalized robustness for focused utility, this specialization makes it a powerful educational resource and an ideal building block for advanced, tailored network security applications, provided the inherent risks of using a partial implementation are properly managed.