# Arti Report 5: August 4 through September 15

## Activities since our last report

I'm back, with updates from the last month! We've spent a lot of time over the last on cleaning up technical debt issues in our code that had accumulated as I wrote it. There are more tests and warnings enabled than before, and we've changed some new internal APIs to make them unable to panic. We're also using the [`derive_builder`][derive_builder] tool to throw out a bunch of boilerplate code.

When I wrote last month, I'd just finished up the implementation for circuit build timeout inference. As followup work to that, I worked with Mike Perry to collect all of the missing specification issues that I'd found while cloning that feature, and [roll them back][torspec-mr-40] into our `path-spec.txt` document. Mike'sw found a couple of mistakes in my implementation that I was able to resolve—fortunately, by removing code from the Arti timeout inference code.

## Getting a head start on API design

API design will be the focus of our 0.1.0 release, but we still want to get it "as right as we can" in the upcoming 0.0.1 version.

With that in mind, we've started enumerating the various kinds of programs and environments that we need to support down the road, and [working on a list of example programs][ticket-164] that we might be able to ship with Arti. (My own experience so far is that writing example code is just about the best way to find API deficiencies.)

## Uplifting new features from C Tor

For our work on congestion control, we're getting a new [circuit extension handshake][prop332]. Going forward, as we add features to C Tor, we're going to try to add them to Arti at around the same time. With that in mind, we have the new handshake implemented (but not enabled): we used its implementation to validate our specifications double-check our test vectors.

## Towards guard support

Our largest remaining priority for Arti 0.0.1 is full support for [guard nodes][guard-spec]. (In Tor, a "guard node" is a relay that a client decides to use as the first hop for all of its circuits for a long time. Using guard nodes improves resistance against many kinds of attacks based on hostile relays.)

We've started laying the groundwork here: we now have support for all of the guard-related consensus parameters, and we've reworked our relay selection code to allow picking multiple weighted random items without replacement. We've also added some previously unneeded lookup-by-ID features to network directory code.

(Fun fact: the Tor implementation of mapping IDs to relays has been historically ugly, since we don't really know a relay's ed25519 identity until we have a microdescriptor for it. In C, this has led to a reasonably messy pile of dangling pointer bugs…which Rust won't even let us write! Also, we've made better design choices in Arti about our directory objects, so we don't have do support all of the strange mutability that our C code had to try to handle.)

We're now in the midst of coding up a guard implementation. The tricky part here is that our guard logic affects circuit building selection (since circuit paths must begin with a guard), but circuit construction affects guard selection. We're experimenting with different designs to try to keep the complexity here under control.

# Thanks to awesome volunteers!

Thanks to Jani Monoses for migrating Arti to the tracing crate and adding journald support; to Robin Leander Schröder for cleaning up some of our `unwrap_or()` code; to S0AndS0 for work enabling the `unwrap_used` Clippy lint; to Daniel Eades for work cleaning up Clippy lints in our test modules, and to Trinity Pointard for work on stream isolation and reproducible builds!

[ticket-164]: https://gitlab.torproject.org/tpo/core/arti/-/issues/164 [prop-332]: https://gitlab.torproject.org/tpo/core/torspec/-/blob/main/proposals/332-nto... [derive_builder]: https://crates.io/crates/derive_builder [torspec-mr-40]: https://gitlab.torproject.org/tpo/core/torspec/-/merge_requests/40 [guard-spec]: https://gitlab.torproject.org/tpo/core/torspec/-/blob/main/guard-spec.txt