Start a changelog for Arti 0.2.0

### Notes

This file describes changes in Arti through the current release.  Once Arti

is more mature, and we start to version crates independently, we will

probably switch to using a separate changelog for each crate.

is more mature, and we start to version crates independently, we may

switch to using a separate changelog for each crate.

# Arti 0.2.0 — XXXX Apr 2022

BLURB

(entries below are taken through 482b2e3256cc0c738dc1deb3029173b8619920dd)

### Breaking changes

Here are the main breaking changes visible from the arti-client crate.

Numerous other lower-level crates have breaking changes not noted here.

- Significant refactoring to our configuration handling logic and APIs.

  The goals here are:

      - To have the current `ConfigBuilder` types

        become the only user-visible configuration objects, and to have the

        current `Config` objects become implementation details.

      - To remove `arti-config` entirely, and fold its contents into

        `arti` or `arti-client` as appropriate.

      - To remove unnecessary ad-hoc accessor functions until they prove to be

        needed.

  This change

  is not done in this release; we expect to have more breakage

  in this area in our next release as well.  ([#314], [#371], [#372],

  [#374], [#396], [#418],

  [!391], [!401], [!417], [!421], [!423], [!425], [!427])

- The [`Runtime`] trait now includes (and requires) UDP support. (Part

  of [!390]'s support for DNS.)

- Stream isolation support is completely revised; see notes on isolation

  below.

### New features

- Experimental feature to allow the [`DirMgr`] to be replaced by

  a user-provided [`DirProvider`]. ([#267], [!318], [!347])

- Arti now tolerates IPv6-only environments, by using a basic form of

  the [RFC 8305] "happy eyeballs" algorithm to try connections to

  relays' IPv4 and IPv6 addresses in parallel. ([!382])

- New experimental APIs for modifying consensus objects ([!318], [!402])

- The `arti` crate now exists as a library, to better expose features

  like its top-level configuration logic. ([!403])

- Arti now supports a `dns_port` to relay A, AAAA, and PTR requests over

  the Tor network, like the C tor implementation's DnsPort. ([!390],

  [!408], [!409])

- Arti has a new full-featured [stream isolation API] that supports more

  complicated isolation rules, including user-supplied rules.  ([#150],

  [#414], [!377], [!418], [!420], [!429], [!434])

- Channel and Circuit objects now remember the peers that they used

  when they were constructed, and allow queries of this information as

  part of their API. ([#415])

- The logic for retrying failed guards has been revised to use

  the same decorrelated-jitter algorithm as directory requests, per

  [proposal 336]. ([cb103e04cf4d9853], part of [#407], [!426])

- When all our guards have failed, we no longer retry them all

  agressively, but rather assume that our net connection is down and

  wait a while. ([eed1f06662366511], part of [#407], [!426])

- When running as a directory client, we now remember more information

  about the source of each request, so we can avoid caches that have

  failed. ([87a3f6b58a5e75f7])

- Experimental feature to install a "filter" for modifying incoming

  directory objects.  Used for testing, to observe client behavior when

  the directory is in an inconsistent or non-working state. ([#397], [!431])

- Arti now has initial support for a "Dormant Mode" where periodic events are

  suspended. Later, even more background tasks will be shut

  down. ([#90], [!429])

### Major bugfixes

### Infrastructure

- We have a new [`arti-testing`] crate (not published on crates.io) to

  perform various kinds of stress-testing on our implementation. It can

  simulate several kinds of failure and overload conditions; we've been

  using it to improve Arti's behavior when the network is broken or

  misbehaving. ([!378], [!392]; see also [#329])

- The [`arti-bench`] tool now constructs streams in parallel and

  supports isolated circuits, so we can

  stress-test the performance of a simulated busy client. ([#380], [!384])

- Reproducible build scripts now use Rust 1.59 and Alpine 3.15. ([#376],

  [!380])

- Improved messages from reproducible build script. ([#378], [!383])

- Scripts to launch chutney are now refactored and de-duplicated ([!396])

### Documentation and Examples

- Better documentation for default configuration paths. ([!386])

- Instructions for using Tor Browser with Arti on Windows. ([!388])

- Better instructions for building Arti on Windows. ([!389], [!393])

- Improved documentation for stress-testing Arti. ([!407])

### Cleanups, minor features, and minor bugfixes

- Use [`derive_more`] and [`educe`] (and simple built-in `derive`) in

  many places to simplify our code. ([!374], [!375])

- Use a [forked version of `shellexpand`] to provide correct behavior on

  Windows. ([!274], [!373])

- Avoid unnecessary `Arc::clone()`s in `arti-client` experimental

  APIs. ([#369], [!379])

- New [`tor-basic-utils`] crates for small pieces of low-level

  functionality.

- Small performance improvements to parsing and allocating directory objects,

  to improve start-up and download times. ([#377], [!381])

- Use significantly less memory (on the order of a few megabytes less per

  running client) to store directory objects. ([#384], [#385], [#386], [#387],

  [#388], [!389], [!398], [!415])

- Avoid allocating a backtrace object for each channel-creation

  attempt. ([#383], [!394])

- Always send an "If-Modified-Since" header on consensus requests, since

  we wouldn't want a consensus that was far too old. ([#403], [!412])

- Actually acknowledge preemptive circuits configuration. Previously,

  we missed a place where we needed to copy it.  (Part of [!417])

- Backend support for collecting clock skew information; not yet

  used. ([#405], [!410])

- Major refactoring for periodic events, to support an intial version of

  "dormant mode." ([!429])

### Acknowledgments

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# Arti 0.1.0 — 1 Mar 2022