https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/blob/v2.1.0/ChangeLog

- Remove support for legacy one shot mode;
- Make connection summary at proxy privacy preserving;
- Add snowflake event API for notifications of connection events;
- Increase capacity of client address map at the server;
- Further clean up snowflake server logs;
- Validate proxy and client supplied strings at broker;
- Update version of DTLS library to include fingerprinting fixes;
- Support recurring NAT type check in standalone proxy.

While here,

* update goptlib from 1.1.0 to 1.2.0;
* https://github.com/torbsd/goptlib/commit/0018750f0851d5b427828bfbdfc7968ae3c398c3