[tor-dev] Failure to connect to a 0.3.4.9 bridge--downgrading to 0.2.9.17 fixes it

[David Fifield]

Here, a user reported a failure to connect to their own bridge, stopping
at 25% bootstrapped. teor and I went through the basic troubleshooting
steps of checking the bridge syntax, system time, and firewall settings.
With or without obfs4 didn't make a difference. The user eventually
tried downgrading the bridge from 0.3.4.9 to 0.2.9.17--and that fixed
it. Their client version was 0.3.4.9.
https://bugs.torproject.org/28717#comment:18

They also tried with two bridges from BridgeDB. The one running 0.3.4.9
didn't work, and the one running 0.2.9.17 did.

A possible lead are these client log messages:
[info] handle_response_fetch_desc(): Received server info (body size 0) from server 'X.X.X.X:YYYY'
[info] handle_response_fetch_desc(): Received http status code 404 ("Servers unavailable") from server 'X.X.X.X:YYYY' while fetching "/tor/server/authority.z". I'll try again soon.