fix issuing of connection IDs when dialing a 0-RTT connections

[marten-seemann]

Fixes #3057.

When dialing a 0-RTT connection, the client first restores the transport parameters from the original connection, and then applies the transport parameters provided by the server on the new connections.

@rip-create-your-account Do you think this fix is correct?

[codecov]

Codecov Report

Merging #3058 (10217a6) into master (2c45f2b) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3058      +/-   ##
==========================================
+ Coverage   86.16%   86.17%   +0.01%     
==========================================
  Files         132      132              
  Lines        9355     9355              
==========================================
+ Hits         8060     8061       +1     
+ Misses        938      937       -1     
  Partials      357      357              

Impacted Files	Coverage Δ
conn_id_generator.go	88.89% <ø> (ø)
internal/utils/rand.go	75.00% <0.00%> (+12.50%)	⬆️

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[rip-create-your-account]

What happens if the (*TransportParameters).ActiveConnectionIDLimit for the new connection is less than that of the 0-RTT params? (*TransportParameters).ValidFor0RTT doesn't check that field and I don't see server validating it elsewhere. So if the server were to reduce its ActiveConnectionIDLimit then same issue would occur as the client would issue CIDs according to the higher limit of the 0-RTT params. Should server reject 0-RTT in such case?

[marten-seemann]

Good catch! That’s definitely an oversight, it’s even in the spec: https://www.ietf.org/archive/id/draft-ietf-quic-transport-34.html#name-values-of-transport-paramet

I’ll create a separate PR for that.

[rip-create-your-account]

In that case this PR looks like good to me