141: exit policy summary

[Peter Palfrader]

On Mon, 11 Aug 2008, Peter Palfrader wrote:

>   Similarly to IP address, ports, timestamp, and bandwidth a consensus
>   should list the exit policy matching the descriptor digest referenced
>   in the consensus document.

That doesn't work so well, since some voters can "abstain" - simply by
being too old to support consensus-method 5 and the associated new
fields in votes.

the new version reads:

| 3.4.1 Consensus selection
| 
|   When building a consensus, authorities have to agree on a digest of
|   the server descriptor to list in the router line for each router.
|   This is documented in dir-spec section 3.4.
| 
|   All authorities that listed that agreed upon descriptor digest in
|   their vote should also list the same exit policy summary - or list
|   none at all if the authority has not been upgraded to list that
|   information in their vote.
| 
|   If we have votes with matching server descriptor digest of which at
|   least one of them has an exit policy then we differ between two cases:
|    a) all authorities agree (or abstained) on the policy summary, and we
|       use the exit policy summary that they all listed in their vote,
|    b) something went wrong (or some authority is playing foul) and we
|       have different policy summaries.  In that case we pick the one
|       that is most commonly listed in votes with the matching
|       descriptor.  We break ties in favour of the lexigraphically larger
|       vote.
| 
|   If none one of the votes with a matching server descriptor digest has
|   an exit policy summary we use the most commonly listed one in all
|   votes, breaking ties like in case b above.

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