[tor-bugs] #26155 [Core Tor/Tor]: Bandwidth file Timestamp is the latest scanner result, not the file creation time

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#26155: Bandwidth file Timestamp is the latest scanner result, not the file
creation time
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 Reporter:  teor                  |          Owner:  teor
     Type:  defect                |         Status:  needs_revision
 Priority:  Medium                |      Milestone:  Tor: 0.3.5.x-final
Component:  Core Tor/Tor          |        Version:
 Severity:  Normal                |     Resolution:
 Keywords:  tor-spec, tor-bwauth  |  Actual Points:
Parent ID:  #25925                |         Points:
 Reviewer:                        |        Sponsor:
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Changes (by teor):

 * status:  needs_review => needs_revision


Comment:

 Please see my comments on those commits.

 Also, it looks like the changes below weren't made in the spec.

 Can you tell me what you decided to do about these issues:

 Replying to [comment:8 teor]:
 > …
 > > When there are not any scan results (similar to the earliest_bandwith
 case https://github.com/pastly/simple-bw-
 scanner/blob/master/sbws/core/generate.py#L136), which should be the
 timestamp?.
 >
 > If there are no results in the file, then it really doesn't matter
 what's in the header.
 >
 > The timestamp is mandatory, so you can't leave it out.
 >
 > Here are your options:
 > 1. specify that the time must be in the past - tor will warn that the
 file is too old
 > 2. don't generate the file, delete any existing file - tor will warn
 that the file is missing
 > 3. generate an empty file, truncate any existing file - old tors will
 log stack contents, see #26007
 >
 > I suggest that we say that generators SHOULD NOT generate a file, and
 SHOULD delete any existing file, because it is the least confusing option.
 > https://gitweb.torproject.org/torspec.git/tree/bandwidth-file-
 spec.txt#n61
 >
 > If you want, you can also say that:
 > * generators SHOULD wait until enough relays are measured before
 generating the file (option 2)
 > * generators MAY use a placeholder timestamp (option 1j, but the time
 MUST be at least 5 days in the past to avoid silent failures.
 > * generators MUST NOT generate an empty file (option 3), because it
 triggers a bug in tor.
 >
 > Please update the spec with these changes.
 >
 > The earliest_bandwidth and latest_bandwidth are optional.
 > If there is no valid value for these lines, the generator SHOULD leave
 them out.
 > Please update the spec with these changes.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/26155#comment:11>
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