[tahoe-lafs-trac-stream] [Tahoe-LAFS] #2930: "AUTO" Tub location detection/assignment is silently broken when system tools are missing

[Tahoe-LAFS]

#2930: "AUTO" Tub location detection/assignment is silently broken when system
tools are missing
---------------------+---------------------------
 Reporter:  exarkun  |          Owner:
     Type:  defect   |         Status:  new
 Priority:  normal   |      Milestone:  undecided
Component:  unknown  |        Version:  1.12.1
 Keywords:           |  Launchpad Bug:
---------------------+---------------------------
 `Node.get_tub_portlocation` attempts to automatically allocate and detect
 a listening address for the Tub if none has been explicitly configured.
 In this case, it uses `allmydata.util.iputil.get_local_addresses_sync`.
 `get_local_addresses_sync` may return an empty list if neither `ip` nor
 `ifconfig` can be found or if both of these tools return only errors or
 only empty address lists.  If an empty address list is returned,
 `get_tub_portlocation` nevertheless proceeds to construct a fURL for the
 Tub which contains no location hints.  Such a fURL is arguably useless
 since no piece of Tahoe-LAFS-related software will be able to use it to
 establish a connection.

 `get_local_addresses_sync` could be made more robust (and probably simpler
 and faster, too) by using something like the `netifaces` package.

 `get_tub_portlocation` could be made less surprising by failing loudly and
 immediately if asked to allocate/detect an address and then discovering it
 is unable to (ie, getting an empty local addresses list) rather than
 quietly writing garbage to a configuration file for someone to later trip
 over (it took me multiple hours to trace the misbehavior from the place
 where the problem was observed and reported back to
 `get_local_addresses_sync` and `get_tub_portlocation`).

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2930>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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