[tahoe-lafs-trac-stream] [Tahoe-LAFS] #1710: Magic Folder: implement "Water Dragons" section of design doc

[Tahoe-LAFS]

#1710: Magic Folder: implement "Water Dragons" section of design doc
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     Reporter:  davidsarah           |      Owner:  daira
         Type:  enhancement          |     Status:  assigned
     Priority:  normal               |  Milestone:  1.11.0
    Component:  code-frontend-       |    Version:  1.9.1
  magic-folder                       |   Keywords:  unlink space-efficiency
   Resolution:                       |  gc otf-magic-folder-objective4
Launchpad Bug:                       |
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Comment (by daira):

 daira: dawuud meejah: the deletion bug is an omission in the design doc.
 in the case of existent files, the event when the file is replaced by the
 downloader will be ignored because the entry for that path in the magic
 folder db has the same size/mtime/ctime as the new file
 daira: the same *should* be the case for a deleted file. so the (size,
 mtime, ctime) in the db needs to be the same as returned by
 `fileutil.get_pathinfo`. the latter is (None, now, now) in the current
 implementation, which I think is probably wrong...
 daira: because the current time at the point of the `get_pathinfo` call
 won't/can't match the time in the database
 daira: the right fix is probably to change `get_pathinfo` to return
 `PathInfo(isdir=False, isfile=False, islink=False, exists=False,
 size=None, mtime=None, ctime=None)` for the `ENOENT` case
 daira: and make sure that's also what is written to the db when the
 downloader detects a deleted file

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1710#comment:42>
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