[tahoe-lafs-trac-stream] [tahoe-lafs] #1756: MDMF publisher sends duplicate write vector elements

[tahoe-lafs]

#1756: MDMF publisher sends duplicate write vector elements
--------------------------+---------------------------
 Reporter:  davidsarah    |          Owner:
     Type:  defect        |         Status:  new
 Priority:  normal        |      Milestone:  undecided
Component:  code-mutable  |        Version:  1.9.1
 Keywords:  mdmf publish  |  Launchpad Bug:
--------------------------+---------------------------
 The MDMF publisher (in mutable/layout.py) sends duplicate write vector
 elements for the start of the MDMF header. This confused the cloud backend
 before I fixed it to tolerate duplicates; in any case, the publisher
 probably shouldn't be doing that.

 IRC log of debugging session:
 {{{
 the write vector that fails is: [(2167, 54), (123, 346), (2221, 32), (469,
 136), (0, 41), (605, 66), (671, 93), (59, 64), (41, 18), (0, 41)]
 (first element of each pair is data offset, second is length of write)
 which contains two writes at offset 0 of length 41
 ***davidsarah looks at the MDMF publisher
 the first 41 bytes is the container type byte (SDMF or MDMF),
    sequence number, and root hash
 which suggests that MDMFSlotWriteProxy.put_root_hash is being
    called twice...
 no, it isn't
 so in that case, put_root_hash is being called, and the
   if not self._written branch in _write is also being taken, maybe
 yep, that's it
 }}}

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/1756>
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