[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3833: Knowledge of mutable and immutable share file formats is spread across the codebase

[Tahoe-LAFS]

#3833: Knowledge of mutable and immutable share file formats is spread across the
codebase
---------------------+---------------------------
 Reporter:  exarkun  |          Owner:  exarkun
     Type:  defect   |         Status:  new
 Priority:  normal   |      Milestone:  undecided
Component:  unknown  |        Version:  n/a
 Keywords:           |  Launchpad Bug:
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 The mutable and immutable container formats each start with a unique
 header.  This header is sometimes inspected to determine if a particular
 file probably contains a mutable container, an immutable container, or
 something unrelated to Tahoe.

 This inspection is done by spreading knowledge of the header format across
 several parts of the codebase.  For example: the test suite searches for a
 specific byte sequence to identify immutable containers; the debug command
 does likewise, and there are similar examples of logic inspecting the
 mutable container's header.

 This is undesirable because duplication of logic allows for divergences to
 arise and increases the maintenance burden.  It also increases the local
 code complexity at each of these sites by involving specific detailed
 information about file formats where the code might otherwise be
 independent of those format details.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3833>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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