arb sometimes produces corrupt quick-save files

[westram]

The case encountered was most likely caused by defect described in #86

The quick-save file was corrupted at a db-entry saved as GB_STRING_SHRT. Such an entry does NOT store it's size/memsize, instead it has to be strictly zero-terminated.

Somehow this got violated and reading the quick-save file lost sync and bailed out later on with some random error.

That problem has occurred with full-saved DBs in the past. [5274] attempted to fix that.

Possible causes:

• string-entries containing zero-bytes (in the "middle" of the entry)
• completely corrupted entries pointing to volatile data

Try to

• provoke the misbehavior described above using a unit-test

[westram]

Reproduce:

• load demo.arb
• destroy group 'inner' and undo (see also #86)
• save quick
• quit & restart demo.arb results in

  arb_ntree: Error: ARB ERROR: I cannot load your quick file '/home/ralf/ARB-bilbo/ARB.trunk.test/demo.a00'
  Reason: Loading failed (file corrupt?)
  [Fail-Reason: 'ARB ERROR: Aborting recovery (because recovery mode is disabled)
  Error causing recovery: 'Unknown func=0'
  Part of data may be recovered using 'arb_repair yourDB.arb newName.arb'
  (Note: Recovery doesn't work if the error occurs while loading a quick save file)']
  
  
  Note: you MAY restore an older version by running arb with:
        arb <name of quicksave-file>
  

Doing the same, but with full- instead of quick-save, leads to corrupted failing on open

arb_ntree: Error: ARB ERROR: ARB ERROR: Aborting recovery (because recovery mode is disabled)
Error causing recovery: 'Unknown DB type 0 (DB version=1)'
Part of data may be recovered using 'arb_repair yourDB.arb newName.arb'
(Note: Recovery doesn't work if the error occurs while loading a quick save file)

Running arb_repair fails to restore anything useful.

[westram]

Another way:

• start demo.arb
• select 'MOVE MODE'
• either
  • move groupinfo of 'inner' to unused branch or
  • exchange groupinfo with 'test'
• undo
  • groupname 'inner' disappears (groupname 'test' does not)
• save → corrupt

[westram]

by [11902]

• corrupted entries are still written into , but remains loadable
• followup ticket:501