[Bug 1876034] [NEW] apt update crashes with "KeyError: 'suite'" in cnf-update-db if index compression is enabled

[Michael Sparmann]

Public bug reported:

On all Ubuntu releases since at least 19.10, enabling compressed APT
package list storage with command-not-found installed leads to this
crash in the cnf-update-db hook called by apt update:

Traceback (most recent call last):
  File "/usr/lib/cnf-update-db", line 26, in <module>
    col.create(db)
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/creator.py", line 93, in create
    self._fill_commands(con)
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/creator.py", line 127, in _fill_commands
    self._parse_single_commands_file(con, fp)
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/creator.py", line 165, in _parse_single_commands_file
    suite=tagf.section["suite"]
KeyError: 'suite'

(To enable compressed APT list storage, add Acquire::GzipIndexes "true";
to an apt.conf fragment.)

This appears to be caused by apt downloading an lz4-compressed command
list for command-not-found and cnf-update-db passing the
/var/lib/apt/lists/*Commands-*.lz4 files to db/creator.py, which does
not know about the compression and attempts to parse them as plain text.

** Affects: command-not-found (Ubuntu)
     Importance: Undecided
         Status: New

** Branch linked: lp:~oheoh/command-not-found/command-not-found

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https://bugs.launchpad.net/bugs/1876034

Title:
  apt update crashes with "KeyError: 'suite'" in cnf-update-db if index
  compression is enabled

Status in command-not-found package in Ubuntu:
  New

Bug description:
  On all Ubuntu releases since at least 19.10, enabling compressed APT
  package list storage with command-not-found installed leads to this
  crash in the cnf-update-db hook called by apt update:

  Traceback (most recent call last):
    File "/usr/lib/cnf-update-db", line 26, in <module>
      col.create(db)
    File "/usr/lib/python3/dist-packages/CommandNotFound/db/creator.py", line 93, in create
      self._fill_commands(con)
    File "/usr/lib/python3/dist-packages/CommandNotFound/db/creator.py", line 127, in _fill_commands
      self._parse_single_commands_file(con, fp)
    File "/usr/lib/python3/dist-packages/CommandNotFound/db/creator.py", line 165, in _parse_single_commands_file
      suite=tagf.section["suite"]
  KeyError: 'suite'

  (To enable compressed APT list storage, add Acquire::GzipIndexes
  "true"; to an apt.conf fragment.)

  This appears to be caused by apt downloading an lz4-compressed command
  list for command-not-found and cnf-update-db passing the
  /var/lib/apt/lists/*Commands-*.lz4 files to db/creator.py, which does
  not know about the compression and attempts to parse them as plain
  text.

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