[Bug 1849368] Re: apt-get update issues invalid range requests for previously completed downloads

[Julian Andres Klode]

My understanding is that this is a server bug and apt is complying with
the http specification.

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Title:
  apt-get update issues invalid range requests for previously completed
  downloads

Status in apt package in Ubuntu:
  New

Bug description:
  When an apt-get update fails, for instance due to a mismatch between
  the Release and Packages.gz due to a mirror sync/index update, it
  leaves files in the /var/lib/apt/lists/partial for the distribution:

  15466565     16 -rw-r--r--   1 root     root        13860 Oct 22 12:50 /var/lib/apt/lists/partial/ourhost_internal_repo_dists_main_Release
   15466663      4 -rw-r--r--   1 root     root          475 Oct 22 12:50 /var/lib/apt/lists/partial/ourhost_internal_repo_dists_main_Release.gpg
   15471150      0 -rw-r--r--   1 root     root            0 Oct 22 12:52 /var/lib/apt/lists/partial/ourhost_internal_repo_dists_main_main_binary-amd64_Packages.gz.FAILED

  In this case both Release and Release.gpg were complete, however when
  running apt-get update again it issues the revalidation requests for
  these resources with Range headers that are the length of the file
  resulting in '416 Requested Range Not Satisfiable':

  GET .../Release HTTP/1.1
  Cache-Control: max-age=0
  Accept: text/*
  Range: bytes=13860-
  If-Range: Tue, 22 Oct 2019 12:50:05 GMT
  User-Agent: Debian APT-HTTP/1.3 (1.6.12)

  HTTP/1.1 416 Requested Range Not Satisfiable

  It appears:

  - There's no way for apt-get to know if the file is complete so this logic will always be hit if the file exists https://github.com/Debian/apt/blob/master/methods/http.cc#L956-L962
  - The logic for determining whether a server supports range requests is only entered if an Accept-Range header exists, however an absence of this header means support is not available - https://github.com/Debian/apt/blob/master/methods/basehttp.cc#L251

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