[Bug 1750625] Re: update misinterprets 304 response on Packages.gz

[Hontvári József Levente]

This is a bug in 20.04 as well. I have no Release file, this is a
private, unsigned repository, only Packages.xz. On first run, apt update
first works. On the second run apt update issues a HTTP GET with an If-
Modified-Since header:

GET /deb/Packages.xz HTTP/1.1
Host: XXX
Cache-Control: max-age=0
If-Modified-Since: Sat, 18 Apr 2020 14:19:16 GMT
User-Agent: Debian APT-HTTP/1.3 (1.6.12)

Apache HTTPD correctly responds that there was no change:

HTTP/1.1 304 Not Modified
Date: Sun, 19 Apr 2020 20:53:02 GMT
Server: Apache/2.4.18 (Ubuntu)
ETag: "960-5a39159dd8574"

Instead of using the existing downloaded version apt update tries to
download Packages.bz2 etc. and finally it displays:

root at pipa11:~# apt update
Hit:1 http://mirror.hk.leaseweb.net/ubuntu bionic InRelease
Hit:2 http://mirror.hk.leaseweb.net/ubuntu bionic-updates InRelease  
Hit:3 http://mirror.hk.leaseweb.net/ubuntu bionic-backports InRelease
Ign:4 http://XXX/deb  InRelease                                                                  
Ign:5 http://XXX/deb  Release                                               
Hit:6 http://security.ubuntu.com/ubuntu bionic-security InRelease
Hit:7 http://XXX/deb  Packages                      
Ign:7 http://XXX/deb  Packages                      
Ign:7 http://XXX/deb  Packages
Ign:7 http://XXX/deb  Packages
Ign:7 http://XXX/deb  Packages
Ign:7 http://XXX/deb  Packages
Ign:7 http://fXXX/deb  Packages
Err:7 http://fXXX/deb  Packages
  lzma_read: Read error (7)
Reading package lists... Done
E: Failed to fetch http://XXX/deb/Packages  lzma_read: Read error (7)
E: Some index files failed to download. They have been ignored, or old ones used instead.

The exit code is 100.

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https://bugs.launchpad.net/bugs/1750625

Title:
  update misinterprets 304 response on Packages.gz

Status in apt package in Ubuntu:
  Confirmed

Bug description:
  Description:	Ubuntu 16.04.3 LTS
  Release:	16.04

  ii  apt                              1.2.24                                      amd64        commandline package manager
  ii  apt-transport-https              1.2.24                                      amd64        https download transport for APT
  ii  apt-utils                        1.2.24                                      amd64        package management related utility programs
  ii  libapt-inst2.0:amd64             1.2.24                                      amd64        deb package format runtime library
  ii  libapt-pkg5.0:amd64              1.2.24                                      amd64        package management runtime library

  Expected behaviour:

  If apt-get gets a 304 Not Modified when requesting Packages.gz, it
  should ignore the package list (i.e., there's no update).

  Observed behaviour:

  Added a local repository to
  /etc/apt/sources.list.d/instafreight_php.list:

  > deb [arch=amd64 trusted=yes] http://ubuntu/instafreight xenial php

  The first time running apt-get update succeeds; in addition,
  apache.log shows:

  > 10.0.4.72 - - [20/Feb/2018:12:01:39 -0500] "GET
  /instafreight/dists/xenial/php/binary-amd64/Packages.gz HTTP/1.1" 200
  745 "-" "Debian APT-HTTP/1.3 (1.2.24)"

  I am able to install packages from that repo without error.

  Running apt-get a 2nd time succeeds. apache.log doesn't show a request
  for Packages.gz

  Running apt-get a 3rd time, apache.log shows:

  > 10.0.4.72 - - [20/Feb/2018:12:04:45 -0500] "GET
  /instafreight/dists/xenial/php/binary-amd64/Packages.gz HTTP/1.1" 304
  124 "-" "Debian APT-HTTP/1.3 (1.2.24)"

  However, on the console where I ran apt-get, the corresponding output
  is:

  > Err:15 http://ubuntu/instafreight xenial/php amd64 Packages
  >   404  Not Found
  > ...
  > E: Failed to fetch http://ubuntu/instafreight/dists/xenial/php/binary-amd64/Packages.gz  404  Not Found
  > E: Some index files failed to download. They have been ignored, or old ones used instead.

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