[Bug 1921626] Re: apt install - File has unexpected size - http pipeline

[Julian Andres Klode]

I tracked it down further today, accidentally finding a reproducer. In
methods/http.cc we check for Req.DownloadSize > Req.MaximumSize and fail
with an error if that's the case; hence ensuring our download was within
the allowed range for the request.

The issue is that Req.MaximumSize is calculated by
BaseHttpMethod::FindMaximumObjectSizeInQueue as  the maximum of all
maximum sizes in the queue; and requests with unknown sizes are encoded
as 0, so FindMaximumObjectSizeInQueue() will return any other size that
is not 0, despite the 0 meaning "unknown". The fix is to return 0 if any
maximum size is 0.

** Also affects: apt (Ubuntu Groovy)
   Importance: Undecided
       Status: New

** Also affects: apt (Ubuntu Hirsute)
   Importance: Undecided
       Status: Triaged

** Also affects: apt (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Also affects: apt (Ubuntu Focal)
   Importance: Undecided
       Status: New

** Summary changed:

- apt install - File has unexpected size - http pipeline
+ size mismatch error if request of unknown size is larger than others

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https://bugs.launchpad.net/bugs/1921626

Title:
  size mismatch error if request of unknown size is larger than others

Status in apt package in Ubuntu:
  Triaged
Status in apt source package in Bionic:
  New
Status in apt source package in Focal:
  New
Status in apt source package in Groovy:
  New
Status in apt source package in Hirsute:
  Triaged

Bug description:
  1) Ubuntu 18.04.5 LTS

  2) apt 1.6.12ubuntu0.2

  3) What you expected to happen

  I set a custom set of repositories in /etc/apt/sources.list and then I
  run "apt install <list of packages>". I expect the command to download
  and install the packages.

  4) What happened instead

  "apt install ..." fails during the download phase with "File has
  unexpected size ...."

  
  5) What I've established trying to debug the issue:

  - Disabling http pipelining resolves the issue: "apt -oAcquire::http::Pipeline-Depth=0 install ..."
  - All the packages, and repo metadata in the referenced repositories is correct
  - The issue is easily reproducible in my setup with different repositories
  - tcpdump shows that requests and responses are in the correct order, and contain the correct data

  More details about the issue:
  https://projects.theforeman.org/issues/32178

  With all the above in mind, it appears that this must be a bug in apt's http pipeline handling.
  It seem that apt is trying to match a request to do wrong response, and size doesn't match. 

  I've attached an example log, where the error pops up for multiple
  packages, and they all appear to be compared to one size (86464
  bytes). That size is correct for one of the package being downloaded,
  but somehow apt is trying to match to multiple other packages.

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