[Bug 1814543] Re: deal with EPIPE from json hooks

[Julian Andres Klode]

Verified - I ran the specified command, and saw exactly two lines for
both bionic's 1.6.9 and cosmic's 1.7.3; as expected (one for each hook
variant).

$ lxc exec apt-bionic --  apt -o AptCli::Hooks::Install::="/usr/bin/printf '{error should be json}\n\n' >&3" install
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'apt autoremove' to remove it.
E: Hook /usr/bin/printf '{error should be json}\n\n' >&3 reported an error during hello: {error should be json}
E: Hook /usr/bin/printf '{error should be json}\n\n' >&3 reported an error during hello: {error should be json}

$ lxc exec apt-cosmic --  apt -o AptCli::Hooks::Install::="/usr/bin/printf '{error should be json}\n\n' >&3" install
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following package was automatically installed and is no longer required:
  libfreetype6
Use 'apt autoremove' to remove it.
E: Hook /usr/bin/printf '{error should be json}\n\n' >&3 reported an error during hello: {error should be json}
E: Hook /usr/bin/printf '{error should be json}\n\n' >&3 reported an error during hello: {error should be json}


** Tags removed: verification-needed verification-needed-bionic verification-needed-cosmic
** Tags added: verification-done verification-done-bionic verification-done-cosmic

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https://bugs.launchpad.net/bugs/1814543

Title:
  deal with EPIPE from json hooks

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Bionic:
  Fix Committed
Status in apt source package in Cosmic:
  Fix Committed
Status in apt source package in Disco:
  Fix Released

Bug description:
  [Impact]
  json hooks ending with EPIPE on first read fail, but should simply do nothing. This causes spurious failures of uninstalled hooks.

  Also, there is a missing error exit, causing errors reported by the
  script to not exit.

  [Test case]
  For the first part, I cannot generate one. This was discovered by snapd ci, but I did not find a reproducer yet.

  FWIW, the change should be tiny enough to see that it is not wrong:
  -        if (errno != ECONNRESET)
  +        if (errno != ECONNRESET && errno != EPIPE)
              _error->Error("Could not read response to hello message from hook %s: %s", Opts->Value.c_str(), strerror(errno));

  
  The missing error handling is the next lines:
         else if (strstr(line, "error") != nullptr)
         {
           _error->Error("Hook %s reported an error during hello: %s", Opts->Value.c_str(), line);                                             
  +        goto out;
         }

  
  that can be checked:

  sudo apt -o AptCli::Hooks::Install::="/usr/bin/printf '{error should
  be json}\n\n' >&3" install

  
  [Regression potential]
  JSON hooks failures with EPIPE are now ignored, so if it fails with EPIPE for other reasons than just exiting, I guess we might miss it

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