Bug#1064036: dpkg: wrong dpkg-query exit status on syntax error?

[Christoph Anton Mitterer]

Package: dpkg
Version: 1.22.4
Severity: normal

Hey.

dpkg-query manpage says:
EXIT STATUS
0 The requested query was successfully performed.

1 The requested query failed either fully or partially, due to no
file or package being found (except for --control-path,
--control-list and --control-show were such errors are fatal).

2 Fatal or unrecoverable error due to invalid command-line usage, or
interactions with the system, such as accesses to the database,
memory allocations, etc.

E.g.:
$ dpkg-query --showformat='${db:Status-Status}' --show --list 2>/dev/null ; echo $?
2
looks good, as does
$ dpkg-query --showformat='${db:Status-Status}' --show not-existing-package 2>/dev/null ; echo $?
1

But e.g.
$ dpkg-query --showformat='${db:Status-Statu' --show 2>/dev/null ; echo $?
1
causes also 1, though it fails because of the syntax error in the format string.

Shouldn't that be a 2?

At least it seems to make it impossible to definitely find out whether a package
is not installed (respectively not existant).

btw. it will also not fail at all in cases like:
$ dpkg-query --showformat='${db:Status-Statu}' --show 2>/dev/null ; echo $?
0
where the field doesn't exist. Not sure whether that’s desired or not

Cheers,
Chris.

-- Package-specific info:

-- System Information:
Debian Release: trixie/sid
APT prefers unstable-debug
APT policy: (500, 'unstable-debug'), (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 6.6.15-amd64 (SMP w/16 CPU threads; PREEMPT)
Locale: LANG=en_DE.UTF-8, LC_CTYPE=en_DE.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages dpkg depends on:
ii libbz2-1.0 1.0.8-5+b2
ii libc6 2.37-15
ii liblzma5 5.4.5-0.3
ii libmd0 1.1.0-2
ii libselinux1 3.5-2
ii libzstd1 1.5.5+dfsg2-2
ii tar 1.35+dfsg-3
ii zlib1g 1:1.3.dfsg-3+b1

dpkg recommends no packages.

Versions of packages dpkg suggests:
ii apt 2.7.11
ii debsig-verify 0.29

-- no debconf information

[Guillem Jover]

Hi!

On Fri, 2024-02-16 at 04:37:47 +0100, Christoph Anton Mitterer wrote:
> Package: dpkg
> Version: 1.22.4
> Severity: normal

> dpkg-query manpage says:
> EXIT STATUS
> 0 The requested query was successfully performed.
>
> 1 The requested query failed either fully or partially, due to no
> file or package being found (except for --control-path,
> --control-list and --control-show were such errors are fatal).
>
> 2 Fatal or unrecoverable error due to invalid command-line usage, or
> interactions with the system, such as accesses to the database,
> memory allocations, etc.

> E.g.:
> $ dpkg-query --showformat='${db:Status-Status}' --show --list 2>/dev/null ; echo $?
> 2
> looks good, as does
> $ dpkg-query --showformat='${db:Status-Status}' --show not-existing-package 2>/dev/null ; echo $?
> 1
>
> But e.g.
> $ dpkg-query --showformat='${db:Status-Statu' --show 2>/dev/null ; echo $?
> 1
> causes also 1, though it fails because of the syntax error in the format string.
>
> Shouldn't that be a 2?

Yeah, I think so. I've looked into this now, and there are several
problems in the dpkg-query code, one is that several of the action
functions only ever return 1 for any direct failure they handle, the
other is that even if they returned something else, the main()
function coerces that return code into a boolean, so it always ends
up being 0 or 1. I'll have a pass over the entire code, and correct
all instances and queue this for the next upload. Thanks!

> At least it seems to make it impossible to definitely find out whether a package
> is not installed (respectively not existant).

Exactly.

> btw. it will also not fail at all in cases like:
> $ dpkg-query --showformat='${db:Status-Statu}' --show 2>/dev/null ; echo $?
> 0
> where the field doesn't exist. Not sure whether that’s desired or not

This is used for field names, be them real or virtual, so erroring out
on fields that do not exist would seem bad. But there's the
distinction between the real fields and virtual ones, where the latter
always contain a colon. So I guess I could make the latter, at least
warn if they do not exist. My main concern with making them errors, is
that this would break backwards and/or forwards compatibility, where
you could not use a new or renamed field with old or new releases.

Thanks,
Guillem

[Christoph Anton Mitterer]

Hey Guillem.

On Fri, 2024-02-16 at 05:26 +0100, Guillem Jover wrote:
>
> Thanks!

Well rather: thank you, for your constant efforts to DPKG and the whole
ecosystem.

> > At least it seems to make it impossible to definitely find out
> > whether a package
> > is not installed (respectively not existant).
>
> Exactly.

Maybe it would also be worth to elaborate on:

1 The requested query failed either fully or partially, due to no
file or package being found (except for --control-path,
--control-list and --control-show were such errors are fatal).

My understanding would have been, that e.g. when searching for a
package, 1 would in practise mean that it doesn't exist at all (when
looking from APT’s PoV) respectively is in the state 'not-installed'.

So I guess for end-users it might be helpful to be told that, i.e. that
these two things (non-existing from APT) and non-installed are the same
from DPKG’s PoV, and would trigger 1.

Also perhaps notifying somewhere that 'not-installed' will never really
show up anywhere as a printed query result.

> This is used for field names, be them real or virtual, so erroring
> out
> on fields that do not exist would seem bad. But there's the
> distinction between the real fields and virtual ones, where the
> latter
> always contain a colon. So I guess I could make the latter, at least
> warn if they do not exist. My main concern with making them errors,
> is
> that this would break backwards and/or forwards compatibility, where
> you could not use a new or renamed field with old or new releases.

Warnings are at last difficult to use when scripting.

And btw: it also succeeds if there's no colon, e.g.:
$ dpkg-query --showformat='${foobar}' --show 2>/dev/null ; echo $?

0


Thanks,
Chris.

PS: In the dpkg-query manpage, there's:
Desired action:

u = Unknown
i = Install
h = Hold
r = Remove
p = Purge

Package status:

n = Not-installed
c = Config-files
H = Half-installed
U = Unpacked
F = Half-configured
W = Triggers-awaiting
t = Triggers-pending
i = Installed

Error flags:

<empty> = (none)
R = Reinst-required

I think, when these are actually printed, the full names are all
lowercase, i.e. installed not Installed ... might perhaps make sense to
align that?