zsh does not offer ssh host from config

zsh does not offer ssh host from config

[Jan Palus]

Hi,

I've got a single real hostname starting with 'build' prefix which is present
in my known_hosts file. I also have a couple Host specifications in ssh config
file having names starting with 'build' but real HostName does not resolve to
name starting with 'build'. When doing `ssh build<tab>` I'd expect to be
offered both real hostname as well as Host specification names, however only
real hostname is immediately completed. That's because of _ssh_hosts returning
on successful hosts completion:

# If users-hosts matches, we shouldn't complete anything else.
if [[ "$IPREFIX" == *@ ]]; then
  _combination -s '[:@]' my-accounts users-hosts "users=${IPREFIX/@}" hosts "$@" && return
else
  _combination -s '[:@]' my-accounts users-hosts \
    ${opt_args[-l]:+"users=${opt_args[-l]:q}"} hosts "$@" && return # <--- HERE
fi

Is this intentional that config file parsing is skipped entirely if host was
completed successfully?

Re: zsh does not offer ssh host from config

[Daniel Shahaf]

Jan Palus wrote on Fri, Dec 09, 2022 at 02:06:50 +0100:
> Hi,
> 
> I've got a single real hostname starting with 'build' prefix which is present
> in my known_hosts file. I also have a couple Host specifications in ssh config
> file having names starting with 'build' but real HostName does not resolve to
> name starting with 'build'. When doing `ssh build<tab>` I'd expect to be
> offered both real hostname as well as Host specification names, however only
> real hostname is immediately completed. That's because of _ssh_hosts returning
> on successful hosts completion:
> 
> # If users-hosts matches, we shouldn't complete anything else.
> if [[ "$IPREFIX" == *@ ]]; then
>   _combination -s '[:@]' my-accounts users-hosts "users=${IPREFIX/@}" hosts "$@" && return
> else
>   _combination -s '[:@]' my-accounts users-hosts \
>     ${opt_args[-l]:+"users=${opt_args[-l]:q}"} hosts "$@" && return # <--- HERE
> fi
> 
> Is this intentional that config file parsing is skipped entirely if host was
> completed successfully?

That «return» was added in https://www.zsh.org/users/11333 with the
intention of skipping config file parsing if a match was found /in the
users-hosts style/.  However, in a quick test with these fictional
values:

[[[
% zstyle -L \* users-hosts; echo $?
1
% tail -2 ~/.ssh/config
Host completion-test1.zsh.org
        HostName 2001:db8::zsh
% tail -1 ~/.ssh/known_hosts
completion-test2.zsh.org,2001:db8::zsh x-not-a-real-identifier abcdef01
% 
]]]

I observe that «ssh completion<TAB>» only offers completion-test2.zsh.org,
not completion-test1.zsh.org.  I take it both should be offered (since
users-hosts is unset).

Re: zsh does not offer ssh host from config

[Roman Perepelitsa]

On Fri, Dec 9, 2022 at 2:07 AM Jan Palus <jpalus@fastmail.com> wrote:
>
> Hi,
>
> I've got a single real hostname starting with 'build' prefix which is present
> in my known_hosts file. I also have a couple Host specifications in ssh config
> file having names starting with 'build' but real HostName does not resolve to
> name starting with 'build'. When doing `ssh build<tab>` I'd expect to be
> offered both real hostname as well as Host specification names, however only
> real hostname is immediately completed.

If you only ever ssh to hosts listed in the ssh config, you can
configure ssh completions to respect that:

    zstyle ':completion:*:(ssh|scp):*:hosts' hosts

Listing all remote machines in the ssh config has other advantages
besides making completions more predictable.

Roman.

Re: zsh does not offer ssh host from config

[Jan Palus]

On 10.12.2022 13:08, Roman Perepelitsa wrote:
> On Fri, Dec 9, 2022 at 2:07 AM Jan Palus <jpalus@fastmail.com> wrote:
> >
> > Hi,
> >
> > I've got a single real hostname starting with 'build' prefix which is present
> > in my known_hosts file. I also have a couple Host specifications in ssh config
> > file having names starting with 'build' but real HostName does not resolve to
> > name starting with 'build'. When doing `ssh build<tab>` I'd expect to be
> > offered both real hostname as well as Host specification names, however only
> > real hostname is immediately completed.
> 
> If you only ever ssh to hosts listed in the ssh config, you can
> configure ssh completions to respect that:
> 
>     zstyle ':completion:*:(ssh|scp):*:hosts' hosts
> 
> Listing all remote machines in the ssh config has other advantages
> besides making completions more predictable.

In my case it's much more practical to ie use pattern in ssh config for
all the test envs instead of listing plenty of them explicitly.

It's nice to have a possibility to customize behavior but I'd say more
sensible default would be to offer both. Or in other words current
default behavior is somewhat counter-intuitive. Doing "build<tab>"
offers single completion, while doing more specific "builder<tab>"
offers 3. Intuitively with every char completion options should be
narrowed (or remain the same) but should not be broadened.

Re: zsh does not offer ssh host from config

[Roman Perepelitsa]

On Sat, Dec 10, 2022 at 9:06 PM Jan Palus <jpalus@fastmail.com> wrote:
>
> On 10.12.2022 13:08, Roman Perepelitsa wrote:
> >
> > If you only ever ssh to hosts listed in the ssh config, you can
> > configure ssh completions to respect that:
> >
> >     zstyle ':completion:*:(ssh|scp):*:hosts' hosts
> >
> > Listing all remote machines in the ssh config has other advantages
> > besides making completions more predictable.
>
>
> It's nice to have a possibility to customize behavior but I'd say more
> sensible default would be to offer both.

Oh, I'm not arguing in favor of the current implementation. I just
thought it might be useful to mention the setup I've made for myself
that works decently well.

> In my case it's much more practical to ie use pattern in ssh config for
> all the test envs instead of listing plenty of them explicitly.

I used to do that but then switched to my current setup where the ssh
config contains all remote machines (I generate it with a script). I
really like the ability to list all machines with a TAB. That said, I
can imagine environments where this kind of setup isn't possible.

Roman.

Re: zsh does not offer ssh host from config

[Bart Schaefer]

On Sat, Dec 10, 2022 at 12:32 PM Roman Perepelitsa
<roman.perepelitsa@gmail.com> wrote:
>
> [...] switched to my current setup where the ssh
> config contains all remote machines (I generate it with a script). I
> really like the ability to list all machines with a TAB.

I've started using this:

zstyle -e ':completion:*:(ssh|scp):*' hosts 'reply=(
    ${(Mu)${(M)=history:#ssh*}:#[^/]##.*} \
    ${=${${(f)"$(cat {/etc/ssh_,~/.ssh/known_}hosts(|2)(N) \
                     /dev/null)"}%%[#| ]*}//,/ }
    ${=${(f)"$(cat /etc/hosts(|)(N) <<(ypcat hosts 2>/dev/null))"}%%\#*}
    )'

That retrieves
 - all hosts mentioned in ssh commands in the current shell history
 - all hosts in known_hosts and known_hosts2 (ignoring hashed hostnames)
 - anything available from the local and network host configurations

My current complaint is that the hosts style is used in preference to
the my-accounts style, so I can't complete user names that are
prefixes of host names.