ssh transport based on ssh command line client

[dmacvicar]

This implementation uses the ssh command line client and therefore respect user settings.

To enable it, you need to use the use_ssh_cmd=1 parameter. Example: qemu+ssh://user@localhost/system?no_verify=1&use_ssh_cmd=1.

It supports the options of the upstream ssh transport.

[jgooge]

TLS connection URI works with this. Fixes #1155

[dmacvicar]

@memetb @scabala @jgooge anyone of you had the chance to try use_ssh_cmd=1 with this branch?

[jgooge]

@dmacvicar not yet, but I can test today.

[memetb]

I will try to make some time this weekend.

[jgooge]

Nit: Terraform commands hang indefinitely if the host key check fails instead of exiting with an error:

5/03/19 20:03:51 [DEBUG] Using auto proxy mode with URI: qemu:///system: timestamp=2025-03-19T20:03:51.407-0600
2025-03-19T20:03:51.407-0600 [INFO]  provider.terraform-provider-libvirt: 2025/03/19 20:03:51 [INFO] SSH command dialer connecting to libvirt_host_1 with args: [-T -o ControlPath=none -e none -o BatchMode=yes -- username@libvirt_host_1 sh -c 'which virt-ssh-helper 1>/dev/null 2>&1; if test $? = 0; then virt-ssh-helper "qemu:///system"; else if "nc" -q 2>&1 | grep "requires an argument" >/dev/null 2>&1; then ARG=-q0; else ARG=; fi; "nc" $ARG -U /var/run/libvirt/libvirt-sock; fi']: timestamp=2025-03-19T20:03:51.407-0600
2025-03-19T20:03:51.567-0600 [WARN]  unexpected data: local/local/libvirt:stderr="@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ED25519 key sent by the remote host is
SHA256:reGjvY02IwsrYvfeX7w04NuKJsFpM9UOKxGBZ8W6cHs.
Please contact your system administrator.
Add correct host key in /Users/james/.ssh/known_hosts to get rid of this message."
2025-03-19T20:03:51.567-0600 [WARN]  unexpected data: local/local/libvirt:stderr="Offending ECDSA key in /Users/james/.ssh/known_hosts:126"
2025-03-19T20:03:51.567-0600 [WARN]  unexpected data: local/local/libvirt:stderr="Host key for libvirt_host_1 has changed and you have requested strict checking.
Host key verification failed."

Otherwise, use_ssh_cmd=1 reads from the default ssh config properly and therefore works as expected.

[dmacvicar]

@jgooge should be fixed now.

[jgooge]

It is!!

[BohdanTkachenko]

This fix seems to work for me as well.

Is there anything apart from lint errors prevents merging this? Is there anything I could help with in this PR?