git ubuntu fails to call ssh on Focal due to mismatched host ssh_config

$ ssh -V
OpenSSH_8.2p1 Ubuntu-4, OpenSSL 1.1.1f 31 Mar 2020

$ snap run --shell git-ubuntu
$ which ssh
/snap/core/current/usr/bin/ssh
$ ssh -V
OpenSSH_7.2p2 Ubuntu-4ubuntu2.8, OpenSSL 1.0.2n 7 Dec 2017

So you are using ssh from the core snap, instead of the host, with host ssh configs.

Either you need to prefer ssh from the host (or all of PATH?), or upgrade git-ubuntu to use "base: core20".

Workaround:
$ sudo mount -o bind /usr/bin/ssh /snap/core/current/usr/bin/ssh

Still fails:
$ git-ubuntu submit
04/30/2020 04:34:15 - ERROR:Unable to create merge proposal: HTTP Error 400: Bad Request
Response headers:
---
connection: close
content-length: 40
content-security-policy: frame-ancestors 'self';
content-type: text/plain;charset=utf-8
date: Thu, 30 Apr 2020 03:34:15 GMT
server: zope.server.http (HTTP)
status: 400
strict-transport-security: max-age=15552000
vary: Accept
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
x-launchpad-revision: fbdff7602bd10fb883bf7e2ddcc7fd5a16f60398
x-lazr-notifications: []
x-powered-by: Zope (www.zope.org), Python (www.python.org)
x-xss-protection: 1; mode=block
---
Response body:
---
b'merge_target: Required input is missing.'
---

@snapd team, surely, on classic systems one wants to run /usr/bin/ssh not /snap/core*/current/usr/bin/ssh by default.....

Classic snaps should never invoke binaries from the core snap, as they will
try to load libraries from the host, which may not be compatible or present.

On Sat, 2 May 2020, 04:21 Dimitri John Ledkov, <email address hidden>
wrote:

> @snapd team, surely, on classic systems one wants to run /usr/bin/ssh
> not /snap/core*/current/usr/bin/ssh by default.....
>
> --
> You received this bug notification because you are a member of Snappy
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> https://bugs.launchpad.net/bugs/1871827
>
> Title:
> git ubuntu submit fails on focal
>
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On Fri, 2020-05-01 at 17:47:28 -0300, Michael Hudson-Doyle wrote:

> Classic snaps should never invoke binaries from the core snap, as they will
> try to load libraries from the host, which may not be compatible or
> present.

Unless the base is made classic safe, which AFAIK requires similar work
to the work we do en Snapcraft for app type snaps.

Since it's a classic snap, I would argue that the problem is outside of snapd scope. Ultimately the snap must figure out which ssh binary to call such that it can operate successfully on a given host.

This is an issue for non-classic Snap packages as well if they make use of the ssh-keys interface.

For example: https://github.com/digitalocean/doctl/issues/809

I asked about this at https://forum.snapcraft.io/t/best-practices-for-classic-snaps/18628

Fixed in 69bf644.

Fix released in git-ubuntu version 1.0