What sort of encoding does the websocket API expect for config-yaml?

[Pete Vander Giessen]

Hi All,

I'm currently working on getting python-libjuju to successfully deploy the
landscape-dense-maas bundle. It fails, as outlined in
https://bugs.launchpad.net/juju/+bug/1651260.

(python-libjuju is a Python client that talks to Juju's websocket API; I'm
currently using it inside the matrix testing framework.)

The comments in that bug suggest that the root of the problem is that I'm
trying to deploy a charm (haproxy) that has an empty string as a default
value, but python-libjuju is using the legacy "config" param when it calls
ApplicationDeploy in the api, rather than the new "config-yaml" param. This
sounds simple to fix -- all I have to do is change an arg from "config" to
"config-yaml", and everything should work!

One hitch: the "config" param expects a json object, which is what we get
back when we make our initial call to the planner, but config-yaml expects
a string with yaml in it (this is per the logic in deployApplication in
juju/apiserver/application/application.go).

That also sounds simple. As we do elsewhere in python-libjuju when we want
to pass a yaml blob to the API, I use Python's handy yaml library, do
yaml.dump(config), where "config" is the json config object I got from the
planner, and everything should work!

This is where I'm stuck. If I pass in such a string, the websocket API
simple hangs, and stops talking to me. I don't even see any error messages
in the logs on my controller :-/

Does anyone have any insight as to what I might be doing incorrectly? In
Python3, yaml.dump will produce a utf-8 string by default. All of that will
get serialized to json before being submitted over the websocket, though,
so I don't *think* that it's an encoding issue. (Passing the bundle in as a
yaml blob to the planner in the first place works.) The config object I get
back from the planner isn't wrapped in an "options" key, but adding that
key before dumping the config to a yaml string doesn't fix the problem -- I
still see the hang.

Apologies for the length of the post. And thanks in advance for anything
you can do to get me unstuck!

~ PeteVG
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