Add "network exists" command

[eclark0426]

Podman has support for a "network exists" command which checks if a network exists. This adds support for that command, although it does so by way of network inspect for compatibility with Docker, which does not have a standalone network exists command.

Closes #618

[LewisGaul]

Should support passing a Network object too, i.e. this should be ValidNetwork as with other methods such as disconnect() above.

[eclark0426]

Updated, along with making sure the test covers that use case.

[LewisGaul]

inspect() doesn't make a lot of sense to take a Network object, since it's used for getting a Network object. Can you instead make exists() do self.inspect(str(network))? (or check how his is handled for other object types such as Container, Pod, ...)

[eclark0426]

It seems like things are slightly inconsistent on whether or not inspect() takes ValidSomeObject or just str. This change was based on ContainerCLI.inspect(), which takes ValidContainer as an argument. PodCLI.inspect() similarly takes ValidPod. However, VolumeCLI.inspect() and ServiceCLI.inspect() only take a str.

Given the inconsistency, sounds like str would be the preferred approach, yes?

[LewisGaul]

Oh dear 🥲 I don't mind - the main thing I noticed is you didn't quite update the type annotations correctly in adding the support. I'd leave it as just str here to keep the scope of the changeset contained.

[eclark0426]

Moved back to str and used self.id in Network.exists().

You'll have to excuse any errors in my type changes, I'm not all that familiar with the codebase. Been using it a lot the last several months, but only recently dived into the actual code. For my own understanding, what was incorrect with how I'd updated the type annotations?

[LewisGaul]

For my own understanding, what was incorrect with how I'd updated the type annotations?

In this commit you had

    @overload
    def inspect(self, x: ValidNetwork) -> Network: ...

    @overload
    def inspect(self, x: List[str]) -> List[Network]: ...

    def inspect(self, x: Union[str, List[str]]) -> Union[Network, List[Network]]:
        if isinstance(x, str) or isinstance(x, Network):
            return Network(self.client_config, x)
        else:
            return [Network(self.client_config, reference) for reference in x]

• The @overload methods say that the two possible invocations are a single ValidNetwork (str | Network) or a list of str. This means there's not support for a list of Network, i.e. the second overload should've had List[ValidNetwork] (although List is a bad choice of type, see Avoid using List and Dict for function argument types #584).
• The actual method signature (without @overload) wasn't updated to support Network at all, so is inconsistent with the overloads.

If we wanted to support Network objects here I would make this:

    @overload
    def inspect(self, x: ValidNetwork) -> Network: ...

    @overload
    def inspect(self, x: Iterable[ValidNetwork]) -> List[Network]: ...

    def inspect(self, x: Union[ValidNetwork, Iterable[ValidNetwork]]) -> Union[Network, List[Network]]:
        if isinstance(x, Iterable) and not isinstance(x, str):
            return [Network(self.client_config, str(net)) for net in x]
        else:
            return Network(self.client_config, str(x))

[LewisGaul]

To be clear, I still think the exists() method should support Network types:

    def exists(self, network: ValidNetwork) -> bool:
        try:
            self.inspect(str(network))
        except NoSuchNetwork:
            return False
        else:
            return True

[eclark0426]

Got it. Overloads are one of things I haven't touched much with type annotations so it doesn't entirely surprise me that that would be where I went awry. Thanks for the clarification!

[LewisGaul]

Thanks for doing this enhancement :) Currently all PRs are blocked on the docs CI job being broken, which I believe I have fixed in #628 but this needs confirming.

[EDIT: now fixed, merge in latest master branch]

[LewisGaul]

Thanks again :)