RUST-1588: Add RunCursorCommand

[drshika]

added operation RunCursorCommand (spec: https://github.com/mongodb/specifications/blob/c09f979ad296400552a98c9b784197ec648c2096/source/run-command/run-command.rst#runcursorcommand)

• implemented Operation which uses default RunCommand behavior for every method but handle_response

[abr-egn]

LGTM! Tagged Isabel in.

[isabelatkinson]

The option type still needs to be updated here

[isabelatkinson]

Rather than cloning the entire options struct, it would be more efficient only to clone the selection_criteria. You should be able to do this by using a reference to the options, which can be done either like this:

let selection_criteria = match options {
    Some(ref options) => options.selection_criteria.clone(),
    None => None,
};

or this:

let selection_criteria = match &options {
    Some(options) => options.selection_criteria.clone(),
    None => None,
}

(I slightly prefer the first one for no good reason; either is totally fine.)

You can also use and_then to achieve the same thing:

let selection_criteria = options
    .as_ref()
    .and_then(|options| options.selection_criteria.clone());

We use as_ref to get a reference to the struct inside the Option rather than an owned version of it so that we can continue to use it later. and_then does something called a flat map (you can read more about it here), which is useful when you want to avoid getting data that's wrapped in multiple layers of Options/Results.

All three of these options would work here, but it's generally considered best practice to use and_then rather than an explicit match in situations like these.

[isabelatkinson]

cloning shouldn't be necessary here

[isabelatkinson]

Rather than creating an empty options struct when the user hasn't provided any options, we can just make the options field on RunCursorCommand an Option<RunCursorCommandOptions>. This will save us an allocation when options is None. (You'll probably need to do similar calls to and_then in handle_response as I described above to extract fields from the options).

[isabelatkinson]

I think the changes still need to be pushed :) it looks like there are also some compilation errors with CSFLE on the CI run

[drshika]

@isabelatkinson changes should be in here: 54185f8

[isabelatkinson]

one tiny suggestion but otherwise lgtm! no need for a re-review

[isabelatkinson]

Ah it actually looks like there are some clippy and cargo-deny failures, those will need to be fixed up as well.