add test that checks for empty body on HEAD req

[fairingrey]

Attempts to address #45.

Description

This adds a test that checks if a response with an empty body is returned on a HEAD request to a resource where GET behavior exists.

For some reason it fails, so there might be something in http_service_mock that needs to be fixed? Attempting an HTTP request to a live server via curl/Insomnia exhibits the normal behavior e.g. #45 (comment), but a non-empty body is returned on server.simulate(req).unwrap(), as if it was making a GET request normally.

EDIT: See my comment below #179 (comment)

Motivation and Context

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[fairingrey]

Looking at it more in detail, I think I know why this doesn't work. Also related to #45 (comment).

My intuition was somehow that the http service and http service mock crates were using Hyper underneath -- this is wrong. Instead, the app server just has an implementation for HttpService via https://github.com/rustasync/tide/blob/master/src/app.rs#L246-L278 which http-service-mock emulates, but doesn't properly simulate the behavior that http-service-hyper exhibits when the app is probably served.

I'll probably start figuring out more on how to do this, but hmm...

[yoshuawuyts]

I think if we want to make this a persistent test, just having this panic might be reasonable to signify it should never be executed.

[fairingrey]

We could do that... Maybe something like this, I'm guessing?

Suggested change

	String::from("this shouldn't exist in the body of a HEAD response")
	panic!("should not go here");
	String::from("this shouldn't exist in the body of a HEAD response")

[yoshuawuyts]

@fairingrey hmm, not sure either. I guess the obvious choice here would be to expand http-service-mock to include this behavior. But that does kind of feel like a band-aid.

Hmm, we could also fix this at the tide-level, where if the request is a HEAD we abort early?

Not sure which is better here.

[yoshuawuyts]

Ping @fairingrey -- do you have an idea how to move forward here?

[fairingrey]

Mmm... I think I would rather just change http-service-mock to fit the test here. It is a bandaid, admittedly -- but since we already know how hyper behaves, it should be fine.

That said, I do think that approach won't necessitate the panic as you suggested originally here: #179 (comment) (The GET response shouldn't panic, but the HEAD response body should be empty)

[yoshuawuyts]

Let's merge this (: