added validation for source and target

[AshwinKul28]

• Fixed a bug where the user can create a reverse proxy even if the host or target is empty

Related issue: #54

[quentinguidee]

Thank you! Here are some request changes that need to be addressed before merging:

[quentinguidee]

Sorry for the confusion; I think the documentation should be more explicit about this.

In fact, both versions were half-right. This new version check the errors at the correct place, but doesn't returns to the client why the request has failed.

• The service should return, for example, an ErrSourceInvalid or ErrTargetInvalid depending on the error;
• Then, the handler should receive the error given by the service (eg. if errors.Is(err, ErrSourceInvalid) {...}) and returns an HTTP response corresponding to the error.

Take for example the feature to delete a container: https://github.com/vertex-center/vertex/blob/dev/apps/containers/handler/container.go#L120:L135. If the service says that the service is still running, the handler returns a response that is adapted to that.

So: the service makes the verification and returns why it fails, and the http handler generates an HTTP response for this error.

But appart from this I think you got it!

For the empty string, this is optional for this PR but you can also use strings.TrimSpace() to also invalidate sources/targets like " " (with only spaces).

[quentinguidee]

(Also don't hesitate to say what should be improved in the documentation about the architecture, the doc is pretty new!)

[AshwinKul28]

Thanks @quentinguidee for the explanation. Actually, my both solutions were half-baked at their own places based on what actually this repo expects.

[AshwinKul28]

fixing the lint errors.

[quentinguidee]

Looks good to me! Thank you for your contribution 🚀