fix(client): Return nil and error if endpoint is empty string

[akosiaris]

Why:
Passing an empty string as an endpoint to Client when instantiating a
new client might seem like something that should never happen but I
managed to trigger it while parsing some input files to register feeds
in bulk.

What:
In the execute() function, check early if the endpoint is "" and then
return immediately nil and a new error, named ErrWrongEndpoint with a
descriptive string

Do you follow the guidelines?

• I have tested my changes
• There is no breaking changes
• I really tested my changes and there is no regression
• Ideally, my commit messages follow the Conventional Commits specification
• I read this document: https://miniflux.app/faq.html#pull-request

[fguillot]

Instead of returning nil, the function execute can return an error if the endpoint is an empty string.

v2/client/request.go

Lines 64 to 72 in 569529d

	func (r *request) execute(method, path string, data interface{}) (io.ReadCloser, error) {
	if r.endpoint[len(r.endpoint)-1:] == "/" {
	r.endpoint = r.endpoint[:len(r.endpoint)-1]
	}
	u, err := url.Parse(r.endpoint + path)
	if err != nil {
	return nil, err
	}

A new error type can be exposed outside the package for this purpose:

v2/client/request.go

Lines 23 to 30 in 569529d

	// List of exposed errors.
	var (
	ErrNotAuthorized = errors.New("miniflux: unauthorized (bad credentials)")
	ErrForbidden = errors.New("miniflux: access forbidden")
	ErrServerError = errors.New("miniflux: internal server error")
	ErrNotFound = errors.New("miniflux: resource not found")
	ErrBadRequest = errors.New("miniflux: bad request")
	)

[akosiaris]

Taking a quick look, I think your solution is better than mine. As long as no Client's endpoint field is used outside of a request context, it shoud work fine.

I 'll try and code it, run it for a few days and then get back to you.

Thanks for the suggestion!

[akosiaris]

Updated per your suggestion. I came up with the error name and string but happy to alter name and wording.