从多重错误类型检测特定错误

Question

Trying to differentiate from a bad user-cookie error vs. an internal error using gorilla/sessions e.g.

import "github.com/gorilla/sessions"

sess, err := store.Get(r, sessName)
if err != nil {
    // either user error (bad-cookie i.e. invalid HMAC)
    //      http.Error(w, "not authenticated", http.StatusUnauthorized)

    // or server error (FileSystemStore i/o)
    //      http.Error(w, "internal error", http.StatusInternalServerError)
    return
}

The underlying securecookie package has an exported error ErrMacInvalid for bad user cookies. So ordinarily one would just check for this specific error, but this does not work:

import "github.com/gorilla/securecookie"

if err == securecookie.ErrMacInvalid {
    // bad user-cookie
} else if err != nil {
    // otherwise internal error
}

The reason it does not work - using say securecookie.NewCookieStore() as a session store - is it will return a error of type securecookie.MultiError (a []error type) with the securecookie.ErrMacInvalid value listed within the error slice.

Trying something like this seems very convoluted:

if e2, ok := err.(securecookie.MultiError); ok && len(e2) > 0 && e2[0] == securecookie.ErrMacInvalid { {
    // bad user-cookie
} else if err != nil {
    // otherwise internal error
}

is there an easier way?

Answer 1

is there an easier way?

No. Sorry.