When using a basepath of /chronograf, the app would present a
never-ending spinner when visiting the root route. This was because the
prefixingRedirector middleware which is responsible for appending the
basepath to redirects from downstream http.Handlers thought that the
prefix was already appended since it saw `/chronograf/v1`. In reality,
it should have produced a location like `/chronograf/chronograf/v1`.
The solution was to look beyond the first instance of a prefix and check
for the presence of another prefix to detect if a prefix was already
applied by a downstream handler.
The router that we use has a feature that will automatically redirect
routes in certain situations where it feels a trailing slash would be
appropriate. Because the underlying router is totally unaware of
upstream prefixing activity, the "Location" that it sends clients to is
incorrect because it doesn't have the prefix.
This introduces a middleware that catches any downstream 3XX class
responses and replaces the Location header with the prefixed version of
it, plus a trailing slash. It does this only when the prefix has not
been applied already by some downstream middleware.
Tim Raymond