Fix local storyboard requests on Crystal >= 1.16.0

Crystal 1.16.0 fixed the parsing of some weird-looking paths meaning
that `//api/v1/storyboards/sb/i/...` will no longer get parsed into a
request target of `/v1/storyboards/sb/i/...` within requests.

But the fix is a bit more convoluted than just changing a path. The new
presence of double slash means that `StaticFileHandler` will process and
redirect the request to a normalized path with only a single slash.
This redirect however does not preserve url query parameters which are
needed to request storyboards from YouTube.

Then there's the fact that the status code error handlers are disabled
for the API routes, meaning that there is no handler to actually process
the request with.

This PR patches Kemal's `StaticFileHandler` to preserve query parameters
when redirecting, and adds the `/api/v1/storyboard/sb/*` ->
`/sb/i/*/` redirect directly into Kemal's `ExceptionHandler` for now.

In the future a dedicated handler should be created to properly handle
http status code conditions on the API routes.

src/ext/kemal_static_file_handler.cr

@@ -191,5 +191,13 @@ module Kemal
         end
       end
     end
+
+    # See https://github.com/crystal-lang/crystal/issues/15788
+    #
+    # URL fragments also aren't passed along but there isn't an easy way
+    # to retrieve that at the moment.
+    private def redirect_to(context, path)
+      context.response.redirect URI.new(path: URI.encode_path(path.to_s), query: context.request.query)
+    end
   end
 end

src/invidious/helpers/handlers.cr

@@ -50,7 +50,30 @@ class Kemal::ExceptionHandler
 
   private def call_exception_with_status_code(context : HTTP::Server::Context, exception : Exception, status_code : Int32)
     return if context.response.closed?
-    return if exclude_match? context
+
+    # Invidious excludes the status code error handlers from running on the api routes
+    # meaning that we are unable to redirect /api/v1/storyboards/sb/... to the right location
+    # within a 404 handler. As a quick fix we'll match it here.
+    #
+    # For future reference this is also why the API will always return a 200 status code
+    # even when a route could not be found.
+    #
+    # TODO: In the future there should be dedicated status code error handlers for the api.
+    #
+    if exclude_match?(context)
+      if status_code == 404
+        # Only necessary on Crystal versions >= 1.16.0
+        {% if compare_versions(Crystal::VERSION, "1.16.0") >= 0 %}
+          if HOST_URL.empty? && context.request.path.starts_with?("/api/v1/storyboards/sb")
+            return context.redirect "#{context.request.path[19..]}?#{context.params.query}", status_code: 302
+          end
+
+          return
+        {% end %}
+      end
+
+      return
+    end
 
     if !Kemal.config.error_handlers.empty? && Kemal.config.error_handlers.has_key?(status_code)
       context.response.content_type = "text/html" unless context.response.headers.has_key?("Content-Type")

src/invidious/routes/errors.cr

@@ -1,9 +1,20 @@
 module Invidious::Routes::ErrorRoutes
   def self.error_404(env)
-    # Workaround for #3117
-    if HOST_URL.empty? && env.request.path.starts_with?("/v1/storyboards/sb")
-      return env.redirect "#{env.request.path[15..]}?#{env.params.query}"
-    end
+    # Workaround for #3117 on versions prior to 1.16.0
+    #
+    # Crystal 1.16.0 fixed the parsing of some weird-looking paths
+    # meaning that `//api/v1/storyboards/sb/i/...` will no longer
+    # get parsed into a request target of `/v1/storyboards/sb/i/...`
+    #
+    # This also means that we won't be able to handle the logic here
+    # because status code error handles are disabled for the API routes
+
+    # We only need to include this workaround on versions prior to 1.16.0
+    {% if compare_versions(Crystal::VERSION, "1.16.0") < 0 %}
+      if HOST_URL.empty? && env.request.path.starts_with?("/v1/storyboards/sb")
+        return env.redirect "#{env.request.path[15..]}?#{env.params.query}"
+      end
+    {% end %}
 
     if md = env.request.path.match(/^\/(?<id>([a-zA-Z0-9_-]{11})|(\w+))$/)
       item = md["id"]