27. Error pages for 404 and other status codes

There are situations when a page can’t be found in a site, and situations when an application returns a status code indicating such a condition, or a similar one. ShimmerCat QS allows for handling these situations in different ways.

27.1. Error pages for electric domains

27.1.1. Default settings

In an electric domain running in devlove mode, when the application backend returns a 404 code ShimmerCat relays that 404 response from the aplication backend to the client. In internet mode, ShimmerCat tries to find a __404.html file, which is looked up exactly as __index.html files would in the views directory.

The rationale is that 404 and other error situations should consume resources from ShimmerCat and be served with cacheable and cached assets, and not from the backend itself since the later is often more expensive.

The same applies to 50x error pages, where the small x represents an actual digit for an HTTP error status code. The rationale here is to avoid leaks of sensitive information that may be present in 500-error application diagnostics from production servers, and to avoid forwarding additional traffic to a backend which is returning error codes due to overload.

In all cases, if there is no custom __40x.html or __50x.html file, ShimmerCat supplies an internal one.

27.1.2. Forwarding the error pages from the backends

Of course, there are situations when it’s desirable to instead return the error pages from the backend. This can be done via a stacked setting forward-error-pages set in either a particular view or for the entire backend.

<!--
shimmercat:
    content-disposition: replace
    forward-error-pages: true
-->

The setting takes a boolean value, with true meaning “send whatever the backend sends back to the browser”.

Even with this setting on, there are still cases where ShimmerCat will try to use the mechanism described in the previous section:

• If there is no view in ShimmerCat QS that would otherwise handle the request, then the request is not sent to any backend, and a default __404.html is looked up.

• If ShimmerCat QS can’t connect to the application backend, then a configured __503.html file or an internal page is used.

27.2. Error pages for API domains

For API domains, whatever the consultant returns is always forwarded to the HTTP client.