I'm coding a web application in Go, and while various mux libraries provide a way to set a custom 404 error handler, there's nothing for other 4xx and 5xx error codes.
One suggestion is to override the WriteHeader method in the ResponseWriter interface and check the status code, but I'm confused as to how this would actually be written (the overriding of ResponseWriter methods, before outputting). One possible example can be found from the negroni package.
Would this be the correct way to serve a custom template for 4xx and 5xx errors? Could anyone provide an example of how this could be implemented?
Update
Big thanks to David and elithrar for their responses and code. The Interceptor
struct that David coded can be used in a wrapper for the server mux, as elithrar shows in the comments. For those looking for further explanation as to why and how this works, this section from astaxie's book gives some very good info on the workings of the net/http package, along with viewing the server.go source code from the net/http package.