Router.NotFoundHandler is not used when the router is a subrouter

[ghost]

I defined specific NotFoundHandler for several subrouters but the NotFoundHandler from the main Router is always used.

[kisielk]

I looked at this today but there doesn't seem to be any obvious way to implement it. NotFoundHandler is only called from ServeHTTP, which is only ever called on the top-level router and not the subrouters. Furthermore there is no concept of a partial match, that is the top-level part of the subrouter path matching but the inner part not matching.

[error10]

I've worked around this by using a PathPrefix() after the home page route for the subroute.

    r := mux.NewRouter()
    s := r.Host("{subdomain}." + domain).Subrouter()
    //...more routes..
    s.Handle("/", commonChain.Then(subdomainHomepageHandler()))
    s.PathPrefix("/").Handler(commonChain.Then(http.HandlerFunc(subdomainNotFound)))

Later, subdomainNotFound(), which for me does some extra work, will generate a (nicely templated) 404 if necessary.

[elithrar]

I'm going to close this as wontfix: if you do need separate a NotFoundHandler you can use nested routers (via mux.NewRouter()). Happy to open it again if there's a desire to.