Proper 404 handling

[raphael]

I could be missing something but it doesn't seem like weasel handles 404s properly. The 404 configured in GCS doesn't seem to take effect and looking at the code I don't see where it would handle it.

404s could be handled by adding a section to the config, something like:
config.json

  "not-found": "404.html"

Which could be used by the server:
server.go

func serveObject(w http.ResponseWriter, r *http.Request) {
    if !weasel.ValidMethod(r.Method) {
        http.Error(w, "", http.StatusMethodNotAllowed)
        return
    }
    if _, force := config.tlsOnly[r.Host]; force && r.TLS == nil {
        u := "https://" + r.Host + r.URL.Path
        if r.URL.RawQuery != "" {
            u += "?" + r.URL.RawQuery
        }
        http.Redirect(w, r, u, http.StatusMovedPermanently)
        return
    }

    ctx := newContext(r)
    bucket := bucketForHost(r.Host)
    oname := r.URL.Path[1:]

    o, err := storage.OpenFile(ctx, bucket, oname)
    if err != nil {
        code := http.StatusInternalServerError
        if errf, ok := err.(*weasel.FetchError); ok {
            code = errf.Code
        }
        if code == http.StatusNotFound {  // *** START OF ADDED CODE ***
            o, err = storage.OpenFile(ctx, bucket, config.NotFound)
            if err == nil {
                goto serve
            }
        }   // *** END OF ADDED CODE ***
        serveError(w, code, "")
        if code != http.StatusNotFound {
            log.Errorf(ctx, "%s/%s: %v", bucket, oname, err)
        }
        return
    }
serve:  // *** ADDED ***
    if err := storage.ServeObject(w, r, o); err != nil {
        log.Errorf(ctx, "%s/%s: %v", bucket, oname, err)
    }
    o.Body.Close()
}

Would you consider a PR that does the above?

[x1ddos]

Sounds like a good idea! Please, do create a PR.

[raphael]

OK I'll work on something. You mentioned you wanted to get rid of the need for a set config structure, how would you suggest storing/retrieving the value of the path to the 404 file? Maybe there's a way to retrieve it from GCS? - that would be ideal but I don't know the API well enough to know whether that's possible.