func handleRootPost(w http.ResponseWriter, req *http.Request, ps URLParams, cs chunks.ChunkStore) {
	d.PanicIfTrue(req.Method != "POST", "Expected post method.")

	params := req.URL.Query()
	tokens := params["last"]
	d.PanicIfTrue(len(tokens) != 1, `Expected "last" query param value`)
	last := hash.Parse(tokens[0])
	tokens = params["current"]
	d.PanicIfTrue(len(tokens) != 1, `Expected "current" query param value`)
	current := hash.Parse(tokens[0])

	// Ensure that proposed new Root is present in cs
	c := cs.Get(current)
	d.PanicIfTrue(c.IsEmpty(), "Can't set Root to a non-present Chunk")

	// Ensure that proposed new Root is a Map and, if it has anything in it, that it's <String, <RefCommit>>
	v := types.DecodeValue(c, nil)
	d.PanicIfTrue(v.Type().Kind() != types.MapKind, "Root of a Database must be a Map")
	m := v.(types.Map)
	if !m.Empty() && !isMapOfStringToRefOfCommit(m) {
		panic(d.Wrap(fmt.Errorf("Root of a Database must be a Map<String, Ref<Commit>>, not %s", m.Type().Describe())))
	}

	if !cs.UpdateRoot(current, last) {
		w.WriteHeader(http.StatusConflict)
		return
	}
}
func handleRootPost(w http.ResponseWriter, req *http.Request, ps URLParams, rt chunks.ChunkStore) {
	d.PanicIfTrue(req.Method != "POST", "Expected post method.")

	params := req.URL.Query()
	tokens := params["last"]
	d.PanicIfTrue(len(tokens) != 1, `Expected "last" query param value`)
	last := hash.Parse(tokens[0])
	tokens = params["current"]
	d.PanicIfTrue(len(tokens) != 1, `Expected "current" query param value`)
	current := hash.Parse(tokens[0])

	if !rt.UpdateRoot(current, last) {
		w.WriteHeader(http.StatusConflict)
		return
	}
}
func HandleRootPost(w http.ResponseWriter, req *http.Request, ps URLParams, rt chunks.ChunkStore) {
	err := d.Try(func() {
		d.Exp.Equal("POST", req.Method)

		params := req.URL.Query()
		tokens := params["last"]
		d.Exp.Len(tokens, 1)
		last := hash.Parse(tokens[0])
		tokens = params["current"]
		d.Exp.Len(tokens, 1)
		current := hash.Parse(tokens[0])

		if !rt.UpdateRoot(current, last) {
			w.WriteHeader(http.StatusConflict)
			return
		}
	})

	if err != nil {
		http.Error(w, fmt.Sprintf("Error: %v", err), http.StatusBadRequest)
		return
	}
}