Add delete token UI for info page

internal/server/pages.go

@@ -124,6 +124,11 @@ type objectPage struct {
 	URL         string
 	InfoURL     string
 	DeleteToken string
+
+	// CanDelete is set when the viewer's own token already authorises removing
+	// this file, so they are offered a button instead of a token field.
+	CanDelete bool
+	Error     string
 }
 
 func (s *Server) handleInfo(w http.ResponseWriter, r *http.Request) {
@@ -137,11 +142,21 @@ func (s *Server) handleInfo(w http.ResponseWriter, r *http.Request) {
 		s.fail(w, r, http.StatusNotFound, "No such file.")
 		return
 	}
-	s.render(w, http.StatusOK, "info.html", objectPage{
-		page:    s.page(r, m.Filename, false),
-		Meta:    m,
-		Size:    config.FormatSize(m.Size),
-		Expires: describeExpiry(m.Expires, s.now()),
+	s.renderInfo(w, r, m, http.StatusOK, "")
+}
+
+// renderInfo draws the file's page, optionally with an error from a failed
+// delete attempt, so a mistyped token lands back on the form rather than on a
+// dead end.
+func (s *Server) renderInfo(w http.ResponseWriter, r *http.Request, m *store.Meta, status int, errMsg string) {
+	s.render(w, status, "info.html", objectPage{
+		page:      s.page(r, m.Filename, true),
+		Meta:      m,
+		Size:      config.FormatSize(m.Size),
+		Expires:   describeExpiry(m.Expires, s.now()),
+		URL:       s.objectURL(r, m.ID),
+		CanDelete: s.mayDelete(m, credential(r)),
+		Error:     errMsg,
 	})
 }