static SS extensionToMimeType_map = litCIMap(
  "cal", "text/plain",
  "zip", "application/zip",
  "svg", svgContentType(),
  "html", "text/html",
  "txt", "text/plain");

static S extensionToMimeType(S s) {
  s = substring(s, lastIndexOf(s, '.')+1);
  ret extensionToMimeType_map.get(s);
}