If an invalid ifstream (e.g. one pointing to a non-existent file) without error bits set is passed to gridfs::bucket::upload_from_stream (or gridfs::bucket::upload_from_stream_with_id), the method will infinitely loop. This is because istream::read only throws an exception if `badbit` is set.

The most straightforward fix for this would be to set the error bits at the beginning of upload_from_stream_with_id so that errors will throw exceptions (and then document that this is the case):

source->exceptions(std::io::failbit | std::io::badbit);