bson_streaming_bson(3) on Linux
The text df29dd2bb6d3, as Debian 10 (Buster) shipped it.
Streaming BSON bson_reader_t provides a streaming reader which can be initialized with a filedescriptor or memory region. bson_writer_t provides a streaming writer which can be initialized with a memory region. (Streaming BSON to a file descriptor is not yet supported.)