A connection, or a string describing the file or pipe to write to, depending on the mode.
simplify
Passed to msgpack_unpack. Default: FALSE.
mode
One of "auto", "file", "gzip" or "pipe". If "auto", detects based on the file string (any space == pipe, ".gz" == gzip, file otherwise). Ignored if file is a connection.
nbytes
If reading from a pipe or gzip, how many bytes to read at a time. Default: 16777216