Function is_stream_head 

pub fn is_stream_head(head: &[u8]) -> bool

Whether head, the first bytes of a file, begins an Arrow IPC stream: a schema message, after the continuation marker or, in a stream older than it, without.

Where head holds the whole message it has to be a schema message. Where it is cut short, the marker followed by a length is taken as a stream; an older stream, with no marker to go on, is not. The message’s fields are not read: Polars panics on a column type it has not implemented, and this runs on any file being opened.