Function parse 

pub fn parse<S, E>(
    input: S,
    boundary: &str,
) -> impl Stream<Item = Result<Part, Error>>
where
    S: Stream<Item = Result<Bytes, E>>,
    E: Into<Box<dyn Error + Send + Sync>>,

Parses a Bytes stream into a Part stream.

boundary should be as in the boundary parameter of the Content-Type header.

This doesn’t allow customizing the parser; use ParserBuilder instead if desired.