Function xmp 

pub fn xmp<R: Resolve>(
    catalog: &Dict,
    r: &R,
    limits: &Limits,
    diags: &mut Diagnostics,
) -> Option<Vec<u8>>

The catalog’s /Metadata stream, decoded.

Returns nothing when the key is absent or does not hold a stream.

use pdfrum_common::{Diagnostics, Limits};
use pdfrum_doc::xmp;
use pdfrum_object::{Dict, NoResolve};

let (limits, mut diags) = (Limits::default(), Diagnostics::default());
// Absent, or not holding a stream: nothing.
assert!(xmp(&Dict::default(), &NoResolve, &limits, &mut diags).is_none());