Function peek_input_until 

pub fn peek_input_until<R, O, P>(
    reader: &mut R,
    buffer: &mut [u8],
    timeout: Option<Duration>,
    predicate: P,
) -> impl Future<Output = PeekOutput<O>>
where
    R: AsyncRead + Unpin,
    P: Fn(&[u8]) -> Option<O>,

Read into buffer until predicate matches, peeking stops, or the optional timeout expires.

This helper is intended for protocol sniffing and similar cases where a caller needs to inspect a small prefix without committing to a full parser.

Peeking stops when one of the following happens:

• predicate returns Some(_);
• the reader returns EOF;
• the reader returns an error;
• the optional timeout elapses;
• the internal read-attempt budget is exhausted.

The attempt budget is capped at max(buffer.len() / 4, 1) + 1 reads. This keeps peeking bounded even for slow or fragmented inputs, but it also means this function can return partial data before the buffer is full.