Function frame_header_input_needed 

pub fn frame_header_input_needed(
    src: &[u8],
    magicless: bool,
) -> Result<usize, ReadFrameHeaderError>

How many bytes from its start the frame header beginning src takes to read whole, judged from what src holds of it: the bytes that hold the descriptor until they are all here (five, or one without the magic number), then the header’s own length, and eight for a skippable frame. A caller reading a header in pieces asks this before read_frame_header_info; upstream’s ZSTD_getFrameHeader_advanced returns the same counts.

use structured_zstd::decoding::frame_header_input_needed;
assert_eq!(frame_header_input_needed(&[0x28, 0xB5], false).unwrap(), 5);
// Magic number and a descriptor announcing a window byte only.
assert_eq!(frame_header_input_needed(&[0x28, 0xB5, 0x2F, 0xFD, 0x00], false).unwrap(), 6);
assert!(frame_header_input_needed(&[0x00, 0x01], false).is_err());

Errors

ReadFrameHeaderError::BadMagicNumber when the bytes start no known magic number.