import re   # RegEx

def extract_header(payload):
    try:
        header_brut = payload[:payload.index(b"\r\n\r\n") + 2]
    except ValueError:
        return None
    
    header = dict(re.findall(
        r"(?P<cle>.*?): (?P<valeur>.*?)\r\n",
        header_brut.decode(errors="ignore")
    ))

    if "Content-Type" not in header:
        return None
    return header