def extreu_esquema_autoritat(uri):
    dpbb = uri.find('://')
    arrb = uri.find('@')
    dppt = uri.find(':', dpbb + 1)
    esquema = uri[:dpbb]
    if arrb == -1:
        usuari = ''
        iserv = dpbb + 3
    else:
        usuari = uri[dpbb + 3:arrb]
        iserv = arrb + 1
    if dppt == -1:
        servidor = uri[iserv:]
        port = -1
    else:
        servidor = uri[iserv:dppt]
        port = int(uri[dppt + 1:])
    return esquema, usuari, servidor, port