decode_asn1.py 文件源码

def _obj2txt(backend, obj):
    # Set to 80 on the recommendation of
    # https://www.openssl.org/docs/crypto/OBJ_nid2ln.html#return_values
    #
    # But OIDs longer than this occur in real life (e.g. Active
    # Directory makes some very long OIDs).  So we need to detect
    # and properly handle the case where the default buffer is not
    # big enough.
    #
    buf_len = 80
    buf = backend._ffi.new("char[]", buf_len)

    # 'res' is the number of bytes that *would* be written if the
    # buffer is large enough.  If 'res' > buf_len - 1, we need to
    # alloc a big-enough buffer and go again.
    res = backend._lib.OBJ_obj2txt(buf, buf_len, obj, 1)
    if res > buf_len - 1:  # account for terminating null byte
        buf_len = res + 1
        buf = backend._ffi.new("char[]", buf_len)
        res = backend._lib.OBJ_obj2txt(buf, buf_len, obj, 1)
    backend.openssl_assert(res > 0)
    return backend._ffi.buffer(buf, res)[:].decode()