"""utils/file.py 魔数校验：读取异常必须 fail-closed 拒绝上传，不得放行伪装文件。"""
import io

from utils.file import verify_file_magic


class _BrokenStream:
    """模拟文件流读取失败（seek/read 抛异常）。"""

    def read(self, n):
        raise OSError('模拟读取失败')

    def seek(self, n):
        raise OSError('模拟 seek 失败')


def test_verify_file_magic_fail_closed_on_read_error():
    is_valid, msg = verify_file_magic(_BrokenStream(), '.jpg')
    assert is_valid is False
    assert '校验异常' in msg


def test_verify_file_magic_accepts_valid_magic():
    png_header = b'\x89PNG\r\n\x1a\n' + b'filler' * 10
    is_valid, msg = verify_file_magic(io.BytesIO(png_header), '.png')
    assert is_valid is True
    assert msg == ''


def test_verify_file_magic_rejects_mismatched_content():
    # 内容与扩展名不符（JPEG 头冒充 .png）→ 拒绝
    jpeg_bytes = b'\xff\xd8\xff\xe0' + b'filler' * 10
    is_valid, msg = verify_file_magic(io.BytesIO(jpeg_bytes), '.png')
    assert is_valid is False
    assert '不匹配' in msg


def test_verify_file_magic_txt_accepts_text_content():
    # 文本无固定二进制签名，可读文本（含空文件）放行
    for content in (b'hello world', b'', '你好，世界'.encode('utf-8')):
        is_valid, msg = verify_file_magic(io.BytesIO(content), '.txt')
        assert is_valid is True, content
        assert msg == ''


def test_verify_file_magic_txt_rejects_binary_content():
    # 二进制内容伪装成 .txt（含 NUL 字节）→ 拒绝，防伪装文件绕过
    binary = b'\x00\x00\x00\xff' + b'filler' * 10
    is_valid, msg = verify_file_magic(io.BytesIO(binary), '.txt')
    assert is_valid is False
    assert '不匹配' in msg