Django视图测试中使用StringIO的“关闭文件的I/O操作”

Question

我继承了以下 Django 视图代码，由另一个 Web 服务用于提供可下载版本的输出数据：

def index(request):
    # ... (snip) ...
    data = base64.decodestring(request.POST['data'])
    filename = request.POST['filename']

    wrapper = FileWrapper(StringIO(data))

    response = HttpResponse(wrapper, content_type=guess_type(str(filename))[0])

    response['Content-Length'] = len(data)
    response['Content-Disposition'] = "attachment; filename=" + filename

    return response

该函数本身（针对 Django 1.0 编写）在升级到 1.5 后仍然可以正常工作。不幸的是，涵盖此视图的测试现在失败了：

    def testDownload(self):
        self.client.login(username='test', password='test')

        real = 'abc' * 100
        data = base64.encodestring(real)
        response = self.client.post("/api/v1/download/", {'data': data, 'filename': 'out.jpg'})

        self.assertEqual(real, response.content)
        self.assertEqual(response['Content-Disposition'], 'attachment; filename=out.jpg')

和错误：

Traceback (most recent call last):
  File "/home/fred/.secret_projects/final/gerbils/tests/amf.py", line 548, in testDownload
    self.assertEqual(real, response.content)
  File "/home/fred/.virtualenvs/cunning_plot/lib/python2.7/site-packages/django/http/response.py", line 282, in content
    self._consume_content()
  File "/home/carl/.virtualenvs/cunning_plot/lib/python2.7/site-packages/django/http/response.py", line 278, in _consume_content
    self.content = b''.join(self.make_bytes(e) for e in self._container)
  File "/home/carl/.virtualenvs/cunning_plot/lib/python2.7/site-packages/django/http/response.py", line 278, in <genexpr>
    self.content = b''.join(self.make_bytes(e) for e in self._container)
  File "/usr/lib64/python2.7/wsgiref/util.py", line 30, in next
    data = self.filelike.read(self.blksize)
  File "/usr/lib64/python2.7/StringIO.py", line 127, in read
    _complain_ifclosed(self.closed)
  File "/usr/lib64/python2.7/StringIO.py", line 40, in _complain_ifclosed
    raise ValueError, "I/O operation on closed file"
ValueError: I/O operation on closed file

所以..有什么想法吗？在需要阅读之前，我看不到任何内容testDownload()或index()必须“关闭”的StringIO内容。如果有什么东西，它会不会影响非测试情况？

非常困惑。帮助表示赞赏。

Answer 1

查看close调用位置的一种简单方法是子类化StringIO并在 close 函数中放置一个断点。

class CustomStringIO(StringIO):
    def close(self):
        import pdb; pdb.set_trace()
        super(CustomStringIO, self).close()

这个堆栈是

-> response = self.client.post("/test/", {'data': data, 'filename': 'out.jpg'})
  ...\venv\lib\site-packages\django\test\client.py(463)post()
-> response = super(Client, self).post(path, data=data, content_type=content_type, **extra)
  ...\venv\lib\site-packages\django\test\client.py(297)post()
-> return self.request(**r)
  ...\venv\lib\site-packages\django\test\client.py(406)request()
-> response = self.handler(environ)
  ...\venv\lib\site-packages\django\test\client.py(119)__call__()
-> response.close()                    # will fire request_finished
  ...\venv\lib\site-packages\django\http\response.py(233)close()
-> closable.close()
> \testapp\views.py(11)close()
-> super(CustomStringIO, self).close()

看起来测试客户端正在关闭响应，它依次调用 close on FileWrapper，然后调用 close on StringIO。这是在您真正到达之前的全部内容response.content。

你有什么需要的理由FileWrapper吗？由于HttpResponse接受字符串内容并base64.decodestring返回一个二进制字符串，似乎您可以直接传递data给HttpResponse而不必创建一个StringIOand FileWrapper。