python - "I/O operation on closed file"在 Django View 测试中使用 StringIO

Question

我继承了以下 Django View 代码，另一个 Web 服务使用它来提供输出数据的可下载版本:

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

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 View 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？我在 testDownload() 或 index() 中看不到任何必须在需要读取之前“关闭” StringIO 的内容。如果有的话，是不是也会影响到非考试的情况？

很迷茫。感谢帮助。

Answer 1

查看调用 close 的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()

这个的堆栈是

-> 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 FileWrapper 上的关闭，然后调用 StringIO 上的关闭。这一切都在您真正到达 response.content 之前。

您需要 FileWrapper 的原因是什么？由于 HttpResponse 接受字符串内容并且 base64.decodestring 返回一个二进制字符串，看来您可以将 data 直接传递给 HttpResponse 而不是必须创建 StringIO 和 FileWrapper。