Uploading a 0 bytes file to owncloud with python requests hangs

Question

I am trying to upload a 0 bytes file with requests to owncloud. I'd like to use a file-like object for that. Normally I'd do it like this:

file_obj = io.BytesIO(b'')
response = requests.put('http://localhost/remote.php/webdav',
                                    auth=('xxx', 'xxx'),
                                    data=file_obj)

But it freezes. If I interrupt the process, I see where it hangs with the stack trace:

Traceback (most recent call last):
  File "/home/julian/cc/client/.venv/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 376, in _make_request
    httplib_response = conn.getresponse(buffering=True)
TypeError: getresponse() got an unexpected keyword argument 'buffering'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/julian/cc/client/cc/storage/webdav.py", line 360, in <module>
    main()
  File "/home/julian/cc/client/cc/storage/webdav.py", line 351, in main
    data=file_obj)
  File "/home/julian/cc/client/.venv/lib/python3.5/site-packages/requests/api.py", line 120, in put
    return request('put', url, data=data, **kwargs)
  File "/home/julian/cc/client/.venv/lib/python3.5/site-packages/requests/api.py", line 53, in request
    return session.request(method=method, url=url, **kwargs)
  File "/home/julian/cc/client/.venv/lib/python3.5/site-packages/requests/sessions.py", line 468, in request
    resp = self.send(prep, **send_kwargs)
  File "/home/julian/cc/client/.venv/lib/python3.5/site-packages/requests/sessions.py", line 576, in send
    r = adapter.send(request, **kwargs)
  File "/home/julian/cc/client/.venv/lib/python3.5/site-packages/requests/adapters.py", line 376, in send
    timeout=timeout
  File "/home/julian/cc/client/.venv/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 559, in urlopen
    body=body, headers=headers)
  File "/home/julian/cc/client/.venv/lib/python3.5/site-packages/requests/packages/urllib3/connectionpool.py", line 378, in _make_request
    httplib_response = conn.getresponse()
  File "/usr/lib64/python3.5/http/client.py", line 1174, in getresponse
    response.begin()
  File "/usr/lib64/python3.5/http/client.py", line 282, in begin
    version, status, reason = self._read_status()
  File "/usr/lib64/python3.5/http/client.py", line 243, in _read_status
    line = str(self.fp.readline(_MAXLINE + 1), "iso-8859-1")
  File "/usr/lib64/python3.5/socket.py", line 575, in readinto
    return self._sock.recv_into(b)
KeyboardInterrupt

Wireshark tells me requests sendet the following request, which seems to be fine, but never gets an answer:

PUT /remote.php/webdav/test.txt HTTP/1.1
Host: localhost
Connection: keep-alive
Accept-Encoding: gzip, deflate
Authorization: Basic ***********
Transfer-Encoding: chunked
User-Agent: python-requests/2.9.1
Accept: */*
Content-Length: 0

If I send an empty string, it works:

response = requests.put('http://localhost/remote.php/webdav/test.txt',
                                    auth=('xxx', 'xxx'),
                                    data='')

HTTP Stream:

PUT /remote.php/webdav/test.txt HTTP/1.1
Host: localhost
Content-Length: 0
Accept-Encoding: gzip, deflate
Connection: keep-alive
User-Agent: python-requests/2.9.1
Accept: */*
Authorization: Basic ******



HTTP/1.1 204 No Content
Date: Thu, 24 Mar 2016 16:14:28 GMT
Server: Apache/2.4.10 (Debian) PHP/5.6.19
X-Powered-By: PHP/5.6.19
Set-Cookie: xxx=xxx; path=/; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: oc_sessionPassphrase=xxxx; path=/; httponly
Content-Security-Policy: default-src 'self'; script-src 'self' 'unsafe-eval'; style-src 'self' 'unsafe-inline'; frame-src *; img-src * data: blob:; font-src 'self' data:; media-src *; connect-src *
X-XSS-Protection: 1; mode=block
X-Content-Type-Options: nosniff
X-Frame-Options: Sameorigin
X-Robots-Tag: none
X-Download-Options: noopen
X-Permitted-Cross-Domain-Policies: none
Set-Cookie: xxx=xxx; path=/; HttpOnly
OC-FileId: xxxxx
Content-Length: 0
ETag: "xxx"
OC-ETag: "xxx"
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8

This works as well:

def chunker(file_obj):
    buf = None
    while buf != b'':
        print('iter')
        buf = file_obj.read(16*1024)
        yield buf

file_obj = io.BytesIO(b'')
response = requests.put('http://localhost/remote.php/webdav/test.txt',
                                    auth=('xxx', 'xxx'),
                                    data=chunker(file_obj))

Any ideas why this is not working with file-like objects? I am using the latest version of requests (2.9.1) and Python 3.5.

Answer 1

There seems to be a bug in requests. Without specifying auth the request uses Transfer-Encoding: chunked and sends the correct last-chunk at the end of the request, but with auth no last-chunk is sent and the headers are confused.

From https://www.rfc-editor.org/rfc/rfc7230#section-4.1:

 chunked-body   = *chunk
                  last-chunk
                  trailer-part
                  CRLF

 chunk          = chunk-size [ chunk-ext ] CRLF
                  chunk-data CRLF
 chunk-size     = 1*HEXDIG
 last-chunk     = 1*("0") [ chunk-ext ] CRLF

 chunk-data     = 1*OCTET ; a sequence of chunk-size octets

and https://www.rfc-editor.org/rfc/rfc7230#section-3.3.2:

A sender MUST NOT send a Content-Length header field in any message
that contains a Transfer-Encoding header field.

Without the auth argument

f = io.BytesIO(b'')
requests.put('http://localhost:8000/asdf', data=f)

the request sent is

PUT /asdf HTTP/1.1⏎
Host: localhost:8000⏎
User-Agent: python-requests/2.9.1⏎
Transfer-Encoding: chunked⏎
Accept-Encoding: gzip, deflate⏎
Connection: keep-alive⏎
Accept: */*⏎
⏎
0⏎
⏎  

(⏎ signifies CRLF above). But if you specify auth

requests.put('http://localhost:8000/asdf', auth=('asdf', 'fdsa'), data=f)

the request is

PUT /asdf HTTP/1.1⏎
Host: localhost:8000⏎
Transfer-Encoding: chunked⏎
Accept-Encoding: gzip, deflate⏎
User-Agent: python-requests/2.9.1⏎
Authorization: Basic YXNkZjpmZHNh⏎
Content-Length: 0⏎
Connection: keep-alive⏎
Accept: */*⏎
⏎

Both Transfer-Encoding and Content-Length are specified, which it should not do, and the last-chunk is not sent, and so the server sits waiting for more chunks to come and requests waits for a response.