Hi,
We are seeing HTTP 400 errors in our OpenStack server logs: ERROR WSGI:
code 400, Bad request syntax ('0'). They appear when sending a GET request.
I traced this bug down and it points to a single-line of code. Removing
the line fixes the problem, BUT I am emailing to ask if there are larger
ramifications of doing so.
Does anyone know the history of this line or why it exists?
*The Problem*
HTTP 400 errors appear in our OpenStack server logs when performing a GET
request: ERROR WSGI: code 400, Bad request syntax ('0').
[image: Screen Shot 2020-08-28 at 9.12.32 AM.png]
*Figure 1.0 Wireshark shows HTTP 400 after GET request.*
*The Line of Code*
The code is in libcoud/http.py and relates to how requests is being used to
prepare requests and potentially affects every HTTP request libcloud makes.
A PreparedRequest is being constructed and then its body is being
overwritten. The reassignment seems redundant to me, as Requests does the
job of translating it.
https://github.com/apache/libcloud/blob/72de440a508fdb4ea546d4e586a452472f1cbd5d/libcloud/http.py#L244
*#libcloud/http.py
#LibcloudConnection class
*def prepared_request(self, method, url, body=None,
headers=None, raw=False, stream=False):
headers = self._normalize_headers(headers=headers)
req = requests.Request(method, ''.join([self.host, url]),
data=body, headers=headers)
prepped = self.session.prepare_request(req)
* prepped.body = body <<<<<< This line.
*
self.response = self.session.send(
prepped,
stream=stream,
verify=self.ca_cert if self.ca_cert is not None else self.verify)
*Why I Think It’s the Problem*
When a request is prepared, if its body is an empty string '', the
preparation step ignores the body and sets the resulting PreparedRequest body
to None. Subsequently setting the body back to an empty string '' breaks
requests logic when sending the request. Requests now thinks the request
should be chunked because body='' breaks this logic:
https://github.com/psf/requests/blob/master/requests/adapters.py#L420
chunked = not (request.body is None or 'Content-Length' in request.headers)
A raw HTTP chunked request is sent with no body. As a result only a 0 is
transmitted to signify the last chunk. This coincides with when our server
receives the HTTP 400 error.
https://github.com/psf/requests/blob/master/requests/adapters.py#L469
*#requests/adapters.py
*for i in request.body:
low_conn.send(hex(len(i))[2:].encode('utf-8'))
low_conn.send(b'\r\n')
low_conn.send(i)
low_conn.send(b'\r\n')
low_conn.send(b'0\r\n\r\n')
*Replicating the Behavior*
You can use this snippet to reproduce the same behavior outside the context
of Libcloud.
import requests
session = requests.Session()
req = requests.Request('GET', 'http://www.google.com', data='')
*# prepare_request() will ignore the empty string and set prepped.body to None.
*prepped = session.prepare_request(req)
*# Overwriting None with '' will break requests logic for sending requests.
*prepped.body = ''
*# Chunked request is sent with a zero length body. Only terminating 0 is sent.
*response = session.send(prepped, stream=False, verify=False)
*Conclusion*
Is there a reason for the body being overwritten that I am overlooking? I
am aware that libcloud's use cases vary greatly and I may be missing
something. Note that this is not a problem for every provider. Some
connection classes set the default value for data as None instead of '' ,
and None does not trigger an issue.
*#libcloud/common/openstack.py OpenStackBaseConnection
*def request(self, action, params=None, *data=''*, headers=None, ...)
*#libcloud/common/base.py Connection
*def request(self, action, params=None, *data=None*, headers=None, ...)
I was able to run the tox test cases and everything was fine. I am in the
process of opening a formal issue and/or PR.
~~~~~~~
Thank for taking time out of your day.
Cheers,
Michael Spagon
@ InfiniteIO
