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Multipart mixed responses generate warnings

See original GitHub issue

If you read a multipart/mixed response, the connectionpool issues a couple of warnings about defects in the message. I’m not sure what the expected, correct behavior is, but these warnings seem spurious.

Stick this perl script somewhere:

#!/usr/bin/perl

print "Server: Some Server Name\r\n";
print "Content-Type: multipart/mixed; boundary=36eeb8c4e26d842a\r\n";
print "Content-Length: 178\r\n";
print "\r\n\r\n";
print "--36eeb8c4e26d842a\r\n";
print "Content-Type: text/plain\r\n";
print "\r\n";
print "7\r\n";
print "--36eeb8c4e26d842a\r\n";
print "Content-Type: text/plain\r\n";
print "\r\n";
print "9\r\n";
print "--36eeb8c4e26d842a\r\n";
print "Content-Type: text/plain\r\n";
print "\r\n";
print "11\r\n";
print "--36eeb8c4e26d842a--\r\n";

Read it with requests (naturally, you’ll have to change the URI to wherever you put the script):

import requests, logging

logging.basicConfig(level=logging.WARNING)
logging.getLogger("requests").setLevel(logging.DEBUG)

headers = {'accept': "multipart/mixed"}
r = requests.get("http://localhost:8124/cgi-bin/mpm.pl", headers=headers)

print(r)

The following errors are displayed:

DEBUG:requests.packages.urllib3.connectionpool:"GET http://localhost:8124/cgi-bin/mpm.pl HTTP/1.1" 200 178
WARNING:requests.packages.urllib3.connectionpool:Failed to parse headers (url=http://localhost:8888/http://localhost:8124/cgi-bin/mpm.pl): [StartBoundaryNotFoundDefect(), MultipartInvariantViolationDefect()], unparsed data: ''
Traceback (most recent call last):
  File "/home/ndw/.virtualenvs/pyapi/lib/python3.4/site-packages/requests-2.8.0-py3.4.egg/requests/packages/urllib3/connectionpool.py", line 390, in _make_request
    assert_header_parsing(httplib_response.msg)
  File "/home/ndw/.virtualenvs/pyapi/lib/python3.4/site-packages/requests-2.8.0-py3.4.egg/requests/packages/urllib3/util/response.py", line 58, in assert_header_parsing
    raise HeaderParsingError(defects=defects, unparsed_data=unparsed_data)
requests.packages.urllib3.exceptions.HeaderParsingError: [StartBoundaryNotFoundDefect(), MultipartInvariantViolationDefect()], unparsed data: ''

It took me quite a while to work out that they were spurious (because in real life, the server side that is generating the multipart/mixed is more complicated!)