Bugs: Content-Length not updated by reused urllib.request.Request/ has_header() case-sensitive

Discussion in 'Python' started by Johannes Kleese, Nov 12, 2012.

  1. Hi!

    (Yes, I did take a look at the issue tracker but couldn't find any
    corresponding bug, and no, I don't want to open a new account just for
    this one.)

    --------------------------------------------------------------------

    I'm reusing a single urllib.request.Request object to HTTP-POST data to
    the same URL a number of times. While the data itself is sent as
    expected every time, the Content-Length header is not updated after the
    first request. Tested with Python 3.1.3 and Python 3.1.4.

    >>> opener = urllib.request.build_opener()
    >>> request = urllib.request.Request("http://example.com/", headers =

    {"Content-Type": "application/x-www-form-urlencoded"})


    >>> opener.open(request, "1".encode("us-ascii"))


    >>> request.data

    b'1'
    >>> request.header_items()

    [('Content-length', '1'), ('Content-type',
    'application/x-www-form-urlencoded'), ('Host', 'example.com'),
    ('User-agent', 'Python-urllib/3.1')]


    >>> opener.open(request, "123456789".encode("us-ascii"))


    >>> request.data

    b'123456789'
    >>> request.header_items()

    [('Content-length', '1'), ('Content-type',
    'application/x-www-form-urlencoded'), ('Host', 'example.com'),
    ('User-agent', 'Python-urllib/3.1')]

    Note that after the second run, Content-Length stays "1", but should be
    "9", corresponding to the data b'123456789'. (Request data is not
    x-www-form-urlencoded to shorten the test case. Doesn't affect the bug,
    though.)




    --------------------------------------------------------------------

    While at it, I noticed that urllib.request.Request.has_header() and
    ..get_header() are case-sensitive, while HTTP headers are not (RFC 2616,
    4.2). Thus the following, slightly unfortunate behaviour:

    >>> request.header_items()

    [('Content-length', '1'), ('Content-type',
    'application/x-www-form-urlencoded'), ('Host', 'example.com'),
    ('User-agent', 'Python-urllib/3.1')]

    >>> request.has_header("Content-Type")

    False
    >>> request.has_header("Content-type")

    True
    >>> request.get_header("Content-Type")
    >>> request.get_header("Content-type")

    'application/x-www-form-urlencoded'

    --------------------------------------------------------------------

    Thanks for taking care.
     
    Johannes Kleese, Nov 12, 2012
    #1
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  2. Johannes Kleese

    Terry Reedy Guest

    On 11/12/2012 10:52 AM, Johannes Kleese wrote:
    > Hi!
    >
    > (Yes, I did take a look at the issue tracker but couldn't find any
    > corresponding bug, and no, I don't want to open a new account just for
    > this one.)


    You only have to open a tracker account just once. I am reluctant to
    report this myself as I do not use the module and cannot answer questions.

    > I'm reusing a single urllib.request.Request object to HTTP-POST data to
    > the same URL a number of times. While the data itself is sent as
    > expected every time, the Content-Length header is not updated after the
    > first request. Tested with Python 3.1.3 and Python 3.1.4.


    3.1 only gets security fixes. Consider upgrading. In any case, suspected
    bugs need to be tested with the latest release, as patches get applied
    daily. As it happens,

    import urllib.request
    opener = urllib.request.build_opener()
    request = urllib.request.Request("http://example.com/", headers =
    {"Content-Type": "application/x-www-form-urlencoded"})

    opener.open(request, "1".encode("us-ascii"))
    print(request.data, '\n', request.header_items())

    opener.open(request, "123456789".encode("us-ascii"))
    print(request.data, '\n', request.header_items())

    exhibits the same behavior in 3.3.0 of printing ('Content-length', '1')
    in the last output. I agree that that looks wrong, but I do not know if
    such re-use is supposed to be supported.


    > While at it, I noticed that urllib.request.Request.has_header() and
    > .get_header() are case-sensitive,


    Python is case sensitive.

    > while HTTP headers are not (RFC 2616, 4.2).
    > Thus the following, slightly unfortunate behaviour:
    >
    >>>> request.header_items()

    > [('Content-length', '1'), ('Content-type',
    > 'application/x-www-form-urlencoded'), ('Host', 'example.com'),
    > ('User-agent', 'Python-urllib/3.1')]
    >
    >>>> request.has_header("Content-Type")

    > False
    >>>> request.has_header("Content-type")

    > True
    >>>> request.get_header("Content-Type")

    # this return None, which is not printed
    >>>> request.get_header("Content-type")

    > 'application/x-www-form-urlencoded'


    Judging from 'Content-type', 'User-agent', 'Content-length', 'Host',
    urllib.request consistently capitalizes the first word of all header
    tags and expects them in that form. If that is not standard, it should
    be documented.

    --
    Terry Jan Reedy
     
    Terry Reedy, Nov 12, 2012
    #2
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  3. Johannes Kleese

    Terry Reedy Guest

    On 11/12/2012 4:35 PM, Terry Reedy wrote:

    > import urllib.request
    > opener = urllib.request.build_opener()
    > request = urllib.request.Request("http://example.com/", headers =
    > {"Content-Type": "application/x-www-form-urlencoded"})
    >
    > opener.open(request, "1".encode("us-ascii"))
    > print(request.data, '\n', request.header_items())
    >
    > opener.open(request, "123456789".encode("us-ascii"))
    > print(request.data, '\n', request.header_items())
    >
    > exhibits the same behavior in 3.3.0 of printing ('Content-length', '1')
    > in the last output. I agree that that looks wrong, but I do not know if
    > such re-use is supposed to be supported.


    I opened http://bugs.python.org/issue16464

    --
    Terry Jan Reedy
     
    Terry Reedy, Nov 13, 2012
    #3
  4. Terry Reedy wrote:
    > On 11/12/2012 10:52 AM, Johannes Kleese wrote:


    >> Tested with Python 3.1.3 and Python 3.1.4.

    >
    > 3.1 only gets security fixes. Consider upgrading.


    Stuck with Debian on a server, thus stuck with 3.1 on development machine.

    > exhibits the same behavior in 3.3.0 of printing ('Content-length', '1')
    > in the last output. I agree that that looks wrong, but I do not know if
    > such re-use is supposed to be supported.


    The Request object should then either get it right on re-use (which I'd
    prefer), or block re-use.

    >> While at it, I noticed that urllib.request.Request.has_header() and
    >> .get_header() are case sensitive,

    >
    > Python is case sensitive.


    True, of course, but

    >> HTTP headers are not (RFC 2616, 4.2).


    and the functions work on HTTP data, not Python data. After all, we are
    lucky to have functions here and not just a dictionary.


    Anyway, thanks for reporting!
     
    Johannes Kleese, Nov 13, 2012
    #4
  5. Johannes Kleese

    Terry Reedy Guest

    On 11/12/2012 8:58 PM, Terry Reedy wrote:
    > On 11/12/2012 4:35 PM, Terry Reedy wrote:
    >
    >> import urllib.request
    >> opener = urllib.request.build_opener()
    >> request = urllib.request.Request("http://example.com/", headers =
    >> {"Content-Type": "application/x-www-form-urlencoded"})
    >>
    >> opener.open(request, "1".encode("us-ascii"))
    >> print(request.data, '\n', request.header_items())
    >>
    >> opener.open(request, "123456789".encode("us-ascii"))
    >> print(request.data, '\n', request.header_items())
    >>
    >> exhibits the same behavior in 3.3.0 of printing ('Content-length', '1')
    >> in the last output. I agree that that looks wrong, but I do not know if
    >> such re-use is supposed to be supported.

    >
    > I opened http://bugs.python.org/issue16464


    A patch has been written by Alexey Kachayev and pushed by Andrew Svetlov
    and the behavior will change in 3.4.0 to allow reuse.

    --
    Terry Jan Reedy
     
    Terry Reedy, Nov 27, 2012
    #5
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