Solve #164, make http.py return ordered headers.

[sunhao2014]

Solve #164, make http.py return ordered headers, also add the related unit test and setup dependencies.

BTW, according to Kiran's suggestion, some invalid http header test cases were added.

[landscape-bot]

Code quality remained the same when pulling 08e6144 on kbandla:http_ordered_header into 5b55332 on kbandla:master.

[sunhao2014]

Just noticed that the PR failed the auto build.

The reason why py26 didn't work is we used the collections.OrderedDict which is supported by py27. Thus how do we deal with this problem? Should we add support to Python versions older than 2.7?

[landscape-bot]

Code quality remained the same when pulling 36b81cd on kbandla:http_ordered_header into 5b55332 on kbandla:master.

[kbandla]

We could have, if ordereddict was a necessity. However:

• many users probably dont need the exact header order
• python2.6 is still widely used

How about doing this instead:
try to import collections. On ImportError, use a standard python dict. If not, use collections.OrderedDict

[brifordwylie]

We could pull https://pypi.python.org/pypi/ordereddict as a dependency. One of the nice things about dpkt is we have no requirements outside the standard library, seems a shame to add a dependency just for this small thing.

[brifordwylie]

Just saw Kiran's comment, yeah that's the right thing to do. Also +10 for automated CI :)

[kbandla]

try:
from collections import OrderedDict
except ImportError:
OrderedDict = dict

[saylenty]

Guys, is it really usefull feature? If we use ordered dict we would lose in speed of execution (and I think even in seconds). Once, I tried to optimise one problem (https://github.com/Saylenty/algorithm_with_dots-matrices) trying to solve it using ordered set, but this was not a good idea.

[obormot]

@saylenty +1

[kbandla]

Well, it is true too. OrderedDict is written in python (vs C).

What if we do this instead? (This will not break any existing code either)

def parse_headers(f, ordered=False):
    d = {}
    if ordered:
        from collections import OrderedDict
        d = OrderedDict()
   ....

[obormot]

@kbandla I like this option... but tbh my favorite solution is to not implement this at all :-) the HTTP protocol spec does not dictate any order in the headers, so dpkt is solid there. If someone wants them in order for their specific use case then it's easy to write their own parse function and feed it tcp.data.

[kbandla]

👍 @obormot. lets not implement this. go ahead and remove it @sunhao2014 (ordereddict support)

[sunhao2014]

Sure. I'll close this PR and send a new PR that only contains the added http invalid test cases.

[saylenty]

@kbandla , Personally, I would rather implement this feature using OrderedDIct as you've written and write a warning only in the documentation that it can be much slower...