SourceForge.net Logo

ClientCookie

Note: this page describes the new >=0.4.3a interface. For old docs, see the source packages here.

Examples

 import ClientCookie
 response = ClientCookie.urlopen("http://foo.bar.com/")

This function behaves identically to urllib2.urlopen, except that it deals with cookies automatically. That's probably all you need to know.

Here is a more complicated example, involving Request objects (useful if you want to pass Requests around, add headers to them, etc.):

 import ClientCookie
 import urllib2
 request = urllib2.Request("http://www.acme.com/")
 # note we're using the urlopen from ClientCookie, not urllib2
 response = ClientCookie.urlopen(request)
 # let's say this next request requires a cookie that was set in response
 request2 = urllib2.Request("http://www.acme.com/flying_machines.html")
 response2 = ClientCookie.urlopen(request2)

 print response2.geturl()
 print response2.info()  # headers
 print response2.read()  # body (readline and readlines work too)

In these examples, the workings are hidden inside the ClientCookie.urlopen method, which is an extension of urllib2.urlopen. Redirects, proxies and cookies are handled automatically by this function. Cookie processing (etc.) is handled by processor objects, which are similar to urllib2's handlers: HTTPCookieProcessor, HTTPRefererProcessor, SeekableProcessor etc. To use, simply pass processors to build_opener as if they were handlers. Processor-aware versions of HTTPHandler and HTTPSHandler (if your Python installation has HTTPS support) are also included, along with a bugfixed HTTPRedirectHandler is also included (the bug, related to redirection, is fixed in 2.3).

An example at a slightly lower level shows how the module processes cookies more clearly:

 # Don't copy this blindly!  You probably want to follow the examples
 # above, not this one.
 import ClientCookie
 import urllib2
 request = urllib2.Request("http://www.acme.com/")
 response = urllib2.urlopen(request)
 c = ClientCookie.CookieJar()
 c.extract_cookies(response, request)
 # let's say this next request requires a cookie that was set in response
 request2 = urllib2.Request("http://www.acme.com/flying_machines.html")
 c.add_cookie_header(request2)
 response2 = urllib2.urlopen(request2)

The CookieJar class does all the work. There are essentially two operations: extract_cookies extracts HTTP cookies from Set-Cookie (the original Netscape cookie standard) and Set-Cookie2 (RFC 2965) headers from a response if and only if they should be set given the request, and add_cookie_header adds Cookie headers if and only if they are appropriate for a particular HTTP request. Incoming cookies are checked for acceptability based on the host name, etc. Cookies are only set on outgoing requests if they match the request's host name, path, etc. Cookies may be also be saved to and loaded from a file. The subclass MozillaCookieJar differs from CookieJar only in storing cookies using a different, Mozilla/Netscape-compatible, file format. This Mozilla-compatible ('cookies.txt') format loses some information when you save cookies to a file. Note that lynx also uses the Mozilla file format. The subclass MSIECookieJar can load (but not save, yet) from Microsoft Internet Explorer's cookie files (on Windows).

Note that if you're using ClientCookie.urlopen (or if you're using ClientCookie.HTTPCookieProcessor by some other means), you don't need to call extract_cookies or add_cookie header yourself. If, on the other hand, you don't want to use urllib2, you will need to use this pair of methods. You can make your own request and response objects, which must support the interfaces described in the docstrings of extract_cookies and add_cookie_header.

Important note

Only use names you can import directly from the ClientCookie package, and that don't start with a single underscore. Everything else is subject to change or disappearance without notice.

Cooperating with Netscape/Mozilla and Internet Explorer

The subclass MozillaCookieJar differs from CookieJar only in storing cookies using a different, Netscape/Mozilla-compatible, file format. This Netscape-compatible format can't store RFC 2965 cookies, so they are downgraded to Netscape cookies on saving. CookieJar itself uses a libwww-perl specific format (`Set-Cookie3'). Python and Netscape/Mozilla should be able to share a cookies file (note that the file location here will differ on non-unix OSes):

WARNING: you may want to backup your browser's cookies file if you use MozillaCookieJar to save cookies. I think it works, but there have been bugs in the past!

import os, ClientCookie
cookies = ClientCookie.MozillaCookieJar()
cookies.load(os.path.join(os.environ["HOME"], "/.netscape/cookies.txt"))
# see also the save and revert methods

Note that cookies saved while Mozilla is running will get clobbered by Mozilla - see MozillaCookieJar.__doc__.

MSIECookieJar does the same for Microsoft Internet Explorer (MSIE) 5.x and 6.x on Windows, but does not allow saving cookies in this format. In future, the Windows API calls might be used to load and save (though the index has to be read directly, since there is no API for that, AFAIK).

import ClientCookie
c = ClientCookie.MSIECookieJar(delayload=True)
c.load_from_registry()  # finds cookie index file from registry

A true delayload argument speeds things up.

On Windows 9x (win 95, win 98, win ME), you need to supply a username to the load_from_registry method:

c.load_from_registry(username="jbloggs")

Using your own CookieJar instance

You might want to do this to use your browser's cookies, to customize CookieJar's behaviour by passing constructor arguments, or to be able to get at the cookies it will hold (for example, for saving cookies between sessions and for debugging).

If you're using the higher-level urllib2-like interface (urlopen, etc), you'll have to let it know what CookieJar it should use:

import ClientCookie
cookies = ClientCookie.CookieJar()
# build_opener adds standard handlers and processors (such as HTTPHandler
# and HTTPCookieProcessor) by default.  The cookie processor we supply
# will replace the default one.
opener = ClientCookie.build_opener(ClientCookie.HTTPCookieProcessor(cookies))

r = opener.open("http://acme.com/")  # GET
r = opener.open("http://acme.com/", data)  # POST

The urlopen function uses a global OpenerDirector instance to do its work, so if you want to use urlopen with your own CookieJar, install the OpenerDirector you built with build_opener using the ClientCookie.install_opener function, then proceed as usual:

ClientCookie.install_opener(opener)
r = urlopen("http://www.acme.com/")

Of course, everyone using urlopen is using the same global CookieJar instance!

You can set a policy object (must satisfy interface defined by ClientCookie.CookiePolicy), which determines which cookies are allowed to be set and returned. Use the policy argument to the CookieJar constructor, or just set the policy attribute directly. The default implementation has some useful switches:

from ClientCookie import CookieJar, DefaultCookiePolicy as Policy
cookies = CookieJar()
# turn off RFC 2965 cookies, be more strict about domains when setting and
# returning Netscape cookies, and block some domains from setting cookies
# or having them returned (read the DefaultCookiePolicy docstring for the
# domain matching rules here)
policy = Policy(rfc2965=False, strict_ns_domain=Policy.DomainStrict,
                blocked_domains=["ads.net", ".ads.net"])
cookies.policy = policy

Optional goodies: HTTP-EQUIV, Refresh, Referer and seekable responses

These are implemented as processor classes. Processors are identical in use to urllib2's handlers: you just pass them to build_opener (example code below).

HTTPEquivProcessor

The <META HTTP-EQUIV> tag is a way of including data in HTML to be treated as if it were part of the HTTP headers. ClientCookie can automatically read these tags and add the HTTP-EQUIV headers to the response object's real HTTP headers. The HTML is left unchanged.

HTTPRefreshProcessor

The Refresh HTTP header is a non-standard header which is widely used. It requests that the user-agent follow a URL after a specified time delay. ClientCookie can treat these headers (which may have been set in <META HTTP-EQUIV> tags) as if they were 302 redirections. Exactly when and how Refresh headers are handled is configurable using the constructor arguments.

SeekableProcessor

This makes ClientCookie's response objects seek()able. Seeking is done lazily (ie. the response object only reads from the socket as necessary, rather than slurping in all the data before the response is returned to you). XXX only works for HTTP ATM, I think

HTTPRefererProcessor

The Referer HTTP header lets the server know which URL you've just visited. Some servers use this header as state information, and don't like it if this is not present. It's a chore to add this header by hand every time you make a request. This adds it automatically. NOTE: this only makes sense if you use each processor for a single chain of HTTP requests (so, for example, if you use a single HTTPRefererProcessor to fetch a series of URLs extracted from a single page, this will break).

import ClientCookie
cookies = ClientCookie.CookieJar()

opener = ClientCookie.build_opener(ClientCookie.HTTPRefererProcessor,
                                   ClientCookie.HTTPEquivProcessor,
                                   ClientCookie.HTTPRefreshProcessor,
                                   ClientCookie.SeekableProcessor)
opener.open("http://www.rhubarb.com/")

Adding headers

Adding headers is done like so:

import ClientCookie, urllib2
req = urllib2.Request("http://foobar.com/")
req.add_header("Referer", "http://wwwsearch.sourceforge.net/ClientCookie/")
r = ClientCookie.urlopen(req)

You can also use the headers argument to the urllib2.Request constructor.

urllib2 (in fact, ClientCookie takes over this task from urllib2) adds some headers to Request objects automatically - see the next section for details.

Changing the automatically-added headers (User-Agent)

OpenerDirector automatically adds a User-Agent header to every Request.

To change this, use your own OpenerDirector:

import ClientCookie
cookies = ClientCookie.CookieJar()
opener = ClientCookie.build_opener(ClientCookie.HTTPCookieProcessor(cookies))
opener.addheaders = [("User-agent", "Mozilla/5.0")]

Again, to use urlopen, install your OpenerDirector globally:

ClientCookie.install_opener(opener)
r = ClientCookie.urlopen("http://acme.com/")

Also, a few standard headers (Content-Length, Content-Type and Host) are added when the Request is passed to urlopen (or OpenerDirector.open). ClientCookie explictly adds these (and User-Agent) to the Request object, unlike urllib2. You shouldn't need to change these headers, but since this is done by HTTPStandardHeadersProcessor, you can change the way it works by replacing that processor or adding a new processor that sets these headers.

Initiating unverifiable transactions

ClientCookie knows that redirected transactions are unverifiable, so it'll handle that on its own.

If you want to initiate an unverifiable transaction yourself (which you should if, for example, you're downloading the images from a page, and 'the user' hasn't explicitly OKed those URLs), you need to set a true request.unverifiable on your Request instance, and also set request.origin_req_host to the request-host of the origin transaction (eg. the URL of the page containing the images). If unverifiable is present and true, but origin_req_host is not present, you'll get an AttributeError. XXX None of this is very nice...

Debugging

First, a few common problems. The most frequent mistake people seem to make is to use ClientCookie.urlopen, and the extract_cookies and add_cookie_header methods on a cookie object themselves. If you use ClientCookie.urlopen (or OpenerDirector.open), the module handles extraction and adding of cookies by itself, so you should not call extract_cookies or add_cookie_header.

If things don't seem to be working as expected, the first thing to try is to switch off RFC 2965 handling. This is because few browsers implement it, so it is likely that some servers incorrectly implement it.

Are you sure the server is sending you any cookies in the first place? Maybe the server is keeping track of state in some other way (HIDDEN HTML form entries (possibly in a separate page referenced by a frame), URL-encoded session keys, IP address, HTTP Referer headers)? Perhaps some embedded script in the HTML is setting cookies (see below)? Maybe you messed up your request, and the server is sending you some standard failure page (even if the page doesn't appear to indicate any failure). Sometimes, a server wants particular headers set to the values it expects, or it won't play nicely. The most frequent offenders here are the Referer [sic] and / or User-Agent HTTP headers (see above for how to set these). The User-Agent header may need to be set to a value like that of a popular browser. The Referer header may need to be set to the URL that the server expects you to have followed a link from. Occasionally, it may even be that operators deliberately configure a server to insist on precisely the headers that the popular browsers (MS Internet Explorer, Netscape/Mozilla, Opera) generate, but remember that incompetence (possibly on your part) is more probable than deliberate sabotage.

When you save to or load/revert from a file, single-session cookies will expire unless you explicitly request otherwise with the ignore_discard argument. This may be your problem if you find cookies are going away after saving and loading.

If none of the advice above solves your problem quickly, try comparing the headers and data that you are sending out with those that a browser emits. Often this will give you the clue you need. Of course, you'll want to check that the browser is able to do manually what you're trying to achieve programatically before minutely examining the headers. Make sure that what you do manually is exactly the same as what you're trying to do from Python - you may simply be hitting a server bug that only gets revealed if you view pages in a particular order, for example. In order to see what your browser is sending to the server (even if HTTPS is in use), see the General FAQ page. If nothing is obviously wrong with the requests your program is sending and you're out of ideas, you can try the last resort of good old brute force binary-search debugging. Temporarily switch to sending HTTP headers (with httplib). Start by copying Netscape/Mozilla or IE slavishly (apart from session IDs, etc., of course), then begin the tedious process of mutating your headers and data until they match what your higher-level code was sending. This will at least reliably find your problem.

You can globally turn on display of HTTP headers:

import ClientCookie
ClientCookie.HTTP_DEBUG = True

(Note that doing this won't work:

from ClientCookie import HTTP_DEBUG
HTTP_DEBUG = True

If you don't understand that, you've misunderstood what the = operator does.)

Alternatively, you can examine your individual request and response objects to see what's going on. ClientCookie's responses can be made seek()able using SeekableProcessor. It's often useful to use the seek method like this during debugging:

...
response = ClientCookie.urlopen("http://spam.eggs.org/")
print response.read()
response.seek(0)
# rest of code continues as if you'd never .read() the response
...

If you would like to see what is going on in ClientCookie's tiny mind, do this:

ClientCookie.CLIENTCOOKIE_DEBUG = True

This can actually be quite useful, as it explains why particular cookies are accepted or rejected and why they are or are not returned. It also defeats the couple of catch-all except: statements in the code, which would otherwise be very confusing.

Also, note the ClientCookie.REDIRECT_DEBUG switch (which prints information about redirections) and HTTPResponseDebugProcessor (which prints out all response bodies, including those that are read during redirections).

Embedded script that sets cookies

It is possible to embed script in HTML pages (sandwiched between <SCRIPT>here</SCRIPT> tags, and in javascript: URLs) - JavaScript / ECMAScript, VBScript, or even Python - that causes cookies to be set in a browser. If you come across this in a page you want to automate, you have three options. Here they are, roughly in order of simplicity. First, you can simply figure out what the embedded script is doing and imitate it by manually adding cookies to your CookieJar instance. Second, if you're working on a Windows machine (or another platform where the MSHTML COM library is available) you could give up the fight and automate Microsoft Internet Explorer (MSIE) with COM. XXX Mozilla automation & XPCOM / PyXPCOM, Konqueror & KParts / PyKDE? Third, you could get ambitious and delegate the work to an appropriate interpreter (Mozilla's JavaScript interpreter, for instance). I'm working on that approach at the moment.

Parsing HTTP date strings

A function named str2time is provided by the package, which may be useful for parsing dates in HTTP headers. str2time is intended to be liberal, since HTTP date/time formats are poorly standardised in practice. There is no need to use this function in normal operations: CookieJar instances keep track of cookie lifetimes automatically. This function will stay around in some form, though the supported date/time formats may change.

Note about cookie standards

The various cookie standards and their history form a case study of the terrible things that can happen to a protocol. The long-suffering David Kristol has written a paper about it, if you want to know the gory details.

Here is a summary.

The Netscape protocol (cookie_spec.html) is still the only standard supported by most browsers (including Internet Explorer and Netscape). Be aware that cookie_spec.html is not, and never was, actually followed to the letter (or anything close) by anyone (including Netscape, IE and ClientCookie): the Netscape protocol standard is really defined by the behaviour of Netscape (and now IE). Netscape cookies are also known as V0 cookies, to distinguish them from RFC 2109 or RFC 2965 cookies, which have a version cookie-attribute with a value of 1.

RFC 2109 was introduced to fix some problems identified with the Netscape protocol, while still keeping the same HTTP headers (Cookie and Set-Cookie). The most prominent of these problems is the 'third-party' cookie issue, which was an accidental feature of the Netscape protocol. When one visits www.bland.org, one doesn't expect to get a cookie from www.lurid.com, a site one has never visited. Depending on browser configuration, this can still happen, because the unreconstructed Netscape protocol is happy to accept cookies from, say, an image in a webpage (www.bland.org) that's included by linking to an advertiser's server (www.lurid.com). This kind of event, where your browser talks to a server that you haven't explicitly okayed by some means, is what the RFCs call an 'unverifiable transaction'. In addition to the potential for embarrassment caused by the presence of lurid.com's cookies on one's machine, this may also be used to track your movements on the web, because advertising agencies like doubleclick.net place ads on many sites. RFC 2109 tried to change this by requiring cookies to be turned off during unverifiable transactions with third-party servers - unless the user explicitly asks them to be turned on. This clashed with the business model of advertisers like doubleclick.net, who had started to take advantage of the third-party cookies 'bug'. Since the browser vendors were more interested in the advertisers' concerns than those of the browser users, this arguably doomed both RFC 2109 and its successor, RFC 2965, from the start. Other problems than the third-party cookie issue were also fixed by 2109. However, even ignoring the advertising issue, 2109 was stillborn, because Internet Explorer and Netscape behaved differently in response to its extended Set-Cookie headers. This was not really RFC 2109's fault: it worked the way it did to keep compatibility with the Netscape protocol as implemented by Netscape. Microsoft Internet Explorer (MSIE) was very new when the standard was designed, but was starting to be very popular when the standard was finalised. XXX P3P, and MSIE & Mozilla options

XXX Apparently MSIE implements bits of RFC 2109 - but not very compliant (surprise). Presumably other browsers do too, as a result. ClientCookie already does allow Netscape cookies to have max-age and port cookie-attributes, and as far as I know that's the extent of the support present in MSIE. I haven't tested, though!

RFC 2965 attempted to fix the compatibility problem by introducing two new headers, Set-Cookie2 and Cookie2. Unlike the Cookie header, Cookie2 does not carry cookies to the server - rather, it simply advertises to the server that RFC 2965 is understood. Set-Cookie2 does carry cookies, from server to client: the new header means that both IE and Netscape completely ignore these cookies. This prevents breakage, but introduces a chicken-egg problem that means 2965 may never be widely adopted, especially since Microsoft shows no interest in it. XXX Rumour has it that the European Union is unhappy with P3P, and might introduce legislation that requires something better, forming a gap that RFC 2965 might fill - any truth in this? Opera is the only browser I know of that supports the standard. On the server side, Apache's mod_usertrack supports it. One confusing point to note about RFC 2965 is that it uses the same value (1) of the Version attribute in HTTP headers as does RFC 2109.

Recently, it was discovered that RFC 2965 does not fully take account of issues arising when 2965 and Netscape cookies coexist. At the time of writing (August 2003), the resulting errata are still being thrashed out (actually, the list traffic seems to have died for the moment).

Because Netscape cookies are so poorly specified, the general philosophy of the module's Netscape cookie implementation is to start with RFC 2965 and open holes where required for Netscape protocol-compatibility. RFC 2965 cookies are always treated as RFC 2965 requires, of course!

FAQs - usage

John J. Lee, November 2003.