Java script FAQ [was Re: :Mechanize]

Hi Andy,

Some time a ago, I sent you the text for the FAQ on Java script. There 
is a section "So what do I do". I would like to suggest that you update 
the text:

Original text:

    So what can I do?

    Since Javascript is completely visible to the client, it cannot be
    used to prevent a scraper from following links. But it can make life
    difficult, and until someone writes a Javascript interpreter for
    Perl or a Mechanize clone to control Firefox, there will be no
    general solution. But if you want to scrape specific pages, then a
    solution is always possible.

    One typical use of Javascript is to perform argument checking before
    posting to the server. The URL you want is probably just buried in
    the Javascript function. Do a regular expression match on
    |$mech->content()| to find the link that you want and |$mech->get|
    it directly (this assumes that you know what your are looking for in
    advance).

    In more difficult cases, the Javascript is used for URL mangling to
    satisfy the needs of some middleware. In this case you need to
    figure out what the Javascript is doing (why are these URLs always
    really long?). There is probably some function with one or more
    arguments which calculates the new URL. Step one: using your
    favorite browser, get the before and after URLs and save them to
    files. Edit each file, converting the the argument separators ('?',
    '&' or ';') into newlines. Now it is easy to use diff or comm to
    find out what Javascript did to the URL. Step 2 - find the function
    call which created the URL - you will need to parse and interpret
    its argument list. Using the Javascript Debugger Extension for
    Firefox may help with the analysis. At this point, it is fairly
    trivial to write your own function which emulates the Javascript for
    the pages you want to process.

Please append to it:

    An Alternative Approach (this is also an answer to the question, "It
    works in Firefox, why not in $mech?" )

    Everything the web server knows about the client is present in the
    HTTP request. If two requests are identical, the results should be
    identical. So the real question is "What is different between the
    mech request and the Firefox request?"

    I would suggest using the Firefox extension "Tamper Data" to look at
    the headers of the requests you send to the server. Compare that
    with what LWP is sending. Once the two are identical, the action of
    the server should be the same as well.

    I say "should", because this is an oversimplification - some values
    are naturally unique, e.g. a SessionID, but if a SessionID is
    present, that is probably sufficient, even though the value will be
    different between the LWP request and the Firefox request. The
    server could use the session to store information which is
    troublesome, but that's not the first place to look (and highly
    unlike to be relevant when you are requesting the login page of your
    site).

    Generally the problem is to be found in missing or incorrect
    POSTDATA arguments, Cookies, User-Agents, Accepts, etc. If you are
    using mech, then redirects and cookies should not be a problem, but
    are listed here for completeness. If you are missing headers,
    $mech->add_header can be used to add the headers that you need.

Is there a preferred way to get the request which mech is going to send? 
I was able to get it by following the code into the innards of 
HTTP::Request, but that seems like the kind of stuff a $mechanize user 
won't want to do.

Cheers,

Peter



Cahoon, Forrest wrote:
> If you're specifically looking at Yahoo! Mail, there's at least one CPAN module for that:
> http://search.cpan.org/~johnsca/MailClientYahoo-1.0/lib/Mail/Client/Yahoo.pm
>
> If it's just something similar to Yahoo!, perhaps that code will give you some clues.
> (I haven't used that module myself, just happened to notice it's existence.)
>
> Forrest
> not speaking for merrill corporation 
>
>   
>> -----Original Message-----
>> From: Roy Lor [mailto:[email protected]] 
>> Sent: Tuesday, April 04, 2006 8:21 AM
>> To: [email protected]
>> Subject: WWW::Mechanize
>>
>> can u give me a code/script that records the information in a 
>> log-in  form with javascript..like that of mail.yahoo.com? i 
>> badly need  this..thanks
>>   
>> 		
>> ---------------------------------
>> On Yahoo!7
>>   Desperate Housewives: Sneak peeks, recaps and more. 
>>
>>     
>
>
>